Showing papers in "Journal of the American Society for Horticultural Science in 1995"

Growth and photomorphogenesis of pepper plants under red light-emitting diodes with supplemental blue or far-red lighting.

Abstract: Light-emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems and photobiological research. They have small size, low mass, a long functional life, and narrow spectral output. In this study, we measured the growth and dry matter partitioning of 'Hungarian Wax' pepper (Capsicum annuum L.) plants grown under red LEDs compared with similar plants grown under red LEDs with supplemental blue or far-red radiation or under broad spectrum metal halide (MH) lamps. Additionally, we describe the thermal and spectral characteristics of these sources. The LEDs used in this study had a narrow bandwidth at half peak height (25 nm) and a focused maximum spectral output at 660 nm for the red and 735 nm for the far-red. Near infrared radiation (800 to 3000 nm) was below detection and thermal infrared radiation (3000 to 50,000 nm) was lower in the LEDs compared to the MH source. Although the red to far-red ratio varied considerably, the calculated phytochrome photostationary state (phi) was only slightly different between the radiation sources. Plant biomass was reduced when peppers were grown under red LEDs in the absence of blue wavelengths compared to plants grown under supplemental blue fluorescent lamps or MH lamps. The addition of far-red radiation resulted in taller plants with greater stem mass than red LEDs alone. There were fewer leaves under red or red plus far-red radiation than with lamps producing blue wavelengths. These results indicate that red LEDs may be suitable, in proper combination with other wavelengths of light, for the culture of plants in tightly controlled environments such as space-based plant culture systems.

Random amplified polymorphic DNA analysis of olive (Olea europaea L.) cultivars

Abstract: Seventeen olive (Olea europaea L.) cultivars, including oil and table olive cultivars originating from throughout the Mediterranean area, were screened using random amplified polymorphic DNA (RAPD) markers. The results indicate that a high degree of polymorphism is evident in the olive germplasm reexamined. Forty random decamer primers were screened; seventeen of these produced 47 reproducible amplification fragments useful as polymorphic markers. Each of the 17 cultivars can be discriminated with a few primers. Results were analyzed for similarity among the cultivars and a cluster analysis was performed. These analyses revealed two main groups: one comprising primarily small-fruited cultivars grown mainly for oil production, and the other characterized by having large fruit. There was no apparent clustering of olive cultivars according to their geographic origins. Olive (Olea europaea) is one of the most ancient cultivated fruit tree species in the Mediterranean basin. It is the only Mediterranean representative of the genus Olea, which includes 35-40 species distributed over tropical and southern Africa, south Asia, eastern Australia, New Caledonia, and New Zealand (Zohary and Hopf 1993). Traditionally, morphological and phonological traits are used to identify olive cultivars. More recently, workers have found isozymes to be useful for cultivar identification and determining patterns of relatedness among cultivars. Pontikis et al. (1980) identified 27 olive cultivars, mostly of Greek origin, using 16 enzyme systems in pollen. Trujillo et al. (1990) found that by using five pollen enzyme systems they could distinguish 134 of 155 cultivars. Ouazzani et al. (1993) distinguished 33 of 44 cultivars using 9 enzyme systems in leaf tissue. Although isozyme analysis has proved useful in olive, mainly due to the high level of isozyme polymorphism present in the species, direct analysis of DNA could increase considerably the number of markers produced. Furthermore, because isozymes are products of gene expression, differential expression by environment, tissue-specificit y, and other factors is common and may make interpretation of results difficult. Random amplified polymorphic DNA (RAPD) analysis, first described by Williams et al. (1990) and Welsh and McClelland (1990), has proven to be a useful tool for genetic typing and mapping. Bogani et al. (1994) described preliminary results of RAPD analyses of olive cultivars. They used 5 decamer nucleotide primers to generate RAPD polymorphisms among 11 olive cultivars, but found no consistent relationships. In this paper, we report the use of RAPD markers to distinguish among 17 olive cultivars, and we discuss the use of RAPDs to study relationships among cultivars of this species. Materials and Methods Plant materials. Seventeen Olea europaea cultivars were used in this study (Table 1). These were obtained from a collection mainor publication 26 Sept. 94. Accepted for publication 11 Jan 1995. We acknowledge K. Pinney for her capable technical assistance and S. for his advice on technique, J. Hormaza was supported by an INIA rom the Spanish Ministry of Agriculture, The cost of publishing this paper d in part by the payment of page charges. Under postal regulations, this fore must be hereby marked advertisement solely to indicate this fact. om Universita degli Studi di Catania, Istituto di Coltivazioni Arboree, Via 5, Catania Italy 95123. To whom reprint requests should be addressed. dress: Dept. Fruticultura, S.I.A.-D.G.A., Apartado 727, Campus de 0080 Zaragoza, Spain. tained in experimental orchards at the Univ. of California, Davis. DNA extraction and RAPD analysis. Young olive leaves were collected in Spring 1993 and stored at –70C before DNA extraction. Total DNA was extracted from leaf tissue following the CTAB method of Doyle and Doyle (1987) with minor modifications. Young leaves (5.0 g) were ground in liquid nitrogen and mixed with 20 ml of CTAB buffer (100 mM Tris-HCl pH 8, 1.4 M NaCl, 20 mM EDTA, 2% CTAB, 1% PVP, 0.2% β− mercaptoethanol, 0.1 % NaHSO4). Samples were incubated at 65C for 1 h, mixed with an equal volume of chloroform–isoamyl alcohol (24:1), and centrifuged at 2000× g for 15 min. The aqueous phase was recovered and mixed with two-thirds volume of isopropanol. The nucleic acid precipitate was recovered with a glass hook, washed with 10 ml of 10 mM ammonium acetate in 76% ethanol, dried overnight, and resuspended in 1 ml of modified TE buffer (10 mM Tris-HCl pH 8, 0.1 mM EDTA). Extracted DNA was diluted to 10 ng·μl and used for PCR amplification. Forty decamer oligonucleotides (Operon Technologies, Alameda, Calif.) were used for PCR amplifications following the procedure of Williams et al. (1990), with some modifications. Amplification reactions were carried out in 25-μl volumes containing 10 mM Tris-HCl, pH 8.3, 50 mM KCl, 1.9 mM MgCl2, 0.00 1% gelatin, 100 μM each of dATP, dGTP, dCTP, and dTTP (Promega, Madison, Wis.), 0.4 μM primer, 0.75 units of AmpliTaq DNA polymerase (Perkin-Elmer-Cetus, Norwolk, Conn.) and 50 ng of genomic DNA. Each reaction mixture was overlaid with 25 μl of mineral oil to prevent evaporation. To destroy putative carryover products, reaction mixtures and mineral oil were placed on a UV (300 nm) transilluminator before addition of template DNA and DNA polymerase (Sarkar and Sommer, 1993). DNA amplification reactions were performed in a thermal cycler (PTC100; MJ Research, Watertown, Mass.) programmed for 1 cycle of 2 min at 94C followed by 40 cycles of 45 sec at 92C, 1 min at 36C, 2 min at 72C, for denaturing, annealing and primer extension, respectively. The last cycle was followed by incubation for 5 min at 72C; PCR products were stored at 4C before analysis. Amplification products were analyzed by gel electrophoresis in 2910 agarose (SeaKem; FMC, Rockland, Maine) in 1 x TBE buffer, stained with ethidium bromide, and photographed under UV light using Type 57 Polaroid film. Molecular sizes of amplification products were estimated using a 123 bp DNA ladder (Sigma Chemical Company, St. Louis). All reactions were repeated at least three times using different lots of Taq polymerase and only reproducible bands were used in further analyses. Each amplification fragment J. AMER. SOC. HORT. SCI. 120(3):538–542. 1995. Table 1. Olive cultivars included in this study and their country of origin.

Glucosinolates in Broccoli Stored under Controlled Atmosphere

Abstract: Content of total and individual glucosinolates were determined in, 'Marathon' broccoli florets (Brassica olerucea L. var. italica stored 7 days at 10C under air, 0.5% O 2, 0.5% O2 + 20% CO2 or 20% CO2 atmosphere, followed by transfer to air for 2 days. 'Marathon' broccoli contained glucoraphanin, glucobrassicin, neoglucobrassicin, glucoiberin, 4- methoxyglucobrassicin, progoitrin, glucoalyssin, and gluconasturtiin. The methylssulfinylalkylglucosinolates (glucoiberin and glucoraphanin) and the indol-3-ylmethylglucosinolates (glucobrassicin, neoglucobrassicin and 4- methoxyglucobrassicin) accounted for 78% and 20% of the total content, respectively, in freshly harvested broccoli. CA treatment and storage time had no significant effect on the relative content of these two groups of glucosinolates. Freshly harvested broccoli contained 47 µmol glucosinolate/g dry weight. The total glucosinolate content increased 42% and 21% during 7 days storage under air and 0.5% O2 + 20% CO2, respectively, as compared to freshly harvested broccoli, and decreased 15% in broccoli stored under 20% CO2. Treatment with 20% CO2 in the absence of 0, resulted in visible CO, injury and water soaking of the tissue. Aeration had no significant effect on total glucosinolate content but reduced the glucobrassicin content 35% in broccoli stored 7 days under 0.5% O 2 + 20% CO2 or 20% CO2atmosphere. In contrast, the 4-methoxyglucobrassicin content increased during storage under low O2 atmosphere and increased further after transfer to air. Plants belonging to the order Capparales including Brassicaceae, are characterized by their content of glucosinolate s (Bjerg and Sorensen, 1987a). Glucosinolates and their breakdown products are important aroma and flavor compounds in Brassica vegetables (MacLeod, 1976), such as cabbage, Brussels sprouts, broccoli, cauliflower, and horseradish. The most notable example is ally1 isothiocyanate in mustard and horseradish arising from enzymic breakdown of sinigrin. This compound causes a pungent and lachrymatory response upon cutting and chewing (Gilbert and Nursten, 1972). Indol-3-ylmethylglucosinolates, which occur in appreciable amounts in several Brassica vegetables, are of interest for their potential contribution of anticarcinoge nic compounds to

Superficial Scald of `Granny Smith' Apples is Expressed as a Typical Chilling Injury

Abstract: To examine the hypothesis that superficial scald of apple (Malus domestics Borkh.) is a chilling injury, 'Granny Smith' apples were stored at temperatures ranging from 0 to 20C, temperature-conditioned before storage, and warmed during storage. Fruit stored at 0 or 4C developed supeficial scald. At 10C, surface defects occurred but they were not typical symptoms of scald, and at 15 or 20C no symptoms developed. Accumulation of faroesene and conjugated trienes in fruit peel correlated with increasing ethylene production, which was greater at higher temperatures. However, concentrations of conjugated trienes were highest at 0 and 4C. When fruit were kept at 10C for 5 or 10 days before storage, scald development after storage was not reduced. An interruption of 0C storage with a single warming period at 10 or 20C reduced scald development after 25 weeks of storage, maximum reduction occurring when fruit were warmed for 3 to 5 days at 20C after 1 to 4 weeks at 0C. Amelioration of scald declined as time at 0C before warming increased. Diphenylamine application after conjugated trienes increased during warming, but at the end of storage (when scald was developing) the conjugated triene concentrations in peel were reduced in fruit that had been warmed. Warming slightly increased yellowing, softening, and greasiness of fruit after storage, We conclude that chilling induced superficial scald on 'Granny Smith' apples.

Browning Potential, Phenolic Composition, and Polyphenoloxidase Activity of Buffer Extracts of Peach and Nectarine Skin Tissue

Abstract: The relationship of phenolic composition and polyphenoloxidase activity (PPO, E.C. 1.14.18.1) to browning potential (BP) was studied in buffer extracts of peach (Prunuspersica L. Batsch) and nectarine (P. persica var. nectarine (L.) Batsch) fruit skin. The BP varied among cultivars with 'Flavorcrest' having the highest value and 'Maycrest' the lowest. On average, over 83% of the browning measured at the end of the 5-hour incubation occurred during the first hour. The total soluble phenolics (TSP), the total anthocyanin (TA), and glutathione content (GLU) varied among cultivars, but were not significantly correlated to the BP. Of the phenolics determined by HPLC, only chlorogenic acid had a significant positive correlation and epicatechin a significant negative correlation with BP by the first hour of incubation. The PPO activity, ranging from 4 to 11 optical density units per gram dry weight per minute among peaches and nectarines, was not significantly correlated with BP. However, no browning was detected if the buffer extract was previously boiled. These results indicated that browning in the buffer extracts of peach and nectarine skin tissue depends on the presence of PPO activity and chlorogenic acid, which are major contributors to enzymatic browning. Fruit browning, as aconsequence of bruising, is due to phenolic oxidation (Mathew and Parpia, 1971; Mayer and Harel, 1979; Vamos-Vigyazo, 1981). The destruction of fruit cellular compartmentation allows the phenolic substrates to be accessible to PPOs which catalyze the phenolic oxidation (Mayer and Harel, 1979). The concentration and composition of phenolic compounds andor activity of PPOs are often the major factors determining tissue browning development and intensity (Mathew and Parpia, 1971; Mayer and Harel, 1979). Furthermore, natural chemicals with antioxidant properties such as thio compounds may also play an important role in fruit browning development (Liyanage et al., 1993; Singleton et al., 1985). Due to the importance of visual appearance as a produce cosmetic quality parameter, tissue browning has long gained attention from horticultural researchers (Vamos-Vigyazo, 198 1). While numerous studies have used juice, whole fruit and fruit flesh systems, few of them have used skin tissue. Research on fruit skin browning, as aresult of friction damage, has only been reported for pears (Mellenthin and Wang, 1974; Ranadive and Haard, 1971). The potential for skin browning on other species including peach and nectarine have not been studied at all. Peach and nectarine skin discoloration is becoming an impor- tant problem for the California stone fruit industry especially on peach cultivars such as 'Flavorcrest', 'Elegant Lady', and 'O'Henry', and nectarine cultivars such as 'Fantasia', 'Royal Giant', and 'Flaming Red'. This skin cosmetic disorder is charac- terized by the formation of dark brown or black spots and/or light brown spots on the surface of the fruit. Dark brown and black spots commonly called black staining or inking occur as a consequence of abrasion damage to epidermal cells in combination with con- taminants (Cheng and Crisosto, 1994; Crisosto et al., 1992, 1993), but light brown spots commonly called skin browning may simply Receivedforpublication2Nov. 1994. Accepted forpublication 10Apr. 1995. This study was funded by a grant from the Califomia Tree Fruit Agreement. We thank Adel A. Kader and Betty Hess for their cooperation. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regula- tions, this paper therefore must be hereby marked advertisement solely to indicate this fact. 'Postdoctoral research associate. ?Assistant pomologist.

Genetic Relationships among Cultivars and Landraces of Lima Bean (Phaseolus lunatus L.) as Measured by RAPD Markers

Abstract: Knowledge of relative genetic distance among genotypes is useful in a breeding program because it permits organization of germplasm resources. Genetic distance (GD) was estimated among 65 Phaselous lunatus L.. accessions, which included 4 large-seeded and 7 small-seeded cultivars and 54 germplasm accessions (landrace's) from the Caribbean and North, Central, and South America. Based on 125 polymorphic random amplification polymorphic DNA (RAPD) bands, two major clusters, which generally correspond in seed size and geographic region to (be Mesoamerican and Andean gene pools, were observed among the landraces (GD = 0.726 ± 0.041). Four Fordhook cultivars and a landrace from the United States formed a separate cluster that is more distantly related to the small- (GD) = 0.561 ± 0.039) than to the large-seeded cluster (GD = 0.303 ± 0.022). The mean GD between the Andean and Mesoamerican (0.726), Mesoamerican and Fordhook (0.561), and Andean and Fordhook (0.303) clusters were all significant. The significant GD between the Andean and Mesoamerican groups supports the hypothesized existence of two major gene pools in lima bean. The RAPD marker diversity of the Mesoamerican group was the largest (0.1 10), followed by the Andean (0.097) and Ford hook (0.062) groups. The plot of the relationship between the coefficient of variation (cv) and sample size (number of bands) indicates that cvs as low as 10% for estimating CD between Andean and Mesoamerican lima bean accessions can be achieved by sampling as few as 100 bands.

Quantifying onion flavor compounds responding to sulfur fertility: sulfur increases levels of alk(en)yl cysteine sulfoxides and biosynthetic intermediates.

Abstract: Three onion (Allium cepa L.) cultivars were grown to maturity at five S fertility levels and analyzed for S- alk(en)yl-L-cysteine sulfoxide (ACSO) flavor precursors, γ- glutamyl peptide (γ- GP) intermediates, bulb S, pyruvic acid, and soluble solids content. ACSO concentration and composition changed with S fertility, and the response was cultivar dependent. At S treatments that induced S deficiency symptoms during active bulbing, (+)S-methyl-L-cysteine sulfoxide was the dominant flavor precursor, and the flavor pathway was a strong sink for available S. As S fertility increased to luxuriant levels, trans(+)-S-(1-propenyl)-L-cysteine sulfoxide (PRENCSO) became the dominant ACSO. (+)S-propyl-L- cysteine sulfoxide was found in low concentration relative to total ACSO at all S fertility treatments. With low S fertility, S rapidly was metabolized and low γ- GP concentration s were detected. As S fertility increased, γ- GP increased, especially γ- L-glutamyl-S-(1-propenyl)-L-cysteine sulfoxide, the penultimate compound leading to ACSO synthesis. Nearly 95% of the total bulb S could be accounted for in the measured S compounds at low S fertility. However, at the highest S treatment, only 40 % of the total bulb S could be attributed to the ACSO and γ- GP, indicating that other S compounds were significant S reservoirs in onions. Concentrations of enzymatically produced pyruvic acid (EPY) were most closely related to PRENCSO concentrations. Understanding the dynamics of flavor accumulation in onion and other vegetable Alliums will become increasing important as the food and phytomedicinal industries move toward greater product standardization and characterization.

Variation in the Quercetin Content in Different Colored Onions (Allium cepa L.)

Abstract: The aglycone, or free quercetin, and total quercetin content of 75 cultivars and selections was analyzed by reverse-phase high-performance liquid chromatography. Quercetin glycosides were hydrolyzed into aglycones. Total quercetin content in yellow, pink, and red onions varied from 54 to 286 mg·kg -1 fresh weight in different onion entries grown during 1992. White onions contained trace amounts of total quercetin. Free quercetin content in all the onions was low (< 0.4 mg·kg -1 ) except in '20272-G' (12.5 mg·kg -1 fresh weight). Bulbs stored at 5, 24, and 30C and controlled atmosphere (CA) for 0,1,2,3,4, and 5 months showed a most marked change in total quercetin content at 24C compared to other treatments, with a rise in mid-storage followed by a drop. Storage at 5 and 30C also demonstrated a similar change. However, total quercetin content did not vary significantly in bulbs stored at CA for 5 months. We conclude that genetic and storage factors affect quercetin content on onions. Given the many positive effects of vegetables on human health, there is increasing interest in foods and beverages that contain quercetin. Onions provide a useful model system to investigate the genetics of plant flavonols (Brown, 1980; Kuhnau, 1976). Another major interest of the food industry in flavonols is their use as therapeutic agents, particularly in cancer. It is surprising that, even though data are available on the presence of quercetin in onion, there has been little research conducted to enhance the content of this compound.

Color Mulches Influence Yield and Insect Pest Populations in Tomatoes

Abstract: Field studies were conducted for three seasons, Fall 1988 and Spring and Fall 1989, on the effect of six mulch colors: blue, orange, red, aluminum, yellow, and white (fall) or black (spring), on fruit yields and on insect vectors of Sunny’ tomato (Lycopersicon esculentum Mill.). Plant growth and yields were inconsistent with mulch colors during the three seasons. In Fall 1988, in a once-over harvest, extra-large (≥ 70 mm diameter) and marketable fruit yields were higher (P ≤ 0.05) on blue than on the conventional white mulch. In Spring 1989, early marketable yields on red mulch were higher than on black mulch, and in Fall 1989, under high stress from tomato mottle virus (TMoV) transmitted by silverleaf whitefly [Bemisia argentifolii (Bellows and Perring)], seasonal yield of extra-large fruit was better on orange than white mulch. In Fall 1988 and 1989, fruit size and marketable yields were reduced on yellow mulch. Aphids (Aphididae), thrips (Thripidae), and whiteflies were counted monthly in traps placed on the mulched beds. Aphids were least numerous on the aluminum and yellow and most numerous on the blue mulch. Where differences occurred, the fewest thrips were captured on aluminum and the fewest whiteflies were captured on the yellow, aluminum and orange mulches. Although differences were not always significant, the fewest adult whiteflies also were observed on foliage of tomato plants grown on these latter three mulches. Later in the seasons, as plant foliage covered the mulch, differences in the number of insects captured were similar for all mulch colors. Low numbers of whiteflies on the orange and aluminum mulches early in Fall 1989 delayed virus symptom development and increased yields. Virus symptom development was not delayed and yields were low on the yellow mulch, in spite of the low number of whiteflies. When averaged over all mulch colors, extra-large and marketable fruit yields increased linearly with delayed symptom development. It is proposed that, under high insect stress, mulches should be selected for their effects on insects in addition to their effects on soil temperature and plant morphology. Tomatoes in Florida are grown on raised beds covered with polyethylene film (Geraldson et al., 1965). In the winter and spring, black, and in the summer and fall, white or white on black polyethylene film (mulch) is used. Mulch cover, especially various color mulch covers, create a specific microenvironment for the plants. The changes in microenvironment, compared to bare ground, include changes in root-zone temperature and in the quantity and quality of light reflected from the mulch surface back to the leaves (Decoteau et al., 1989; Lamont, 1993). The reflected energy from the mulch affects not only plant growth, development, fruit yields (Decoteau et al., 1989; Schalk et al., 1979), and the behavior of insects that visit the plants (Kring, 1972). Yellow and, to a lesser degree, orange mulches attracted green peach aphids [Myzus persicae (Sulzer)], while aluminum and silver mulches repelled aphids (Adlerz and Everett, 1968; Wolfenbarger and Moore, 1968). Thrips [Thrips tabaci (Lindeman)] and Frankliniella sp. were also repelled by reflective (aluminum or silver) mulches (Brown and Brown, 1992; Scott et al., 1989). Since aphids and thrips are important vectors of plant pathogenic viruses (Matthews, 1991), the property of mulches to attract or to repel insects can be very important in protecting plants from virus diseases. Mulch color may also influence the insect species that visit plants. For example, Schalk and Robbins (1987) found that aphids were repelled by aluminum mulch, but fruit injury increased due to or publication 6 Sept. 1994. Accepted for publication 20 Apr. 1995. ricultural Experiment Station Journal series no. R-04000. The cost of this paper was defrayed in part by the payment of page charges. Under ations, this paper therefore must be hereby marked advertisement solely

Stem water potential and apple size.

Abstract: The sensitivity of leaf (ψ leaf) and stem (ψ stem) water potential and stomatal conductance (g S) to soil moisture availability in apple (Malus domestics Borkh.) trees and their correlation with yield components were studied in a field experiment. Two drip irrigation treatments, 440 mm (H) and 210 mm (L), were applied to a 'Golden Delicious' apple orchard during cell enlargement stage (55-173 days after full bloom). Data collected included ψ ψ stem, y leaf, gS, and soil water potential at 25 (ψ (ψ soil-25) and 50 cm (ψ soil-50). No differences in midday ψ leaf's were found between irrigation treatments. Stem water potential was higher in the H treatment than in the L treatment in diurnal measurements, and at midday throughout the season. Stomatal conductance of the H treatment was higher than the L treatment throughout the day. Stomatal conductance between 0930 and 1530 HR were highly correlated with ψ stem. The H treatment increased the percentage of fruit >65 mm, and increased the proportion of earlier harvested fruit reaching marketable size compared to the L treatment. Fruit size in the first harvest and the total yield were highly correlated with ψ stem. The degree of correlation between plant water stress indicators and yield component decreased in the following order: ψ stem > ψ ψ soil-25, > ψ ψ soil-50 > ψ leaf. The data suggest that midday ψ stem may serve as a preferable plant water stress indicator with respect to fruit size.

Identifying Olive Cultivars by Isozyme Analysis

Abstract: Pollen samples of 155 olive (Olea europaea L.) cultivars from different origins were analyzed to study isoenzymatic variability in five enzyme systems: alcohol dehydrogenase (ADH), esterase (EST), glucose phosphate isomerase (GPI), leucine aminopeptidase (LAP), and malic enzyme (ME) using starch gel electrophoresis. Polymorphism was observed in all of the isozyme systems. ME, GPI, EST, and LAP were the most useful systems for identification of cultivars. Different combinations of banding patterns of these systems allowed us to identify 85% of the cultivars. The remainder were separated into groups of two or three cultivars that could be identified using morphological character- istics. No intracultivar polymorphisms were observed.

Benzyladenine Affects Cell Division and Cell Size during Apple Fruit Thinning

Abstract: Benzyladenine (BA), carbaryl (CB), daminozide (DM), and naphthaleneacetic acid (NAA) were applied postbloom as fruitlet thinning agents to mature ‘Empire’ apple (Malus domestica Borkh.) trees. BA, NAA, and CB reduced fruit set and yield per tree, and increased fruit size, percent dry weight, soluble solidscontent and return bloom. Fruit size was reduced, return bloom, length : diameter ratio and flesh firmness were increased, and fruit set and yield unaltered by DM. Although fruit set and yield were similar for BA, NAA, and CB, BA treated fruit were larger, indicating that BA increased fruit size beyond the effect attributable to chemical thinning alone. BA increased the rate of cell layer formation in the fruit cortex, indicating that BA stimulated cortical cell division. NAA, CB and DM had no effect on cell division rate. Mean cortical cell diameter at harvest was increased by NAA and CB and reduced by DM. Cell diameter at harvest in BA-treated fruit was similar to the control. These data support the hypothesis that BA-induced fruit size increase in ‘Empire’ apple results from greater numbers of cells in the fruit cortex, whereas the fruit size increase due to NAA or CB is a consequence of larger cell size. Chemical names used: N(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; 1-napthaleneacetic acid (NM); 1naphthalenyl methylcarbamate [carbaryl (CB)]; butanedioic acid mono (2,2dimethyl hydrazide) [daminozide (DM)]. Fruitlet thinning is an essential part of the commercial production of quality apples. Blossom or fruitlet thinning early in the season improves fruit size at harvest and increases return bloom, thereby reducing the biennial bearing habit of apple trees (Westwood, 1993). The cytokinin benzyladenine (BA) is now registered for use as a chemical thinner for apple as a formulation containing both BA and gibberellic acid (Abbott Laboratories, 1993). BA effectively thins many cultivars, including ‘Empire’ (Elfving and Cline, 1993a, 1993b; Greene et al., 1990) ‘McIntosh’, (Greeneand Autio, 1989), ‘Golden Delicious’ (Greene et al, 1990), and ‘Idared’ (Elfving, 1989). BA thins most cultivars at concentrations from 25 to 100 mg·liter (Bound et al., 1991; Byers and Carbaugh, 1991; Elfving, 1991; McLaughlin and Greene, 1984). BA also increases return bloom in many apple cultivars (Bound et al., 1991; Elfving and Cline, 1993a, 1993b; Greene et al, 1990) and increases fruit size more than would be expected from thinning alone (Greene et al., 1992; McLaughlin and Greene, 1984). Cytokinins promote cell division in apple tissue (Letham, 1958) and cell division is still underway in fruits when BA is applied for thinning (Denne, 1963a, 1993b; Schechter et al, 1993a, 1993b). These circumstances have led to speculation that BA used as a thinner may affect the rate and/or duration of cell division in the apple fruit. The objective of this investigation was to examine the effect of BA used as a chemical thinner on cell division and cell size in ‘Empire’ apple in comparison to the chemical thinners or publication 23 Dec. 1994. Accepted for publication 14 Apr. 1995. ch was supported by operating grant no. A6697 of the Natural Sciences ering Research Council (NSERC) of Canada held by J.T.A.Proctor and graduate scholarship held by Paul T. Wismer. We gratefully acknowlsistance of Larry Peterson, Dean Louttit, Jean Gerrath, Mary Born, and val. Mention of a product or trade name does not constitute a guarantee of the product by the Univ. of Guelph or the Horticultural Research Ontario nor an endorsement over similar products not mentioned. The lishing this paper was defrayed in part by the payment of page charges. al regulations, this paper therefore must be hereby marked advertiseto indicate this fact. dress: Tree Fruit Research and Extension Center, Wash. State Univ., estern Avenue, Wenatchee, WA 98801. naphthaleneacetic acid (NAA) and carbaryl (CB) and the growth regulator daminozide (DM), which inhibits cell division in apple under some circumstances (Martin et al., 1968). Materials and Methods All trees used for this investigation were mature, annually bearing ‘Empire’ growing at the Horticultural Research Institute of Ontario Horticultural Experiment Station in Simcoe, Ontario. The trees were growing in north-south rows and were trained to a conventional central leader form (Tehrani et al., 1988). Standard commercial practices for fertilization and pest control were followed (Ontario Ministry of Agriculture and Food, 1990). BA effects, Expt. 1. In 1990 a block of 68 lo-year-old ‘Empire’/ M.26 trees spaced at 3.7 × 5.5 m was used. The trees were of similar size and bloom density, and the single-tree plots were distributed in a completely randomized design. Full bloom occurred on 9 May. On 31 May (mean fruit diameter 10.5 ± 1.4 mm), 20 or 30 trees were each sprayed to the drip point with 50 or 100 mg·liter BA (ABG-3062, Abbott Laboratories, North Chicago, Ill.), respectively. This formulation contains no gibberellic acid. The remaining 18 trees were left unsprayed to serve as control. More trees were used in the two chemically thinned groups than in the control group to avoid excess fruit load reduction from repeated removal of fruit samples for microscopic tissue analyses. At final harvest all fruit from each tree were counted and weighed to determine total yield per tree. The number of normally developed seeds per fruit was counted in a 30-fruit sample from each treatment. In Spring 1991, one representative limb per tree was selected, the circumference measured and all bloom clusters counted (Forshey and Elfving, 1979a, 1979b; Lombard et al., 1988). Chemical thinner effects, Expt. 2. In 1991 a block of lo-yearold ‘Empire’/M.7 trees spaced at 4.9 × 6.7 m was used. Trees were grouped into ten randomized complete-blocks of five trees according to tree size, bloom density and location. Before bloom, one representative limb 12 to 15 cm in circumference was tagged on each tree for use in bloom and fruit set counts (Forshey and Elfving, 1979a, 1979b). Full bloom occurred 13 May. On 27 May (mean J. AMER. SOC. HORT. SCI. 120(5):802-807. 1995. fruit diameter 13.1 ± 1.4 mm), one tree in each block was sprayed with either BA 100 mg·liter (ABG-3062), NAA 15 mg·liter, CB 1000 mg·liter or DM 1500 mgliter’. The fifth tree in each block was not sprayed and served as the control. Blossom clusters were counted on each tagged limb before full bloom and the number of fruit counted after June drop. At final harvest the total number and weight of fruit on each tree were recorded. Twenty fruit per tree were sampled for length, diameter, fresh and dry weight measurements. Fruit length and diameter were measured by laying the fruit end-to-end and side-toside in a V-shaped trough and measuring total length and diameter. After removing the pedicel, each fruit was weighed fresh (FW) and then cut into slices and oven-dried to a constant dry weight (DW) at 80C. Ten of these same fruit were cut and the numbers of aborted and apparently viable seeds were determined. For the remaining 10 fruit, flesh firmness was determined with a penetrometer (Effegi, Alfonsine, Italy; tip diameter 11.1 mm) on two sides of each fruit. Juice was collected during the firmness test and soluble solids content (SSC) was determined on a composite sample using a hand refractometer (Fisher Scientific, Unionville, Ont.). Return bloom counts were taken on the tagged limbs in spring 1992. Cell division and diameter, Expt. 1. To examine the number of cell layers and cell diameter in the fruit cortex, five well exposed fruit from 1 to 2 m height in the canopy were harvested randomly from each treatment on each sample date and preserved and stored in formalin-acetic acid-alcohol (FAA) [per 100 ml: 50 ml ethanol (95%), 5 ml glacial acetic acid, 10 ml formalin (37% formaldehyde), 35 ml distilled water] (O’Brien and McCully, 1981). Small fruits were preserved whole, while larger fruits were cut into pieces to allow for rapid fixation of the inner tissue. The samples were preserved so fruit cortex tissue could be examined at the cellular level at a later date following embedding, sectioning and staining of the tissue. For paraffin embedding and microtome sectioning, whole apples or apple pieces were removed from the FAA and rinsed in running water for 5 min. Equatorial transverse sections 3 to 4 mm thick were cut from each apple. For small apples (<2.5 cm in diameter) the whole disc was used, while for larger fruit, 2 quarters of the disc from opposite sides of the fruit were used. Discs were held in 70% ethanol until the paraffin embedding procedure began. The tissue discs were dehydrated in a graded alcohol series and cleared with xylene, embedded in paraffin and sectioned at 5 to 10 μm on a rotary microtome (Leica 1512, Willowdale, Ont.). Sections were stained with the periodic acid/Schiff’s reaction (O’Brien and McCully, 1981) and permanent mounts made. Using a light microscope (Zeiss Photomicroscope III, Oberkschen, W. Germany, magnification 63 to 400×), the number of cell layers in the cortex was determined using methodology similar to Denne (1960). For each apple the number of cells in a radial line from a sepal vascular strand and from a neighboring petal vascular strand to the epidermis was counted. Four counts were made per fruit, two from each side of the fruit. Cortex width was determined by measuring the distance from the same vascular strands to the epidermis. The mean radial cell diameter was calculated from width of the cortex divided by mean number of cells across the cortex. In 1991, fruit sampling was similar to that of 1990. Fruit sampling began at full bloom and at each sample date six fruit per treatment were harvested randomly. For fruit sampled up to 35 days after full bloom (DAFB), the paraffin embedding procedure and cellular analysis were the same as used in 1990. For fruit sampled 35 DAFB and later, sections were prepared by hand. Hand sectioning. Frui

Regulation of Fermentative Metabolism in Avocado Fruit under Oxygen and Carbon Dioxide Stresses

Abstract: Hass' avocado (Persea americana Mill.) fruit were kept in air, 0.25% O 2 (balance N2), 20 % O2 + 80% CO2, or 0.25% O2 + 80% CO2 (balance N2) at 20C for up to 3 days to study the regulation of fermentative metabolism. The 0.25% 02 and 0.25% 02 + 80% CO2 treatments caused accumulations of acetaldehyde and ethanol and increased NADH concentration, but decreased NAD level. The 20% O2+ 80% CO2 treatment slightly increased acetaldehyde and ethanol concentrations without significant effects on NADH and NAD levels. Lactate accumulated in avocadoes kept in 0.25 % 0 2. The 80% CO, (added to 0.25% O2) did not increase lactate concentration and negated the 0.25% O 2-induced lactate accumulation. Activities of PDC and LDH were slightly enhanced and a new isozyme of ADH was induced by 0.25% O 2, 20% O2 + 80% CO2, or 0.25 % O2+ 80% CO2; these treatments partly reduced the overall activity of the PDH complex. Fermentative metabolism can be regulated by changes in levels of PDC, ADH, LDH, and PDH enzymes and/or by metabolic control of the functions of these enzymes through changes in pH, ATP, pyruvate, acetaldehyde, NADH, or NAD. Chemical names used: alcohol dehydrogenase (ADH), adenosine triphosphate (ATP), lactate dehydrogenase (LDH), nicotinamide adenine dinucleotide (NAD), reduced NAD (NADH), pyruvate decarboxylase (PDC), pyruvate dehydroge- nase (PDH).

Reducing External Chilling Injury in Stored 'Hass' Avocados with Dry Heat Treatments

Abstract: Hass' avocados (Persea americana Mill.) were heated in air at 25 to 46 °C for 0.5 to 24 hours and stored at 0, 2, or 6 °C. After storage, fruit were ripened at 20 °C and their quality was evaluated. In unheated fruit, external chilling injury occurred in fruit stored at 0 or 2 °C, but not 6 °C. Chilling injury was also evident after storage at 2 °C in fruit heated at 34 °C, and to a lesser extent in fruit heated at 36 °C. A heat treatment (HT) of 38 °C for 3, 6, or 10 hours and 40 °C for 0.5 hour further reduced external chilling injury induced by storage at 2 °C. These HT's did not reduce internal fruit quality and resulted in more marketable fruit than unheated fruit stored at 6 °C. Low-temperature storage and HT slowed avocado ripening, resulting in longer shelf life after storage. In flesh tissue sampled directly after selected HT's, the levels of mRNA homologous to cDNA probes for two plant heat-shock protein (HSP) genes (HSP17 and HSP70) increased to a maximum at 40 °C and declined at higher temperatures. These increases in gene expression coincided with the extent to which HT's prevented chilling injury. Hot- air HT's confer significant protection against low-temperature damage to avocados.

Characterizing and Quantifying Anthocyanins in Red Pears and the Effect of Light Quality on Fruit Color

Abstract: Additional index words. Pyrus communis, Rosaceae, chromaticity Abstract. The anthocyanin in 'Sensation Red Bartlett' pear skin was characterized and quantified, and the effect of light quality on fruit color development was evaluated. Anthocyanin concentration was related to fruit chromaticity values. Pigments were analyzed using high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC). One of two spots detected in the TLC chromatogram did not change color with molybdate sprays, indicating the possible presence of peonidin. HPLC analysis confirmed the presence of a major and a minor pigment, which co-eluted with cyanidin 3-galactoside and peonidin 3-galactoside. Monomeric anthocyanins in the pear skin extract were 6.83 mg/100 g of fruit peel. To study light quality, gelatin filters allowing passage of different wavelengths of-light were attached over the exposed side of 'Sensation Red Bartlett' pears 1 month before harvest. Chromaticity was recorded before the filters were attached and after their removal at harvest using the Commission Internationale del'Eclairage (L*, a*, and b*) color space coordinates. Following color measurements, anthocyanin was extracted from individual skin disks. Skin beneath all filters yielded less hue than the control. Wavelengths that transmit above 600 nm had the largest effect on chroma, a*, and b* values. Fruit wrapped in aluminum foil to obscure all light had the highest luminosity. Wavelengths from 400 to 500 nm gave darker, less chromatic, and redder pear fruit. All treatments yielded higher anthocyanin content than the control. There was a tendency toward increased anthocyanin content with longer wavelengths. The simple linear regression of the log anthocyanin content on L* value and (a*/b*) 2 provided an R 2 = 0.41.

End-product Inhibition of Photosynthesis in Prunus cerasus L. in Response to Whole-plant Source-Sink Manipulation

Abstract: The source-sink ratio of l-year-old, potted 'Montmorency' sour cherry (Prunus cerasus) trees was manipulated by partial defoliation (D) or continuous lighting (CL) to investigate the phenomenon of end-product inhibition of photosynthesis. Within 24 hours of D, net CO2 assimilation rate (A) of the most recently expanded source leaves of D plants was significantly higher than nondefoliated (control) plants throughout the diurnal photoperiod. Between 2 and 7 days after D, A was 30% to 50% higher and stomatal conductance rate (g,) was 50% to 100% higher than in controls. Estimated carboxylation efficiency(k) and ribulose-1,5-bisphosphate (RuBP) regeneration rate increased significantly within 2 days and remained consistently higher for up to 9 days after D. Leaf starch concentration and dark respiration rate decreased but sorbitol and sucrose concentration increased after D. The diurnal decline in A in the afternoon after D may have been due to feedback inhibition from accumulation of soluble carbohydrates (sucrose and sorbitol) in the cytosol. This diurnal decline indicated that trees were sink limited. By 9 days after D, photochemical efficiency was significantly higher than in control plants. In the long term, leaf senescence was delayed as indicated by higher A and g S in combination with higher chlorophyll content up to 32 days after D. CL resulted in a significant reduction of A, g S, k, variable chlorophyll fluorescence (FV), photochemical efficiency, and estimated RuBP regeneration rate of the most recently expanded source leaves within 1 day. During the exposure to CL, A was reduced 2- to 3-fold and k was reduced up to 4-fold. The normal linear relationship between A and gS was uncoupled under CL indicating that A was not primarily limited by g S and since internal CO2 concentration was not significantly affected, the physical limitation to A imposed by the stomata was negligible. The decrease in FV and photochemical efficiency indicated that leaves were photoinhibited within 1 day. The decrease in instantaneous chlorophyll fluorescence after at least 1 day of CL indicated that there was a reversible regulatory mechanism whereby the damage to photosystem II reaction centers was repaired. Leaf chlorophyll content was not altered by 1,2, or 3 days of exposure to CL, indicating that photooxidation of chlorophytl did not occur. The time to full photosynthetic recovery from CL increased as the duration of exposure increased. CL plants that were photoinhibited accumulated significant starch in the chloroplast in a companion study (Layne and Flore, 1993) and it is possible that an orthophosphate limitation in the chloroplast stroma was occurring. D plants that were continuously illuminated were not photosynthetically inhibited. After 7 days of CL, plants that were then partially defoliated yet remained in CL photosyntheti- cally recovered within 5 days to pre-CL values. Under the conditions of this investigation, end-product inhibition of A occurred in young, potted sour cherry trees but the mechanism of action in D plants was different than in CL plants. Plant growth and productivity may be limited by the production or use of photosyntheti c carbon compounds (photoassimilates). Sucrose and starch are the primary end-products of leaf photosyn- thesis inmost higher plants, where sucrose is the main translocated carbohydrate and starch is a temporary storage carbohydrate that accumulates in the chloroplast. Sorbitol, a sugar alcohol, is an additional important translocated form of photoassimilate in Pru- nus species (Loescher, 1987). The capacity of sink tissues to use

Development of Aroma Volatiles and Color during Postharvest Ripening of `Kent' Strawberries

Abstract: Kent' strawberries were harvested at red, pink, and white stages of development, and stored at 15C in the light. Fruit were sampled over a 10-day period and evaluated for volatile production and surface color. Volatile production by red and pink fruit peaked after 4 days of storage. Maximum volatile production by red fruit was 8- and 25-fold greater than maximum production by pink and white fruit, respectively. Aroma volatiles were not detected in the headspace over white berries until 4 days following harvest after which volatile production increased through the tenth day of storage. Changes in the surface color of white berries during postharvest ripening coincided with the production of volatiles. In another experiment, red, pink, and white 'Kent' strawberries were stored for 3 days at 10 or 20C in the dark or light. Fruit were then evaluated for volatile production, weight loss, anthocyanin content, and surface color changes. White berries produced volatile esters after 3 days of storage at 20C in the light. Both light and temperature influenced the relative production of the volatiles produced by pink fruit. Fresh weight loss, color change, and anthocyanin content were temperature and light dependent. The strawberry is a nonclimacteric fruit in which ripening is characterized by softening, anthocyanin synthesis, synthesis of flavor, a decrease in acidity, and an increase in sugar content (Abeles and Takeda, 1990; Hulme, 1971; Woodward, 1972). Fruit harvested slightly underripe will ship better and have a longer shelf-life than fully ripe fruit (Mitchell et al., 1964). These less mature berries are firmer, will maintain their shine longer, and decay less (Pritts et al., 1976; Skrede, 1984), but are usually poorer in overall flavor than fully ripe berries (Smith and Heinze, 1958). The flavor and aroma of strawberries are important quality attributes that influence consumer acceptability. The relative im- portance of aroma compounds to the flavor of fresh strawberries has been rated by many investigators (Dirinck et al., 1981; Hirvi, 1983; Larsen and Poll, 1992; Perez et al., 1992; Schreier, 1980). While the volatiles contributing to aroma vary among cultivars, some of the most important contributors to aroma include ethyl butanoate, 2, 5-dimethyl-4-hydroxy-3(2H)-furanone, ethyl hexanoate, methyl butanoate, linalool, and methyl hexanoate. Investigations of changes in the profile of volatile compounds during strawberry maturation are limited. Yamashita et al. (1977) monitored the conversion of added pentanal to pentanol, pentyl acetate, and pentyl butanoate during maturation of 'Hoko' straw- berries. Immature fruit, 5 days after flowering, converted added pentanal to 1-pentanol. But no ester formation was observed. However, the production of 1-pentyl acetate and 1-pentyl n- butanoate increased dramatically between 30 and 40 days after flowering. Ito et al. (1990) analyzed volatile components in headspace vapors of an unpicked strawberry fruit and reported an increase in the total amount of the volatile compounds produced during ripening of the berry. The volatiles produced were mainly esters, including large amounts of methyl acetate and methyl Received for publication 9 June 1994. Accepted for publication 22 Dec. 1994. Contribution no. 2136. We thank K.B. McRae for advice on experimental planning, statistical analysis, and presentation of results, W. Kalt for advice on anthocyanin determination method and manuscript review, and P. Harrison and M. Jordan for technical assistance. This work was conducted with the financial support of the Canada-Poland Agricultural agreement. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1

Soil Temperature and Tomato Growth Associated with Black Polyethylene and Hairy Vetch Mulches

Abstract: Temperature and root length at selected locations within a raised bed under black polyethylene, hairy vetch (Vicia villosa Roth) residue, or bare soil were measured and correlated with tomato (Lycopersicon esculentum Mill.) growth. Early in the season, before the tomato leaf canopy closed, soil temperature was influenced more by vertical depth in the bed than by horizontal position across the bed. Maximum soil temperatures under black polyethylene averaged 5.7 and 3.4C greater than those under hairy vetch at 5 and 15 cm deep, respectively. More hours at optimum temperatures for root growth (20 to 30C) during the first 4 weeks of the season probably accounted for greater early root and shoot growth and greater early yield of tomatoes grown with black polyethylene than hairy vetch residue or bare soil. After canopy closure, soil temperatures under tomato foliage within the row were reduced by an average of 5.2 and 2.2C at 5 and 15 cm deep, respectively, compared to those on the outer edge of the beds. Most tomato roots were in areas of the bed covered by the tomato canopy where temperatures in all treatments remained in the optimum 20 to 30C range almost continuously. Soil temperature, therefore, did not explain why tomato plants in the hairy vetch treatment had equal or higher total yields than the black polyethylene or unmulched treatments.

Retention and the Kinetics of Uptake and Export of Foliage-applied, Labeled Boron by Apple, Pear, Prune, and Sweet Cherry Leaves

Abstract: 10 B, fruit trees Abstract. Leaf retention, uptake kinetics, total uptake (per unit leaf area), export kinetics, and the total export of foliage- applied, labeled B ( )O B-enriched boric acid) were determined for apple (Malus domestics Borkh.), pear (Pyrus communis L.), prune (Prunus domestics L.), and sweet cherry (P. avium L.). Foliar uptake of labeled B by shoot leaves was 88% to 96% complete within 24 hours of application. More than 50% of the B retained on shoot leaf surfaces following application was absorbed and exported within 6 hours of application. Genotypic differences in shoot leaf surface characteristics among the species tested greatly influenced the amount of solution retained per unit leaf area. Leaf retention capacity was the primary determinant of the quantity of B absorbed by and exported from shoot leaves following foliar application. On average, apple shoot leaves retained, absorbed, and exported at least twice as much labeled B per unit leaf area as prune and pear shoot leaves and three to four times as much as sweet cherry shoot leaves. The sink demand of nearby, mature apples did not affect the export of labeled B when applied to adjacent spur leaves, but the fruit imported 16% of their total B from the applied solution during a 10-day period. Despite extensive documentation for the immobility of B accumulated by leaves naturally (e.g., from the soil), the B accumulated by leaves following foliage application was highly mobile in all four species tested. Foliar B fertilization provides beneficial effects for a number of fruit crops. Increases in pollen germination rate (de Wet et al., 1989), fruit yield (Hanson, 1991a), fruit set (Batjer and Thompson, 1949), and fruit quality (Holevas and Biris, 1980) have occurred in response to foliar B applications made near the bloom period or during the growing season. The extent of nutrient redistribution from treated leaves to target organs partly determines the effectiveness of foliar nutrient applications (Weinbaum, 1988). Boron is considered to be among the least mobile of the essential plant nutrients, and under natural conditions (soil-derived B), B redistribution from leaves is very limited (Epstein, 1973; Raven, 1980; Larcher, 1975; Loneragan et

Sensitivity of Yield and Fruit Quality of French Prune to Water Deprivation at Different Fruit Growth Stages

Abstract: Additional index words. deficit irrigation. flowering, fruit growth stage, stem water potential, water stress Abstract. The sensitivity of French prune (Prunus domestica L. syn. 'Petite d'Agen') to water deprivation at various fruit growth stages was studied over 3 years in a drip-irrigated orchard. The soil was a poorly drained Rocklin fine sandy loam with a hardpan that varied from 4.75 to I m from the surface at the northern end of the orchard (shallow soil condition) to no hardpan apparent to 2 m below the surface at the southern end of the orchard (deep soil condition). Water deprivation during a) the first exponential phase of fruit growth or stage I, b) lag phase of fruit growth or stage II, c) first half of stage II, d) second half of stage II, e) second exponential fruit growth phase or stage III, and f) postharvest was compared to a fully watered control. Water deprivation caused the most severe reduction in tree water status when it was imposed over longer periods of time and during periods of high evaporative demand and also had mm-e severe effects under shallow soil conditions. Compared to the control treatment, deprivation during all of stage II (the most severe deprivation treatment) was associated with increased Ilowering, reduced fruit hydration ratio, and smaller fruit size under all soil conditions. Under deep soil conditions, deprivation during all of stage II resulted in increased return bloom, which was reflected in higher fruit loads and dry t-ha-' fruit yield. However, under shallow soil conditions, even though return bloom was increased with this treatment, fruit loads and dry t·ha -1 fruit yields were the lowest of all treatments. These differences in treatment effects in shallow vs. deep soil conditions were most likely the result of increased fruit drop, which occurred under shallow soil conditions as a result of rapid onset and increased severity ofstress. Treatments that had parallel effects in shallow and deep soil conditions resulted in statistically significant overall treatment effects, while those that had opposing effects in shallow vs. deep soil conditions did not show significant overall treatment effects. Substantial alternate hearing occurred, and, in general, dry fruit yields above ≈9 dry t·ha -1 resulted in a decrease in fruit load the following year, while loads below this value showed a subsequent increase. Based on a separate estimate of the theoretically stable value for each treatment, all deprivation treatments resulted in a higher sustainable fruit load compared to the fully irrigated control. This suggests that, for the purpose of prune fruit production, there may be an optimal level of tree water stress. California experienced drought cycles from 1976-80 and again from 1985-92. In Spring 1991 and 1992. many growers received reduced or no allocation from irrigation district surface water supplies. During these shortages, growers were faced with allocat- ing limited water to minimize detrimental effects on fruit yield and quality in the short term while striving to maintain healthy trees in the long term. Although weather related droughts are periodic. chronic shortages of agricultural water supplies arc likely due to increased urban and environmental demands. Previous work on water deprivation in prune has shown that it is relatively tolerant of water stress. Hendrickson and Veihmeyer (1934) showed that it took 4 years of no irrigation to obtain decreased trunk growth and 5 years to obtain decreased fruit yields relative to irrigated control trees. This study was conducted with widely spaced trees on deep valley soils. Both of these factors delay the development and reduce the severity of water stress, especially with high winter rainfall. Prune fruit hydration ratios were shown to be related to crop load, with lower fruit hydration ratios during light crop years (Hendrickson and Veihmeyer, 1939). Fruit hydration ratios have also been shown to be lowered by water

Leaf Carbohydrates and Flower Formation in Citrus

Abstract: The carbohydrate contents of the leaves of satsuma mandarin (Citrus unshiu Marc.) trees were altered before or during the low temperature flower induction period to determine the relationship between gross levels of carbohydrates and flower formation. Early removal of the fruit and girdling of the branches on either fruiting or defruited trees caused an accumulation of carbohydrates in the leaves and increased flower formation. Shading the trees resulted in a transient reduction in leaf carbohydrate levels and in a decrease in flower formation. Although a relationship between carbohydrate levels and flowering was consistently found, our results show that the gross levels of carbohydrates do not appear to limit flower formation in citrus.

Origin and Inheritance of Dwarfing by the Citrus Rootstock Poncirus trifoliata `Flying Dragon'

Abstract: Flying Dragon' Poncirus trifoliata L. Raf. is a dwarfing rootstock for citrus. Inheritance of dwarfing ability was studied in a population of open-pollinat ed seedlings of 'Flying Dragon'. Molecular marker genotypes suggest that all seedlings originated from selfing. Progeny seedlings were budded with 'Cutter Valencia' orange and planted in the field to evaluate the dwarfing effect of the seedling rootstock. At 5 years after planting, rankit analysis of the frequency distributions of trunk cross-sectional area and canopy volume suggested the presence of two overlapping distributions of 34 dwarf trees and 7 nondwarf. This ratio is consistent with inheritance of rootstock dwarfing as a single dominant gene for which 'Flying Dragon' is heterozygous. Two morphological characteristics of 'Flying Dragon', curved thorns and twisted trunk growth, were closely linked to, or pleiotropic effects of, the dwarfing gene. Bulked segregant analysis was used to identify three RAPD markers linked to the dwarfing gene. 'Flying Dragon' was identical to nondwarfing cultivars of trifoliate orange at 40 homozygous and heterozygous isozyme and RFLP markers; therefore, it is likely that 'Flying Dragon' originated as a mutant of a nondwarfing genotype and has not undergone sexual recombination since this event.

Synthetic cytokinin-1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU)-promotes fruit set and induces parthenocarpy in watermelon

Abstract: Applying a 200 ppm solution of CPPU to pollinated ovaries of watermelon (Citrullus lunatus Matsum) at anthesis increased fruit set from 26.9% (control) to 95%. Applying CPPU solutions to nonpollinated ovaries at anthesis induced parthenocarpy, yielding 65% and 89.5% fruit set, respectively with 20 and 200 ppm applications. However, 64% of the 20 ppm CPPU-treated parthenocarpic fruit stopped growth 10 days after treatment. Growth of CPPU-treated, pollinated, and nonpollinated fruit increased significantly compared with growth of control fruit during the first 10 days after treatment, but, except for the 20 ppm CPPU parthenocarpic fruit, growth subsequently slowed, resulting in fruit equal in size to the control by harvest. CPPU application did not affect soluble solids content of pollinated fruit, but reduced content of parthenocarpic fruit treated with 20 ppm. Fructose content was generally higher than glucose and sucrose at harvest. However, in pollinated fruit treated with 20 ppm CPPU, sucrose levels were higher than glucose and fructose. These results suggest that CPPU is practical for promoting fruit set and seedless fruit without adversely affecting fruit quality and development.

Stable Transformation of Gladiolus Using Suspension Cells and Callus

Abstract: More than 100 transgenic Gladiolus plants were recovered after particle bombardment of regenerable suspension cells and callus. For transformation, Gladiolus callus and suspension cells were co-bombarded with phosphinothricin acetyltransferase-(PAT) and s- glucuronidase (GUS) -expressing plasmids. Stably transformed calli were selected on medium containing either phosphinothricin (PPT) or bialaphos followed by transfer to a regeneration medium to recover transgenic plants. Stable transformation was confirmed by detection of the PAT gene by DNA gel blot analysis and by enzymatic assays to measure GUS activity. In general, particle bombardment of regenerable suspension cells rather than callus resulted in the largest number of transformants . The rate of co-expression for GUS in PPT-resistant plants was high (≈ 70%). Promoters that are typically more efficient in dicotyledonou s plants were very active in Gladiolus, a monocotyledono us bulb plant. Establishment of an efficient transformation protocol for Gladiolus will now allow the introduction of transgenes to confer resistance to the viral and fungal pathogens that decrease Gladiolus production.

Stigmatic Receptivity Limits The Effective Pollination Period In Kiwifruit

Abstract: The effective pollination period was determined in kiwifruit (Actinidia deliciosa (Chev.) Liang and Fergusonl and the factors affecting it were evaluated. The effective pollination period, measured as the capability to set fruit after hand- pollinating flowers of different ages, was 4 days; 5 days after anthesis fruit set decreased and 2 days later it was nil. Pollen tube growth did not appear to he a limiting factor since pollen tubes grew quickly and reached the base of the style 2 days after pollination and reached the ovules 1 day later. Ovules appeared viable for the 7 days following anthesis, and visibly degenerated within the following 3 days. Stigmatic receptivity was determined by the ability to sustain pollen germination after hand pollinating flowers of different ages. The duration of stigmatic receptivity closely fit the effective pollination period determined through fruit set. Thus, it appears that stigma receptivity is the main factor responsible for the short effective pollination period.

Spectral Filters and Growing Season Influence Growth and Carbohydrate Status of Chrysanthemum

Abstract: Additional index words. Dendranthema × grandiflorum, photomorphogenesis, light quality, plant growth regulation Abstract. The interactions of light quality and growing season on growth and carbohydrate content of chrysanthemum (Dendranthema × grandiflorum (Ramat.) Kitamura) plants were evaluated using 6% CuSO4and water (control) as spectral filters. Light transmitted through the CUSO4 filter significantly reduced plant height and internode length compared to control plants regardless of the season. However, the degree of response varied with growing season. Light transmitted through CUSO4 filters delayed flowering. Total number of flowers was not affected by spectral filter, but plants grown under CUSO4 filter had smaller flowers than those grown under the control filter. Light transmitted through CuSO 4 filter resulted in reduced leaf and stem soluble sugar (sucrose, glucose, and fructose) and starch concentrations regardless of the growing season. However, the magnitude of reduction was greater in spring- than in fall-grown plants. Stems of fall- grown plants had more starch deposition than spring-grown plants under both filters. Filters with specific spectral characteristics can be used as alternative means of producing compact plants in the greenhouses, however, the delay in flowering and smaller flowers could limit their use for growth control of plants intended for flower production. A wide range of nonchemical methods for growth regulation of ornamental crops has received much attention in recent years (Heins and Erwin, 1990; Latimer et al., 1991; McMahon and Kelly, 1990; Mortensen and Stromme, 1987). Our research focusing on manipulation of greenhouse light quality as a nonchemical alterna- ative indicated that light transmitted through CUSO 4 filters reduced plant height similar to chemical growth regulators and produced compact plants in a range of horticultural crops (McMahon and Kelly, 1990; Rajapakse and Kelly, 1992). Our results with minia- ture roses indicated that light transmitted through CUSO 4 filters interacted with growing season and altered flower development (Rajapakse and Kelly, 1994). Alteration of light quality in the greenhouse for plant growth regulation may be feasible with the use of electric light sources with various spectral qualities, by appropriate fluid roof greenhouses, and/or by developing green- house construction material with specific spectral properties. How- ever, further research is needed to enhance our knowledge of light quality as a nonchemical alternative. Although the light transmitted through CUSO4 filters reduced plant height and internode length, the mechanism of height control by CuSO4 filters is not well understood. In our previous experiments, we observed that the reduction of plant height and internode length by light transmitted through CUSO4 spectral filters could be reversed by weekly application of gibberellic acid (GA 3) or by exposure to end- of-day far-red (FR) light, suggesting that GA and phytochrome may be involved in the growth regulation under CuSO4 filters (Rajapakse and Kelly, 199 1; Rajapakse et al., 1993). Gibberellic acid increases soluble sugar and starch content in soybean (Glycine max L.) and Phalaenopsis amabilis leaves and promotes sink activity in the apical meristem (Cheikh and Brenner, 1992; Chen et al., 1994). Gibberellic acid also increases the activity of two key enzymes in sucrose metabolism, sucrose phosphate synthase activity (SPS) of soybean

Citrus Scion and Rootstock, Topping Height, and Tree Spacing Affect Tree Size, Yield, Fruit Quality, and Economic Return

Abstract: A factorial experiment begun in 1980 included 'Hamlin' and 'Valencia' sweet-orange scions (Citrus sinensis (L.) Osb.), and Milam lemon (C. jambhiri Lush) and Rusk citrange (C. sinensis x Poncirus trifoliata (L.) Raf.) rootstocks, tree topping heights of 3.7 and 5.5 m, between-row spacings of 4.5 and 6.0 m, and in-row spacings of 2.5 and 4.5 m. The spacing combinations provided tree densities of 370, 494, 667, and 889 trees ha. Yield increased with increasing tree density during the early years of production. For tree ages 9 to 13 years, however, there was no consistent relationship between yield and tree density. Rusk citrange, a rootstock of moderate vigor, produced smaller trees and better yield, fruit quality, and economic returns than Milam lemon, a vigorous rootstock. After filling their allocated space, yield and fruit quality of trees on Milam rootstock declined with increasing tree density at the lower topping height. Cumulative economic returns at year 13 were not related to tree density. Citrus and other tree fruits yield more during the early years of and then becomes less vigorous is desired. The range of dwarfing production when planted at higher densities (Cary, 1981; Jackson, rootstocks used by apple growers to manipulate tree size and 1985; Patil, 1987). However, the advantage of higher densities at fruiting characteristics is not currently available to citrus growers. tree maturity is less certain. For citrus, we proposed that yield at Although no satisfactory dwarfing rootstock for citrus is commer- maturity is independent of tree density over a range of densities cially available, citrus rootstocks do provide a modest range of tree (Wheaton et al., 1978). Production of modern mature apple or- vigor and final tree size (Castle et al., 1989). Another method of chards increased with tree density, however, possibly due to reducing vigor and tree size at maturity is the introduction of improved genetic material with a higher harvest index, rather than dwarfing citrus viroids into trees on susceptiblero otstocks (Hutton, from higher tree density per se (Jackson, 198.5).

Papaya fruit growth, calcium uptake, and fruit ripening

Abstract: The uptake of Ca by 'Sunset' papaya (Carica papaya L.) fruit and its role in ripening was studied. The highest mesocarp Ca uptake rate occurred in fruit that were <40 days postanthesis when fruit transpiration was probably highest. Ca uptake rate by the mesocarp was low, from 60 to 80 days postanthesis when fruit fresh and dry weight increased. Mesocarp Ca uptake rate increased again from 100 to 140 days postanthesis when fruit fresh weight growth rate declined and dry weight growth rate increased. Mesocarp Ca concentration did not significantly differ from the peduncle to the blossom end. although Ca was significantly higher in the outer than inner mesocarp at the fruit equator. Mesocarp Ca concentration fluctuated significantly throughout the year ranging from 68 to 204 µg·g -1 fresh weight (FW). Soil Ca application did not always increase fruit mesocarp Ca concentration, while K and N fertilization decreased mesocarp Ca concentration. Attempts to increase mesocarp Ca concentration by spraying CaCl 2 onto papaya fruit during growth and by postharvest vacuum infiltration and dipping of the cut peduncle into CaCl 2 were unsuccessful. Mesocarp Ca concentration was positively correlated to the firmness of ripe papaya fruit and the rate of softening of mesocarp plugs. Less correlation was found between fruit firmness and the ratio of Ca concentration to K or Mg concentration, or to Mg plus K concentrations. Mesocarp Ca concentration of 130 µg·g -1 FW or above was associated with slower fruit softening

Growth Analysis of Watermelon Plants Grown with Mulches and Rowcovers

Abstract: Crimson Sweet' watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of 'Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the 'Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom. In cool regions of the world, watermelon growth is limited by short growing seasons and low air and soil temperatures, particu- larly early in the growing season. Low air and soil temperatures, which occur in the spring and early summer, especially during the nights, often delay harvest dates and reduce yield. Rowcovers enhance plant growth and development by modifying air tempera- ture, soil temperature, humidity and light around the covered plants (Mansour, 1989).