Showing papers in "Journal of the American Society for Horticultural Science in 1992"

Stem-water Potential as a Sensitive Indicator of Water Stress in Prune Trees (Prunus domestica L. cv. French)

Abstract: Additional index words. evapotranspiration, leaf-water potential, soil water, stomatal conductance Abstract. The relative sensitivity of plant- and soil-based measures of water availability were compared for prune trees subjected to a range of irrigation regimes under field conditions. Over the growing season, leaf- and stem-water potentials (ψ) measured at midday exhibited clear differences between frequently irrigated trees and unirrigated trees that were growing on stored soil moisture. Stem ψ was less variable than leaf ψ, ψ, and the daily variability in stem ψ ψ was closely related to daily variability in evaporative demands, as measured by vapor pressure deficit (VPD). As a result of lower variability, stem ψ reflected the small stress effect of a moderate, 50% soil moisture depletion irrigation interval, whereas leaf ψ did not. The relation between soil water content and estimated orchard evapo- transpiration (ET) was influenced by local differences in soil texture within the experimental plot. The relation between stem ψ and ET, however, was not influenced by soil texture and, in addition, was very similar to the relation between stem ψ and leaf stomatal conductance. Both relationships indicated that a 50% reduction in leaf and canopy level water loss characteristics was associated with relatively small reductions (0.5 to 0.6 MPa) in stem ψ. ψ. Stem ψ appears to be a sensitive and reliable plant-based measure of water stress in prune and maybe a useful tool for experimental work and irrigation scheduling. Plant water stress under dry soil conditions is associated with various physiological responses, such as growth reductions and stomatal closure, which can reduce plant water use and can also limit overall plant productivity (Bradford and Hsiao, 1982). Ir- rigation to avoid plant water stress is a common practice, and the need for irrigation is often based on a soil-water balance approach, using estimates of environmental water demand (e.g., reference crop evapotranspiration (ET 0), Burman. 1980) and/or measures of soil-water status (Campbell and Campbell, 1982). The value of both of these measures, however, is limited, be- cause they are not directly related to the occurrence of plant water stress and hence may not be directly related to the symp- toms that ultimately reduce plant productivity. For instance, Denmead and Shaw (1962) found that under high ET0 conditions (6 to 7 mm·day -1 ), a relatively wet soil (soil matric potential greater than - 0.03 MPa) was required to support maximum plant transpiration. Under lower ET0 conditions, however (1.4

Foliar applications of potassium silicate reduce severity of powdery mildew on cucumber, muskmelon, and zucchini squash

Abstract: The effect of soluble potassium silicate applied to cucumber (Cucumis sativus L.), muskmelon (C. melo L.), and zucchini squash (Cucurbita pepo L.) on the severity of powdery mildew was examined. Application methods included amending nutrient solutions to a concentration of 1.7 mM Si and foliar sprays containing 1.7, 8.5, 17, and 34 mM Si. Untreated plants and plants sprayed with distilled water were used as controls. The leaves of all plants were inoculated with known concentrations of conidia of Sphaerotheca fuliginea (Schlecht.:Fr.) Poll. (cucumber and mum Mathai et al., 1978; Volk et al., 1958) and powdery mildew diseases of barley (Erysiphe gruminis DC. f. sp. hordei E m . Marchal on Hordeum vulgare L.) (Jiang et al., 1989), wheat (E. graminis D.C. f. sp. tritici Em. Marchal on Triticum aestivum L.) (Leusch and Buchenauer, 1989), and cucumber (S. fuliginea) (Menzies et al., 1991a). Previous studies of Si effects on plant disease have involved root absorption of Si from either soil or soilless media. Although the amendment of soilless media with Si can be adapted to greenhouse and similar industries (Menzies et al., 1991a; Samuels et al., 1991b), large amounts of Si must be applied to soils to adequately control diseases. For example, basal dressings of 250 and 500 kg sodium silicate/ha were required to reduce sheath blight of rice (Mathai et al., 1978) and an equivalent of 4500 kg SiO2/ha was necessary to control powdery mildew of wheat (Leusch and Buchenauer, 1989). A reduction of the incidence of a wilt pathogen of cucumber requires the application of 2000 to 4000 kg calcium silicate/ha or 2250 to 4500 kg potassium silicate/ ha (Miyake and Takahashi, 1983b). Foliar application of Si to field plants is potentially a viable alternative to root-zone applifor publication 5 Nov. 1991. Accepted for publication 6 May 1992. esearch Station Contribution no. 440. We acknowlege the assistance muels, D. Vianzon, C. Koch, and T. Helmer, the statistical advice , Research Station, Agriculture Canada, Vancouver, B.C., and the the B.C. Greenhouse Vegetable Research Council and the Science B.C. Mention of a trademark or proprietary product does not imply nt of the products named or criticism of other products that may also . The cost of publishing this paper was defrayed in part by the payage charges. Under postal regulations, this paper therefore must be rked advertisement solely to indicate this fact. Scientist. cation. This method of Si application to control disease has been reported only once, to our knowledge. Aleshin et al. (1986) applied sprays of sodium metasilicate (440 mg·liter-1) and 1-ethoxysilatran (180 mg·liter -l) and reduced the degree of rice blast infestation on both resistant and susceptible rice cultivars. The objective of our study was to determine the extent of control of powdery mildew diseases of cucumber, muskmelon, and zucchini squash achieved through foliar or root applications of soluble potassium silicate, and the duration of control that may be obtained with foliar applications. Materials and Methods Long English cucumber (‘Corona’), muskmelon (‘Earlisweet’) and zucchini squash (‘Select’) were used in the experiments. Effective Si concentrations for foliar application. Cucumber, muskmelon, and zucchini squash plants were grown from seed sown in rockwool cubes (Grodan, Roermond, Holland), arranged at random on three greenhouse benches. Eight randomly chosen plants of each species were watered as needed with a nutrient solution containing ( in mM ): 1.75 Si, 13.0 NO3, 1.5 H 2P O4, 7.5 K, 3.5 Ca, 1.0 Mg, and 1.0 to 1.5 SO4; and (in μ M ) 18.8 Fe, 5.5 Mn, 0.9 Zn, 0.2 Cu, 18.1 B, and 1.0 Mo, with a pH of 6.0. Silicon was added in the form of potassium silicate as product K6 (National Silicates Ltd., Toronto, Ont.). The remaining plants were watered with a solution (pH 6.0) containing the same nutrients but without added potassium silicate (the Si and K contents of the solution were 0.05 and 7.0 m M , respectively). Foliar treatments were applied when cucumber and zucchini squash had two fully expanded leaves and muskmelon had three. Treatments included an untreated control, a distilled water spray (pH 5.5), and Si sprays of 1.7, 8.5 (not applied to the zucchini squash), and 17.0 mM (also containing 0.5, 2.5, and 5.0 mM K, respectively). The Si sprays were prepared by diluting the appropriate amount of potassium silicate in distilled water and adjusting to pH 5.5 with phosphoric acid. A drop of Tween 20 J. Amer. Soc. Hort. Sci. 117(6):902-905. 1992. Table 1. The effect of Si treatments on the number of colonies of powdery mildew on cucumber, muskmelon, and zucchini squash. z Colonies established (no.)

Soluble silicon sprays inhibit powdery mildew development on grape leaves

Abstract: The effect of root or leaf applications of soluble Si on severity of grape (Vitis vinifera L.) powdery mildew (Uncinula necator (Schwein) Burrill) was determined. On potted plants, root-feeding at 1.7 m M Si had no effect on disease severity, but foliar sprays at 17 m M Si substantially reduced the number of mildew colonies that developed on inoculated leaves. Scanning electron micrographs showed that, on Si-sprayed leaves, hyphae did not develop in areas where thick Si deposits were present on the leaf surface; and where surface deposits were not present, Si was translocated laterally through the leaf and surrounded the appressoria. Leaves on plants that were fed Si via roots showed a similar deposition of Si surrounding the appressoria. On water-sprayed leaves and leaves from untreated plants, internal deposition of Si was more variable and generally less than on Si-sprayed or root-fed plants. Conidia germination and germtube development on agar media were weakly promoted by the presence of Si. Reduced severity of grape mildew by Si sprays may be partly due to a physical barrier to hyphal penetration and to a resistance response involving the lateral movement of Si and its deposition within the leaf at fungal penetration sites. In monocot crops, the association between Si and reduced severity of fungal diseases has been known for some time. Ger- mar (1934) reported that wheat (Triticum aestivum L.) plants supplied with Si are more resistant to powdery mildew (Erysiphe graminis f. sp. hordei) than control plants. Since then, Si has been implicated in several other monocot disease resistance re- sponses, including sorghum (Sorghum vulgare Pert.) resistance to anthracnose (Colletotricum graminicolum) (Narwal, 1973), barley (Hordium vulgare L.) and wheat resistance to powdery mildew (E. graminis f. sp. hordei) (Jiang et al., 1989; Kunoh and Ishizaki, 1976; Leusch and Buchenauer, 1989; Sargent and Gay, 1977), and rice (Oryza sativa L.) resistance to blast (Pir- icularia oryzae Cav.), brown spot (Bipolaris oryzae Shoemaker) and sheath blight (Corticium sasakii Shiriai) (Aleshin et al., 1986; Datnoff and Snyder, 1991; Mathai et al., 1978; Volk et al., 1958). The exact role silica plays in enhancing disease re- sistance in monocots is as yet undetermined, but localized de- posits of Si have been found in host tissue surrounding fungal haustoria (Kunoh and Ishizaki, 1976; Sargent and Gay, 1977). In dicots, less attention has been paid to the association be- tween Si and resistance to fungal infection. Although Wagner (1940) reported that cucumber powdery mildew severity was reduced by supplying plants with Si, current interest in this phenomenon was not spawned until the mid-1980s, when it was reported that the natural incidence of powdery mildew was re- duced by feeding Si to solution-cultured cucumbers (Adatia and Besford, 1986; Miyake and Takahashi, 1983). The reduction in

Modified-atmosphere Packaging of Blueberry Fruit: Effect of Temperature on Package O2 and CO2

Abstract: Highbush blueberry (Vaccinium corymbosum L. 'Bluecrop') fruit sealed in low-density polyethylene pack- ages were incubated at 0, 5, 10, 15, 20, or 25C until O 2 and CO2 levels in the package reached a steady state. A range of steady-state O2 partial pressures (1 to 18 kPa) was created by placing a range of fruit weights within packages having a constant surface area and film thickness. The steady-state O 2 partial pressure in packages containing the same weight of fruit decreased as temperature increased, indicating the respiratory rate rose more rapidly (i.e., had a greater sensitivity to temperature) than O 2 transmission through the film. Steady-state O 2 and CO2 partial pressures were used to calculate rates of O 2 uptake. CO2 Production. and the respiratory quotient (RO). The effects of tem- perature and 02 partial pressure on O 2 uptake and CO2 production and the RQ were characte~zed. The steady-state O, partial pressure at which the fruit began to exhibit anaerobic CO 2 production (the RQ breakpoint) increased with increasing temperature, which implies that blueberry fruit can be stored at lower O 2 partial pressures when stored at lower temperatures. Studies using controlled-atmosphere (CA) storage techniques have indicated that shelf-life extension can be obtained for blue- berry (Vaccinium spp.) fruit using combinations of elevated CO 2 and reduced O 2 in the storage environment (Ceponis and Cap- pellini, 1985; Smittle and Miller, 1988). CA storage of high- bush blueberry fruit is now a commercial reality and current conditions range from 1.5 to 2.5 kpa O 2 (1% O2 = 1.013 kPa O 2 at 1 atm) and 5 to 12 kPa CO2 at 0C. Present-day commercial techniques for packaging blueberry fruit do not modify O 2 and CO 2 to levels that would enhance storage. Modified-atmosphere packaging (MAP) has the poten- tial to provide low O 2/high CO2 regimes similar to those of CA storage, but throughout the marketing chain. Ideally, a package should maintain the appropriate atmospheric composition over the range of temperatures commonly encountered between har- vest and consumption. Poor temperature control, however, can cause package O 2 levels to drop low enough to induce anaerobic

A Theoretical Concept of Compositional Nutrient Diagnosis

Abstract: The premises underlying univariate (CVA = critical value approach) and bivariate (DRIS = diagnosis and recommendation integrated system) diagnostic systems were reexamined with regard to compositional data analysis (CDA). CDA recognizes a structure of dependence among plant nutrients, the bounded sum constraint to one (the whole composition equals 100% or 1), and removes the curvature problem carried by crude components and by dual ratios or logratios when treated in isolation. Linearization by “rowcentered logrationing” of nutrient fractions shows great potential for carrying multivariate diagnosis and principal component analysis on nutrient data. Compositional nutrient diagnosis (CND) is supported by the theory of CDA. CND is the multivariate expansion of CVA and DRIS and is fully compatible with PCA. CND takes all possible nutrient interactions into account. CND nutrient indices are composed of two separate functions, one considering differences between nutrient levels, another examining differences between nutrient balances (as defined by nutrient geometric means), of individual and target specimens. These functions indicate that nutrient insufficiency can be corrected by either adding a single nutrient or taking advantage of multiple nutrient interactions to improve nutrient balance as a whole. A theoretical interpretative table is presented for CND. Mineral composition of plant tissues, expressed as concentrations or relative (ratio) values, forms the basic numerical information for diagnosing nutrient status in plants. Bates (1971) reported that the CVA to the interpretation of nutrient deficiency, sufficiency, or excess was affected to a large extent by nutrient interactions and plant age. DRIS was found to improve diagnosis as compared with CVA by taking into account dual interactions expressed as nutrient ratios (Walworth and Sumner, 1987). Inconsistency between CVA and DRIS has been reported (Alkoshab et al., 1988; Beverly, 1987a), but DRIS generally shows greater diagnostic efficiency (Walworth and Sumner, 1989). Beverly (1987a, 1987b) used the logarithmic transformation to improve data distribution of nutrient ratios from population data to generate DRIS norms. When dry matter values (DM) are identical over all nutrients components, i.e., in individual plant tissues, dual logratioing can provide a single correction factor for a nutrient xi given another nutrient xk in conformity with the DRIS approach: log(x i/xk) = log(xi) – log(xk) [1] Holland (1966) observed that as the number of nutrients to be examined simultaneously increases, the consistency of diagnosis increases until the method of interpretation involves all nutrients. “He concluded that a reasoned application of principal component analysis, possibly after logarithmic transformation to linearize functions of original variates, could improve the understanding of leaf composition as compared with any examination of nutrients by univariate (CVA), bivariate (dual ratios or logratios as of DRIS), or trivariate (ternary diagrams) diagnostic tools. Indeed, the constancy of forms of nutrient expression has still not been adequately researched, and the premises underlying interpretation of foliar analysis as practiced today should be reexamined (Walworth and Sumner, 1989). for publication 12 July 1991. Accepted for publication 12 Nov. 1991. rch was supported by the Natural Sciences and Engineering Research f Canada. The cost of publishing this paper was defrayed in part by ent of page charges. Under postal regulations, this paper therefore ereby marked advertisement solely to indicate this fact.

The Role of Carbohydrates in Active Osmotic Adjustment in Apple under Water Stress

Abstract: Greenhouse grown 2-year-old potted 'Jonathan' apple trees (Malus domestica Borkh.) were subjected to various levels of water stress in February. Midday leaf water potential (ψ w), leaf osmotic potential (ψ S), soluble sugars, and starch contents of mature leaves were measured throughout the development of water stress to determine whether active osmotic adjustment could be detected and whether carbohydrates were involved. Active adjustments of 0.6 MPa were observed 3 and 5 days, respectively, after water stress was initiated. Leaf turgor potential (ψ P) could not be maintained through the osmotic adjustment when ψ W dropped below -1.6 MPa. Sorbitol, glucose, and fructose concentrations increased while sucrose and starch levels decreased significantly as water stress developed, strongly suggesting that sugar alcohol and monosaccharide are the most important osmotica for adjustment. Sorbitol was a primary carbohydrate in the cell sap and accounted for > 50% of total osmotic adjustment. The partitioning of newly fixed W-labeled photosynthates in mature leaves was not affected by water stress immediately after the 30-min 14 CO2 treatment. All the W-labeled carbohydrates decreased in the labeled leaves very rapidly after 14 CO2 labeling. The decrease in 14 C-sorbitol was greater than the decrease in other carbohydrates under both well-watered and stressed conditions. After 24 hours of water stress, however, the percentage of 14 C-sorbitol increased while the percentages of sucrose, starch, glucose, and fructose decreased significantly with increasing levels of stress. The ratio of 14 C-sorbitol in leaves with ψ ψ W = -3.5 MPa to leaves with ψ W = -0.5 MPa was significantly higher than that of 14 C-sucrose, 14

Gas Permeability of Fruit Coating Waxes

Abstract: The permeability to O2, CO2, C2H4, and water vapor was determined for 19 commercial fruit wax coatings, four ingredients thereof, and one shrink-wrap film. For the commercial coatings, the O 2 permeability at 50% relative humidity and 30C ranged from 470 to 22,000 ml (STP) × mil/(m 2 × day × atm) (1 mil = 0.0254 mm) with CO)2 . permeability two to eight times as high. Permeability to noncondensable gases tended to be higher for coatings made from carnauba wax than for those made from shellac and rosin. Commercial fruit wax had sufficiently low noncon- densable gas permeability to account for large reductions in the respiration rate of coated fruit. Wax coatings could be improved if permeability were controlled: Coatings applied to the surfaces of fruits and vegetables are commonly called 'waxes, whether or not any component thereof is actually a wax. Commodities that are waxed include apples, avocados, citrus, cucumbers, eggplant, peaches, sweet peppers, and tomatoes. Waxing improves appearance, but waxes are often selected with little consideration for other properties. The extensive literature documents various properties that are altered by the waxing of fruits and vegetables. Hardenburg's bibliography (1967) covers 292 papers on waxing. Since then, further studies have described the effects of waxing on diverse crops. Perhaps the most-studied property of waxed fruit is its weight

Lettuce Genetics: Inheritance, Linkage, and Epistasis

Abstract: Two new lettuce (Luctuca sativa L.) genes are described and named truncated leaf (tn), and sickly (si). A gene for reflexed involucre is identical to that previously described in wild lettuce (L. serriola L.). Mosaic reaction (me) and light green (lg) are linked, with P = 0.448. Six gene pairs tested for linkage are independently inherited. Sickly is epistatic to light green. This paper continues the description of major genes, linkages, epistasis, and other interactive relationships in lettuce. Eventually, the accumulated information of this type will be suitable to be combined with information from RFLP and similar analyses to provide a comprehensive lettuce genome map. I report here two new genes, one linkage and one epistatic combination. Materials and Methods Eight experiments were conducted. The study of truncated leaf began with the observation of off-type plants in a field planting. These plants were in a group of BC2F3 families from the cross M631 × ‘Salinas’, which were segregating for mosaic resistance. The off-type plants were darker green and smaller than the normal plants’ and had entire leaf margins and lessblistered leaves. The reduced size was partially due to truncation of the leaves. The truncated plant, 78-162-1, was crossed to ‘Vanguard 75’, a crisphead cultivar. Plant type was observed and recorded in Fl, F2, and F3 families. A slow-growing, sickly appearing plant (85-1174cd) was observed in the F2 progeny of a cross 82-1061-1 x ‘Vanguard 75’. The plant was severely stunted, chlorophyll deficient, and had necrotic areas on the leaves. It survived to produce flowers and was crossed by ‘Vanguard 75’ and ‘Prizehead’, a red leaf lettuce. Plant type was observed in F1 and F2 populations of both crosses and in F3 families of the ‘Prizehead’ cross. The latter cross also segregated for dark vs. light green, which led to a study of epistasis with the sickly character. ‘Australian’, a light-green leaf lettuce, produces reflexed mature involucres. A study of shattering (reflexed) vs. nonshattering (erect) -was reported by Whitaker and McCollum (1954) in a cross between wild (L. serriola) and cultivated lettuce. A single gene controlled the trait, with shattering dominant. The gene was designated as b and later renamed er (Robinson et al., 1983). Whitaker and McCollum footnoted a personal communication from R.C. Thompson that ‘Australian’ was the only known cultivated form with “. . . some degree of shattering. . . .“ To study the inheritance of reflexed as manifested in ‘Australian’, an F2 population from a cross ‘Calmar’ × ‘Australian’, planted for a linkage study, was also observed for involucre type. To confirm the involucre observations, a random ed for publication 15 Oct. 1991. Accepted for publication 4 Feb. 1992. S. Milligan provided technical help. This research was partiallv supported California iceberg Lettuce Research Board. The Costof publishing this was defrayed in part by the payment of page charges. Under postal ions, this paper therefore must be hereby marked advertisement solely ate this fact. sample of 80 F3 families was grown. A reflexed plant from another ‘Australian’ cross was crossed with L. serriola to test for gene identity. A possible linkage relationship between lettuce mosaic (LMV) reaction and darkvs. light-green leaves was studied in F2 populations of three crosses: ‘Australian’ × ‘Vanguard 75’, ‘Chung Chuk Myun’ × ‘Vanguard 75’, and ‘Vanguard 75’ × ‘Prizehead’. ‘Vanguard 75’ is dark green and LMV resistant (LgLgmomo), while the three other parents are light green and susceptible (lglgMoMo). ‘Chung Chuk Myun’ is a Korean leaf lettuce. Several other linkage studies were based on F2 populations of the crosses: M400-27-23 × ‘Golden Bibb’, yellow vs. salmon, normal vs. virescent, LMV reaction; and ‘Calmar’ × ‘Australian’, yellow vs. pale, black seed vs. white, dark vs. light green, reflex vs. erect. All plantings were in a greenhouse. Plants were grown in flats or plastic pots of various sizes, in soil or sand-soil mixtures. The containers were fertilized and hand-watered as needed. Crosses were made by the method of Oliver (1910), modified to maximize the number of hybrid seeds (Ryder and Johnson, 1974; E. J. R., unpublished). Genetic ratios were compared by standard x2 procedure. Maximum likelihood tables were used to calculate recombination values (Allard, 1956). Recombination values are denoted by p and probability values by P. Results and Discussion

Phenylureas cppu and thidiazuron affect yield components, fruit composition, and storage potential of four seedless grape selections

Abstract: One of three levels (O, 1, 10 mg·liter) of the cytokinin-active substituted phenylurea compound CPPU was applied with or without 100 mg GA/liter to developing clusters of ‘Sovereign Coronation’ and Summerland Selection 495 grapes (Vitis spp.). In a similar experiment, one of three levels (0, 1, 10 mg·liter ) of either CPPU or the related compound thidiazuron was applied to ‘Simone’ and Summerland Selection 535. Both phenylurea chemicals tended to linearly increase cluster weight and berry weight while reducing degrees Brix, pH, and anthocyanins and increasing titratable acidity. A subsequent trial with O, 4, and 8 mg thidiazuron/liter on all four varieties yielded similar results. GA had no individual or synergistic effects. Due to the very low concentrations required, CPPU and thidiazuron show great promise as chemical tools for the increase of berry weight in seedless table grapes. Chemical names used: N-(2-chloro-4-pyridyl) -N'-phenylurea (CPPU); N-phenyl-N'-l,2,3thiadiazol-5-yl urea (thidiazuron); Berry size and cluster conformation of seedless table grapes are customarily improved through the application of growth regulators. Growers of ‘Thompson Seedless’ in California apply as much as 40 mg GA/liter during each of two annual applications to thin berries and increase berry size. One result of public pressure to reduce agricultural chemical use has been a renewed interest in finding even more powerful growth regulators that can be used at very low concentrations months ahead of harvest to eliminate product residues. Another strategy is to target specific plant organs with the chemical to reduce the amount of chemical applied per hectare. The cytokinins are plant growth regulators with the ability to enhance plant cell division and cell expansion, as well as delay senescence. However, their use in viticulture has been relatively limited. Weaver et al. (1966) found that cluster dips of benzyladenine and 6-(benzylamino)-9-(2-tetra-hydropyranyl)-9H-purine (BTP) at 500 to 1000 mg·liter led to increased berry set and size, but with some reduction in degrees Brix, in several varieties. More recently, interest has been shown in the substituted phenylurea compounds in terms of their activity on grapes and tree fruits. Nickell (1985) first reported on the benefits of CPPU cluster dips on ‘Thompson Seedless’ berry weight. He found that 2.5 to 10.0 mg·liter cluster dips were effective, but that full-vine sprays at these rates achieved only 60% of the response obtained from the cluster dips. These results were later confirmed with ‘Flame’ (Nickell, 1986a) and ‘Perlette’ (Nickell, 1986b). A related compound, CN-11-3183, has been shown by Morris et al. (1986) to increase berry size of ‘Concord’ and ‘Reliance’ (V. labruscana L.). The beneficial effects of both CPPU and CN-11-3183 were enhanced by GA (Morris et al. 1986; Nickell, 1985). Fruit size increases resulting from CPPU have also been reported for other fruits (Iwahori et al., 1988; Nickell, 1986b; Ogata et al., 1988). Seedless table grapes are a relatively new and expanding infor publication 19 Mar. 1991. Accepted for publication 10 Sept. 1991. ion no. 779. The cost of publishing this paper was defrayed in part yment of page charges. Under postal regulations, this paper therefore ereby marked advertisement solely to indicate this fact.

Long-term Response of Early Maturing Peach Trees to Postharvest Water Deficits

Abstract: Early maturing peach trees (Prunus persica (L.) Batsch cv. Regina) growing on a deep sandy loam soil were subjected to three levels of postharvest irrigation over 4 years. The control treatment was irrigated with ≈ 10 to 15 cm of water at 2- to 3-week intervals, the medium treatment received a single irrigation (20 to 30 cm) in early August, and the dry treatment was not irrigated between early to mid-June and mid-October. All received a pre- dormancy irrigation of 10 to 15 cm in mid- to late October. Flower and fruit density were greater in the dry treatment than the control. The occurrence of double fruit was also greatly increased in the dry treatment but not in the medium treatment, when compared with the control. After normal commercial hand thinning, yields and fruit size were no different among the three treatments over all 4 years. Vegetative growth as measured by dormant pruning weights, trunk radial growth, and canopy shaded area was reduced in the dry treatment, but there was no indication of progressively declining vigor. Soil moisture determinations indicate that water use by the control occurred mainly in the upper soil profile. In the dry treatment, as the upper profile dried, water was extracted progressively deeper, down to at least 300 cm. The main disadvantage of severe postharvest water stress was the substantial increase of double fruits.

Ultraviolet Illumination Induces Scoparone Production in Kumquat and Orange Fruit and Improves Decay Resistance

Abstract: Additional index words. postharvest, phytoalexin, Fortunella margarita, Citrus sinensis Abstract. Ultraviolet (UV) illumination (254 nm) induced production of the phytoalexin scoparone in flavedo of kumquat (Fortunella margarita Lour. Swingle cv. Nagami) and orange (Citrus sinensis (L.) Osbeck cvs. Shamouti and Valencia). Trace amounts of scoparone (<2.0 µg·g -1 fresh weight of flavedo) were detected in nontreated fruits. Phytoalexin accumulation in kumquat reached a peak of 530 µg·g -1 11 days after illumination, hut the amount declined rapidly, returning to a trace level 1 month after treatment.. Production of scoparone in illuminated fruits was enhanced by increasing the UV dose from 1.5 × 10 3 to 9.0 × 10 3 J·m -2 for orange and from 0.2 × 10 3 to 1.5 × 10 3 J·m -2 for kumquat and by raising the storage temperature from 2 to 17C. Phytoalexin accumulation correlated with an increase in antifungal activity of flavedo extracts. UV-illuminated kumquat fruit inoculated with Penicillium digitatum Sacc. 2 days after treatment had a lower incidence of decay than the control. Illumination of previously inoculated fruit failed to prevent decay. Kumquat fruit stored at 17C showed signs of UV-induced peel damage. Chemical name used: 6,7-dimethoxycoumarin (scoparone). Phytoalexins, the low-molecular antimicrobial substances of various chemical structures, are elicited in plant tissues by either biotic (pathogen challenge) or abiotic (wounding, chemicals, irradiation, etc.) (Bailey and Mansfield, 1982) stresses. Short- wave ultraviolet light (UV) is known as a nonspecific phyto- alexin elicitor. Since 1971, when Hadwiger and Schwochau described the induction of the isoflavonoid phytoalexin pisatin in UV-treated pea pods, many studies on diverse plants have been devoted to this subject (Beier and Oertli, 1983; Bridge and

Matriconditioning of Vegetable Seeds to Improve Stand Establishment in Early Field Plantings

Abstract: A matricondition ing procedure based on the matric properties of Micro-Cel E and expanded vermiculite #5 has proved effective in improving seedling emergence in growth chambers. The major objectives of this study were to examine some physical characteristics of the carriers and their effectiveness as preplant conditioning media in improving stand establishment of vegetable seeds in field plantings. Carrier characteristics included no detectable solute or osmotic potential, low electrical conductivity (0.48-0.04 mmho/cm), high water-retaining capacity (450% to 600%), a pH range of 7.0 to 8.4, and ability to effectively control seed hydration (conditioning) at low matric potential. The seed : carrier : water ratio for seed conditioning ranged from 1:0.3-0.5:1-2 (by weight). In a field trial, condi- tioning of 'Long Imperator' and 'Nantes' carrot (Daucus carota var. sativus Hoffm.) seeds reduced the time to 10% of final emergence (T1O) by 2.6 to 2.8 days and to 50% of final emergence (T 50) by 2.1 to 3.0 days. Conditioning increased the final emergence percentage by 39% in 1-year-old 'Long Imperator' compared to 150% in 4-year-old 'Nantes' seeds. In another field trial, the effect of conditioning on stand establishment was evaluated in 'Jackpot' tomato (Lycopersicon esculentum Mill.), 'California Wonder' pepper (Capsicum annuum L.), and 'BBL 47' snap bean (Phaseolus vulgaris) seeds. In tomato, conditioning reduced the T 10 by 0.9 day, had no effect on T 50, and increased the emergence percentage by 86%. In pepper, conditioning reduced the T 10 and T50 by 1.5 days and increased the percentage emergence by 30%. In snap bean seeds, conditioning in Micro-Ccl E reduced the T 1O and T50 by 0.8 day but adversely affected the percentage emergence. Further reductions in T 10 and T50 (1.2 and 1.6 days, respectively) and restoration of percentage emergence to control level occurred upon addition of 0.001 mM GA 3 during conditioning. Fungicides added to carrot, tomato, and pepper seeds, with or without conditioning, showed no additional improve- ments and, in a few cases, adversely affected emergence. A preplant conditioning in Micro-Ccl E, alone or in combination with GA3, smears to be a viable alternative to conditioning! seeds in liquid carriers. Chemical name used: gibberellic acid (GA3 ) Osmoconditioning or priming of seeds in solutions of low water potential, e.g., polyethylene glycol (PEG) and salts, has been used extensively as a preplant seed treatment to reduce germination or seedling emergence time, synchronize emer- gence, and improve stand establishment and yield (Bradford, 1986; Heydecker and Coolbear, 1977; Khan, 1991; Khan et al., 1978). A preplant seed conditioning has also been achieved by mixing seeds with moist solid or semisolid carriers (e.g., ver- miculite, expanded calcined clay, Agro-Lig, sodium polypro- pionate gel, synthetic calcium silicates) (Bennett and Waters, 1987; Callan et al., 1990; Khan et al., 1990; Kubik et al., 1988; Parera and Cantliffe, 1990; Peterson, 1976; Taylor et al., 1988; Zuo et al., 1988). Postplant conditioning of beet seeds in moist soil microenvironment in the field has been achieved by incor- porating PEG into solid material used for seed pelleting, as indicated by improved emergence and yield (Khan and Taylor, 1986). Hydration or conditioning of seeds can be regulated by os- motic and/or matric components of the carrier matrix water po- tential. The water potential component(s) of the carrier can be

The Time of Floral Induction in the Olive

Abstract: Additional index words. alternate bearing, flowering, fruit removal, gibberellic acid, Olea europaea, paclobutrazol, seed destruction Abstract. GA3 scaffold injections applied between May and November to nonbearing olive (Olea europea L.) trees inhibited flowering the following year, increased shoot width when applied in May, June, and July, and increased inflorescence length when applied in November and February. Fruit removal and seed destruction were effective in improving the return bloom in 'Manzanillo' olives when done before endocarp sclerification. Depending on-the year, endocarp sclerification takes place 7 to 8 weeks after full bloom (AFB), usually about 1 July. Fruit removal had no effect on flowering when done after this time. Scaffold injection of paclobutrazol applied to bearing trees between May and September did not affect flowering the following year. The results of our research supports the hypothesis that olive flower induction occurs around the time of endocarp sclerification. Chemical names used: gibberellic acid (GA3), (2RS,3RS)-1-(4-chlorophenyl)-4-dimethyl-2-1,2-4-triazol-1-yl) pentan-3-ol(paclobutrazol). Alternate bearing affects many fruit tree species, including olive, and is characterized by a large crop load in the "on" year followed by a small crop in the "off" year. Lack of flower bud formation during the on year is the common characteristic of most alternate-bearing species, including olive (Monselise and Goldschmidt, 1982). The mechanism of alternate bearing is unknown, but environmental conditions and endogenous fac- tors affect flower induction (Bernier, 1988; Monselise and Goldschmidt, 1982). From a practical standpoint, fruit thinning is the best available technique to reduce alternate bearing prob- lems in many species.

Regulation of Chrysanthemum Growth by Spectral Filters

Abstract: The role of light quality and quantity in regulating growth of vegetative Dendranthema × grandiflorum (Ramat.) Kitamura was evaluated using CuSO4 solutions and water (control) as spectral filters. Copper sulfate filters increased the red (R) : far-red (FR) and the blue (B) : R ratios (R = 600 to 700 nm; FR = 700 to 800 nm; B = 400 to 500 urn) of transmitted light. Photosynthetic photon flux (PPF) under 4%, 8% and 16% CuSO 4 filters was reduced 26%, 36%, and 47%, respectively, from natural irradiance in the greenhouse, which averaged ≈ 950 µmol·m -2 ·s -1 . Control treatments were shaded with Saran plastic film to ensure equal PPF as the corresponding C USO4 chamber. Average daily maxima and minima were 26 ± 3C and 16 ± 2C. At the end of the 4-week experimental period, average height and internode length of plants grown under CUSO4 filters were ≈ 40% and 34% shorter than those of plants grown under control filter. Reduction in plant height and internode length was apparent within 1 week after the beginning of treatment. Total leaf area (LA) was reduced by 32% and leaf size (LS) was reduced by 24% under CUSO4 filters. Specific leaf weight (SLW) was higher under CuSO 4 filters than for the controls. Irradiance transmitted through CUSO4 filters reduced fresh and dry leaf weights by 30%. Fresh and dry stem weights of plants grown under CUSO4 filters were 60% lower than those of controls. Relative dry matter accumulation into leaves was increased in plants grown under CUSO4 filters while it was reduced in stems. A single application of GA 3 before irradiation partially overcame the height reduction under CuSO4 filters, suggesting GA biosynthesis/ action may be affected by light quality. Our results imply that alteration of light quality could be used to control chrysanthemum growth as an alternative method to conventional control by chemical growth regulators. Chemical names used: gibberellic acid (GA) Chemical control of plant height is used extensively in or- namental plant production. Due to perceived risks to humans and the environment, the use of some chemical growth regu- lators recently has been restricted.

Cell Wall Modification during Ripening of `Keitt' and `Tommy Atkins' Mango Fruit

Abstract: ‘Keitt’ and ‘Tommy Atkins’ mango (Mangifera indica L.) fruit were evaluated for selected ripening criteria at six ripening stages, from mature green to overripe. ‘Tommy Atkins’ mangos developed more red and yellow pigmentation (CIE a* and b*) in peel and mesocarp tissues than ‘Keitt’. The outer mesocarp of ‘Keitt’ remained firm longer than ‘Tommy Atkins’, and the inner mesocarp was softer than the outer at each stage in both cultivars. Cell wall neutral sugars, particularly arabinosyl, rhamnosyl, and galactosyl residues, decreased with ripening in both cultivars. ‘Keitt’ had more loosely associated, chelator-soluble pectin, accumulated more soluble polyuronides, and retained more total pectin at the ripe stage than ‘Tommy Atkins’. Both cultivars had similar polygalacturonase (EC 3.2.1.15) activity which increased with ripening. The amount and molecular weight of cell wall hemicellulose decreased with ripening in both cultivars. These data indicate that enzymatic and/or nonenzymatic processes, in addition to polygalacturonase activity, are involved in the extensive softening of mango fruit. The mango is one of the most popular tropical fruits worldwide, second only to banana. More than 14 million tons are produced worldwide, with 65% produced in India (Food Agriculture Organization, Annual Statistics, 1986). Southern Florida is the only location in the continental United States where mangos are commercially produced. With expanding production in southern Florida, mango consumption in the United States has increased due to increased availability of more desirable cultivars, such as ‘Keitt’ and ‘Tommy Atkins’. There is tremendous potential for export, particularly to countries such as the United Kingdom, whose consumers prefer the brightly colored Florida cultivars (Jabati, 1989). Despite the potential, there are several problems associated with the marketing of mango fruit. Mangos soften very quickly and extensively. Loss of fruit firmness increases susceptibility to bruising and decay during shipping and storage. Also, mangos are very susceptible to anthracnose (Colletotrichum gloeosporioides Penz.) and stem-end rot (Diplodia natalensis P.; Phomopsis citri). No fungicides are approved for postharvest use on mango fruit, and prospects for future approval are poor. High-temperature water dips help, although up to 80% of the fruit can be lost to fungal attack before fully ripe. It is important to reduce the rate of fruit softening to maintain the fruit’s inherent resistance to bruising and decay. Softening in fleshy fruits is primarily due to cell wall modification. Limited information is available on mango cell walls and the softening process during ripening (Brinson et al., 1988; Lazan et al., 1986; Roe and Bruemmer, 1981; Seymour et al., 1989). There are considerable differences between cultivars (Selvaraj and Kumar, 1989). We have conducted an analysis of the biochemistry of mango fruit softening, including cell wall r publication 11 Mar. 1992. Accepted for publication 15 June 1992. ledge the excellent technical assistance of Heather Gallagher. We Campbell of J.R. Brooks and Son, Homestead, Fla., for supplying ed in these studies. Mention of a trademark, warranty, proprietary vendor does not constitute a guarantee by the U.S. Dept. of Agridoes not imply its approval to the exclusion of other products or t may also be suitable. The cost of publishing this paper was deart by the payment of page charges. Under postal regulations, this fore must be hereby marked advertisement solely to indicate this dress: Department of Pomology, 1045 Wickson Hall, Univ. of Calavis, CA 95616-8683. Soc. Hort. Sci. 117(6):919-924. 1992. composition and molecular weight analysis using two commercially important Florida-grown cultivars, ‘Keitt’ and ‘Tommy Atkins’. Materials and Methods Mango fruit were obtained from a commercial packinghouse in Homestead, Fla. (‘Tommy Atkins’ in June 1990 and ‘Keitt’ in July 1990). Fruit were transported to Orlando, Fla., dipped 3 min in 1000 ppm Imazilil at 35C to reduce decay, and stored at 20C, 85% ± 5% RH. Some fruit were analyzed immediately, while other fruit were allowed to ripen at 20C. Four fruit at each of six ripeness stages, determined subjectively by firmness, were selected for analysis: immature green (IG), fruit hard, mostly flat with undeveloped shoulders; mature green (MG), fruit hard, shoulders well rounded; firm (F), fruit yields slightly under pressure; fairly firm (FF), fruit yields significantly under pressure; soft ripe (SR), fruit soft; overripe (OR), fruit extremely soft, mushy. Respiration. Individual fruit, four at each stage, were sealed in 3.8-liter jars at 20C. After 15 min, l-ml gas samples from jar headspaces were analyzed for CO2 using a Hewlett Packard 5880 gas chromatograph (Hewlett Packard, Palo Alto, Calif.) equipped with a Porapak Q column and a thermal conductivity detector. Nitrogen, at a flow rate of 30 ml·min, was the carrier gas. Color. Color measurements (CIE L*a*b*) were taken on four fruit at each ripeness stage. A Minolta CR200 Colorimeter (Minolta, Ramsey, N.J.) was used to measure external and internal color. For external (peel) color, the mean of six measurements per fruit (stem and blossom end and four equator readings) was determined. For internal color, a 3-cm diameter section of peel was removed from each of the two fruit lobes. The mean of six measurements per fruit (three per lobe) was determined. Firmness. Mesocarp firmness was measured using an Instron 4301 (Instron, Canton, Mass.). Two lobes were cut from a fruit by slicing parallel to the seed. Resistance to compression (3 mm) with a 7-mm diameter probe was measured on the inner Abbreviations: ASP, alkaline-soluble pectin; CSP, Chelator-soluble pectin; F, firm; FF, fairly firm; HF, hemicellulosic fraction; IG, immature green; MG, mature green; OR overripe; SR, soft ripe.

Levels and role of sucrose synthase, sucrose-phosphate synthase, and acid invertase in sucrose accumulation in fruit of Asian pear

Abstract: Soluble sugar content and activities of the sucrose-metabolizing enzymes sucrose synthase (SS) (EC 2.4.1.13), sucrose-phosphate synthase (SPS) (EC 2.4.1.14), and acid invertase (EC 2.4.1.26) were analyzed in the pericarp of fruit from pear cultivars that differed in their potential to accumulate sucrose to identify key enzymes involved in sucrose accumulation in Asian pears. The Japanese pear 'Chojuro' (Pyrus pyrifolia (Burro. f.) Nakai) was characterized as a high-sucrose-accumulating type based on the analysis of mature fruit, while the Chinese pear 'Yali' (P. bret- schneideri Rehd.) was a low-sucrose-ac cumulating type throughout all developmental stages. The activity of SS and SPS in 'Chojuro' increased during maturation concomitant with sucrose accumulation, whereas the activity of these enzymes in 'Yali' did not increase during maturation. The activity of SS and SPS in the former were seven and four times, respectively, higher than those in the latter at the mature stage. Further, among 23 pear cultivars, SS activity was closely correlated with sucrose content, while SPS activity was weakly correlated. Soluble acid invertase activity in 'Chojuro' and 'Yali' decreased with fruit maturation, but the relationships between soluble invertase activity and sucrose content were not significant. The results indicate that SS and SPS are important determinants of sucrose accumulation in Asian pear fruit and that a decrease of soluble acid invertase activity is not absolutely required for sucrose accumulation.

Molecular Weight and Degree of Methoxylation in Cell Wall Polyuronide during Softening in Pear and Apple Fruit

Abstract: The concentrations of water-soluble polyuronides in apples (Malus domestica Borkh.) and pears (Pyrus communis L.) increased, but those of EDTA- and HCl-soluble polyuronides decreased during softening. Total polyu- ronide content decreased slightly during softening in both fruits. Depolymerization of polyuronides was observed only in the water-soluble fraction in pear fruit during softening, concomitant with an increase in polygalacturo nase (PG) activity. No detectable depolymerization was observed in any of the polyuronide fractions during softening of apple fruit nor was any PG activity detected. The polyuronide fractions extracted from pear and apple cell walls contained various amounts of methoxyl groups. Polyuronides with a high degree of methoxylation were preferentially lost from EDTA- and HCl-soluble polyuronides during softening of both fruit. The water-soluble polyuronide had a lower degree of methoxylation than those lost in the EDTA- and HCl-soluble fractions. These results suggest de-esterification of polyuronides with a high degree of methoxylation rather than the depolymerization of polyuronides in the solu- bilization of polyuronides during ripening of apples and pears.

Foliar Raffinose and Sucrose in Four Conifer Species: Relationship to Seasonal Temperature

Abstract: Foliar raffinose and sucrose concentrations in eastern white pine (Pinus strobus L.), eastern redcedar (Juniperus virginiana L.), Leyland cypress (xCupressocyparis leylandii Dallim.), and Virginia pine (Pinus virginiana L.) were measured monthly over 2 years. During cold weather, foliage of white pine and redcedar contained higher concentrations of raffinose and sucrose than did Leyland cypress and Virginia pine. Rafflnose concentrations were highest during winter and were best correlated with the frequency of occurrence of daily minima ≤ 1.7C during the 30 days before sampling. Sucrose concentrations, which also reached maximum levels during the winter, were best correlated with the frequency of occurrence of daily minima ≤ 7.2C in the prior 30 days. Sucrose concentrations were relatively high during fall and spring. Raffinose and sucrose concentrations increased in response to recurring low temperature, with correlations highest for raffinose. In the fall and winter, foliar raffinose concentration increases in conifers (Little, 1970; Parker, 1959). Raffinose accumulates in Fraser fir (Abies fraseri (Pursh) Poir.) in response to low temperature and short days (Mitcham-Butler et al., 1986). This response is not confined to higher plants. A brief cold treatment (4C) of algae (Chlorella vulgaris Beyerinck) induces an accu- mulation of raffinose, and concentrations decrease when the algae are transferred to warmer temperatures (Salerno and Pon- tis, 1989). In general, high foliar raffinose concentrations are associated with greater cold hardiness (Kandler and Hopf, 1980; Parker, 1959). Fraser fir Christmas trees that are harvested after experiencing low temperatures have higher foliar raffinose concentration and exhibit better postharvest needle retention than trees precondi- tioned with higher temperatures (Mitcham-Butler et al., 1986). Although raffinose increases in the foliage of several conifers during the winter and might be involved in cold hardiness, there are no studies that compare seasonal sugar levels of different conifer species growing in the same environment. Thus, com- parisons among species from available data are difficult. Our research had two objectives: 1) determine seasonal raffinose and sucrose concentrations in the foliage of four conifer species that differ in hardiness and are important to the Christmas tree in- dustry and 2) determine if foliar raffinose and sucrose concen- trations are correlated with the occurrence of different baseline (daily minimum) temperatures during the week or month pre- ceding sampling.

Respiration Rate of Blueberry in Modified Atmosphere at Various Temperatures

Abstract: Respiration rates of three blueberry (Vaccinium corymbosum L.) cultivars (Coville, Blueray, and Jersey) were measured as a function of O2, CO2, and temperature using the closed system method. The data conformed well to a recently proposed Michaelis-Menten type respiration (r) model (r = V m (O2)/{Km + (1 + (CO2)/Ki)(O2)}), where Vm was maximum respiration rate, Km was Michaelis-Menten constant, and Ki was inhibition constant. The model predictions were used to examine the behavior of respiration rates. In general, the respiration rates decreased with increasing CO2, but were little affected by changes in O 2. 'Coville' blueberries had the highest respiration rate, followed by 'Blueray' and 'Jersey'. The temperature dependence of the respiration rates followed the Arrhenius relationship. The major causes of spoilage for blueberries are fungal decay and physiological changes (Cappellini et al., 1982). Ceponis et al. (1983) and Smittle et al. (1988) have shown that storing blueberries in a CO2-enriched atmosphere is a fairly effective way to inhibit postharvest decay without fungicidal treatment. Therefore, controlled atmosphere storage (CA) or modified at- mosphere packaging (MAP) possibly can serve as an alternative to fungicides to extend the shelf life of fresh blueberries. Table 1. Estimated values for Vm , K m , and Ki at 5, 15, and 25C using multiple linear regression of Eq. (6). r 2 is the coefficient of determination. z

Ethylene-increased Accumulation of Fluorescent Lipid-peroxidation Products Detected during Senescence of Parsley by a Newly Developed Method

Abstract: A newly developed rapid and convenient method was used for fractionation and analysis of fluorescent compounds (FCs) formed during lipid peroxidation in parsley (Petroselinum crispum Mill.) leaves. These lipofuscin- like FCs (which arise in vivo from reaction of malondialdehy de (MDA) with amino acids) were found to increase during the senescence of detached parsley leaves, following the commencement of chlorophyll degradation and pro- teolysis. However, accumulation of FCs in response to exogenous ethylene coincided with the onset of chlorophyll loss and proteolysis on day 2 and was accelerated markedly later. Unlike FC accumulation, levels of aldehydes and MDA in control leaves increased more drastically during senescence, but were not affected significantly by exogenous ethylene. The results suggest that the accumulation of FCs in detached parsley leaves exposed to exogenous ethylene is an early senescence-associated process.

Chilling Injury in Peaches: A Cytochemical and Ultrastructural Cell Wall Study

Abstract: Fruits of mid- ('O'Henry'), late ('Airtime'), and extra-late-season ('Autumn Gem') peach (Prunus persica (L.) Batsch) cultivars were examined for changes in cell wall structure and cytochemistry that accompany the onset of mealiness and leatheriness of the mesocarp due to chilling injury. The peaches were stored at 10C for up to 18 days or at SC for up to 29 days. Plastic-embedded sections were stained by the Schiff's-periodic acid reaction, Calcofluor white MR2, and Coriphosphine to demonstrate total insoluble carbohydrates, s-1,4 glucans, and pectins, respectively. Mealiness was characterized by separation of mesocarp parenchyma cells leading to increased intercel- lular spaces and accumulation of pectic substances in the intercellular matrix. Little structural change was apparent in the cellulosic component of the cell walls of these fruits. In leathery peaches, the mesocarp parenchyma cells collapsed, intercellular space continued to increase, and pectin-positive staining in the intercellular matrix increased greatly. In addition, the component of the cell walls that stained positively for s-1,4 glucans became thickened relative to freshly harvested or mealy fruit. At the ultrastructural level, dissolution of the middle lamella, cell separation, irregular thickening of the primary wall, and plasmolysis of the mesocarp parenchyma cells were seen as internal breakdown progressed.

Biomass and Fruit Production for the Prickly Pear Cactus, Opuntia ficus-indica

Abstract: Productivity of irrigated prickly pear cactus (Opuntia ficus-indica (L.) Miller) was studied over 3 years in central Chile using two planting densities. A low-density planting (0.25 plants/m 2 ), traditionally favored for fruit production, had maximal fruit productivity in the 2nd year (6 Mg dry weight/ha per year). A high-density planting (24 plants/m 2 ), which assured almost full interception of incident solar radiation, led to an extremely high shoot dry- weight productivity (50 Mg·ha -1 ·year -1 ) in the 2nd year and maximal fruit productivity (6 Mg·ha -1 ·year -1 ) in the 3rd year. Cladode dry weight tended to increase with cladode surface area. However, fruit production did not occur until the dry weight per cladode exceeded the minimum dry weight for a particular cladode surface area by at least 33 g. The year-to-year variation in fruit production apparently reflected variations in such excess dry weight and, hence, in the storage reserves of individual cladodes. The genus Opuntia contains ≈180 of the 1600 species in the Cactaceae and consists mostly of platyopuntias , meaning that the stems occur as flattened segments termed "cladodes" (Ben- son, 1982; Britton and Rose, 1963; Gibson and Nobel, 1986). Certain platyopuntias are commercially important, such as the prickly pear cactus (Opuntia ficus-indica), which is cultivated in more than 20 countries (Hernandez Xolocotzi, 1970; Nobel, 1988; Russell and Felker, 1987). This prickly pear cactus is cultivated primarily for its fruit, but also, its young cladodes are used as a vegetable and mature ones are used as cattle forage and fodder. About 70,000 ha have been devoted to platyopuntia cultivation in Tunisia, 100,000 ha in Italy, and 300,000 ha in Brazil, in addition to large areas in Algeria, Argentina, Chile, Mexico, and South Africa (Domingues, 1963; Monjauze and Le Houerou, 1965). Because. platyopuntias exhibit Crassulacean acid metabolism (CAM) and are drought-tolerant, they can be successfully cultivated in arid and semi-arid regions, which rep- resent about one-third of the earth's land area (Fischer and Turner, 1978; Leith and Whittaker, 1975). Although the above-ground vegetative dry-weight productiv- ity of O. ficus-indica and other platyopuntias is generally below 10 Mg·ha -1 ·year -1

Dark Preconditioning, CPPU, and Thidiazuron Promote Shoot Organogenesis on Seedling Node Explants of Common and Faba Beans

Abstract: Dry seeds from two lines of common bean (Phaseolus vulgaris L.) and one cultivar of faba bean (Vicia faba L.) were germinated on Murashige and Skoog (MS) medium containing B5 vitamins, 30 g sucrose/liter, and either 2.5, 5.0, or 7.5 µM benzyladenine (BA). Axenic seed cultures were grown at 22 to 24C in darkness and under continuous light from cool-white fluorescent tubes (40 µmol·m -2 ·s -1 ). Explant tissues were prepared from cotyledonary nodes (CN) and primary nodes (PN) of 14-day-old seedlings. Explants were cultured on corresponding seedling growth medium and maintained under continuous cool-white light (40 µmol·m -2 ·s -1 ). The percentages of CN and PN (in one line of common bean) explants that regenerated shoots and the number of shoots per explant (in all germplasm) were highest when nodal tissues were prepared from seedlings germinated in darkness. These responses were optimal on medium containing 5 µM BA during seedling growth and subsequent culture of explants. The number of shoots per explant was two to five times higher on explants cultured on medium with 0.25 to 1.0 µM forchlorfenuron (CPPU) or thidiazuron (TDZ) than on medium with 5 µM BA. Higher (2.5 and 5 µM) CPPU and TDZ concentrations inhibited shoot elongation and stimulated callus production. Histological analyses indicated that adventitious meristems formed 6 to 8 days after explant culture. Progenies from regenerated plants appeared similar to plants raised from the original seed stocks. Chemical names used: N- (phenylmethyl) -1 H- purin-6-amine (benzyladenine, BA); N- (2-chloro-4-pyridyl)- N'- phenylurea (forchlorfenuron, CPPU); N- phenyl -N' -1,2,3-thiadiazol-5-ylurea (thidiazuron, TDZ). Tissue culture of grain legumes using cotyledonary node ex- plants from in vitro-grown seedlings has been documented for organogenic competence (Jackson and Hobbs, 1990; McClean and Grafton, 19889; Wright et al., 1986). BA supplements (5 to 10 µM) in the medium during germination and subsequent explant culture were one of the most critical factors for organ- ogenic differentiation and shoot multiplication in this regener- ation system. N- (2-furanylmethyl)-1 H- purin-6-amine (kinetin) was ineffective (McClean and Grafton, 1989) for inducing mul- tiple-shoot organogenesis in common bean or in pea (Pisum sativum L.) (Jackson and Hobbs, 1990), and neither (E)-2-methyl- 4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin) nor N- (3-methyl- 2-butenyl)-1 H- purin-6-amine (2iP) could be substituted for BA in soybean (Glycine max (L.) Merr.) shoot regeneration studies

Cell Count and Size in Relation to Fruit Size Among Strawberry Cultivars

Abstract: Fruit size, number of receptacle cells, and mean cell size were determined throughout development of secondary fruit of three day-neutral strawberry (Fragaria ×ananassa Duch.) cultivars grown in a greenhouse. Cells were counted after enzymatic separation of receptacle tissue, and mean cell volume was estimated from cell count and receptacle tissue volume. Size of mature fruit was small (3.8 g) in 'Tillikum', medium (11.5 g) in 'Tristar', and large (15.6 g) in 'Selva'. Fruit size was correlated with the number of achenes per berry. Mature fruit of 'Tillikum' had a lower fruit fresh weight per achene and lower achene population density (achenes per square centimeter) than the larger-fruited cultivars. The average number of cells per mature fruit was 0.72 × 10 6 , 1.96 × 10 6 comparison of cell size. Darrow (1966) noted that cells of the fruit cortex in the cultivated strawberry are four to five times as wide at those of the smaller-fruited Fragaria vesca. Growth of the strawberry receptacle depends on auxin sup- plied by developing achenes on the berry surface (Nitsch, 1950). Final fruit size is correlated with the number of achenes per berry, which is determined during floral development. Much of the variation in fruit size among strawberry cultivars can be accounted for by differences in achene count (Moore et al., 1970; Oydvin, 1984), although size is also affected by environ- mental and internal factors (Strik and Proctor, 1988). Each ach- ene may be envisioned as associated with a contiguous group of fruit cells whose division and enlargement increases fruit size. This expansion decreases the number of achenes per unit berry surface during fruit development (Abbott et al., 1970; Forney and Breen, 1985). Conversely, fruit weight per achene increases as the fruit enlarges, and it may be a genotypic char- acter that reflects differences in auxin release, tissue respon- siveness, and photoassimilate supply. The main objectives of this study were to determine the du- ration of cell division and the contribution of cell count and size to differences in fruit size among three strawberry cultivars. In addition, achene count and spacing were measured to determine their relationship to the number and size of receptacle cells.

Substantial errors in estimates of sap flow using the heat balance technique on woody stems under field conditions

Abstract: The heat balance method was used to estimate transpirational sap flow through 60- to 75-mm-diameter stems (trunks) of 3-year-old peach (Prunus persica (L.) Batsch. cv. O'Henry) trees under field conditions. On rare occasions, heat balance estimates agreed well with independent lysimetric measurements, but on most occasions, heat balance estimates of sap flow were unrealistic in both direction and magnitude. In some cases, the errors in sap flow approached two orders of magnitude and were always the result of a calculation involving division by a very small and sometimes negative temperature differential between the stem surface temperature above and below the gauge heater. The occurrence of negative temperature differentials under positive transpiration conditions may be incon- sistent with a fundamental assumption in the heat balance model, namely that temperature differentials are solely a consequence of the dissipation of energy supplied to the gauge heater. In the absence of heating power applied to the gauge, temperature differentials exceeding - 1C were correlated with the rate of change in stem temperature, indi- cating that ambient conditions themselves can impose a bias in gauge signals and, hence, influence gauge accuracy. Our results suggest that the effect of ambient conditions on gauge signals should be critically evaluated before considering heat balance estimates of sap flow as reliable under any given conditions. Some recent papers have reported accurate in situ estimates of sap flow (transpiration) through both herbaceous (Ham and Heilman, 1990) and woody (Steinberg et al., 1990b) plant stems using the heat balance technique. The most recent development of this technique has been based on a constant heating gauge described by Sakuratani (1981, 1984) and further modified by Baker and Van Bavel (1987). In most of these reports, the theory of operation for the gauge itself has been described, but only in terms of the numerical calculations needed to convert gauge signals (largely thermojunction-measured temperature differentials) into sap mass flow. Some of the assumptions un- derlying the heat balance technique have been evaluated with a finite element model (Baker and Nieber, 1989) that showed that gauge accuracy may be influenced by factors such as stem vas- cular anatomy, with potentially greater accuracy in dicots than in monocots. The same analysis indicated that overall gauge accuracy could be relatively good, however, depsite the pres- ence of systematic errors in estimates of some of the heat bal- ance components. In view of the accuracy reported in some studies (Steinberg et al., 1989) and reproducibility reported in others (Heilman et al., 1989), it is reasonable to assume that heat balance estimates of sap flow are reliable and that errors, if present, are of minor significance. One class of errors that has not been considered, however, are those associated with the measurement of the temperature differential on the stem surface from below to above the gauge heater. Baker and Nieber (1989) recognized that this temperature differential is critical in the calculation of sap flow, but also that errors in its determination could not be formally considered within the theoretical model of gauge function. In effect, the heat balance theory is limited to considering only temperature differentials that result from heat energy applied to the stem itself. Since large and diurnally fluctuating differences between soil and air temperature are commonplace under many field conditions, and since the plant represents a bridge between these two thermal regimes, it is reasonable to examine to what extent such environmental tem- perature differentials lead to differentials within the plant stem, and the impact of these on the measurement of sap flow. This study documents that such differentials do occur and may be potentially large enough to cause substantial errors in the mea- surement of sap flow by the heat balance technique.

Foliar absorption of urea, ammonium, and nitrate by perennial ryegrass turf

Abstract: 2. Absorption of the fertilizer-N over 48 hours, as measured by 15 N analysis of tissue digests, amounted to 35%, 39%, and 40% for the urea, (NH4)2 SO4, and KNO3, respectively. Absorption was also estimated by a washing procedure that measured the urea remaining on the foliage and by the increase in total N in the ryegrass tissue. There were no significant differences between the three methods for absorption of (NH 4 )2SO 4 and KNO 3. The washing method, however, significantly overestimated absorption of urea. Partitioning of the absorbed N between tissues was similar at 48 hours for all three N sources, averaging 32% in new leaves, 52% in old leaves and shoot tissue, and 16% in the roots. Most of the absorbed urea- and NH4-N was assimilated by 48 hours, whereas only half of the NO 3-N was reduced during that period.

Firmness measurement of stored 'Delicious' apples by sensory methods, Magness-Taylor, and sonic transmission

Abstract: Additional index words. Malus domestica, ripeness, quality, postharvest Abstract. 'Delicious' apples (Malus domestica Borkh.) from five major U.S. production areas were tested after ≈3 months of commercial storage. Soluble solids concentration (SSC), titratable acidity (TA), Magness-Taylor (MT) firmness, and sonic transmission spectra were compared with ripeness (maturity in trade terminology) scores assigned by six U.S. Dept. of Agriculture (USDA)-licensed apple inspectors according to USDA Grades and Standards inspec- tion procedures. USDA ripeness categories are defined by textural and flavor terms. Inspectors in this test used visual, manual, oral, and auditory sensations to make their judgments, but firmness was the paramount characteristic judged. SSC and TA did not correlate with inspectors' scores, MT, or sonic measurements and thus are not satisfactory indices of ripeness for stored apples. Sonic resonance functions correlated significantly with mean inspectors' scores and with MT firmness. Inspectors' scores correlated slightly better with MT firmness than with sonic terms. MT is destructive and site-specific; in contrast, sonic measurements are nondestructive and representative of the entire fruit. Apple production in the United States in 1987 was nearly 4.9 million tons, valued at more than $906 million (U.S. Dept. Agr., 1989). Effective merchandising of such a volume of fruit requires effective sorting for several characteristics, particularly those in the Grade Standards (U.S. Dept. Agr., 1976). Domestic and foreign buyers both continuously demand better quality and a more uniform degree of ripeness. Renewed interest in apple ripeness (maturity in trade termi- nology) by the Agricultural Marketing Service (AMS) caused us to reevaluate simple tests that AMS inspectors could use and to examine the characteristics and methods that inspectors pres- ently use. It also afforded an opportunity to reexamine sonic vibrational characteristics for measuring texture in view of re- cent advances in electronic instruments and computers. SSC and TA content of apples are known to change with maturation and ripening. Texture often is equated with quality in apples, with firm, crisp apples being the ideal. Firmness is also frequently used as a measure of maturity and ripeness. In fact, the USDA-AMS Standards for maturity/ripeness cate- gories for fresh apples are Immature, Hard, Firm, Firm-ripe, Ripe, and Overripe (U.S. Dept. Agr., 1976). AMS inspectors rely mostly on firmness to make those assessments, particularly on apples that have been stored. Firmness is most commonly measured by a puncture test using a MT type fruit firmness tester (Abbott et al., 1976; Blanpied et al., 1978; Bourne, 1974; Magness and Taylor, 1925). Pro- vided that the probe geometry is comparable to that of the orig-