Showing papers in "Journal of the American Society for Horticultural Science in 2002"

Correlations among Predawn Leaf, Midday Leaf, and Midday Stem Water Potential and their Correlations with other Measures of Soil and Plant Water Status in Vitis vinifera

Abstract: A study was conducted to compare three measurements of determining water status of grapevines (Vitis vinifera L.) in the field. Predawn leaf water potential (ΨPD), midday leaf water potential (Ψl), and midday stem water potential (Ψstem) were measured on 'Chardonnay' and 'Cabernet Sauvignon' grapevines grown in Napa Valley, California late in the 1999 growing season. Both cultivars had been irrigated weekly at various fractions (0, 0.5, and 1.0 for 'Chardonnay' and 0, 0.5, 0.75, and 1.5 for 'Cabernet') of estimated vineyard evapotranspiration (ETc) from approximately anthesis up to the dates of measurements. Predawn water potential measurements were taken beginning at 0330 HR and completed before sunrise. Midday Ψl and Ψstem measurements were taken only between 1230 and 1330 HR. In addition, net CO2 assimilation rates (A) and stomatal conductance to water vapor (gs) were also measured at midday. Soil water content (SWC) was measured in the 'Chardonnay' vineyard using a neutron probe. Values obtained for ΨPD, Ψl, and Ψstem in this study ranged from about -0.05 to -0.8, -0.7 to -1.8, and -0.5 to -1.6 MPa, respectively. All three measurements of vine water status were highly correlated with one another. Linear regression analysis of Ψl and Ψstem versus ΨPD resulted in r 2 values of 0.88 and 0.85, respectively. A similar analysis of Ψl as a function of Ψstem resulted in an r 2 of 0.92. In the 'Chardonnay' vineyard, all three methods of estimating vine water status were significantly (P < 0.01) correlated with SWC and applied amounts of water. Lastly, ΨPD, Ψl, and Ψstem were all linearly correlated with measurements of A and gs at midday. Under the conditions of this study, ΨPD, Ψl, and Ψstem represent equally viable methods of assessing the water status of these grapevines. They were all correlated similarly with the amount of water in the soil profile and leaf gas exchange as well as with one another. vine YPD among three watering treatments but no differences in Ψl were found when measured at 1000 and 1600 HR. They concluded that ΨPD better reflected soil water availability than Ψl. van Zyl (1987) concluded that ΨPD detected the onset of water stress in grapevines earlier and more accurately than Ψl.

Genotypic and Environmental Variation in Antioxidant Activity, Total Phenolic Content, and Anthocyanin Content among Blueberry Cultivars

Abstract: Dietary antioxidants may have a role in preventing some of the chronic diseases in humans resulting from free radical oxidation of lipids and other cellular components. Blueberries ( Vaccinium L. sp.) are considered one of the best fresh fruit sources of antioxidants, and there is the potential to increase the antioxidant activity further through breeding. Thus, the variability of fruit antioxidant activity (AA) was examined among a set of 16 highbush and interspecific hybrid cultivars grown at locations in Minnesota (MN), Michigan (MI), and Oregon (OR) over 2 years (1998 and 1999) to determine effects of genotype, year, and location. Nine cultivars were common to all three locations in both years. Antioxidant activity, total phenolic content (TPH), and total anthocyanin content (ACY), were determined in triplicate samples from each genotype. Cultivars differed significantly ( P ≤ 0.05) in AA, TPH, and ACY both within and over locations. The single location mean AA for all cultivars changed significantly between the 2 years in OR and in MI, while the single location mean for TPH differed between the 2 years in MN and MI. Changes in cultivar rank were significant for AA, TPH, and ACY between years within each location. Significant changes in rank for TPH and ACY were also noted between pairs of locations as well. Pearson's correlation for AA (based on cultivar means) appeared highest between MN and OR (r = 0.90) and MN and MI (r = 0.69) in 1998; correlations between locations for the combined years were 0.74 for MN and OR, 0.55 for MN and MI and 0.45 for MI and OR. For the group of nine cultivars, AA correlated well with TPH within each location, with r ranging from 0.67 to 0.95 for data from individual and combined years. Correlation of AA with ACY at each location was lower than that for AA with TPH, in both individual and combined years. This study demonstrates significant genotype × environment interaction for AA in blueberry.

A Reflective, Processed-Kaolin Particle Film Affects Fruit Temperature, Radiation Reflection, and Solar Injury in Apple

Abstract: Particle film technology is a new tool for tree fruit production systems. Trials were performed in Santiago, Chile, and Washington and West Virginia to evaluate the effect of particle film treatments on apple (Malus sylvestris (L.) Mill var domestica (Borkh.) Mansf.) fruit temperature and the incidence of solar injury. Fruit surface temperature was reduced by the application of reflective particles and the amount of temperature reduction was proportional to the amount of particle residue on the fruit surface. Effective solar injury suppression was achieved with spray applications of 45 to 56 kg·ha -1 of a reflective, processed-kaolin particle film material in concentrations ranging from 3% to 12% in some of the locations. The timing of application to suppress solar injury was not clearly defined. The processed-kaolin particle film material was highly reflective to the ultraviolet wavelengths and this characteristic may be important in reducing solar injury to both fruit and leaves.

Glucosinolate profiles in Broccoli: Variation in levels and implications in breeding for cancer chemoprotection

Abstract: Ten broccoli (Brassica oleracea L. (Botrytis Group)) accessions were grown in several environments to estimate glucosinolate (GS) variability associated with genotype, environment, and genotype × environment interaction and to identify differences in the stability of GSs in broccoli florets. Significant differences in genetic variability were identified for aliphatic GSs but not for indolyl GSs. The percentage of GS variability attributable to genotype for individual aliphatic compounds ranged from 54.2% for glucoraphanin to 71.0% for progoitrin. For total indolyl GSs, the percentage of variability attributable to genotype was only 12%. Both qualitative and quantitative differences in GSs were detected among the genotypes. Ten-fold differences in progoitrin, glucoraphanin, and total aliphatic GS levels were observed between the highest and lowest genotypes. Only two lines, Eu8-1 and VI-158, produced aliphatic GSs other than glucoraphanin in appreciable amounts. Differences in stability of these compounds among the cultivars were also observed between fall and spring plantings. Results suggest that genetic factors necessary for altering the qualitative and quantitative aliphatic GS profiles are present within existing broccoli germplasm, which makes breeding for enhanced cancer chemoprotectant activity feasible. (Wattenberg, 1985). Bioactive breakdown products from indi- vidual GSs differ in their potency as inducers of these enzymes

Shoot and Cluster Thinning Influence Vegetative Growth, Fruit Yield, and Wine Quality of `Sauvignon blanc' Grapevines

Abstract: Effects of two shoot densities (14 and 44 shoots/vine) and two crop levels (one and two fruit clusters per shoot) on yield, pruning weight, crop load, and juice and wine quality of field-grown 'Sauvignon blanc' grape (Vitis vinifera L.) were studied in a factorial experiment over 3 years. Main shoot length, lateral shoot length and number, shoot diameter, leaf area per shoot, and specific leaf weight were greater at the lower compared with the higher shoot density for all years whereas pruning weight was significantly increased only in the third year. Crop yield increased proportionally with the number of clusters, up to 44 clusters per vine, by both shoot and cluster thinning; a lower rate of yield increase was apparent when the number of clusters per vine was increased further, probably because of increasing source limitation. Berry maturation was delayed in the 44 shoots per vine treatment. Unchanged soluble solids, higher total acidity, and lower pH in the 44-shoot vine treatment in the third year indicated that the effect of cluster number on the must quality was not due to delayed maturation. No effect of cluster number per shoot on vegetative parameters was apparent. Berry size and number were affected by cluster thinning only in the 44 shoot/vine treatment. Both the number of shoots per vine and the number of clusters per shoot affected wine sensory attributes. Herbaceous aroma scores increased with increasing pruning weight. The wine sensory evaluation score decreased with increasing crop load. Total wine sensory scores decreased with decreasing leaf area to fruit weight ratio below ≈18 cm 2 ·g -1 , whereas a critical value of the crop to pruning weight ratio, for wine quality, was not apparent. Crop load expressed as crop to pruning weight ratio (kg·kg -1 ) was highly correlated with fruit weight to leaf area ratio (g·cm -2 ) (r 2 = 0.86), providing a biological rationale for the relevance of crop load and wine quality relations.

Colored Plastic Film Mulches Affect Tomato Growth and Yield Via Changes in Root-zone Temperature

Abstract: Soil warming is one of the benefits associated with use of plastic film mulches. However, under high temperature conditions during the summer, especially in the southeastern United States, some mulches warm the soil to temperatures that might be deleterious to plant growth. Tomato ( Lycopersicon esculentum Mill.) plants grown in the field were exposed to a range of root-zone temperatures (RZTs), resulting from growing the plants in different seasons and by using colored mulches that differed in their soil-warming ability. The objective was to determine the relationship of mean seasonal RZT, as affected by different colored plastic film mulches, with plant growth and fruit yield. The study consisted of experiments carried out in three seasons: Fall 1999 (five mulches, one cultivar), Spring 2000 (eight mulches and three cultivars), and Fall 2000 (four mulches and three cultivars). Treatments were black (n = 2), gray, red, silver (n = 3), and white (n = 2) mulches, and bare soil. Over the season, mean RZT decreased in the fall (from 32 to 24 °C) and increased in the spring (from 20 to 29 °C). Daily mean values of RZT over the season under plastic mulches were higher (1 to 5 °C) than those of air temperature. The highest RZT at midday occurred under black mulch, and the lowest under bare soil and white mulch. Bare soil showed the largest diurnal RZT fluctuation. RZT at midday was up to 4 °C higher under black or gray mulch compared to the other mulches or bare soil. The degree of soil warming was correlated with reflectivity of the mulch. Black mulch had the lowest light reflectance (10% photosynthetically active radiation (PAR)) while silver mulch had the highest (55% PAR). There were, however, differences in reflectance among mulches of the same color depending on the manufacturer. RZT affected vegetative top fresh weight (FW), fruit yield, fruit number, and individual fruit FW. All these growth attributes fitted a quadratic relationship with mean RZT for the season, with an optimal that ranged between 25.4 and 26.3 °C. The effects of colored mulches on plant response depended on the impact of the mulch on RZT. Plant growth and yield were highest as RZT approached the optimal RZT for the plants. In the southeastern United States, most of tomato ( Lycopersi- con esculentum Mill.) and pepper (Capsicum annum L. var. annum) crops are produced on plastic mulch. The benefits asso- ciated with use of plastic mulches include higher yields, earlier harvests, improved weed control, and increased efficiency in the use of water and fertilizers (Lamont, 1993). Plastic mulches affect plant microclimate by modifying the soil energy balance and by restricting soil water evaporation (Liakatas et al., 1986). Modifi- cation of these microclimate factors influence soil temperature, which affects plant growth and yield (Voorhees et al., 1981). Increased root-zone temperature (RZT) is one of the main ben- efits associated with use of plastic mulches (Wien and Minotti, 1987). However, under conditions of high ambient temperature and high solar radiation as they occur during the summer in the southeastern United States, plants often show poor growth and low yield. Under these conditions, mulches warm the soil to

Sugar Alcohols, Salt Stress, and Fungal Resistance: Polyols—Multifunctional Plant Protection?

Abstract: The traditional use of polyols as osmotica in plant culture media is based on the assumption that polyols are not taken up or metabolized by cells. In reality, polyols are significant photosynthetic products and efficiently utilized metabolites in a large number of plants. In addition to these metabolic roles, initial interest in polyols focused primarily on their function as osmoprotectants. This was hypothesized to be due to their ability to act as compatible solutes. More recent research, however, indicates much broader roles for polyols in stress responses based on their significant antioxidant capacity. These include protection against salt and photooxidative stress as well as a potential role in plant pathogen interactions.

Genetic Divergence and Chimerism within Ancient Asexually Propagated Winegrape Cultivars

Abstract: In total, 25 clones of Vitis vinifera 'Pinot noir' and 22 clones of 'Chardonnay' were analyzed with 100 microsatellite markers, selected from an initial screening of 228 markers. Of the 100 markers, 17 detected polymorphism within one or both of the cultivars. In 'Pinot noir', 15 polymorphic markers detected 15 different genotypes, uniquely distinguished 12 clones out of the 25 and separated the remaining 13 clones into 3 groups. In 'Chardonnay', 9 polymorphic markers detected 9 genotypes and uniquely distinguished 6 clones out of the 22. The remaining 16 clones were separated into 3 groups. For markers that were polymorphic in 'Pinot noir' and 'Chardonnay', none of the variant alleles were common to both cultivars. It is inferred from this result that the natural cross that produced 'Chardonnay' probably occurred when 'Pinot' was still relatively young. Many of the variant genotypes were expressed as three alleles. Further analysis revealed the presence of chimeras in which the third allele was present in leaf but not root or wood tissues, confirming that the grape apical meristem is functionally two-layered. Some clones that share the same microsatellite genotype are documented to have originated in the same locality, suggesting that the origins of undocumented clones may be traced by comparing their microsatellite genotypes with those of well-documented clones. Because clones of 'Pinot noir' and 'Chardonnay' are often visually indistinguishable, microsatellite genotyping may also be useful to detect identification errors in collections and nurseries. Because winemakers have strong preferences for certain clones, it has become increasingly important to be able to identify them. Morphological differences between clones are slight at best and are often obscured by environmental variables and cultural practices. An objective means by which to distinguish them has long been sought.

Methyl Jasmonate Enhances Anthocyanin Accumulation and Modifies Production of Phenolics and Pigments in `Fuji' Apples

Abstract: Effects of artificial ultraviolet-visible light and methyl jasmonate (MJ) treatment on 'Fuji' apple (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.) fruit peel anthocyanin, phenolic, carotenoid, and chlorophyll production were examined using tristimulus color analysis and reverse-phase high performance liquid chromatography. Anthocyanin synthesis was enhanced by light and MJ treatment. Chlorogenic acid and most cyanidin, quercetin, and phloretin glycosides increased with MJ treatment concentration. Light alone also promoted increased production of most of these compounds. Production of catechin, (-)epicatechin, quercetin, and quercetrin was not enhanced by either light or MJ treatment. Light and MJ enhanced s-carotene and chlorophyll b, synthesis but not xanthophyll or chlorophyll a synthesis. The chlorophyll a/b ratio decreased with MJ dosage. Results suggest MJ may provide a viable means of enhancing apple fruit coloration and other photoprotective mechanisms. Chemical name used: methyl 3-oxo-2-(2- pentenyl)cyclopentane-1-acetate (methyl jasmonate).

Postulated Physiological Roles of the Seven-carbon Sugars, Mannoheptulose, and Perseitol in Avocado

Abstract: Avocado (Persea americana Mill.) tissues contain high levels of the seven-carbon (C7) ketosugar mannoheptulose and its polyol form, perseitol. Radiolabeling of intact leaves of 'Hass' avocado on 'Duke 7' rootstock indicated that both perseitol and mannoheptulose are not only primary products of photosynthetic CO 2 fixation but are also exported in the phloem. In cell-free extracts from mature source leaves, formation of the C7 backbone occurred by condensation of a three-carbon metabolite (dihydroxyacetone-P) with a four-carbon metabolite (erythrose-4-P) to form sedoheptulose-1,7- bis-P, followed by isomerization to a phosphorylated D-mannoheptulose derivative. A transketolase reaction was also observed which converted five-carbon metabolites (ribose-5-P and xylulose-5-P) to form the C7 metabolite, sedoheptu- lose-7-P, but this compound was not metabolized further to mannoheptulose. This suggests that C7 sugars are formed from the Calvin Cycle, not oxidative pentose phosphate pathway, reactions in avocado leaves. In avocado fruit, C7 sugars were present in substantial quantities and the normal ripening processes (fruit softening, ethylene production, and climacteric respiration rise), which occurs several days after the fruit is picked, did not occur until levels of C7 sugars dropped below an apparent threshold concentration of ≈20 mg·g -1 fresh weight. The effect of picking could be mimicked by girdling the fruit stalks, which resulted in ripening on the tree. Again, ripening followed a decline in C7 sugars to below an apparent threshold level. Taken together, these data indicate that the C7 sugars play important roles in carbon allocation processes in the avocado tree, including a possible novel role as phloem-mobile ripening inhibitors.

Pistachio Rootstocks Influence Scion Growth and Ion Relations under Salinity and Boron Stress

Abstract: ADDITIONAL INDEX WORDS biomass production, chlorophyll, foliar injury, ion relations, Pistacia vera, salt tolerance, trunk diameter ABSTRACT Performance of 'Kerman' pistachio (Pistacia vera L) trees on three rootstocks (P atlantica Desf, P integerrima Stewart and 'UCB-1', a P atlantica x P integerrima hybrid) was evaluated with 2-year-old trees grown in sand-tank lysimeters under combined SO4 2- and Cl - salinity and boron (B) stress for 6 months Four salinity treatments were imposed by irrigating the plants with water at electrical conductivity (ECiw) of 35, 87,12, or 16 dS·m -1 each containing B at 10 mg·L -1 Growth of 'Kerman' was evaluated based on increase in total leaf area, increase in trunk diameter, and total above-ground biomass production All growth parameters decreased as salinity increased, but were not significant until ECiw exceeded 12 dS·m -1 However, growth of 'Kerman' on P atlantica and 'UCB-1' was considerably better than on P integerrima at 16 dS·m -1 The onset and severity of foliar injury differed among scions and treatments and was attributed primarily to B toxicity, rather than the effects of salinity Concentrations of B in injured leaf tissue ranged from 1000 to 2500 mg·kg -1 Leaf injury decreased with increasing salinity, although leaf B was not significantly reduced suggesting an internal synergistic interaction between B and other mineral nutrients However for P vera on P integerrima, the highest level of salinity produced the greatest injury, possibly as a combination of B plus Cl - and/or Na + toxicity Leaf transpiration, stomatal conductance, and chlorophyll concentration of P vera, determined by steady-state porometry, were also reduced to a greater degree by combined salinity and B when budded on P integerrima than on the other two rootstocks

Variability in Antioxidant Activity in Blueberry and Correlations among Different Antioxidant Activity Assays

Abstract: ADDITIONAL INDEX WORDS. Vaccinium sp., blueberry breeding, phenolics, anthocyanins, ferric-reducing antioxidant power, oxygen radical absorbance capacity ABSTRACT. Variation in antioxidant activity (AA), total phenolic content (TPH), and total anthocyanin content (ACY) was examined in 1998 and 1999 in fruit of 52 (49 blue-fruited and 3 pink-fruited) genotypes from a blueberry breeding population. The species ancestry included Vaccinium corymbosum L. (northern highbush blueberry), V. angustifolium Ait. (lowbush blueberry), V. constablaei Gray (mountain highbush blueberry), V. ashei Reade (rabbiteye blueberry), and V. myrtilloides Michx. (lowbush blueberry). Using a methyl linoleate oxidation assay (MeLO) on acidified methanolic extracts of the berries, a 5-fold variation was found in AA in 1998 and a 3-fold variation in 1999 among the blue-fruited genotypes. Analyses of variance (ANOVA) revealed variation among genotypes (P < 0.0001) in single and combined years, regardless of inclusion of pink-fruited selections and adjustment for berry size. While mean AA of all genotypes did not change between the 2 years, ranking of some genotypes for AA changed significantly between 1998 and 1999. Of the 10 genotypes that demonstrated the highest AA in 1998, four were among the 10 genotypes that demonstrated highest AA in 1999. Similarly, of the 15 genotypes with the highest AA, 10 were the same both years. As with AA, mean TPH of all genotypes did not change between years and ANOVA demonstrated genotypic variation regardless of adjustment for berry size/weight or exclusion of pink-fruited selections. Changes in genotype rank occurred between years. The difference in TPH between lowest- and highest-ranking blue-fruited genotypes was ≈2.6-fold in both 1998 and 1999. Seven of the 10 highest-ranking genotypes were the same both years and TPH correlated with AA (r = 0.92, P < 0.01) on a genotype mean basis for combined years. ACY correlated less well with AA (r = 0.73, P < 0.01 for combined years). When genotypes were categorized into six groups according to species ancestry, V. myrtilloides and V. constablaei x V. ashei crosses ranked highest and second highest, respectively, for AA in both years. The groups comprised of V. corymbosum genotypes, V. angustifolium genotypes, and those with both V. corymbosum and V. angustifolium in their lineage were indistinguishable from each other. Samples from some of the genotypes were analyzed for oxygen radical absorbance capacity and ferric-reducing antioxidant power, and these aqueous-based antioxidant assays correlated well with the lipid emulsion-based MeLO (all r ≥ 0.90, P < 0.01). The three antioxidant assays may be equally useful for screening in a blueberry breeding program and the choice of assay may depend on the goal of the program and the resources available.

Genetic Relationships of Pyrus Species and Cultivars Native to East Asia Revealed by Randomly Amplified Polymorphic DNA Markers

Abstract: A total of 118 Pyrus sp. (pear) and cultivars native mainly to east Asia were subjected to randomly amplified polymorphic DNA (RAPD) analysis to evaluate genetic variation and relationships among the accessions. Two hundred fifty RAPD markers were scored from 20 decamer primers. RAPD markers specific to species were identified. Clustering analysis revealed two divisions: one comprising cultivars of P. communis L., and the other including all accessions of Pyrus native to east Asia. The grouping of the species and cultivars by RAPD data largely agrees with morphological pear taxonomy. However, some noted incongruence existed between two classification methods. Pyrus calleryana Dcne. clustered together with P. koehnei Schneid., P. fauriei Schneid. and P. dimorphophylla Makino. Pyrus betulaefolia Bge. clustered with P. ×hopeiensis Yu and P. ×phaeocarpa Rehd. A noncultivated clone of P. aromatica Kikuchi et Nakai grouped with P. aromatica cultivars. Pyrus hondoensis Nakai et Kikuchi and cultivars of P. ussuriensis Max. formed a single group. Some accessions from Korea (named Korean pear) had species-specific RAPD markers and comprised an independent group. Most of the Chinese white pears clustered together with most of the Chinese sand pears. Based on the present results, the new nomenclature P. pyrifolia var. sinensis (Lindley) Teng et Tanabe for Chinese white pear was suggested. Most accessions of Japanese pears fell into one main group, whereas pear cultivars from Kochi Prefecture of Japan subclustered with some Chinese sand pears and one accession from Korea. Our results infer that some local Japanese pear cultivar populations may have been derived from cultivars native to Kochi Prefecture in Shikoku region, and that the latter may have been introduced from ancient China and/or Korea. The genus Pyrus, with the common name pear, belongs to the subfamily Pomoideae, and the family Rosaceae. The basic Pyrus stock is believed to have arisen during the Tertiary period in the mountainous regions in western and southwestern People's Re- public of China (China) (Rubtsov, 1944). From the geographical point of view, pears are traditionally divided into two native groups: Occidental pears and Oriental pears (Layne and Qua- mme, 1975; Lee, 1948; Rubtsov, 1944). The exact number of species in the genus Pyrus varies among taxonomists. According to Rubtsov (1944), the Occidental pears include over 20 species found in Europe, northern Africa, Asia Minor, Iran, central Asia, and Afghanistan; the majority of cultivars grown in these areas have originated primarily from Pyrus communis. The Oriental pears include 12 to 15 species, distributed from the Tian-Shan and Hindu Kush Mountains eastward to Japan. In a detailed taxo- nomic study of Pyrus, Challice and Westwood (1973) suggested 21 primary species and four geographic groups of species, of which 10 species native to east Asia were assessed. These east Asian pears are distributed primarily in China, Japan, and Korea. China contains a majority of the most important pear species native to east Asia, and is also a world leader in pear production. Received for publication 20 Feb. 2001. Accepted for publication 3 Oct. 2001. We gratefully acknowledge Zhicheng Lu and Yufeng Cao, Research Institute of Pomology, Chinese Academy of Agricultural Sciences, Liaoning Province, People's Republic of China, and Yinsheng Li and Chunhui Ma, Gansu Pomology Institute, Gansu Province, People's Republic of China for their generous assis- tance and cooperation in taking pear leaf samples. This work was supported by a postdoctoral fellowship from Japan Society for the Promotion of Science (JSPS) to Yuanwen Teng, Grant-in Aid 98464 for JSPS fellows from the Ministry of Education, Science, and Culture, Japan. 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.

Leaf Expansion, Stomatal Conductance, and Transpiration of Vegetable Amaranth (Amaranthus sp.) in Response to Soil Drying

Abstract: This study was designed to quantify the responses of leaf expansion, stomatal conductance, and transpiration of four genotypes of vegetable amaranth (Amaranthus tricolor L. (Hin Choi), A. tricolor L. (Co. 2), A. blitum L. (WS80-192), and A. cruentus L. (RRC 1027)) to soil drying. Two greenhouse experiments were conducted during 1999 and 2000. Soil water status was expressed as the fraction of transpirable soil water (FTSW). Leaf expansion rates, stomatal conductances, and transpiration rates of the stressed plants were determined relative to those of nonstressed plants, and expressed as relative leaf expansion (RLE), relative stomatal conductance (RSC), and relative transpiration (RT), respectively. The rate of soil water extraction differed among genotypes, with RRC 1027 depleting soil water fastest and Hin Choi slowest. Whereas in 1999 all genotypes were equally efficient in soil water use, RRC 1027 extracted a greater volume of transpirable soil water than the other genotypes in 2000. The responses of RLE, RSC, and RT to FTSW were well described by linear-plateau models which allowed calculation of soil-water thresholds for leaf expansion (CL), stomatal conductance (CS), and transpiration (CT). Values for CL were higher than for CS and CT. CL was similar for the four genotypes in each year, whereas, CS and CT differed among genotypes. CS and CT was lowest for Hin Choi and highest for WS80-192. Differences of CL, CS, and CT between the two experiments might have been due to the different soils used in the experiments and the different evaporative demands during the drought cycles. Under drought stress, the reduction of transpiration of vegetable amaranth was due mainly to reduction of stomatal conductance, not to reduction of leaf expansion. The relative reduction of dry weight caused by drought stress was positively correlated with CS or CT across the four genotypes. Variation in CS and CT among amaranth genotypes revealed different responses to drought stress, which could make them suitable for different drought situations. Amaranths (Amaranthus L. sp.) are protein-rich, annual, herba- ceous dicotyledoneous plants of worldwide distribution (Martin and Telek, 1979). Their use as vegetables in tropical agriculture has been well documented (Martin and Ruberte, 1975). Like many C4 crops, amaranths flourish in warm, humid, sunny environments and have lower rates of water loss and greater water use efficiency than C3 plants, especially in dry conditions (Field and Mooney, 1986; Sage and Pearcy, 1987). Therefore, amaranth has often been described as a drought tolerant crop (Myers, 1996; Whitehead and Singh, 1992). However, no quantitative information is available about the re- sponses of leaf expansion, stomatal conductance, and transpiration of these species to soil water deficits. Also, little is known about possible genotypic differences in these traits and their relations to plant performance under drought stress. Therefore, the objectives of this study were to quantify sensitivity of leaf area expansion, stomatal conductance, and transpiration among four genotypes of vegetable amaranth to soil drying and to evaluate the importance of these responses for crop performance during soil drying.

CBF1 Orthologs in Sour Cherry and Strawberry and the Heterologous Expression of CBF1 in Strawberry

Abstract: Orthologs of CBF1, a cold-induced transcription factor important in the cold acclimation response in Arabidopsis thaliana were cloned from strawberry (Fragaria ×ananassa Duchesne) and sour cherry (Prunus cerasus L.) with degenerate PCR primers. The putative orthologs (Fragaria ×ananassa CBF1 (FaCBF1) and Prunus cerasus CBF1 (PcCBF1)) have 48% amino acid identity to CBF1 and mRNA levels were up-regulated in leaves of both crops following exposure to 4 °C from 15 minutes to 24 hours. However, mRNA of FaCBF1 and PcCBF1 was not detected in pistils of strawberry and sour cherry following 4 °C exposure. Agrobacterium-mediated transformation of a CaMV35S-CBF1 construct was conducted on Fragaria ×ananassa 'Honeoye' crown discs. Two transgenic lines were regenerated that expressed the transgene at low levels in both leaves and receptacles. Receptacles of the transgenic lines showed no significant change in freezing tolerance when compared to wild type plants, although the temperature at which 50 % electrolyte leakage occurred in detached leaf discs from the two transgenic lines was -8.2 °C and -10.3 °C, respectively. These freezing tolerance values were significantly greater than the value for the wild-type 'Honeoye' leaf discs of -6.4 °C. trait, manipulation of just one gene, CBF1, has been shown to improve the whole plant freezing tolerance of arabidopsis (Jaglo- Ottosen et al., 1998). Because CBF genes are key regulators of cold acclimation and overexpression of CBF1, 2, or 3 is capable of improving the freezing tolerance of arabidopsis, there is significant interest in determining if orthologs of the CBF gene family exist in cultivated species and function in a similar fashion to improve freeze tolerance. The distribution of many temperate fruit crops is restricted by low temperature stress. Floral damage is often the main form of freeze injury, particularly in several of the early blooming mem- bers of the Rosaceae (e.g., strawberry (Fragaria ×ananassa), cherry (Prunus avium and P. cerasus), peach, almond (Prunus dulcis), apricot (Prunus armeniaca) ) (Rodrigo, 2000). Many cultural techniques are used to mitigate the damage caused by freezes during bloom (Rieger, 1989). However, improved culti- vars with enhanced floral freezing tolerance would be of consid- erable interest to help prevent crop loss caused by freeze damage and to help stabilize yearly yield fluctuations. One approach to develop cultivars with enhanced freezing tolerance is to identify and use candidate genes playing important roles in this trait. It is plausible that cold-induced genes exist within the Rosaceae that are orthologous to those in arabidopsis capable of improving freezing tolerance. Whether these genes can be used, through either biotechnological manipulation or exploitation of natural variation, to improve floral freezing toler- ance in rosaceous crops is unknown. It is also unknown if the same relationship exists between cold-induced gene expression and onset of cold-acclimation in rosaceous flowers. The interaction between low temperature and photoperiod on cold acclimation of woody fruit crops has been extensively studied (Howell and Weiser, 1970; Weiser, 1970), and it is known that the over-wintering structures of perennial, temperate fruit crops possess the ability to cold acclimate. When tested under controlled conditions, detached pistils from sour cherry (Prunus cerasus) do not appear to have the ability to cold acclimate (C. Owens, unpublished results). In contrast, receptacles with at- tached pistils of strawberry show an improvement in freezing

Intersimple Sequence Repeat Markers for Fingerprinting and Determining Genetic Relationships of Walnut (Juglans regia) Cultivars

Abstract: The utility of intersimple sequence repeat (ISSR) markers for identification of English or Persian walnut ( Juglans regia L.) cultivars was explored. Four cultivars were screened with 47 ISSR primers; eight of these primers, which generated reproducible and informative data, were selected for further study. Two individuals from each of 48 cultivars, including many currently important in the California walnut industry as well as accessions from Europe and Asia, were then examined with the eight ISSR primers. Polymerase chain reaction (PCR) products were separated on agarose gels and stained with ethidium bromide. Fifty-four bands were scored as present or absent in each cultivar; of these, 31 (57%) were polymorphic among the 48 cultivars. Combined data from the eight ISSR primers provided a unique fingerprint for each of the cultivars tested. Fifteen of the cultivars could be distinguished from all others with just one primer, 31 with a minimum of two primers, and two required three primers. Pairwise genetic distances between the cultivars were calculated and a dendrogram was generated using the neighbor-joining algorithm. Some of the groupings in the dendrogram corresponded to groups which, based on known pedigrees, are genealogically closely related. Others included accessions from diverse genetic and/or geographic origins. These results can be attributed to a combination of the limitations of the ISSR method for inferring geneti c relationships, on the one hand, and the complex history of walnut cultivar development involving extensive exchange and breeding of germplasm from different geographic regions, on the other.

Variation and Heritability Estimates for Antioxidant Activity, Total Phenolic Content, and Anthocyanin Content in Blueberry Progenies

Abstract: Narrow-sense heritability and among-family and within-family variance components were estimated for antioxidant activity (AA), total phenolic content (TPH), and anthocyanin content (ACY) in blueberry ( Vaccinium L. sp.) fruit. AA, TPH, and ACY were determined in the parents and in 10 offspring from each of 20 random crosses for each of 2 years at Becker, Minn. Offspring-midparent regression analysis provided combined-year heritability estimates of 0.43 ± 0.09 (P ≤ 0.0001) for AA, 0.46 ± 0.11 (P ≤ 0.0001) for TPH, and 0.56 ± 0.10 (P ≤ 0.0001) for ACY. Analyses of variance delineated variation among and within families for AA, TPH, and ACY (P ≤ 0.001). Year-to-year variation in the means for all offspring genotypes was not significant for AA or TPH, but there were changes in rank between years for families and for offspring within families for these traits. Year-to-year variation in the mean for all offspring genotypes was significant for ACY, but rank changes were observed only among offspring within families, not among families. In total, 18 of 200 offspring from 7 of the 20 crosses were transgressive segregants for AA, exceeding the higher parent of the cross by at least two SDs. Estimates of variance components showed that variation among families accounted for 24% to 27% of total variance for the three traits. However, variation within families was greater than that among families, accounting for 38% to 56% of total variance for the three traits. These results suggest that increasing antioxidant activity in blueberry through breeding is feasible, and tha t the breeding strategies utilized should exploit the large within-family variation that exists.

Changes in the Expression of Anthocyanin Biosynthetic Genes during Apple Development

Abstract: ADDITIONAL INDEX WORDS. coloring, cyanidin 3-galactoside, Malus sylvestris var. domestica, RNA, UDP-glucose: flavonoid 3-O-glucosyltransferase ABSTRACT. Cyanidin 3-galactoside was the primary anthocyanin in red 'Tsugaru' apples (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.). The concentration of cyanidin 3-galactoside in the skin decreased from 20 to 62 days after full bloom (DAFB), then increased rapidly after 104 DAFB. Small amounts of cyanidin 3-arabinoside and cyanidin 3- glucoside were detected at 122 and 133 DAFB (harvest). The expression of five anthocyanin biosynthetic genes of chalcone synthase (MdCHS), flavanone 3-hydroxylase (MdF3H), dihydroflavonol 4-reductase (pDFR), anthocyanidin synthase (MdANS), and UDP glucose-flavonoid 3-O-glucosyltransferase (pUFGluT) was examined in the skin of red and nonred apples. In general, the expression of anthocyanin biosynthetic genes in red apples was strong in juvenile and ripening stages. The expression of MdCHS, MdF3H, pDFR, and MdANS was observed before ripening stage when anthocyanin was not detected. In contrast, the expression of pUFGluT was detected in the development stage only when anthocyanin was detected. However, the expression of all five genes was observed at 20 DAFB in fruit bagged after fertilization, and anthocyanin was not detected. The expression of MdCHS, MdF3H, pDFR, and MdANS, excluding pUFGluT, was detected at 98 DAFB in fruit bagged after 30 DAFB, and anthocyanin was not detected. These results suggest that pUFGluT may be closely related to the anthocyanin expression in apple skin at the ripening stage.

Development and Characterization of PCR Markers in Cucumber

Abstract: Highly polymorphic microsatellites or simple sequence repeat (SSR), along with sequence characterized amplified region (SCAR) and single nucleotide polymorphisms (SNP), markers are reliable, cost-effective, and amenable for large scale analyses. Molecular polymorhisms are relatively rare in cucumber (Cucumis sativus L.) (3% to 8%). Therefore, experiments were designed to develop SSR, SCAR and SNP markers, and optimize reaction conditions for PCR. A set of 110 SSR markers was constructed using a unique, strategically applied methodology that included the GeneTrapper (Life Technologies, Gaithersburg, Md.) kit to select plasmids harboring microsatellites. Of these markers, 58 (52%) contained dinucleotide repeats (CT, CA, TA), 21 (19%) possessed trinucleotide repeats (CTT, ATT, ACC, GCA), 3 (2.7%) contained tetranucleotide repeats (TGCG, TTAA, TAAA), 4 (3.6%) enclosed pentanucleotide repeat (ATTTT, GTTTT, GGGTC, AGCCC), 3 (2.7%) contained hexanucleotide repeats (CCCAAA, TAAAAA, GCTGGC) and 21 possessed composite repeats. Four SCARs (L18-3 SCAR, AT1-2 SCAR, N6-A SCAR, and N6-B SCAR) and two PCR markers based on SNPs (L18-2H19 A and B) that are tightly linked to multiple lateral branching (i.e., a yield component) were also developed. The SNP markers were developed from otherwise monomorphic SCAR markers, producing genetically variable amplicons. The markers L18-3 SCAR and AT1-2 SCAR were codominant. A three-primer strategy was devised to develop a codominant SCAR from a sequence containing a transposable element, and a new codominant SCAR product was detected by annealing temperature gradient (ATG) PCR. The use of a marker among laboratories can be enhanced by methodological optimization of the PCR. The utility of the primers developed was optimized by ATG-PCR to increase reliability and facilitate technology transfer. This array of markers substantially increases the pool of genetic markers available for genetic investigation in Cucumis.

Tagging and Mapping Scab Resistance Genes from R12740-7A Apple

Abstract: ADDITIONAL INDEX WORDS. Venturia inaequalis, RAPD markers, V r , V x , SSR, STS, Malus ABSTRACT. The genetic basis of resistance to apple scab (Venturia inaequalis (Cke.) Wint.) in the Russian apple seedling R12740-7A (Malus Mill. sp.) was investigated. Segregation ratios obtained in crosses with susceptible cultivars suggested that at least two genes were involved, and three foliar resistance reactions (chlorotic, stellate necrotic, and pit type) were observed after inoculation. DNA markers were identified for both the stellate necrotic (Vr) and pit type (no locus designation, Vx suggested) resistance phenotypes. Comparison of resistance phenotypes with marker segregation demonstrated that only two major dominant genes were present in R12740-7A, one producing the stellate necrotic lesion and the other the pit-type lesion. The chlorotic lesion could be attributed to either unclear expression of the resistance phenotype or to susceptible genotypes not contracting the disease. These markers along with a previously published marker for Vf were used to analyze inheritance of resistance in a Vr x Vf cross in advanced breeding material. The markers identified successfully all susceptible progeny, as well as apparent escapes and individuals possessing both Vf and Vr. Thus, the markers should be useful in future screening of segregating progeny and in the pyramiding of scab resistance genes in new cultivars.

A Genetic Map of Squash (Cucurbita sp.) with Randomly Amplified Polymorphic DNA Markers and Morphological Markers

Abstract: A molecular and morphological marker map would improve our knowledge of Cucurbita genetics, and would facilitate efforts to breed improved summer and winter squash cultivars. Random amplified polymorphic DNA (RAPD) markers were used to construct a partial map of the Cucurbita genome. The mapping population was the BC1 progeny of the Cucurbita pepo L. yellow straightneck inbred A0449 and the tropical Cucurbita moschata Duchesne ex Lam. landrace 'Nigerian Local'. A0449 was the recurrent parent. This cross was chosen because of the relatively greater economic importance of summer squash, traits of value to be introgressed from the C. moschata parent, and maximized genetic variation from the interspecific cross. The map contains 148 RAPD markers in 28 linkage groups. Loci controlling five morphological traits were placed on the map. The map covers 1,954 cM, which is estimated to be 75% of the Cucurbita genome. The qualitative traits placed on the map include the B gene for fruit which turn yellow before anthesis, the M gene for silver mottling of leaves, and a locus controlling the intensity of rind color on mature fruit. Quantitative trait loci (QTL) associated with fruit shape and the depth of the indentations between primary leaf veins were identified.

Responses of `Bing' and `Rainier' Sweet Cherries to Ethylene and 1-Methylcyclopropene

Abstract: ADDITIONAL INDEX WORDS. Prunus avium, nonclimacteric fruit, respiration, fruit quality, stem browning ABSTRACT. 'Bing' and 'Rainier' sweet cherry (Prunus avium L.) fruit treated with 1-methylcyclopropene (1-MCP) were stored at 20 °C in air or 35 µL·L -1 ethylene. Ethylene production by both 'Bing' and 'Rainier' fruit stored in air was transiently stimulated following 1-MCP treatments, however, there were no significant effects of 1-MCP on respiration rate. Exogenous ethylene stimulated respiration regardless of prior treatment with 1-MCP. Although 1-MCP treatment reduced the increase in 'Bing' respiration induced by ethylene, the reduction was less than reported previously for climacteric fruit. These results suggest that stimulation of sweet cherry fruit respiration by ethylene occurs via a process that may be independent of receptors to which 1-MCP binds. Postharvest changes in fruit color and development of stem browning were not altered by 1-MCP treatment, and exogenous ethylene accelerated the development of stem browning regardless of prior treatment with 1-MCP.

Molecular diversity analysis of cultivated carrot (Daucus carota L.) and wild Daucus populations reveals a genetically nonstructured composition

Abstract: A sample of 124 Daucus carota L. accessions, including cultivated carrot (D. carota ssp. sativus (Hoffm.) Arcangeli) and related wild subspecies, using a variety of molecular markers was examined. Represented within the samples were wild accessions from 18 countries, 14 of 16 major root types of European origin, and examples of major North American and Asian cultivated carrot types. Amplified fragment length polymorphism (AFLP) and inter-simple sequence repeat (ISSR) markers revealed extensive variation within D. carota. Although cultivated carrot and wild D. carota subspecies can cross freely, cultivated and wild carrots clustered separately, supporting the possibility that human selection for desirable horticultural traits has artificially reduced gene flow between cultivated and wild forms. Our analyses support the likelihood that North American D. carota populations arose due to introduction of weedy materials rather than escape of cultivated forms. With the exception of wild vs. cultivated types, no genetic alliances were evident in dendrogram topology. Furthermore, between and even within nonmapped marker classes, dendrogram topology predictions were not consistent. Generally poor correlations among root types, geographic origin, mitochondrial, plastid, and specific nuclear diversity and AFLP/ISSR data were also observed. We concluded that genetic diversity in carrot is extensive and relatively nonstructured in nature.

Use of a Hydrophobic Particle Film as a Barrier to Extrinsic Ice Nucleation in Tomato Plants

Abstract: Extrinsic ice nucleating agents (such as ice-nucleation-active bacteria, dew, etc.) significantly limit the ability of herbaceous plants to supercool. It is believed that with an absence of these extrinsic nucleating agents, a plant could supercool to less than -4 °C. Other evidence, however, indicates that intrinsic nucleating agents may limit the extent of supercooling. Infrared video thermography was used to study freezing in young, 'Rutgers' tomato (Lycopersicon esculentum L.) plants and to determine if a hydrophobic barrier on the plant surface could prevent extrinsic nucleating agents such as Ice + bacterial strain (Cit7) of Pseudomonas syringae Van Hall from initiating freezing within a plant. Freezing tests were conducted in a programmable freezing chamber, a radiative frost chamber, and outdoors. Freezing was visualized and recorded on videotape using an infrared radiometer. Freezing of the plants was induced extrinsically by application of droplets (5 to 7 µL) of water containing Cit7. To provide a barrier to the action of extrinsic ice nucleating agents, an emulsion of hydrophobic kaolin (aluminum silicate mineral) was applied to the plant surface before application of an extrinsic nucleating agent. Results indicate that dry, young tomato plants can supercool to as low as -6 °C whereas plants having a single droplet of Cit7 would freeze at -1.5 to -2.5 °C. Application of the hydrophobic barrier blocked the effect of Cit7 and allowed whole plants to also supercool to -6 °C, despite the presence of frozen droplets on the leaf surface. When whole plants were sprayed with water and Cit7 using an aerosol sprayer and exposed to -3 °C, plants coated with the hydrophobic particle film exhibited significantly less foliar injury then nontreated plants. Similar results were obtained using the radiative frost chamber. Experiments conducted under natural frost conditions also resulted in less injury to the coated plants. The hydrophobic kaolin particle film performed better at preventing plants from freezing due to extrinsic ice nucleation than nonaltered, hydrophyllic kaolin alone or an antitranspirant with putative frost protection properties.

Ascorbic Acid, Folic Acid, and Potassium Content in Postharvest Green-flesh Honeydew Muskmelons: Influence of Cultivar, Fruit Size, Soil Type, and Year

Abstract: ADDITIONAL INDEX WORDS. Cucumis melo (Inodorus Group), 5-methyl-tetrahydrofolic acid, phytonutrients ABSTRACT. Two important chemicals and an essential mineral (phytonutrients) for human health and well-being are ascorbic acid, 5-methyl-tetrahydrofolic acid (folic acid) and potassium. The influence of cultivar, fruit size, soil type and year on these compounds in (Cucumis melo L. (Inodorous Group)) was determined. Fully mature (abscised) commercial size fruit: 4, 5, 6, 8, and 9 (fruit/0.031 m 3 shipping box) from three commercial cultivars: Mega Brew, Morning Ice, and TAM Dew Improved (TDI); and one experimental hybrid 'TDI' x 'Green Ice' were grown on both clay loam and sandy loam soils. Total ascorbic acid and folic acid content increased with an increase in fruit size up to a maximum (size 6 or 5), then decreased with further fruit size increase. Total ascorbic acid and folic acid content for most fruit sizes were higher when grown on clay loam versus sandy loam soils. The experimental hybrid compared to the commercial cultivars contained generally higher total ascorbic acid levels and significantly higher folic acid levels regardless of fruit size or soil type. Free ascorbic acid and dehydroascorbic acid contents were generally higher from clay loam versus sandy loam soils and in the experimental line versus the commercial cultivars. However, free ascorbic acid content was high in small fruit and remained unchanged with an increase in fruit size until size 6 or 5 then significantly decreased; while dehydroascorbic acid content linearly increased with an increase in fruit size. Potassium content averaged 1.7 mg·g -1 fresh weight for each line and did not significantly differ due to fruit size, but did for soil type and year. Analyses of variance for the phytonutrients assayed demonstrated that cultivar (genetics) always was very highly significant (P = 0.001), whereas, soil and year (environment) were not.

Rootstock influences changes in ion concentrations, growth, and photosynthesis of 'Hass' avocado trees in response to salinity

Abstract: ADDITIONAL INDEX WORDS shoot growth, leaf necrosis, sodium, chloride, Persea americana ABSTRACT Effect of salinity (15, 30, 45, or 60 dS·m -1 ) on growth and physiology of 1-year-old 'Hass' avocado (Persea americana Mill) trees on one of three rootstocks, 'Thomas', 'Toro Canyon', or 'Duke 7', was investigated to determine the relative salinity tolerance of these rootstocks and to determine possible reasons for any observed differences in tolerance Leaves of trees on 'Thomas' rootstock had the highest leaf Na + , Cl - , and necrosis compared to trees on the other two rootstocks Exposure to salinity resulted in decreased growth of shoots on all rootstocks, but was greatest on 'Thomas' and least on 'Duke 7' The oldest leaves on all rootstocks had the highest proportion of leaf necrosis, whereas younger leaves exhibited almost no necrosis Salinity reduced net CO2 assimilation (A) and chlorophyll concentrations of scion leaves on all rootstocks, but more in older leaves than in younger leaves Although the effects of salinity on A were greater for trees on 'Thomas' on one measurement date, overall, rootstock differences in A were not significant for any leaf age Differences in response to salinity among rootstocks were noted primarily in morphological traits such as growth and leaf necrosis, rather than physiological traits such as gas-exchange and water relations Based on overall growth and physiological response to salinity, trees on 'Thomas' performed poorest, whereas trees on 'Duke 7' exhibited the greatest salt tolerance The relative tolerance of the various rootstocks appeared to be due primarily to their ability to exclude Na +

Resistance to Sweetpotato Chlorotic Stunt Virus and Sweetpotato Feathery Mottle Virus Is Mediated by Two Separate Recessive Genes in Sweetpotato

Abstract: When sweetpotato chlorotic stunt crinivirus (SPCSV) and sweetpotato feathery mottle potyvirus (SPFMV) infect sweetpotato (Ipomoea batatas (L.) Lam.), they interact synergistically and cause sweetpotato virus disease (SPVD), a major constraint to food productivity in east Africa. The genetic basis of resistance to these diseases was investigated in 15 sweetpotato diallel families (1352 genotypes) in Uganda, and in two families of the same diallel at the International Potato Center (CIP), Lima, Peru. Graft inoculation with SPCSV and SPFMV resulted in severe SPVD symptoms in all the families in Uganda. The distribution of SPVD scores was skewed toward highly susceptible categories (SPVD scores 4 and 5), eliminating almost all the resistant genotypes (scores 1 and 2). Likewise, when two promising diallel families ('Tanzania' x 'Bikilamaliya' and 'Tanzania' x 'Wagabolige') were graft inoculated with SPCSV and SPFMV at CIP, severe SPVD was observed in most of the progenies. Individual inoculation of these two families with SPCSV or SPFMV, and Mendelian segregation analysis for resistant vs. susceptible categories led us to hypothesize that resistance to SPCSV and SPFMV was conditioned by two separate recessive genes inherited in a hexasomic or tetradisomic manner. Subsequent molecular marker studies yielded two genetic markers associated with resistance to SPCSV and SPFMV. The AFLP and RAPD markers linked to SPCSV and SPFMV resistance explained 70% and 72% of the variation in resistance, respectively. We propose naming these genes as spcsv1 and spfmv1. Our results also suggest that, in the presence of both of these viruses, additional genes mediate oligogenic or multigenic horizontal (quantitative) effects in the progenies studied for resistance to SPVD.

Determining Ploidy Level and Nuclear DNA Content in Rubus by Flow Cytometry

Abstract: Nuclear DNA flow cytometry was used to differentiate ploidy level and determine nuclear DNA content in Rubus. Nuclei suspensions were prepared from leaf discs of young leaves following published protocols with modifica- tions. DNA was stained with propidium iodide. Measurement of fluorescence of 40 genotypes, whose published ploidy ranged from diploid to dodecaploid, indicated that fluorescence increased with an increase in chromosome number. Ploidy level accounted for 99% of the variation in fluorescence intensity (r 2 = 0.99) and variation among ploidy levels was much higher than within ploidy levels. This protocol was used successfully for genotypes representing eight different Rubus subgenera. Rubus ursinus Cham. and Schldl., a native blackberry species in the Pacific Northwest, which has been reported to have 6x, 8x, 9x, 10x, 11x, and 12x forms, was extensively tested. Genotypes of R. ursinus were predominantly 12x, but 6x, 7x, 8x, 9x, 11x, and 13x forms were found as well. Attempts to confirm the 13x estimates with manual counts were unsuccessful. Ploidy level of 103 genotypes in the USDA-ARS breeding program was determined by flow cytometry. Flow cytometry confirmed that genotypes from crosses among 7x and 4x parents had chromosome numbers that must be the result of nonreduced gametes. This technique was effective in differentiating chromosome numbers differing by 1x, but was not able to differentiate aneuploids. Nuclear DNA contents of 21 diploid Rubus species from five subgenera were determined by flow cytometry. Idaeobatus, Chamaebatus, and Anaplobatus were significantly lower in DNA content than those of Rubus and Cylactis. In the Rubus subgenus, R. hispidus and R. canadensis had the lowest DNA content and R. sanctus had the highest DNA content, 0.59 and 0.75 pg, respectively. Idaeobatus had greater variation in DNA content among diploid species than the Rubus subgenus, with the highest being from R. ellipticus (0.69 pg) and lowest from R. illecebrosus (0.47 pg).

Relationship Between Plant Density and Fruit and Seed Production in Muskmelon

Abstract: ADDITIONAL INDEX WORDS. Cucumis melo, germinability, marketable yield, seed yield index, yield quality ABSTRACT. Field experiments were conducted in 1996 and 1997 to examine the effects of plant density on yield and quality of fruit and seeds of muskmelons (Cucumis melo L.). Two open-pollinated cultivars, Noy Yizre'el (Ha'Ogen type) and TopMark (western U.S. shipper type), were grown at plant densities ranging from 0.5 to 16.0 plants/m 2 under commercial conditions. The highest marketable fruit yields were achieved with plant densities of 2 to 4 plants/m 2 . In contrast, the highest seed yields were obtained at 8 to 12 plants/m 2 . Seed yield index (seed yield (g)/fruit yield (kg)) was used as a parameter to define seed production efficiency. High seed yield was closely related to high value of the seed yield index. High seed yield indexes resulted from high plant densities (up to 12 plants/m 2 ), at which the crops produced many, but relatively small fruit. In all cases, the seed yield per fruit (seed number and seed size) increased with increasing fruit weight. However, the sum of the seed yield of two small fruit was always greater than the seed yield of one, double-sized fruit. There was a clear exception with extremely small fruit (<500 g), which produced both low seed yields and poor seed quality. A positive relationship was found between fruit size and seed size in both cultivars. Nevertheless, relatively small seeds (25 to 30 mg) extracted from relatively small fruit (500 to 1000 g) showed the best performance in terms of germination and emergence percentages and rates, and in the vegetative development vigor of the seedlings. range of densities was evaluated (2.2 to 15.2 plants/m 2 ) and it was found that 4.3 plants/m 2 produced the highest seed yield (Zemer et al., 1987). The main purpose of the present study was to determine the influence of plant density on fruit and seed yields in two types of muskmelon. The quality of both fruit and seeds, and the relation- ships among fruit and seed yield and quality were also investigated.

Fruit Maturity and Storage Temperature Influence Response of Strawberries to Controlled Atmospheres

Abstract: Chandler' strawberries (Fragaria ×ananassa Duch.) harvested three-quarter colored or fully red were stored in air or a controlled atmosphere (CA) of 5% O2 + 15% CO2 at 4 or 10 °C to evaluate the influence of fruit maturity and storage temperature on the response to CA. Quality evaluations were made after 1 and 2 weeks in air or CA, and also after 1 and 2 weeks in air or CA plus 1 day in air at 20 °C. By 2 weeks, strawberries of both maturities stored in air at 10 °C were decayed, however, strawberries stored in CA at 4 or 10 °C or air at 4 °C had no decay even after 2 weeks plus 1 day at 20 °C. Three- quarter colored fruit stored in either air or CA remained firmer, lighter (higher L* value) and purer red (higher hue and chroma values) than fully red fruit, with the most pronounced effect being on CA-stored fruit at 4 °C. CA was more effective than air storage in maintaining initial anthocyanin and soluble solids contents (SSC) of three-quarter colored fruit and fruit stored at 10 °C. Strawberries harvested three-quarter colored maintained initial hue and chroma values for 2 weeks in CA at 4 °C, becoming fully red only when transferred to air at 20 °C. Although three-quarter colored fruit darkened and softened in 10 °C storage, the CA-stored fruit remained lighter colored and as firm as the at-harvest values of fully red fruit. After 1 or 2 weeks in CA at either 4 or 10 °C plus 1 day at 20 °C, three-quarter colored fruit also had similar SSC levels but lower total anthocyanin contents than the initial levels in fully red fruit. CA maintained better strawberry quality than air storage even at an above optimum storage temperature of 10 °C, but CA was more effective at the lower temperature of 4 °C. Three- quarter colored fruit responded better to CA than fully red fruit, maintaining better appearance, firmness, and color over 2 weeks storage, while achieving similar acidity and SSC with minimal decay development. and degradation of anthocyanins in the inner and outer tissues, and to modification in the anthocyanin type due to changes in fruit pH caused by high CO2 levels (Gil et al., 1997; Holcroft and Kader, 1999a, 1999b; Lidster et al., 1990). Fruit injury due to exposure to high CO2 concentrations may be temperature dependent, since Woodward and Topping (1972) re- ported that the higher the temperature, the longer strawberries can be stored in ≈20% CO2 without damage to the tissues. This could be due to reduced solubility of CO2 in the fruit at higher temperatures. There are several reports of off-flavor development in strawberries held at ≈20% CO2 at 0 to 2 °C (Larsen and Watkins, 1995a; Li and Kader, 1989; Ueda and Bai, 1993). Although ripe strawberries develop the strongest off-flavors, unripe fruit also develop off-flavors in 20% CO2. High CO2 levels can also cause increases in pH and decreases in ascorbic acid content (Ke et al., 1991; McGill et al., 1966). The O2 concentration in the storage atmosphere is also important, since at low levels of O2 the strawberry fruit can undergo a shift from aerobic to anaerobic respiration (Woodward and Topping, 1972). Ueda and Bai (1993) suggested that the critical O2 level at which strawberry fruit shift from aerobic to anaerobic respiration is lower than 1% O2, and that the level is temperature dependent. For example, storage of strawberries at concentrations of ≤0.25% O2 at 3 to 5 °C for more than 1 week may cause off-flavors as a consequence of anaerobic respiration (Couey et al., 1966; Ke and Kader, 1989). Perez and Sanz (2001) found that combinations of elevated O2 (80% or 90%) and CO2 (10% or 20%) at 8 °C exacer- bated off-flavor development related to ethyl acetate and ethanol synthesis. Thus, the levels of O2 and CO2 that will extend shelf life without inducing fruit injury depend on time of exposure, storage temperature, and most likely other factors such as cultivar and fruit maturity (Harris and Harvey, 1973; Ke and Kader, 1992). To prevent development of undesirable flavors as well as detri- mental compositional changes, an appropriate CA composition