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Sandra M. Reed

Japanese snowbell (Styrax japonicus Sieb. & Zucc.) is an outstanding small ornamental tree that is underused in the U.S. One of the reasons this Asian native is not more widely planted is that it is subject to spring freeze damage. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants better adapted to areas of the country that frequently experience late spring freezes. During Spring 1999 and 2000, budbreak was evaluated weekly in 224 open-pollinated seedlings. While weather conditions varied greatly between the 2 years, there was good consistency between 1999 and 2000 data. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003 and 2004. All of the selections broke bud later and suffered less freeze damage than the cultivars `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.

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S. Wolf, Y. Lensky and N. Paldi

Fruit and seed set in insect-pollinated agricultural crops rely primarily on honeybees because of their ease of management and transportation. In many fruit and vegetable crops, the number of bee visitations can be the limiting step in obtaining optimal yield. Increasing the attractiveness of flowers to honeybees could, therefore, provide a useful means of improving fruit yield and seed production. Genetic variability in attractiveness to honeybees was found within the genus Citrullus. The number of daily visits per flower ranged from six to 12 among cultivars. Moreover, most of the visits to the more attractive cultivars occurred in the first hour of bee activity, whereas visits to the less attractive cultivars started later in the morning. A positive relationship was found between the frequency of bee visitations and seed number per fruit. Analyses of floral attributes indicated no genetic variability in flower size, amount of pollen grains, or nectar volume; however, differences were observed in the concentration of sucrose and total sugars in the nectar. A positive relationship was found between attractiveness to bees and nectar sugar concentration, suggesting that this characteristic is one of the parameters responsible for variability in attractiveness to honeybees.

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Abraham J. Escobar-Gutiérrez and Jean-Pierre Gaudillére

The aim of this study was to investigate variability in the sorbitol: sucrose ratio (SSR) in source leaves of different peach [Prunus persica (L.) Batsch] cultivars. Four- and 5-year-old trees of 58 cultivars were examined. Mature leaves were sampled on three dates in middle to late summer and analyzed for neutral soluble sugars using high-performance liquid chromatography. Differences in SSRs were observed. In most cultivars, the sorbitol content was at least twice that of sucrose. The maximal range of SSR occurred on the third date and ranged from 1.5 to 4.3. There was a date × genotype interaction (P < 0.01). When cultivars were grouped by country of origin, the mean ratios of the Japanese group were lower than those of the Italian and American groups for all three sampling dates. The SSRs of nectarines were higher than those of peach and canning clingstone-type cultivars. In general, variations in SSR were due mostly to differences in sucrose content. The SSR was negatively correlated with flowering date. These results indicate variability in SSR in peach germplasm, variability that seems to be related to the geographical origin of the cultivars.

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S. Pereira-Lorenzo, J. Fernández-López and J. Moreno-González

Two-hundred and ninety-five trees sampled from seventy-five local chestnut (Castanea sativa Mill.) cultivars in northwestern Spain, which had been previously studied morphologically, were further analyzed for five isoenzyme systems, encoded by seven loci. Objectives of this study were to 1) describe the intracultivar and intercultivar variability by isoenzyme analysis and to compare it with the morphological variation and 2) establish a classification of the cultivars and to discuss its relation to the morphological classification. Variability within and among cultivars was detected, confirming the previous morphological results. The level of the observed heterozygosity in this Spanish population was higher than expected and also higher than that found in other European populations. Because of the great diversity discovered, this material seems to be worthy for introducing and maintaining in a germplasm bank. Nineteen main clusters were identified for the twenty-three most widely distributed cultivars. On the average, 61% of the trees belonging to a specific cultivar was included in the same cluster. The remaining 39% was scattered in other clusters, which indicates intracultivar variability. Therefore there is opportunity for selection within cultivars. Two clusters included three important cultivars each. This suggests possible synonymies. No correlation between morphological traits and the isoenzymic alleles was detected. The isoenzyme technique identified a higher number of cultivars increasing the information obtained with morphological traits. Correlations between the frequency of some of the alleles and the altitude and other environmental variables suggest that selection of the best adapted genotypes has occurred.

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Kanta Kobira, Khalid Ibrahim, Elizabeth Jefferey and John Juvik

Considerable epidemiological evidence exists on the association between consumption of antioxidant-rich vegetables and incidence of chronic diseases, including cancer and cardiovascular disease. Broccoli (Brassica oleracea L. sp. italica) florets are relatively abundant sources of antioxidants, and potentially amenable to genetic manipulation to enhance this vegetable's health-promoting properties. This investigation focuses on the identification of chromosomal segments in the nuclear genome of broccoli associated with antioxidant carotenoid and tocopherol variability. A broccoli F2:3 population consisting of 163 families derived from a cross between two parents (VI-158 and BNC) and previously mapped with 62 polymorphic SSR and SRAP marker loci was evaluated for carotenoid and tocopherol concentration in floret tissue over two growing seasons. Significant differences were observed among F2:3 family means for concentrations of lutein (10-fold difference between the lowest and highest family), beta-carotene 17-fold), alpha-tocopherol (8-fold) and gamma-tocopherol (6-fold). On a concentration basis, beta-carotene, lutein, alpha-tocopherol, and gamma-tocopherol were the most abundant antioxidant forms in broccoli. Heritability estimates of primary phytochemicals ranged from 0.35 to 0.38, 0.40, and 0.44 for beta-carotene, alpha-tocopherol, gamma-tocopherol, and lutein, respectively. Composite interval mapping (CIM) identified two quantitative trait loci (QTL) associated with carotenoid variability on two linkage groups and five QTL associated with tocopherol variability on four linkage groups. The QTL identified in this study have potential for use in marker-assisted crop improvement programs to develop elite germplasm designed to promote health among the consuming public.

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Mirko Siragusa, Fabio De Pasquale, Loredana Abbate and Nicasio Tusa

A collection of 18 accessions of sour orange (Citrus aurantium L.) coming from Sicily and other countries was investigated by two polymerase chain reaction (PCR)-based DNA marker technologies. Ten inter-simple sequence repeat (ISSR) primers and fifteen randomly amplified polymorphic DNA (RAPD) primers were used to identify and to evaluate the genetic variability and relationship of accessions. A total of 111 ISSR and 145 RAPD amplified fragments were used to estimate the Dice's coefficient of similarity for cluster analysis using a unweighted pair-group method using an arithmetic averaging (UPGMA) algorithm. The genetic relationships identified using ISSR and RAPD markers were highly concordant, such that the correlation between ISSR and RAPD genetic distance (GD) estimates was r = 0.93. The ISSR and RAPD analysis of 18 sour orange accessions found a high grade of genetic diversity in foreign accessions, while a low variability was detected in local accessions. Sicilian accessions could be grouped in two distinct clusters, including indistinctly plants from three origin regions. Some markers could be linked to the different growing areas. The ISSR and RAPD molecular reference system seems to be suitable for a fine identification of tightly related plants and the obtained results can form the basis for future setting up of Citrus rootstock genetic improvement projects.

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Sandra E Vega, Jiwan P. Palta and John B. Bamberg

Frost injury limits the cultivation of potatoes in many regions around the world. We are currently studying the factors that contribute to frost survival in potato in an attempt to improve its frost tolerance. Wild potato species have been distinguished for their high degree of non-acclimated frost tolerance (growing under normal conditions) and their high cold acclimation capacity (able to increase frost tolerance upon exposure to cold). Cold acclimation can be reversed upon exposure to warm temperatures (deacclimation). The ability to gain freezing tolerance rapidly in response to low temperatures as well as not being able to deacclimate rapidly in response to warm daytime temperatures would be advantageous for a plant against spring or fall freezes. Last year we presented evidence for the variability in the speed of cold acclimation among 7 wild tuber-bearing potato species (S. acaule, S. commersonii, S. megistacrolobum, S. multidissectum, S. polytrichon, S. sanctae-rosae and S. toralapanum). The same set of species was used for the present study to find out if there is also variability for the speed of deacclimation. Relative freezing tolerance of these species was measured before and after cold acclimation as well as after one day of deacclimation (exposure to warm temperatures). Our results suggest that there are differences in the speed of deacclimation among these species. We found that while some species lost near a half of their hardiness, others lost only a third or less of their hardiness after one day of deacclimation.

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Mark S. Strefeler and Robert-Jan W. Quené

Six commercial cultivars (Anna, Aurore, Danhill, Danlight, Melanie, and Thelca), one drought tolerant cultivar (Orangeade), nine breeding selections, and one check genotype of Impatiens hawkeri Bull were evaluated for differences in drought tolerance based on water loss and time to wilt. The six commercially available cultivars had significantly higher mean water loss than the breeding selections and `Orangeade'. These cultivars wilted in 5.11 vs. 7.33 days for `Orangeade' and 9.10 days for the breeding selections. These results suggest that sufficient variability exists in New Guinea impatiens germplasm for the reduction of water loss to improve drought tolerance. Regression analysis revealed that total transpirational water loss 96 hours after withholding water was an excellent predictor of the time to wilting (a simple measure of drought tolerance) after water was withheld (R2 = 0.95). Thus, a simple, efficient and objective method for selection of drought tolerant genotypes has been developed for New Guinea impatiens. A comparison of offspring to parental genotypes showed that after only one cycle of selection, water loss was significantly reduced by >30%. These results suggest that there is sufficient genetic variability present for the development of more drought tolerant cultivars.

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Unaroj Boonprakob and David H. Byrne

Six controlled crosses of cultivated and advanced selection Japanese-type plums adapted to southeast and southwest regions of the United States were made in 1990 and 1991. Over 800 seedlings from these crosses along with open pollinated seedlings of the parents were established in Suiting nurseries. The long range objective of this study is to determine linkage relationships between RAPD markers and commercially important traits (soluble solid, resistance to bacterial leaf spot, chilling requirement, fruit development period). The first step in the projects to characterize RAPD genotypes in the progenies. Eighty oligodecamers have been screened and 57 yielded successful reactions with an average of two to three bands per primer. The variability and inheritance of the RAPD markers in these plum populations will be described.

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Kenneth R. Tourjee, Diane M. Barrett, Marisa V. Romero and Thomas M. Gradziel

The variability in fresh and processed fruit flesh color of six clingstone processing peach [Prunus persica (L.) Batsch] genotypes was measured using CIELAB color variables. The genotypes were selected based on the relative fruit concentrations of β-carotene and β-cryptoxanthin. Significant (p < 0.0001) differences were found among the genotypes for the L*, a*, and b* color variables of fresh and processed fruit. Mean color change during processing, as measured by ΔELAB, was greatest for `Ross' and least for `Hesse'. A plot of the first two principal components (PCs) obtained from PC analysis of the L*, a*, and b* variables for fresh and processed fruit revealed three clusters of genotypes that match groupings based on the relative concentrations in fresh fruit of carotenoid pigments. Path analysis showed that variation in β-cryptoxanthin concentration was more precisely determined from color data than β-carotene concentration. Chemical names used: β-β-carotene (β-carotene), (3R)-β-β-caroten-3-ol (β-cryptoxanthin).