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A. Naor and S. Cohen

The sensitivity of water stress indicators to changing moisture availability, and their variability, determine the number of measurements that should be taken in order to represent properly plant water status in a certain orchard. In the present study we examined the sensitivity and variability of maximum daily trunk shrinkage, midday stem water potential, and daily transpiration rate in their responses to withholding irrigation from field-grown drip-irrigated `Golden delicious' apple trees in a commercial orchard. Irrigation was withheld from the stressed trees for 17 days starting in mid-July, and the control trees were irrigated daily at 100% of the “Class A” pan evaporation rate. The courses of daily transpiration rate, maximum trunk shrinkage, and midday stem water potential before and 10 days after the drying period were similar in the control and the stressed trees. Highly significant differences between the stressed and the control trees in their midday stem water potentials were apparent from the early stages of the stress period. Daily transpiration rate and maximum daily shrinkage were more variable than midday stem water potential, and differences between treatments became significant only after measurements were expressed relative to the initial values before irrigation was witheld. Differences between treatments (as percentages of the values obtained for the control trees) increased after irrigation stopped where these differences were greatest for maximum daily shrinkage, which reached 90%; moderate for stem water potential (60%); and least for daily transpiration rate, for which the differences remained below 20%. Our data show that the choice of a certain water stress indicator should be based on both the sensitivity to changing moisture availability and the degree of variability. Possible reasons for the different sensitivity to moisture availability and the different variability between the water stress indicators under study are discussed.

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Michelle L. Paynter, Elizabeth Czislowski, Mark E. Herrington, and Elizabeth A.B. Aitken

isolates. The number of single isolate groups (11) is high. Hyun and Park (1996) from Korea identified four major VCGs, with only one of these being a single isolate group. Phylogenetic analysis based on EF-1α sequences showed variability among isolates

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Irene Kadzere, Chris B. Watkins, Ian A. Merwin, Festus K. Akinnifesi, John D. K. Saka, and Jarret Mhango

The full commercial potential of wild loquat [Uapaca kirkiana (Muell. Arg.)], a fruit that is widely used for food and income in parts of Africa, is restricted by its short shelf life and variability in postharvest quality. We have evaluated within and among tree variability in fruit size and color at harvest, and changes of color, soluble solids concentrations (SSC) and pulp deterioration during storage, of fruit harvested during the maturation period. The relationships between fruit shape, size, seed number and SSC of fruit harvested at the ripe stage of maturity was also assessed. Size and color of fruit within and among trees at harvest varied greatly within the same location on the same harvest date. The a* values (redness) were more variable than for other color attributes, reflecting a range of fruit colors from greenish to brown. During a 6 day storage period, fruit color lightness and yellowness decreased, while redness increased, and variation in color attributes decreased. Although fruit color intensified during storage, the SSC of fruit after ripening was linked more with fruit color at harvest, with mean concentrations ranging from 6.7% to 13.8% among trees. When fruit were harvested four weeks later and categorized by color at harvest, SSC varied from 11.8% in greenish-yellow fruit to 14.5% in browner fruit. Pulp deterioration of stored fruit harvested unripe was observed by 6 days. The SSC of fruit harvested when ripe was not significantly correlated with shape, size or seed number. These observations have important implications for germplasm selection and collection of U. kirkiana for domestication purposes. Timing of harvest and/or postharvest sorting of fruit is likely to reduce variability in SSC during the postharvest period.

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K.H.S. Peiris, G.G. Dull, R.G. Leffler, and S.J. Kays

Spatial variation in soluble solids content (SSC) of fruits of apple (Malus ×domestica Borkh. cv. Red Delicious), cantaloupe (Cucumis melo L. Cantaloupensis group), grapefruit (Citrus paradisi Macf. cv. Indian River Ruby Red), honeydew melon (Cucumis melo L. Inodorus group), mango (Mangifera indica L. cv. Hayden), orange (Citrus sinensis L. Osbeck. cv. Valencia), peach (Prunus persica L. Batsch. cv. Windblow), pineapple (Ananas comosus L. Merr. cv. Kew) and tomato (Lycopersicon esculentum Mill.), and of bulbs of onion (Allium cepa L. Cepa group) and in dry-matter content (DMC) of potato (Solanum tuberosum L. cv. Russet Burbank) tubers was measured along three directional orientations (i.e., proximal to distal, circumferentially midway along the proximal to distal axis, and radially from the center of the interior to the outer surface). The pattern and magnitude of constituent variation depended on the type of product and the direction of measurement. Radial and proximal to distal variation was greater than circumferential variation in all the products tested. Honeydew had the highest radial variation with a SSC difference of 6.0 % and a cv of 22.8%, while tomato displayed lower radial variation with a cv of 1.0%. Pineapple had a proximal to distal SSC difference of 4.6% with a cv of 13.8%, while the difference in tomato was 0.6% with a cv of 5.1%. Circumferential variation of SSC in all products tested was <2% with cv ranging from 1.1% to 3.8%. The results confirm that considerable constituent variability exists within individual fruit and vegetable organs. This variability may affect the accuracy of calibration equations and their prediction capability. Therefore, within-unit constituent variability should be meticulously assessed when an NIR spectrometric method is being developed for the nondestructive quality evaluation and sorting of a product.

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Santiago Pereira-Lorenzo, Ana M. Ramos-Cabrer, Belén Díaz-Hernández, Javier Ascasíbar-Errasti, Federico Sau, and Marta Ciordia-Ara

Chestnut (Castanea sativa Mill.) is an important crop in Spain. This inventory of chestnut cultivars complements previous studies. We have located 152 chestnut cultivars in 131 municipalities covering 108.6 ha, with 72 new cultivars in addition to the 80 previously found. Fewer than 50% of these cultivars are extensively cultivated. Chestnuts in Spain are grown from sea level to 1100 m, but are more frequent between 200 and 800 m on northern-facing slopes. Most of the chestnuts are harvested from 25 Oct. to 10 Nov.

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Katharina S. Wigg and Irwin L. Goldman

the accessions at the susceptible end displayed a quick constant disease progression. Although some variability may occur between the first and second evaluation periods due to individual plant differences as well as variability in response over time

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Paul R. Hepler and David E. Yarborough

One hundred lowbush blueberry (Vaccinium angustifolium Ait.) clones were randomly sampled from a commercial field to estimate potential productivity. Yield data exhibited a normal distribution ranging from 300 to 17,000 kg·ha-1 with a mean of 7726 kg·ha-1. Commercial use of selected clones or improved cultivars through new plantings, interplanting into existing clones, or replacement of low-yielding clones in native stands and increasing the intensity of field management would increase the yielding potential of native lowbush blueberry fields.

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Patrick P. Moore

Cultivated raspberries may include North American red raspberry (Rubus idaeus strigosus Michx), European red raspberry (R. idaeus vulgatus Arrhen.) or black raspberry (R. occidentalis in their pedigrees. Twenty-one raspberry clones were investigated using chloroplast restriction fragment length polymorphisms to determine the cytoplasm type and the amount of cytoplasmic diversity among these selected clones. The raspberry clones were selected representing North American red raspberry, European red raspberry, black raspberry and cultivars with divergent maternal lineages. Total cellular DNA was probed with two 32P-labelled fragments of tomato chloroplast DNA. Probe-restriction enzyme combinations were selected which discriminated between representatives of the two red raspberry subspecies. Raspberry clones were grouped according to the chloroplast restriction fragment patterns. The composition of the groups was compared with their pedigrees.

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Himayat H. Naqvi, Mitsuo Matsumura, and Irwin P. Ting

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Clarissa J. Maroon-Lango, Mary Ann Guaragna, Ramon Jordan, John Hammond, Murali Bandla, Steve Marquardt, and John R. Stommel

Pepino mosaic virus (PepMV) was first found in pepino (Solanum muricatum) growing in coastal Peru in 1974 and described in 1980; it reappeared in protected tomato (Lycopersiconesculentum) in the Netherlands in 1999. Since then, it has been reported to occur in tomato in several countries including Austria, Belgium, Canada, France, Germany, Italy, Peru, Spain and the Canary Islands, the United Kingdom, and in 11 states within the United States. Three strains of PepMV found in the United States have been cloned and sequenced. Full-length genomic sequences were obtained for two strains, PepMV-US1 and PepMV-US2, from co-infected tomato plant samples from Arizona. The 3'-end sequence of PepMV-US3 came from infected tomato fruits from Maryland. The genome organization, motifs and domains typical of the genus Potexvirus, and of other PepMV isolates, were found in full-length sequences of both US1 and US2 isolates. Direct comparison of US1 and US2 at the nucleotide level revealed an 86.3% identity; whereas, when individually compared to the French and Spanish isolates, which share ∼99% identity at the nucleotide level, US1 and US2 had 82% and 79% identities to each, respectively. Pair-wise gene-for-gene comparisons between United States and European isolates revealed a similar trend. While unique, US1 is more closely related to the previously reported European isolates than is US2. The CP of US3 is nearly identical to the European isolates at the amino acid level. None of 18 tomato germplasm accessions or 10 cultivars were resistant to mechanical inoculation with US3; in contrast, no infection was detected in nine pepper cultivars or four germplasm accessions. Plants grown from seeds of infected tomato fruits did not test positive for PepMV.