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green. Our hypothesis was that a difference in ploidy level among cultivars is related to the variation in winter color and that cultivars that remain greener during winter were tetraploids. The current study was conducted to determine the ploidy level

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The higher productivity of modern fruit tree cultivars, compared with wild trees, is mostly related to their higher partitioning of dry matter into fruit [i.e., higher harvest index (HI)] ( Patrick, 1988 ), rather than to differences in

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Abstract

Bolting (premature production of flowers or seeds) of leaf lettuce (Lactuca sativa L.) results in elongated seedstalks and bitter leaves (1). Seed companies often refer to differences in bolting in their advertisements for leaf lettuce cultivars. However, scientific studies that substantiate or refute these claims are not readily available.

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Abstract

Cultivar differences in the heat deactivation temperature of trypsin inhibitors in an extract of chopped tissue were examined. In addition, the distribution of trypsin inhibitor activity in the root and existence of different trypsin inhibitor proteins within and among 4 cultivars were investigated. There was a significant cultivar-by-temperature interaction during the heat deactivation test. Activity in ‘Jewel’ was decreased by 50% at a significantly lower temperature (65°C) than the other cultivars (75°) indicating that ‘Jewel’ contains more heat labile trypsin inhibitors. The longitudinal distribution of trypsin inhibitor activity was dependent on the cultivar. All cultivars had increased levels of trypsin inhibitor activity in the proximal or stem end. Sectioning of roots, in order to eliminate high trypsin inhibitor activity, would not be reliable since there is a cultivar-by-section interaction, and the gradients are not large enough to eliminate the majority of trypsin inhibitor activity by removal of one section. The cross-sectional gradient of trypsin inhibitor activity in the roots also depended on the cultivar. There was a high level of trypsin inhibitor activity in the cortical region of all cultivars. The concentration (over 50%) of trypsin inhibitor activity in the cortical area of the root in ‘Jewel’ and ‘Caromex’ could be important when heat deactivating the whole root. Disc-gel electrophoresis revealed that the trypsin inhibitor fraction isolated via affinity chromatography was heterogenous. There were 7 different trypsin inhibitor bands after electrophoresis at pH 8.9 in 7.5% acrylamide gels. The quantitative distribution of these seven trypsin inhibitor proteins differed among cultivars. These different distributions may be responsible for the cultivar differences previously observed.

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The growth in diameter of large-(`Loring' and `Suncrest') and small-fruited (`Bailey' and `Boone County') peaches [Prunus persica (L.) Batsch] was recorded at weekly intervals from 175 days prebloom to ripening. Samples collected at three dates prebloom, full bloom (FB), and four dates postbloom, including ripe fruit, were sectioned and stained. Total cell count and mean cell size were determined for prebloom ovaries and postbloom mesocarp tissue. Large-fruited cultivars had significantly more cells (up to 3.7 times) than small-fruited cultivars at all sampling dates. Cell sizes increased dramatically with fruit development, but were similar for all cultivars within each sampling date. These results suggest that mesocarp cell count is the major difference between small- and large-fruited peach cultivars and that this difference is determined early in the growth of the ovary.

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We have compared reproductive processes and fruit set in Manzanillo and Frantoio olive cultivars which are reported in the literature respectively as incompatible and partially compatible. The same incompatibility reaction was observed in both cultivars. Pollen tube growth was almost completely inhibited beyond the stigma, but some degree of self-fertilization was accomplished. However, in both cultivars cross-pollination provided a earlier and higher level of fertilization. Differences in self-incompatibility behavior seemed related to the level and the amount of delay in self-fertilization. In the compatible variety, Frantoio, self-pollen tube growth was accomplished more rapidly and showed a higher level of self-fertilization than in the incompatible Manzanillo cultivar. Fruit set matched reproductive behavior.

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Abstract

Wounding freshly harvested or cured sweet potato [Ipomoea batatas (L.) Lam.] roots by either breaking, or cutting them in half stimulated C2H4 production in all 13 cultivars and selections examined. Ethylene production was stimulated within 1 day of wounding and generally continued to increase for 7 days before decreasing. At the peak of production, wounded freshly harvested roots produced about 22 times more C2H4 than controls, while C2H4 production from wounded cured roots of the same cultivar or selection increased about 86 times. Wounding stimulated CO2 production by about 72% over the controls. There were marked cultivar differences in the maximum rate of wound-induced C2H4 production.

Open Access

Fruit growth in saskatoons (Amelanchier alnifolia Nutt.), an emerging horticultural crop across the Canadian prairies, results from development of the mesocarp and the endocarp-locular-ovular structure which includes the developing seeds. Contribution of these tissues to fruit size was assessed using transverse sections of ovaries sampled at six developmental stages among large- and small-fruited cultivars. Mesocarp development was similar among the larger-fruited cultivars (Thiessen, Northline, and Smoky); the number of cells increased rapidly through Stage I [162 to 293 growing degree days (GDDs)] of fruit growth, and cell number increase was minimal during Stages II (293 to 577 GDDs) and III (577 to 747 GDDs). In `Regent' fruit (a small-fruited cultivar), the maximal rate of cell division was delayed until Stage II and the mesocarp contained fewer cells than the larger-fruited cultivars at harvest maturity. Mesocarp cell enlargement was similar among all of the cultivars studied where cell expansion was maximal during Stage I and continued at a slower rate during Stages II and III. The area of the endocarp-locular-ovular structure was greatest for `Thiessen' and `Northline', midrange for `Smoky', and smallest for `Regent'. Data suggest that a minimum number of mesocarp cells early in fruit development is required to attain maximal mesocarp size, and that differences in cultivar fruit size are a function of both the mesocarp and the endocarp-locular-ovular structure.

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Cultivars of bell pepper differ in susceptibility to bud/flower abscission. Reduction in the level of assimilate, and alterations in assimilate partitioning may be involved in the processes leading to bud/flower abscission. Four growth analysis experiments were conducted to determine whether two pepper cultivars differing in susceptibility to stress-induced abscission showed corresponding differences in growth and rates and dry matter partitioning when subjected to shade stress. The reduction in RGR and NAR with shading was significantly greater for the abscission-susceptible `Shamrock' than the more tolerant `Ace'. Partitioning of dry matter to reproductive structures was reduced by shading. There were no cultivar differences in the proportion of dry matter partitioned to young developing leaves. Fully expanded leaves comprised a larger proportion of total dry matter in `Shamrock'. The lower NAR of `Shamrock' under stress may have led to greater bud/flower abscission than `Ace' under shade stress. If preferential partitioning of dry matter to competing structures (developing leaves) is also involved, it was not detected using this technique.

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, Legacy, and Patron) and four hybrid cabbage cultivars (Bravo, SC 100, Stonehead, and Vantage Point) were chosen for this study based on differences in tolerance observed in a preliminary screening experiment or previously reported research ( Hopen et al

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