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- Author or Editor: H.C. Wien x
- HortScience x
Abstract
Under conditions of environmental stress, many pepper (Capsicum annuum L.) cultivars lose flower buds, probably due to production of the abscission-causing hormone ethylene. Field applications of the ethylene-generating chemical ethephon (0 to 300 µl liter-1) were made to five cultivars of bell pepper growing under nonstressed conditions, but differing in resistance to stress-induced bud abscission. Cultivars were seeded at several times in 1985 to synchronize stages of plant development and allow a single simultaneous spray application to all plots. In the two 1986 experiments, all cultivars were sown on the same date and either two or three sprays were applied to all plots to more closely approximate screening conditions used by plant breeders. One week after application of ethephon at 300 µl.liter-1, virtually no flower buds remained on any cultivar in either year. Susceptible cultivars exhibited significantly greater abscission than resistant ones at ethephon concentrations of 75 to 200 µl.liter-1. The use of ethephon shows promise as a simple screening method for resistance to stress-induced flower bud abscission in pepper. Chemical name used: 2-chloroethyl phosphonic acid (ethephon).
Although it has been known since the 1930s that long photoperiods and high temperatures hasten bulb formation in onions, the time at which onion cultivars under field conditions in New York start forming bulbs has not been previously reported. In the 1997 and 1998, onion cultivars were seeded in three commercial onion production areas at normal early spring planting dates. In 1998, a time-of-planting study was carried out in Ithaca, N.Y., in which three transplanted crops and three direct-seeded crops were established at monthly intervals beginning at the end of March. Bulb ratios (bulb diameter: neck diameter) were measured at 2-week intervals during the season in all plantings. Initiation of bulbs (assumed to occur 3 weeks before bulb ratio reached 2) was then related to the photoperiod and air temperature up to that point. A comparison of early, mid-season, and late cultivars indicated that bulbs are initiated in commercial plantings in New York at close to the longest day of the year (15.6 h), at a time when mean temperature is still rising. In the time of planting study, delay of planting resulted in fewer days from emergence to bulb initiation and a reduction in growing degree-day accumulation. If planted later than 15 June, some cultivars failed to initiate bulbs, but others, such as `Quantum' and `Winner', initiated bulbs but did not mature them. The results indicate that photoperiod appears to be the primary factor for the initiation of bulbs, but that bulb initiation can be modified strongly in some cultivars by temperature.
High temperatures during flowering frequently limit yields of some bell pepper cultivars in New York fields. Previous research has shown that subjecting the plants to low light at flowering can have similar effects. To determine if cultivar differences in flower abscission and yield could be accentuated by such a shade stress, field plots of six cultivars were subjected to 1 week of low light during flowering. Shade cloth tunnels were erected over the plant rows in two experiments, reducing incident light by 80%. Nondestructive abscission counts were taken at the start, and 7 days after the end of a 7-day shade period. Mature green fruit were harvested periodically. Low light stress resulted in 68% and 86% abscission at the first three fruiting nodes in 1992 and 1994, respectively. Cultivars showed differential abscission in unshaded plots, and after shade, producing a significant cultivar: shade interaction. `Ace' showed least abscission and maintained yields with shading; `Camelot' lost nearly all flowers and buds with low light stress, and was reduced by 75% and 91% in marketable yield in 1992 and 1994, respectively. Results indicate that shade stress accentuates abscission susceptibility in bell pepper cultivars. Pepper lines selected for low light tolerance may show promise in resisting flower abscission at high temperature.
Field production of decorative pumpkins (Cucurbita pepo L.) in New York occasionally results in markedly delayed fruit production in spite of normal vine growth. These episodes of fruitlessness appear to be associated with periods of high temperatures. To determine the link between temperature and pumpkin flowering and fruiting, a series of multilocational field trials and confirmatory greenhouse experiments were carried out. The field trials were conducted in the summer seasons of 1996 and 1997 in Ithaca and Albany, N.Y.; Queenstown, Md.; and Bradenton, Fla.; and in Ithaca and Bradenton in 1998. Mean growing season temperatures were 20, 21, 24 and 28 °C, respectively, at the four locations in 1996 and 1997. Delay in fruit formation was indicated by the main stem node number at which the first fruit developed. In Ithaca and Albany, the six cultivars formed their first fruit at node 17, but fruit production shifted to node 24 at Queenstown, and to node 26 or more at Bradenton. The prolonged delay in fruiting at the warmest site resulted in a 74% decrease in total yield of the C. pepo cultivars in 1996 and 1997, compared to Ithaca and Queenstown. In contrast, the yields and yield components of the C. maxima cultivar Prizewinner were similar at all four sites. Greenhouse trials in which `Howden' and `Baby Bear' were grown at 32/27, 25/20, and 20/15 °C confirmed that high temperatures delay formation and anthesis of female flowers. This and other published work indicates that there are genetic differences in susceptibility to high temperature flower delay that could be exploited to improve pumpkin performance.