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  • Author or Editor: H.C. Wien x
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In one greenhouse and two field experiments, eight or ten pepper (Capsicum annuum L.) cultivars were subjected to low-light stress by use of shade cloth (reducing light by 80%) or to foliar sprays of ethephon at 75 or 150 pi-liter-]. Both low-light stress and ethephon identified `Ace', 'Canape', and. `Belrubi' as less susceptible to flower and flower bud abscission than other cultivars in the first field experiment. In the 2nd year, air mean maxima of 32C caused severe abscission in controls and shaded plants, and complete loss of flowers in those sprayed with ethephon. Abscission of disbudded pedicels was not related to abscission susceptibility of eight cultivars when subjected to shade. While ethephon spray can serve as a satisfactory abscission screening tool under unstressed growing conditions, low-light stress imposed by shading may be used under a wider range of conditions. Chemical name used: 2-chloroethyl phosphoric acid (ethephon).

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When pumpkins are grown in elevated temperatures (32/27 °C day/night) for 1 week during flower development, fewer female flower buds are formed than at normal temperatures (20/15 °C) and only a small percentage of these reach anthesis. To determine if application of the ethylene-releasing compound ethephon can overcome the suppression of female flowers at high temperatures, `Baby Bear' pumpkin plants were sprayed at the two-leaf stage with 100 or 300 μL L–1 ethephon and then grown in hot and cool greenhouse compartments. At 20/15 °C, 17% of the first 15 main stem nodes produced female flower buds on control plants and virtually all of these developed into open flowers. The higher rate of ethephon increased female bud percentage to 37%. At 32/27 °C, only 3% of the nodes formed female flower buds and 2% flowered. Application of ethephon did not significantly increase female expression at high temperature, and none of the buds reached anthesis. Treatment with the inhibitor of ethylene action silver thiosulfate reduced female flower bud formation at the low temperature and entirely suppressed female flower buds at high temperature. In two additional experiments, these treatments were applied to two cultivars grown at a less extreme 32/20 and at 20/15 °C. Female buds and open flowers were moderately increased by ethephon in the high temperatures, suggesting that ethephon might foster female flowering in less extreme temperatures. Further work is needed to determine if ethephon treatment can overcome the heat-induced inhibition of female flowers in pumpkin under field conditions.

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Abstract

Choice of the most appropriate cultivars is a key decision that vegetable growers face every growing season, and one on which the profitability of the crop depends. Evaluation of cultivars for adaptation to local growing conditions is therefore of crucial importance to extension and research personnel that serve the vegetable industry and the companies that are developing and releasing vegetable cultivars. The present-day climate of restricted budgets and pressure to move from applied to more basic research has forced experiment station and university personnel in North America to abandon or greatly reduce vegetable cultivar testing. The seed industry has traditionally relied on both public institutions and its own grower–cooperators to evaluate the merits of new lines. Increasingly, seed companies face requests for funding of these public trials, or are asked to pay entry fees to submit new cultivars for testing.

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Tomato plants were induced to produce fruit with abnormally large blossom-end scars (catfaces) by exposing them to 16/10C (day/night) for 2 weeks, starting at the six-leaf stage. Fruit of the second and third, but not the first, cluster showed catface symptoms. To identify the initial period of susceptibility to catfacing, `Revolution' tomatoes were greenhouse-grown for 34,48, or 62 days and induced to catface by a gibberellic acid (GA) foliar spray (43 μM) when transplanted to the field. Catfacing was significantly increased by GA sprays (23% vs. 11% of all fruit in 1989, 22% vs. 8% in 1990). There was a highly significant interaction between plant age and catfacing, with high levels for young and medium-aged, but lower levels for old GA3-treated transplants. The early-maturing `Revolution' is susceptible to catfacing from ≈25 to 60 days after sowing. Marketable yields were highest for young and medium-aged plants in 1989 and 1990, respectively. Old plants were checked in growth after being transplanted and produced lowest yields. Avoiding catfacing by using old transplants has doubtful practical value.

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A series of greenhouse experiments was conducted with `Shamrock' bell pepper (Capsicum annuum L.) to gain insight into the flower abscission mechanism and to investigate methods to reduce reproductive structure abscission due to low light intensity. Foliar sprays of STS reduced stress-induced abscission. Application of the synthetic auxin NAA to the ovary substituted for pollination to effect fruit set under nonstress conditions, but did not improve fruit set compared to pollinated controls under low-light stress. Ovary treatment with GA3 and BA either alone or combined with NAA had similar results to NAA treatment alone. Foliar sprays of NAA or CPA also did not improve fruit set under low-light stress conditions. Application of NAA in an aqueous paste to the abscission zone prevented abscission but inhibited fruit growth. Taken together, the results indicate that stress-induced abscission is not prevented by auxin application to the ovary or foliage. The interaction of ethylene and auxin in reproductive structure abscission under stress conditions requires further investigation. Chemical names used: 6-benzylaminopurine (BA), p-chlorophenoxy acetic acid (CPA), gibberellic acid (GA,), silver thiosulfate (STS).

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Increase in plant density often results in reduction in reproductive potential of individual plants in cucurbits. The reduction may be due to reduced female flower production or a reduction or a delay in fruit set or to decreased fruit size. To determine the cause of the reduction, flowering, and fruiting of two pumpkin cultivars was evaluated in four field experiments under four plant densities ranging from 4483 plants/ha to 23,910 plants/ha and in a greenhouse using three levels of shade. Weekly flower and flower bud counts were made in the field experiment starting at first anthesis. Flowers were determined to have either set or aborted or not have reached anthesis. Increasing plant population from 4483 plants/ha to 23,910 plants/ha resulted in an increase in number of flowers per unit area up to 11,955 plants/ha, beyond which there was a steep decline. Increased plant density also resulted in an increase in aborted female flower buds that did not reach anthesis. Increase in plant density only reduced fruit set at very high populations. Number of fruits per area increased linearly with plant density up to 11,955 plants/ha, but decreased at higher plant populations. Reducing incident light by 30%, 60%, and 80% in a greenhouse experiment resulted in reduction of both male and female flowers. At 80% shade, there was a complete suppression of female flowers, whereas male flowers were still being produced. The number of female flowers reaching anthesis was positively correlated with total shoot dry weight while floral buds and male flowers were not. Reduction of individual plant biomass under high-density plantings might therefore be limiting female flower production and yield.

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The response of corn, beans and potato was evaluated in a 3 crop intercropping system at constant population density of corn (37,050 plants/ha) and three densities of beans (66,000 132,000 200,000 plants/ha) and potato (13,000, 36,000, 44,000 plants/ha) at low soil nitrogen in 2 seasons. Intercropping at the highest plant densities of beans and potatoes reduced the yield of corn, beans and potatoes by 65, 80 and 51 per cent respectively and produced a land equivalent ratio (LER) of one. The LER increased with decrease in the density of companion crops up to 1.24, indicating that intercropping at lower densities was more beneficial than monocultures. Increasing the density of beans and potatoes reduced corn height, leaf width and size of ears as well as leaf N, P and K. In beans the number of pods per plant was reduced while seeds per plant and seed weight were constant. In potatoes tuber size and numbers per plant declined.. The results indicate that the triple crop density which maximizes yield and income should not exceed 2/3 of optimum bean and potato sole crop densities.

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