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- Author or Editor: H.C. Wien x
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When GA3 foliar sprays are applied to tomatoes at transplanting (7.5 ppm, twice, one week apart) the lowest main stem clusters bear fruits which have large blossom-end scars (catfacing). Later flowering clusters are less affected as long as the plants are being grown under normal temperature conditions. Preliminary trials (Wien and Zhang, Hort Sci. 26:583-585, 1991) indicated that cultivar differences in catfacing susceptibility were reflected in GA3-induced catfacing differences. In 1990 and 1991, field trials were conducted in Freeville, N.Y. to compare the catfacing susceptibility of 14 and 18 fresh tomato cultivars respectively, using GA3 treatment. Catfacing was measured by counting the percentage of fruit on the third main stem, primary branch and two basal clusters that had blossom scars longer than 1 cm. Of the 14 cultivars common to both seasons, Valerie, Sunrise and Basketvee were least affected by catfacing in both control and GA3-treated plots, and Starfire, New Yorker and Olympic were most catfaced. GA3 spray shows promise for selecting catfacing-susceptible tomato cultivars.
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.
Pepper cultivars differ in susceptibility to stress-induced bud abscission. The stress susceptible cultivar `Shamrock' undergoes a larger reduction in net assimilation rate (NAR) under low light stress, and partitions less dry matter (DM) to reproductive structures than the more tolerant cultivar `Ace'. To determine if photosynthetic rates under low light stress could explain NAR differences, photosynthesis was measured on `Ace' and `Shamrock'. Assimilate partitioning was compared through measurement of leaf and bud respiration rates and analysis of bud sugar concentrations. Cultivar photosynthetic rates of exposed leaves did not differ under low light. Bud respiration rates fell to a lower level in `Shamrock' than `Ace' in low light-stressed plants, while expanded leaves respired at higher rates in `Shamrock' than `Ace' under both full and low light. Bud sugar concentrations were significantly lower in `Shamrock' than `Ace' after 3 days of low light stress. Susceptibility to low light stress-induced bud abscission in `Shamrock' appears to be associated with reduced assimilate partitioning to buds, perhaps caused by high assimilate consumption in maintenance of expanded leaves.
In previous research, pepper flower abscission has been brought about by ethylene, and prevented under greenhouse conditions by the ethylene action inhibitor silver thiosulfate (STS). Field experiments in 1991 and 1992 compared the abscission response and yield of `Shamrock', `Ssupersweet 860' and `Lady Bell' when treated with foliar sprays of STS (l×l0-3 M or 5×l0-3 M), or the ethylene synthesis inhibitor AVG (50 or l00ppm), applied at flowering. Abscission, measured a week after the chemicals were applied, was reduced from 16 to 4% in 1991, and from 16 to 5% in 1992 by the higher STS rate but not affected by AVG. `Ssupersweet' and `Shamrock' averaged 14% abscission during the measurement interval, while `Lady Bell' had 8%. Treatments did not change marketable yields, but the high rate of STS increased total and cull fruit numbers by 35 and 41%, respectively. All cultivars showed similar abscission and yield responses to the treatments.
Investigations of varietal differences in pumpkin flowering and fruitset patterns were initiated in response to reports of poor fruitset by NYS growers. In addition, pollination requirements for marketable fruit were explored in one cultivar. Flowering date, fruitset, and fruit characteristics were recorded for 2 consecutive years in a RCBD of six popular Cucurbita pepo cultivars (Wizard, Happy Jack, Autumn Gold, Ghost Rider, Howden and Baby Bear). On average, female blossoms opened 38 days after 3-wk-old seedlings were transplanted into the field. Flowering period lasted for 3 to 4 weeks. No consistent pattern was found in female flower production nor fruitset until the last week when significant declines occurred. Each blossom only opens for one day and typically closes between 10 am and noon, limiting pollination opportunities. H and-pollination of Wizard' with various dilutions of pollen revealed that a minimum of approximately 2000 grains of pollen is necessary for fruitset. Removal of 66-75% of the stigmatic surfaces did not affect seed number or their location in the fruit, nor fruit shape or size. Fruit size was not correlated with seed number, although no fruit developed with less than 100 seed.
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.
In a preliminary experiment, tomatoes were induced to catface by a temperature treatment of 2 weeks at 16/10C (day/night), starting at the 6-leaf stage. Fruits of the second and third, but not the first cluster showed catface symptoms. If catfacing induction could be further delayed by growing transplants in a non-inducing environment until most flower primordia have been initiated, plants might escape the disorder. In 2 field trials, plants were greenhouse-grown for 33, 47, or 61 days, and induced to catface by a GA3 foliar spray (15 ul·1-1) at transplanting. Catfacing was significantly increased by GA, sprays (23 vs 11% of all fruits in 1989, 22 vs 8% in 1990). In both years, there was a highly significant interaction between plant age and catfacing incidence, with high levels for young and medium-aged, but lower levels for old GA-treated transplants. Marketable yields were highest for youngest and medium-aged plants in 1989 and 1990, respectively. Old plants were checked in growth after transplanting and produced lowest yields in both years. Avoiding catfacing by use of old transplants thus has doubtful practical value.
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.
Abstract
Vegetable cultivar testing in the tropics is faced with fundamental problems that occur less frequently in the temperate areas. First, it must be decided what species of vegetables should be tested. Second, availability of planting materials, not only for the trial but also for the producer, can be a major limiting factor. Third, the methodology of testing is frequently different than in the temperate world, both in the cultural practices used and in the characteristics evaluated. Each of these points will be elaborated in the following paper, placing particular emphasis on the situation in Southeast Asia.
Growing a main vegetable crop for harvest and a cover crop for residue return to soil in the same growing season is a promising strategy to sustain soil quality in vegetable rotations. Our research evaluated cover crop strips interseeded between pumpkins (Cucurbita pepo L.) as a way to implement such a strategy. Cover crop types were lana vetch (Vicia villosa ssp. dasycarpa Ten.) and a lana vetch–winter rye (Secale cereale L.) mix, interseeded before, at the same time, or after pumpkins. The competitive impact of different cover crop strips was assessed using pumpkin yield, cover strip biomass, crop nitrogen status, soil nitrate status, and soil water potential. Cover strips were also assessed for competitiveness with native weeds. Seeding date affected the competitiveness of cover strips with pumpkins, while cover type did not. Cover crops seeded before pumpkins or at the same time reduced pumpkin yield in proportion to biomass produced by the cover strips early in pumpkin growth. Cover strips seeded after pumpkins did not reduce yield. Tilling in a before-seeded cover strip at 30 days after pumpkin seeding gave higher pumpkin yield than before-seeded cover strips that were not tilled. At three of four sites, after-seeded cover strips had the lowest percent weed biomass in strips, and at two sites with moderate weed pressure vetch–rye strips were more effective than vetch alone in suppressing weeds. Cover strips seeded before or at the same time as pumpkins reduced pumpkin yield by taking up resources that were otherwise available to pumpkins. At a high-rainfall site, competition for soil nitrate by cover crop strips was the dominant factor in reducing pumpkin yield. At a low-rainfall site, the dominant factor was competition for water. Because of effective weed suppression and lack of pumpkin yield reduction, interseeding vetch–rye strips after pumpkins was a promising practice, as was tilling in preexistent cover strips at an interval <30 days after pumpkin seeding. Good previous weed management and rye–vetch mixes at high seeding rates are necessary to allow interseeded cover strips to outcompete weeds.