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When bell pepper plants are subjected to high temperatures or low irradiance during flowering, abscission of flowers and flower buds can be severe enough to limit yields. Both types of stresses may lead to reduction of carbohydrate levels in the reproductive structures, and evolution of the abscission-causing hormone ethylene. In two greenhouse experiments, plants were subjected to combinations of 30 or 20 C air temperature and unshaded or heavily shaded conditions for one week at anthesis of the first flower. In a third experiment, plants were subjected to total darkness and temperatures of 30, 20 or 15 C for one week at the same stage of growth. In all experiments, levels of soluble carbohydrates and starch declined under low or zero light conditions, with rate of decrease proportional to the air temperature. Abscission of reproductive structures was not well correlated with carbohydrate levels: in spite of low sugars and starch, plants darkened for 7 days at 15 C showed no abscission. Levels of the ethylene precursor ACC in the buds, though variable, rose just before abscission began, but remained low in non-abscising treatments.
The growth processes of most horticultural crops are too slow to be visually interesting to students. Time lapse photography has been used for years to speed up the action and make plants “come alive.” With the advent of video technology, time lapse techniques have become convenient, easy, and affordable. The system which we have found satisfactory consists of a time lapse video cassette recorder, linked by optical fiber cable to a closed circuit color video camera in a ventilated housing. Typically, the camera has been set up in a greenhouse compartment, monitoring growth processes of vegetable crops, and linked by cable to the VCR in an office 80 m away. Equipment costs with one camera are less than $3000. Two cameras can be set up to do comparative growth studies, with two images side-by-side, using a screen splitter. Costs of the latter system is about $4500. Growth processes such as cabbage head formation, curd growth in cauliflower, and weed-crop competition of mustard and peas have been the subjects so far. The technique lends itself to increasing the visual impact of teaching, and gaining a better understanding of plant growth processes in research.
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.
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.
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.
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.
Catfacing of tomato (Lycopersicon esculentum Mill.) fruit describes the enlarged blossom-end scar and ridged, flattened or irregular fruit shape often found on plants subjected to low temperature during ovary development. Experiments were conducted to determine if GA3 foliar sprays could be used as a screening tool for catfacing. Concentrations of 5 to 50 μM of GA3, applied once at transplanting, significantly increased catfacing incidence on the susceptible `Revolution', whereas the resistant `Valerie' was less affected. Two applications 8 days apart extended symptoms to later clusters formed on branches and may be useful for screening cultivars of a wide range of earliness. Plant apex removal may also be possible as a fruit catfacing screening tool. Chemical name used: gibberellic acid (GA3).
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.
Abstract
The system of using a living sod intercropped with row crops is aimed at alleviating soil compaction, a major problem for commercial vegetable producers in the United States. Monoculture screening of 30 grasses and 52 legumes was conducted to select groundcovers suitable for use as living mulches with little or no crop suppression. Five turfgrasses and 3 dwarf white clover cultivars were selected from the trial and grown between rows of sweet corn (Zea mays L.) and cabbage (Brassica oleracea var. capitata L.) in the following year. Colonial bentgrass, creeping bentgrass, and a Kentucky bluegrass/white clover mixture significantly reduced sweet corn and cabbage yields. Red fescue adversely affected sweet corn, whereas 2 American white clover cultivars caused yield reductions in cabbage. Growth of Chewing’s fescue, Kentucky bluegrass, and the wild white clover cultivar ‘Kent’ had no effect on sweet corn or cabbage yields. Correlations of living mulch dry weight to vegetable yield parameters were negative and highly significant in both experiments.