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  • Author or Editor: A.D. Turner x
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The blossom-end scarring of tomato fruit caused by exposure of the plant to cool weather during ovary formation, commonly termed catfacing, can also be induced by GA3 foliar sprays. To determine if GA3 treatment could serve as a cultivar screening tool to identify lines susceptible to the disorder, we compared the catfacing incidence in 14 fresh-market tomato cultivars after GAS sprays and in nontreated controls in two field experiments. In 1 year, removal of the plant's apex was also imposed. GA3 sprays (22 μm twice, applied 1 week apart to tomato seedlings ≈5 weeks old) increased catfacing incidence in both years and accentuated cultivar differences in the disorder. Topping did not increase catfacing significantly. The cultivars Valerie, Sunrise, and Basketvee were least affected by catfacing in the experiments, while `Starfire', `New Yorker', and `Olympic' had the highest percentage of catfaced fruit. The GA3 screening method shows promise for identifying cultivar differences in susceptibility to blossom-end scarring. Chemical name used: gibberellic acid (GA3).

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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.

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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.

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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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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.

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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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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.

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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.

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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.

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Abstract

A series of field and greenhouse experiments was conducted with three cultivars of bell pepper (Capsicum annuum L.) to determine the hormonal basis for flower bud and flower abscission as induced by low light intensity (LLI). Imposition of 80% shade for 6 days increased abscission of reproductive structures by 38% and resulted in an increase in bud ethylene production. Concomitantly, bud reducing sugars and sucrose decreased and these were negatively correlated with ethylene levels and those of its precursor, ACC. Infusion of ACC into the pedicel resulted in flower bud abscission within 48 hr. The results indicate that ethylene is the primary causal agent of pepper flower bud abscission. Production of auxin by the bud plays a role in prevention of abscission. The abscission of disbudded pedicels was prevented by infusion of NAA. Although the three cultivars had similar responses to ACC, they differed in the amount of abscission under stress, bud sugar levels, and the time of onset of ACC and ethylene production. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); α-napthaleneacetic acid (NAA); (2-chloro-ethyl)phosphonic acid (ethephon).

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