Two experiments were conducted to evaluate the effect of the plant regulator uniconazole on plant height, flowering, and fruit yield of vegetable transplants. In the first experiment, seedlings of tomato (Solanum lycopersicum ‘Early Girl’), pepper (Capsicum annuum ‘Jalapeno’), and eggplant (Solanum melongena ‘Millionaire’), were sprayed with water (untreated control) or with 2.5, 5, and 10 mg·L−1 of uniconazole. Five weeks after treatment (WAT), application of 2.5 mg·L−1 of uniconazole reduced the height of tomato by 17%, and of 5 and 10 mg·L−1, by 25%. The effect of 10 mg·L−1 of uniconazole on tomato plant height persisted until 13 WAT, but did not affect fruit yield. ‘Early Girl’ tomato plants treated with 10 mg·L−1 of uniconazole were still shorter than the untreated control at this time, but there were no significant differences in the number or weight of the fruit produced by the plants treated with 10 mg·L−1 of uniconazole, and the untreated controls. In contrast, as the rate of uniconazole increased, the height of ‘Jalapeno’ pepper and ‘Millionaire’ eggplant decreased. Application of uniconazole had no effect on the number of fruit produced by ‘Millionaire’ eggplant. However, treatment with 10 mg·L−1 of uniconazole reduced the number of fruit produced by pepper plants by 50%, and reduced the total weight of fruit produced by pepper and eggplant plants by 30% and 50%, respectively, compared with the untreated control. The second experiment analyzed the effects of 5, 8, and 10 mg·L−1 of uniconazole on two cultivars of tomato with different growth habit, Early Girl (determinate) and Sun Sugar (indeterminate). Application of all rates of uniconazole decreased plant height but not the final fruit yield of the two tomato cultivars.
Lucia E. Villavicencio, James A. Bethke and Lea Corkidi
Lucia E. Villavicencio, Sylvia M. Blankenship, G. Craig Yencho, Judith F. Thomas and C. David Raper
Sweetpotatoes [Ipomoea batatas (L.) Lam.] often experience significant epidermal loss during harvest and postharvest handling. Skin loss causes weight loss, shriveling of the root surface, and increased susceptibility to pathogen attack as well as poor appearance. It is not known if sweetpotatoes show variation in skin adhesion, cell wall enzyme activity and components, and growth parameters with growth temperature or if skin loss can be explained on the basis of variation among these variables. Skin adhesion, polygalacturonase (PG) and pectin methylesterase (PME) activity, lignin, anthocyanin, and dry matter content were measured in the periderm of ‘Beauregard’ roots grown at various temperatures under controlled conditions. Biomass dry matter content, storage root yield, root length, diameter, and weight at harvest were recorded. Histochemical and anatomical characteristics of periderm of roots were studied. Growth temperature affected skin adhesion, PG and PME activity, periderm and biomass dry matter content, yield, storage root weight, and diameter. High temperatures (34/31 °C day/night) yielded roots that were smaller and more resistant to skin loss. These roots had a periderm composed of more cell layers with a lower dry matter content than roots grown at lower and intermediate temperatures (27/24 °C and 20/17 °C). In cured roots, the correlation between skin adhesion and PG activity was negative (r = 0.544, P = 0.0006) and positive between skin adhesion and PME (r = 0.319, P = 0.05). For most of the variables studied, the interaction between growing temperature and curing was significant. Curing improved skin adhesion, but the effect of curing was dependent on the root growth temperature. The periderm of roots grown at higher temperatures was thicker and had more layers than that of roots grown at lower temperatures. Histochemical studies of the periderm of sweetpotato showed that the anatomical and structural composition of the cell walls differ depending on growth temperature.
Lucia Villavicencio, Sylvia M. Blankenship, Douglas C. Sanders and William H. Swallow
Bell peppers (Capsicum annuum L.) are classified as nonclimacteric fruits while some hot peppers have been reported as climacteric. Responses of peppers to exogenously applied ethylene-releasing compounds suggest ethylene involvement in the ripening process. Ethylene production and respiration rates in 13 cultivars of pepper: `Camelot', `Cherry Bomb', `Chiltepin', `Cubanelle', `Banana Supreme', `Habanero', `Hungarian Wax', `Mesilla', `Mitla', `Savory', `Sure Fire', `Tabasco', and `King Arthur' were studied under greenhouse and field conditions. Fruit from each cultivar were harvested at different maturity stages determined by color, ranging from mature-green to full red-ripe. Carbon dioxide and ethylene production were measured by gas chromatography. Both variables were significantly different among maturity stages for all cultivars. Respiration rates were between 16.5 and 440.3 mg·kg-1·h-1 CO2. Ethylene production ranged from 0.002 to 1.1 μL·kg-1·h-1. Two patterns of CO2 production were identified: higher CO2 production for mature-green fruit with successive decreases for the rest of the maturity stages or lower respiration rates for mature-green fruit with an increase in CO2 production either when fruit were changing color or once fruit were almost totally red. A rise in CO2 production was present for most cultivars. Ethylene evolution increased significantly at maturity or before maturity in all cultivars except `Cubanelle' and `Hungarian Wax'. Respiration rates and ethylene production were significantly different among cultivars at the mature-green and red stages.