ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
INHIBITION OF NAPA GAMAY AND THOMPSON SEEDLESS BERRY DEVELOPMENT BY HEAT STRESS AND ITS PARTIAL REVERSIBILITY BY APPLICATIONS OF GIBBERELLIC ACID AND PROMALIN. |
| Authors: | S. Matsui, K. Ryugo, W.M. Kliewer |
| Abstract:
When grapevines are exposed to temperatures exceeding 40°C during the growing season, berry growth, anthocyanin formation, and accumulation of soluble solids are retarded (Kliewer, 1964, 1970, Kobayashi, et al., 1965, Sepulveda, 1982). Harvest is delayed and fruits do not reach the desirable dessert flavor or the sugar:acid ratio for attaining optimum wine quality. Stressed plants wilt because of stomatal closure which is attributed to increase in abscisic acid level (Loveys and Kriedemann, 1973) and/or decrease in cytokinins (Kuiper, 1972). Applications of hormones are known to enhance berry size (Ito, et al., 1969, Weaver and Sachs, 1968). In this study, 4-year-old glasshouse-grown Napa Gamay grapevines were transferred to a phytotron kept at 43/22°C (day/night) temperatures for 4 days when the berries were in Stage I. Although the pots were water-cooled, leaves became chlorotic and the berries were smaller in size, containing less total soluble solids and titratable acidity than those on non-stressed vines. Stressede berries and comparable ones on non-stressed vines were sprayed 2 days later with 20 ppm gibberellic acid-3, (GA). Stressed, GA-treated berries grew to near normal size but those treated with benzyladenine (BA) did not grow as well and were the smallest of all treatments. Different clusters on Thompson Seedless vines were sprayed with 20 ppm Promalin, a mixture of GA 4+7 and BA or with GA before or after exposure to 40/22°C for 4 days. Pretreated, heat-stressed Thompson Seedless berries lagged in their growth during Stage II but grew more rapidly during Stage III than post-treated ones so that by harvest all were of equal size. Hormone-treated berries were larger than non-stressed, untreated berries. Promalin-treated, non-stressed berries were largest of the group. Bioassays of stressed and non-stressed berries using a modified barley endosperm test (Ryugo and Sansavini, 1972) revealed that the former had lower gibberellin-like substances than the latter. Porometer readings indicated that the stomates were closed during the stress period and stomatal conductance did not normalize for 4 to 6 days after the heat spell at which time leaves became turgid and re-greened. The decrease in gibberellin content of berries indicates that fruit cells lose their ability to synthesize or import the growth-promoting hormone and photosynthates from leaves and buds when they are stressed. This growth inhibition resulting from decreased GA level was partially reversible by exogenous applications of GA and Promalin, the latter being more effective than the former. Whether | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
