EFFECT OF CYTOKININS AND GIBBERELLINS ON FLOWERING AND FRUIT SET OF TOMATO (LYCOPERSICON ESCULENTUM MILL.) UNDER HIGH TEMPERATURE

Tomato plants (Lycopersicon esculentum Mill.) were grown in the greenhouse and in the field during 1979 and 1980. The inflorescences were treated with gibberellin (GA4/7) and/or benzyladenine (BA). Root exudate was collected at various stages of growth and development for the estimation of the levels of cytokinins in the plant. Soluble sugars and starch were determined in inflorescences at different stages of development. Partitioning of dry matter between the different plant portions was studied to evaluate growth of tomato plants in two different conditions. The application of GA4/7 and BA to tomato inflorescences promoted the development and increased the number of flowers. These growth regulators substantially increased fruit set and yield of tomatoes in both greehouse and field experiments. Determinations of carbohydrates in inflorescences treated with growth regulators showed higher amounts of soluble sugars and starch over a considerable period of development. The level of cytokinins in root exudate was higher during early phase of vegetative growth. At the time of bud formation and anthesis, the level of cytokinins declined. The quantity of translocated cytokinins in the greenhouse was 4 to 5 times higher than under high temperatures in the field. The low levels of cytokinins were associated with poor flower development. Field grown tomato plants produced more vegetative growth and fewer inflorescences than plants in the greenhouse. Allocation of assimilates to newly developed leaves and low level of growth regulators in buds and inflorescences might contribute towards more vegetative growth but poor flowering under high temperatures