SOIL AERATION, HORMONAL RELATIONSHIPS AND GROWTH OF TOMATO (LYCOPERSICON ESCULENTUM MILL.) UNDER DIFFERENT ENVIRONMENTS.

Abstract

Tomato plants (Lycopersicon esculentum Mill.) were grown in a greenhouse in Arizona in order to determine the effect of aeration, flooding, and exogenously applied benzyladenine (BA) on growth and cytokinin production at different growth stages. The structural changes in roots at different soil environments were also studied. Fresh and dry weight of roots and shoots and root exudate were collected at various stages of growth. Results showed that aerated plants significantly outperformed flooded and BA treated plants due to increased root and shoot output. The level of cytokinin in root exudate was higher during the early phase of vegetative growth. At the time of bud formation and anthesis, the level of cytokinin declined. In the vegetative stage, the competition between removed sinks and the rest of the shoot was reduced and, as a result, more cytokinin was believed to come from the roots to the shoots. Besides, additional carbohydrates were available to the roots. Determination of cytokinins in aerated plants showed a significant increase. However, in flooded plants, a smaller amount of cytokinin was detected. This is believed to be due to death of root apices, a major site for cytokinin production. Under experimental conditions, the application of BA to foliage of flooded plants had an adverse effect on growth of roots and shoot of tomato plants. However, a slight increase in cytokinin level was detected. Histological studies showed an increase in air-spaces (aerenchyma) in roots of flooded plants. This acclimation improved survival in inadequately aerated plants that were waterlogged.