Hormonal activity in tomato flowers in relation to their abscission under water stress

Ethylene and indole acetic acid (IAA) concentrations were investigated in the flowers of four tomato (Lycopersicon esculentum Mill.) cultivars, e.g. Mruthyunjaya, Pusa Early Dwarf (PED), Pusa Ruby and Arka Ahuthi under water stress, imposed at flowering stage (40 days after transplanting) for a period of one month by withholding irrigation. Arka Ahuthi and Pusa Ruby were found more susceptible to flower abscission compared to Mruthyunjaya and PED under water stress. Ethylene production in the flowers of different varieties increased under stress and ranged from 36.2 to 62.7 nl g⁻¹ h⁻¹, from 15.1 to 19.1 nl g⁻¹h⁻¹ in the control plants. In the abscission susceptible Arka Ahuthi and Pusa Ruby such increase under the water stress was four times of the control plants. The IAA level in the flowers under stress decreased to 22.3 - 48.4 ng g⁻¹ from 38.0 - 71.0 ng g⁻¹ range in the control plants and it was more in the abscission susceptible tomato cultivars. Decrease in IAA level in association with increase in the ethylene level in the flowers might be the important factors causing flower abscission under water stress.