SUNFLOWER RESPONSE TO A RANGE OF SOIL-WATER CONTENTS

The objective of the study was to investigate the effect of different water stress intensities on the fraction of carbon partitioned to the head. Water consumption, yield and its components, leaf area, and net photosynthesis were also measured. Plants were grown in plastic pots i n a greenhouse. At the eight-leaf stage, water stress was imposed and held until physiological maturity. Three levels of stress intensity, d efined by pre-dawn leaf water potential, were studied. Water stress re sulted in an increase in harvest index and water-use efficiency. In st ressed treatments, leaf area decreased through a drop in leaf expansio n and net photosynthesis declined linearly with leaf water potential. At anthesis, water stress induced an increase in the fraction of assim ilates partitioned to the head. The relationship between net photosynt hesis and leaf water potential was not affected by the level of stress intensity and the allocation of photosynthates to the head was simila r in all stressed treatments. Thus, in this study it is concluded that sunflower responded to water stress in the same way at all stress int ensities.