Recovery From Water Stress In Five Sunflower (Helianthus Annuus L.) Cultivars. I. Effects Of The Timing Of Water Application On Leaf Area And Seed Production
For sunflower (Helianthus annuus L.) plants grown at a density of 5 m-2, maximum leaf areas per plant ranging between 0.2 and 2.2 m2 resulted from using five cultivars of different maturity and imposing four different water treatments. Seed production increased with the number of irrigations supplied, and in the irrigated treatments it was positively correlated with time to anthesis: later cultivars yielded better. Lateness was no advantage in crops grown on stored soil moisture and the best yielding cultivar was one which ranked only third when it was irrigated. All cultivars showed a remarkable ability to produce leaf area whenever water was available. Moreover, seed production was positively correlated with the maximum leaf area achieved by crops: the relationship between leaf area and seed yield was curvilinear across cultivars and irrigations, though a linear regression provided a significant fit to the data. The highest oil percentages occurred in a recently released commercial cultivar, but this vatiety did not produce the moist oil per plant. In addition, the line which ranked highest for oil production varied with water availability. It is concluded that, within the material studied, the longer duration lines were most suited to irrigation, since they permitted the establishment of more leaf area. The interaction between the effects of irrigation management and plant maturity on seed yield is discussed.