Leaf senescence did not account for variations in grain and oil yield observed in sunflower under radiation limiting conditions

Abstract

The objective of this work was to study the effect of the decrease in incident solar radiation on leaf senescence, its consequence on the fraction of radiation intercepted by the leaves and on the grain and oil yield in sunflower. Five field experiments were conducted in Balcarce, with three hybrids, maintaining non limiting soil water conditions and nutritional status, and controlling weeds and insects. Treatments of different shading levels (50 or 80% of radiation interception) were applied during different periods of crop development (around flowering, during a window within the grain filling period or during the complete grain filling period). Shading levels were more intense than those expected by cloudiness in field conditions. The number, weight and oil concentration of grains, leaf area, incident radiation (I0) and the transmitted to incident radiation ratio (the fraction of radiation intercepted by leaves, I/I0) by different leaves strata were measured. Intercepted radiation (iPAR) was calculated as the product between I0 and I/I0. Shading treatments reduced grain and oil yield between 23 and 51%. No differences among periods or levels of shading were observed on grain and oil yield. Both the number and weight of grains decreased by shadings. Oil concentration decreased (between 5 and 21%) only when shading was applied during the window within the grain filling period or during the complete grain filling period. Shading accelerated leaf senescence but it did not affect the ratio I/I0. Intercepted PAR accumulated during the grain filling period was not related to the ratio I/I0. Incident radiation (I0) accounted for differences in grain and oil yield observed among treatments and experiments. It is concluded that the higher leaf senescence by decrease in I0 did not affect grain and oil yield through a decrease in the ratio I/I0.