Light, Leaf Expansion and Seed Yield in Sunflower

Abstract

Two sunflower hybrids, Hysun 31 and Suncross 150, were grown in the field with adequate irrigation and given three light treatments throughout their life cycle. The treatments were 100, 50 and 20% sun (high, medium and low light); during the vegetative period the high light treatment averaged more than 20 MJ m-2 day-1 total short-wave radiation. The two cultivars, although differing in many of the leaf and plant growth parameters measured, followed the same trends with respect to light. A reduction from 100 to 50% light delayed the appearance of leaves slightly but had no effect on patterns of leaf-area expansion such as the rate and duration of expansion of individual leaves and the distribution of leaf area among nodes. A further reduction in light, however, significantly reduced the size of all leaves through effects on the rates at which leaves expanded. There was no effect of light level on the period for which leaves expanded. Whilst leaf expansion remained unaffected by a reduction from high to medium light, specific leaf weight was significantly reduced to 76% of control levels. The lowest light regime further reduced specific leaf weight to only 59% of control levels. Total plant weights declined to 89% (not significant) at the medium light level and significantly to 47% at the low level and as harvest index was marginally, though not significantly, decreased by a reduction in light, these values translated into significant reductions in seed production (86 and 44% of controls).