Effects of seed size, cotyledon removal and nitrogen stress on growth and on yield components of oilseed sunflower

Abstract

We investigated the effects of seed size on the growth and yield of a hybrid oilseed sunflower. The effects of removal of cotyledons after seedling emergence were also investigated, and we grew the plants at two levels of nitrogen supply to see if N stress modified responses to seed size or cotyledon removal. Seedlings from small seeds had less dry-matter, but the same number of leaves, as those from large seeds. Cotyledon removal resulted in reduced growth and leaf number per plant in young seedlings. However, by the flower-bud-visible stage the effects of seed size and cotyledon removal on growth had disappeared. The timings of floret initiation, anthesis and maturity were unaffected by seed size or cotyledon removal, and neither were yield components affected. The effects of N stress included fewer leaves and reduced dry-matter per plant. Low N supply delayed the onset of floret initiation by 7 days but had no effect on the end of floret initiation. Nitrogen stress decreased the area for floret production on the receptacle by 74%. The number of seeds per plant and, to a lesser extent, single-seed dry-weight were reduced by low N supply; consequently, oil yield per plant was reduced by 85%. The results indicate that there is no advantage in using large seeds at conventional sowing depths, and that oilseed sunflower can compensate for damage to cotyledons after seedling emergence.