Influence of level and timing of shading on seed production in Panicum maximum cv. Gratton

Abstract

Artificial swards of P. maximum cv. Gatton were shaded to 25% (L25) or 54% (L54) of the sunlight received in a glasshouse for various periods related to the floral initiation, exsertion, anthesis and ripening stages of the first-formed inflorescences. Shading did not significantly reduce shoot yield. Seed yield was 93 g m-2 in the control treatment, relative to 32-48 g m-2 in the L54 series; in the L25 series, yields varied from 4 g m-2 in the continuously shaded treatment to 29 g m-2 in a late-shaded treatment. Reduction in seed yield was caused by a substantial decrease in the ratio of spikelets setting seed, and to a lesser extent by a decreased number of spikelets differentiated per inflorescence primary branch. A brief period of shading or early shading reduced seed setting in inflorescences emerging subsequent to the removal of shades. Shade slightly reduced 100-seed weight, and slightly increased branch number per inflorescence, and early shade delayed the time at which inflorescences reached anthesis. These findings require field confirmation. It is postulated that districts with high radiation receipt may have higher potential seed production and that crop management should be directed to promoting developmental phases in non-cloudy periods.