THE INFLUENCE OF IRRADIANCE ON RATE OF DEVELOPMENT AND COMPONENTS OF YIELD IN BARLEY

A field study was conducted to investigate the effects of variation in levels of daily irradiance on the level of spikelet abortion and the rate of development using two cultivars of spring barley (Hordeum vulg are L.), Schooner and Weeah. Three different irradiance treatments wer e imposed from the cessation of spikelet primordia initiation until an thesis: a reduced irradiance treatment (high competition treatment, HC T); an untreated control (or medium competition treatment; MCT); and a n increased amount of irradiance (low competition treatment, LCT). Var iation in natural daily irradiance (MCT) was imposed by either shading plants with shadecloth (HCT) or by exposing plants to relatively low inter-row irradiance competition effects by obstructing adjoining plan t rows with plastic mesh (LCT). The duration of the spikelet growth ph ase was longer by 5 days (Schooner) and 9 days (Weeah) for HCT when co mpared to MCT, but there was no difference in its duration between LCT and MCT. Spikelet abortion occurred at 8-16 days before anthesis, but this was dependent on treatment. LCT for both cultivars showed a tren d towards higher spikelet numbers per spike, although the increase was not significant over MCT, and HCT was significantly lower in both cul tivars. Grain yield and biomass were lower (P < 0.05) for HCT compared to both LCT and MCT.