Grain growth and malting quality of barley. 1. Effects of heat stress and moderately high temperature

In this study, controlled-environment conditions were used to compare the effects of moderately high and very high temperatures during grain filling on grain growth and malting quality of barley. Heat stress applied from 15 to 20 days after anthesis (DAA) reduced grain weight by about 35%, whereas longer periods (15-20 days) of moderately high temperature applied from 20 DAA to maturity reduced grain weight by about 6%. Both heat stress and moderately high temperature resulted in reduced grain weight through a reduction in the duration of grain filling. Grain composition was altered by both moderately high and very high temperatures, although the changes were larger under very high temperatures. In general, there was a decrease in starch content, resulting from the reduction in both volume and number of A- and B-type starch granules. Nitrogen concentration was significantly increased only in the 30/25 degrees C treatments, and changes in diastatic power were only minor. There was a reduction in beta-glucan content, together with an increase in beta-glucan degradation. However, malt extract was not significantly affected by these stresses.