Are temperature effects on weight and quality of barley grains modified by resource availability?

Under field conditions the occurrence of brief periods of moderately high (30-32 degrees C) and very high temperatures (> 35 degrees C) is quite common during grain filling in small-grain cereals. These events occur under a wide range of different management and environmental conditions, such as different nitrogen supplies and source-sink ratios after flowering. The objective of the present work was to study whether the effect of a brief heat stress is modified by resource availability for the growing grains. We subjected spikes of barley 10 days after flowering to a heat treatment in factorial combination with different nitrogen availabilities and source-sink ratios during post-flowering to determine effects on grain weight and major malting quality attributes. Grain weight and screening percentage ( proportion of grains < 2.5 mm) were reduced by the mild heat stress. However, the magnitude of the effect was dependent on the nitrogen fertilisation and the source-sink treatments in which the heat stress was imposed. Grain protein and beta-glucan percentages were increased by both nitrogen fertilisation and heat stress. Again, the magnitude of the increase was dependent upon the availability of resources. There was a trend to reduce malt extract in all treatments with respect to the control, but the reduction was only statistically significant with heat stress.