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The responses of sweet corn biomass and yield to timing and severity of water deficit were determined in an experiment using a mobile rainshelter. Six irrigation treatments were applied such that plots experienced: (1) no water deficit; (2) full water deficit; (3) moderate pre-silking deficit; (4) severe pre-silking deficit; (5) moderate post-silking deficit; or (6) severe post-silking deficit. Drought was quantified using the concept of potential soil moisture deficit, which was calculated from climatic data. Potential soil moisture deficit can be related simply to a wide range of plant performance variables, making it possible to compare the relative importance of variables in determining the overall response of the crop to drought. For all treatments, yield was related strongly to biomass, especially that accumulated after silking. Biomass, in turn, was reduced by water deficit, mainly because of reduced radiation use efficiency, but also because of reduced total radiation interception, particularly in early deficit treatments. Both water use efficiency and transpiration efficiency increased with water deficit, even though soil evaporation as a proportion of total water use also increased with deficit. There was no stage of crop development at which yield was particularly sensitive to water deficit, although yield components changed with timing of deficit. Importantly, measures of potential soil moisture deficit integrated the effects of timing and severity of drought, making it possible to simply and mechanistically account for the effects of water deficit on biomass and particularly yield.

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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°C treatments, and changes in diastatic power were only minor. There was a reduction in β-glucan content, together with an increase in β-glucan degradation. However, malt extract was not significantly affected by these stresses.

Cereal Chem. 75(1):43-50In an attempt to further elucidate the molecular mechanisms that determine the loss of dough strength associated with heat stress of growing wheat, the roles of heat-shock proteins (HSP) and heat-shock elements upstream of glutenin genes were investigated. A range of genotypes differed in the extent of synthesis of high molecular weight glutenin subunits (HMW-GS) and HSP during heat stress. The concentration of HSP 70 remaining in mature grain increased as a result of a few days' heat stress of wheat plants. The amount of HSP 70 in mature grain samples from heat-stressed plants of 45 genotypes was not strongly correlated with loss of dough strength. There was much less evidence for this mechanism than for other molecular hypotheses from the literature, particularly, changes in glutenin-to-gliadin ratio, size distribution of the glutenin polymer, and the involvement of HSP and chaperones during grain-protein synthesis. HSP 70 was purified from heat-stressed grain,