TEMPERATURE-VARIATION DURING GRAIN FILLING AND CHANGES IN WHEAT-GRAINQUALITY

There have been a few notable occasions when the Australian wheat segr egation system (mainly based on specification of variety and protein c ontent) has failed to produce grain which gives dough properties expec ted for the wheat grade. The reasons for this are likely to relate to growing and storage conditions; of these, variations in temperature du ring grain filling appear to be a major factor. Observations of crop s tatistics, field and glasshouse experiments indicate that as growth te mperatures increase up to 30 degrees C, there is a general increase in dough strength (as indicated by Extensograph maximum resistance, R(ma x), and as Farinograph development time and stability). However, a dec line in dough strength is observed following periods of heat stress (e .g. a few days with maxima of over 35 degrees C). Increasing temperatu res during grain filling have also been observed to produce grain with a higher protein content, but this observation is not as consistent n or as marked as the effects on dough strength. We have sought to ident ify genotypes that do not follow this general trend in response to hea t stress, and thus could be used as parents to breed for heat toleranc e and greater stability of dough quality. A glasshouse experiment invo lving 45 genotypes has indicated that there is some variation in the r esponse to heat stress, with a few genotypes being promising sources o f tolerance. A second important approach to minimising the effects of heat stress is to develop a model to predict grain-quality changes, th us enabling a marketing authority to be forewarned of significant vari ation from the quality attributes normally expected for a wheat grade, and assisting breeders to better interpret the results of quality tes ting of lines grown at various sites.