Temperature Variation During Grain Filling and Changes in Wheat-Grain Quality

Abstract

There have been a few notable occasions when the Australian wheat segregation system (mainly based on specification of variety and protein content) has failed to produce grain which gives dough properties expected for the wheat grade. The reasons for this are likely to relate to growing and storage conditions; of these, variations in temperature during grain filling appear to be a major factor. Observations of crop statistics, field and glasshouse experiments indicate that as growth temperatures increase up to 30°C, there is a general increase in dough strength (as indicated by Extensograph maximum resistance, Rmax, and as Farinograph development time and stability). However, a decline in dough strength is observed following periods of heat stress (e.g. a few days with maxima of over 35°C). Increasing temperatures during grain filling have also been observed to produce grain with a higher protein content, but this observation is not as consistent nor as marked as the effects on dough strength.We have sought to identify genotypes that do not follow this general trend in response to heat stress, and thus could be used as parents to breed for heat tolerance and greater stability of dough quality. A glasshouse experiment involving 45 genotypes has indicated that there is some variation in the response to heat stress, with a few genotypes being promising sources of tolerance. A second important approach to minimising the effects of heat stress is to develop a model to predict grain-quality changes, thus enabling a marketing authority to be forewarned of significant variation from the quality attributes normally expected for a wheat grade, and assisting breeders to better interpret the results of quality testing of lines grown at various sites. Growth Temperature as a Major Determinant of Wheat-grain QualityWheat is a temperate cereal generally adapted to temperatures well below 30°C. It might be expected, therefore, that when there are conditions of heat stress (over 35"C), there will be unusual responses both in grain yield and grain quality. Although the more spectacular changes in grain quality may occur in response to heat stress (reviewed by Blumenthal et al. 1993), there is also evident variation in grain quality due to rising temperatures in the moderate range (e.g. 15-35°C).Throughout the heat-variation range (15-35°C and heat stress episodes), there is the likelihood of a progressive decrease in grain size, which in turn causes a decrease in milling quality due to a reduction in the proportion of endosperm that can be extracted as flour and an increase in the difficulty in doing so. On the other hand, if the consequent decrease in grain weight is severe enough, it will probably result in a lower test weight (bulk density) and consequent failure of the grain to qualify for the top milling grades.

Ultrastructure and biochemical traits of bread and durum wheat grains under heat stress

“…During grain filling, the modifications in the grain protein content (Table 3), associated with high temperatures (> 30ºC), have been related to reductions in the sedimentation index SDS (Graybosh et al, 1995) and seemed to promote a decrease in gluten strength. Data obtained in several studies carried out in the field and confirmed under controlled environments (Blumenthal et al, 1993;Stone and Nicolas, 1994;Wrigley et al, 1994;Panozzo and Eagles, 2000), indicate that a few days of maximum daily temperatures surpassing 32ºC produce grains with weaker dough. This effect on the dough properties, involving modifications in the protein composition associated with high temperatures during grain growth has also been pointed out by several authors (Blumenthal et al, 1993;Wrigley et al, 1994).…”

“…Data obtained in several studies carried out in the field and confirmed under controlled environments (Blumenthal et al, 1993;Stone and Nicolas, 1994;Wrigley et al, 1994;Panozzo and Eagles, 2000), indicate that a few days of maximum daily temperatures surpassing 32ºC produce grains with weaker dough. This effect on the dough properties, involving modifications in the protein composition associated with high temperatures during grain growth has also been pointed out by several authors (Blumenthal et al, 1993;Wrigley et al, 1994). The lack of interaction genotype x treatment for protein content in the bread wheat, and also in SDS for the bread and durum wheat (Table 3), might indicate an absence of genetic variability in the response of these traits to high temperatures.…”

Rising atmospheric carbon dioxide on grain quality in crop plants

“…It was observed that the increase in temperature (2-4°C) had a larger effect than elevated CO 2 on grain quality (Tester et al 1995;Williams et al 1995). Moreover, the effects of elevated CO 2 on grain quality may be partially balanced because temperature increase can enhance grain protein content (Randall and Moss 1990;Wrigley et al 1994). …”

Heat and drought stress on durum wheat: Responses of genotypes, yield, and quality parameters

“…Heat shock takes different forms, which are characterized by timing (days after anthesis) and by duration, which may also gave rise to different effects on the durum wheat quality (Corbellini et al, 1997). A "strengthening" effect has been observed with chronic heat stress whereas heat shock may have a "weakening" effect, both in common and durum wheat (Borghi et al, 1995;Wardlaw and Wrigley, 1994;Wrigley et al, 1994).…”