THE UNIVERSITY OF ADELAIDE
Waite Campus, Plant Science, Glen Osmond, SA 506, Australia.
Daryl Mares and Kolumbina Mrva.
Preharvest sprouting periodically causes massive losses to the Australian wheat industry and affects all states, albeit with different frequency. Understandably, in 2002, when most of Australia was gripped by severe drought, there were few reports of sprouting damage. Cultivar improvement, using dormancy from older white-grained genotypes introduced from South Africa and, more recently, landraces from China, has proven to be quite difficult due to inefficient screening techniques, strong environmental effects, a complex mode of inheritance, and a need for extensive capital and labor infrastructure. Despite these obstacles, parental germ plasm has now been developed that combines sprouting tolerance (tolerance equivalent to the South African parental genotype AUS1408) with black point tolerance, absence of late maturity a-amylase, and low polyphenol oxidase in a locally adapted, semidwarf background. A major QTL associated with dormancy in this germ plasm corresponded to a QTL on chromosome 4A previously identified in the partially dormant Australian white wheat Halberd and in some dormant red-grained cultivars overseas.
The impact of black point in reducing the grain dormancy phenotype has been clearly demonstrated in several seasons where this defect was evident. This interaction also was captured in mapping studies where grain dormancy phenotypic data from black point-affected trials was used. QTL known to be associated with black point were identified as dormancy QTL even though grains with obvious black point symptoms were carefully excluded from dormancy testing. By contrast, when dormancy data for the same populations was obtained from trials free from black point, the black point QTL was not significant. These results suggest that the physiological/biochemical changes that lead to the appearance of black point symptoms may affect the dormancy phenotype even before significant amounts of black pigment are formed in the seed coat overlying the embryo.
Kolumbina Mrva and Daryl Mares
Progeny from three DHs and one RIL population, involving three different sources of late-maturity alpha-amylase (LMA) (Spica, Seri, and Cranbrook) and containing either the Rht1, Rht2, or Rht1 + Rht2 genes were phenotyped following exposure to a standard cool-temperature treatment designed to promote expression of LMA. The genetic control of LMA was reëxamined, and the interaction of dwarfing genes with putative LMA genes or QTL was investigated. In all the populations, there were a greater proportion of low LMA and non-LMA lines in semidwarf subpopulations providing further evidence that Rht1 and Rht2 reduced expression of LMA. Significantly, LMA was reduced even further in lines that contained both Rht1 and Rht2. Late maturity a-amylase in Spica and Cranbrook appears to be controlled by similar genes or mechanisms, but that these differ from Seri where the response is more extreme and less sensitive to the effects of dwarfing genes.