The hardness locus in Australian wheat lines

The genetic factors that determine grain hardness in Australian wheat (Triticum aestivum L.) germplasm were investigated by studying the grain from 4 crosses (160-180 lines per cross). Although not all the crosses were between hard and soft wheats, the doubled haploid lines derived from the crosses showed significant variation in hardness as assessed either by the Single-Kernel Characterisation System (SKCS 4100) or the scanning electron microscopy appearance of cut surfaces. The wheat cultivars used in the study were Cranbrook, Halberd, CD87, Katepwa, Sunco, Tasman, Egret, and Sunstar and of these only Egret is normally regarded as soft. The quantitative information from the SKCS 4100 was integrated into the genetic map information established for the Cranbrook x Halberd, CD87 x Katepwa, and Sunco x Tasman crosses. For the Egret x Sunstar cross, the limited information available from the positioning of genetic markers was used to specifically examine the linkage between the hardness trait and the Pina-D1 (puroindoline) genetic locus on 5DS, and very close linkage was established. The Egret x Sunstar cross was also used to develop a more rigorous rheologically based analysis of the raw SKCS crush response data. In addition, the cut surface of the lines was analysed and most (98%) of the samples showed a genetic linkage between the appearance of the cut surface (related to vitreousness) and the SKCS hardness index. Among the other crosses only Cranbrook x Halberd showed linkage of the hardness trait to the previously identified hardness locus (ha) located on 5DS as defined by DNA markers for the Pina-D1 locus, and the microsatellite wmc233. The statistical association was shown to be highly significant, with approximately 30% of the variation accounted for by the 5DS region. Another region on chromosome 4D showed a significant association in the Cranbrook x Halberd cross. The CD87 x Katepwa cross did not show any consistent associations between the SKCS measures and chromosome region, whereas in the Sunco x Tasman cross a highly significant association only on chromosome 4B (accounting for 20% of the variation) was suggested. The Sunco x Tasman cross showed an overlap of the chromosome region that accounted for variation in both grain weight and hardness and this influence of grain weight on hardness was independently confirmed by a detailed qualitative rheological analysis of the crush response profiles for the Egret x Sunstar lines. It is evident from the study that, in Australian wheat lines, there are some major effects on grain hardness that are not associated with the classical ha locus located on 5DS.