Validation of black point QTL in wheat

Black Point (BP) is a dark discolouration of the embryo end of wheat and barley grains. It can result in reduced grain quality and value and is a significant problem in most Australian wheat growing areas. Estimated losses through downgrading have been as high as $50 million annually. Quantitative trait loci (QTL) for BP resistance have previously been identified in Sunco and Cascades. The aim of this study was to use a full diallele to validate these QTL and also to determine if two other varieties with increased resistance mirror existing sources of resistance or are potentially novel sources of resistance for BP. The BP resistant lines Lang, Cascades, SW95-50213, and Genaro, and one BP susceptible line, Cunningham were used as parental lines in the full diallele. As both Lang and Sunco are Cook derivatives, Lang was used to validate the Sunco QTL. Marker regression analysis confirmed the QTL on chromosome 2BS in Lang crosses. Genaro and SW95-50213, which are more resistant to BP than Sunco or Cascades, indicated an association between BP resistance and chromosomes 2B and 2A, respectively. The identification of markers for BP resistance in a number of different resistant sources will facilitate the pyramiding of genes for BP resistance in wheat

Curation of wheat maps to improve map accuracy and QTL detection

Three Australian doubled haploid populations were used to illustrate the importance of map curation in order to improve the quality of linkage maps and quantative trait locus (QTL) detection. The maps were refined and improved by re-examining the order of markers, inspection of the genetic maps in relation to a consensus map, editing the marker data for double crossovers, and determining estimated recombination fractions for all pairs of markers. The re-ordering of markers and replacing genotypes at double crossovers with missing values resulted in an overall decrease in the length of the maps. Fewer apparent genotyping errors, associated with the presence of double recombinants, were identified with restriction fragment length polymorphisms (RFLPs) than with other types of markers used in this study. The complications that translocations may cause in the ordering of markers and subsequent QTL analysis were investigated. QTL analysis using both the original and revised maps indicated that QTL peaks were more sharply located or had improved log-likelihood (LOD) scores in the revised maps. An accurate indication of the QTL peak and a significant LOD score are both essential for the identification of markers suitable for marker-assisted selection. Recommendations are provided for the improvement of the quality of linkage maps