The application of molecular markers for partial resistance against fusarium crown rot in hexaploid and tetraploid wheats

Abstract

In most cereal-growing regions of Australia, the principal cause of crown rot in winter cereals is Fusarium pseudograminearum, although F. culmorum is a significant cause in cooler Southern regions. Analysis of Australian populations to date indicates that while there is variation in aggressiveness, there is no evidence for pathogenic race structure. Using wheat doubled haploid mapping populations incorporating a range of resistance sources (2-49,CPI133814, IRN497, Sunco and W21MMT70), quantitative trait loci (QTL) conditioning partial resistance to crown rot have been identified in seedling and field trials. Different sources of seedling resistance have unique but overlapping combinations of contributing loci, while seedling and field resistance QTL may differ within single host genotypes. Resistance to crown rot in these sources appears to be independent from resistance to head blight, caused by F. graminearum. The degree of phenotypic variation contributed by particular loci varies across genetic backgrounds and trial environments, consistent with the epistatic interactions that are detected by the analysis tools Epistat and QTLNetwork 2.0. Nevertheless, attempts to pyramid resistances from several sources have met with some success. Tetraploid durum wheats are highly susceptible to crown rot under favourable field conditions and the disease is a major constraint on durum production in Australia. While partial resistance has not yet been identified in any durum breeding lines, recent attempts to cross improved resistance from hexaploid sources into tetraploid wheats are encouraging. Currently resistance QTL from hexaploid sources are being analysed for their effectiveness in subsequent generations derived from hexaploid x durum crosses.