Relationship between resistance and tolerance of crown rot in bread wheat

Abstract

Crown rot of wheat and barley is a serious disease caused by the fungus Fusarium pseudograminearum; a stubble-borne pathogen common in no-till farming systems in many wheat growing regions. Evidence suggests that partial resistance and a degree of tolerance exists in wheat. To assess the relationship between resistance and tolerance, 207 wheat genotypes developed from the same population including parents and check cultivars, were evaluated in the field under crown rot pressure in yield loss experiments. Yield loss was determined in replicated, inoculated and un-inoculated paired plots in 2014 and 2015 and resistance assessed by the extent of stem browning on plants sampled from the same plots grown at Narrabri in northwestern NSW. The population was genotyped using a high-density 90 K SNP array and a genome wide association analysis conducted to identify QTLs for both tolerance and resistance. Transgressive segregation was observed for crown rot resistance and tolerance in the population. Forty-three QTLs were associated with resistance and tolerance traits and 8 previously reported QTLs were confirmed. Comparison of linked marker positions indicated that QTL for yield in the presence of crown rot inoculum located on chromosomes 2B, 2D, 4B, 6A and 6B were previously unreported. Stem browning was effective in determining resistance only and was not associated with tolerance, determined as yield under crown rot pressure or yield loss.