Genotypic Differences in Resistance and Tolerance to Crown Rot Caused By Fusarium Pseudograminearum of Wheat.

Crown rot of wheat and barley is a serious disease caused by the fungus Fusarium pseudograminearum, a stubble-borne pathogen commonly found in no-till farming systems in semi-arid grain growing regions. Infected plants display characteristic honey-brown discoloration on the crown and lower stem. Premature ripening of developing heads caused by disruption of vascular tissue results in whiteheads under post-anthesis drought, directly leading to grain yield loss. To understand the relationship between resistance and tolerance, and to identify the genotypic difference in resistance and tolerance, yield loss trials were conducted under crown rot inoculated and non-inoculated field conditions at the IA Watson Grain Research Centre, The University of Sydney, Narrabri in 2014 and 2015 (May-October). The average percentage of white heads was 14.3 (range 0.1-79.5) and percentage yield loss ranged from 0.6-52.9. Yield loss in crown rot infected plots was positively correlated with the percentage of white heads (r=0.54), suggesting that white head expression is directly related to yield loss. A positive correlation was also observed between the percentage of grain screenings (<2.0mm) and yield loss (r=0.35), indicating that shrivelled grains are a primary cause of yield loss under crown rot infection. These findings indicate that resistance determined by white head expression is related to tolerance defined as yield under crown rot inoculation.