Grain yield and quality losses caused by tan spot in wheat cultivars in Australia

Abstract

Tan spot (TS), known in Australia as yellow leaf spot, is caused by the fungal pathogen Pyrenophora tritici-repentis, a major foliar disease of wheat. Four experiments were conducted between 2016-2017 in two different climatic zones of south-eastern Australia, to determine the impact of TS on grain yield and quality in six wheat cultivars with different resistance ratings. In each experiment, high and low TS disease scenarios were applied to each cultivar. Disease severity was assessed as either whole plot percentage leaf area affected (%LAA) or top three leaf (flag – flag-2) %LAA. Whole plot %LAA was analysed using both repeated measurements and area under the disease progress curve (AUDPC). For whole plot %LAA, the repeated measurements identified differences in epidemic progression at key growth stages not identified through AUDPC. Both AUDPC and end-of-season flag – flag-2 %LAA were negatively correlated with grain yield and screenings. Increased rainfall impacting disease development (RIDD) and number of rain days >5 mm increased TS severity across both climatic zones. Cultivar resistance ratings influenced grain yield loss, with moderately resistant, moderately susceptible, and susceptible cultivars losing up to 6%, 18% and 24% grain yield, respectively. High disease significantly increased screenings by up to 1%, 3% and 5% for moderately resistant, moderately susceptible, and susceptible cultivars, respectively. This study demonstrated that TS can cause significant grain yield losses in south-eastern Australia, and a minimum cultivar rating of moderate resistance - moderate susceptibility (MRMS) was required to prevent severe TS and associated grain yield and quality losses.