Physiological Races and Virulence Dynamics of Setosphaeria turcica in Northeast China

Northern corn leaf blight (NCLB), caused by Setosphaeria turcica, is an important foliar disease in corn. Since 2005, the damage from NCLB has increased in Northeast China, probably from the emergence of new physiological races. In this study, 883 single conidial isolates of S. turcica were obtained from 12 sites across three provinces of Northeast China between 2007 and 2017. The virulence of the isolates was evaluated in five corn lines (B37, B37Ht1, B37Ht2, B37Ht3, and B37HtN). Sixteen physiological races (0, 1, 2, 3, N, 12, 13, 1N, 23, 2N, 3N, 123, 12N, 13N, 23N, and 123N) were obtained, depending on their resistance or susceptibility. Three races (0, 1, and 2) were most prevalent, with frequencies of 40.5, 19.6, and 11.3% in all isolates, respectively. Races varied across provinces and years. Virulence to more than one Ht resistance genes occurred in 21.5% of isolates, with 8.5% virulent to three or more genes. Overall, 41% of isolates were avirulent to all Ht genes, 36% were virulent to Ht1, 28% to Ht2, 11% to Ht3, and 16% to HtN. Isolates from Heilongjiang had a greater frequency of virulence to Ht2 and Ht3, whereas isolates from Jilin and Liaoning were more frequently virulent to Ht1 and HtN, respectively. The frequency of isolate virulence to Ht2 ranged from 8% in 2009 to a maximum of 29% in 2015, and in 2015, isolates were more virulent to Ht2 than Ht1. This study will help growers to purposefully select commercial hybrids with multiple effective Ht resistance genes, and reduce the utilization of Ht1 and Ht2 genes in the process of corn production to strengthen NCLB control.