Assessment of Spot Blotch Resistance and Yield Traits in Wheat Genotypes in a Subtropical Agro-Ecology of Nepal

A field and laboratory study was conducted from November 2021 to April 2022 at Debchuli-2, Nawalpur (East), Nepal, to evaluate 50 wheat genotypes for resistance to spot blotch (caused by Bipolaris sorokiniana) and associated traits. The experiment followed an alpha-lattice design with three replications. Disease severity was assessed using single and double-digit scales at four intervals post-heading, and area under disease progress curve (AUDPC) was computed to categorize genotypes into resistant, moderately resistant, susceptible, and highly susceptible groups. Laboratory seed health testing was performed using the blotter method to assess seed infection by B. sorokiniana. AUDPC values varied significantly among genotypes, ranging from 178.4 (resistant) to 487.5 (highly susceptible). Genotype YMI#6 had the lowest AUDPC, while RR 21 exhibited the highest, indicating loss of previously reported resistance. Root rot index (RRI) ranged from 17% to 44% and positively correlated with AUDPC. Significant variation was observed in yield and yield-attributing traits, including thousand kernel weight (TKW), grain yield, and spike characteristics. Grain yield showed a significant negative correlation with AUDPC (r = -0.280*), while TKW was positively correlated with grain yield. Phenological observations revealed that susceptible genotypes had earlier booting, heading, and maturity. A negative correlation was found between AUDPC and days to maturity (r = -0.57*), indicating accelerated development in diseased plants. Plant height also differed significantly among resistance categories. The study highlights genetic variability among genotypes in response to spot blotch and identifies promising resistant lines for wheat improvement programs in subtropical regions.