Evaluation of disease progress and resistance levels among wheat genotypes against spot blotch (Bipolaris sorokiniana)

Abstract

Spot blotch, caused by Bipolaris sorokiniana (Sacc.) Shoem, is one of the most important foliar
diseases of wheat worldwide, occurring in nearly all wheat-growing areas and causing significant
annual yield losses. A field study was conducted during the Rabi seasons of 2023–24 and 2024–
25 at the Main Experiment Station, NDUA&T, Kumarganj, Ayodhya, to evaluate the resistance
of 89 wheat genotypes under artificial epiphytotic conditions. Each genotype was sown as a single
1 m row in mid-December. The susceptible variety Raj 4015 was used as a check and was sown
after every 20 genotypes. A pure culture of the pathogen was sprayed on the genotypes in the
evening using a cleaned sprayer. Disease assessments were made on the flag leaf and the leaf
immediately below it using the double-digit scale (percent blighted area). For both seasons, scores
were recorded three times at ten-day intervals. Disease severity and the area under the disease
progress curve (AUDPC) were calculated for each genotype. Disease severity and AUDPC varied
considerably among genotypes in both seasons. None of the 89 genotypes was immune (score
00–01) and six were classified as resistant (score 12–24). Forty six genotypes were rated as
moderately resistant, thirty genotypes were moderately susceptible, seven were susceptible and
none of the were highly susceptible. These results indicate that, planting fully resistant genotypes
and moderately resistant varieties can help reduce yield losses from spot blotch.