Screening of advance wheat genotypes against spot blotch disease (Bipolaris sorokiniana) under varying sowing dates at Chitwan, Nepal

Spot blotch of wheat caused by Bipolaris sorokiniana is a problematic biotic constraint that causes 15-80% yield abatement in the Indian subcontinent and other parts of the world. The most effective means of managing crop diseases is to develop resistant varieties against crop diseases. 25 wheat genotypes were evaluated against spot blotch (Bipolaris sorokiniana) under natural epiphytotic conditions sown on two dates (26 November and 18 December) at Rampur, Chitwan from November 2015 to April 2016. The experiment was laid out in a split plot design with three replications where dates of sowing were taken as the main plot and wheat genotypes were taken as sub-plots. Genotypes RR-21 and Morocco were taken as a susceptible check. Disease scoring for both sowing date was done 3 times at an interval of seven days. Disease severity and Area Under Disease Progressive Curve (AUDPC) were calculated. Among the tested genotypes, disease severity and AUDPC values varied significantly for both the normal and late sowing dates. The six genotypes were found resistant and eight genotypes were found moderately resistant under normal sowing conditions. None of the genotypes were found to be resistant and moderately resistant under late sowing conditions. This indicates that timely sowing of wheat is important for reducing yield loss caused by spot blotch disease irrespective of wheat genotypes grown. Seed infection percent for normal sowing was lower (25 to 85 percent) than late sowing (31 to 91 percent). This concluded that if farmers have to use the seed for sowing from their own field they should use the seeds harvested from the normal sowing date. The genotypes BL-4350, BL-4463, NL-1094, Aditya, BL-4316 and NL-971 were found resistant to spot blotch under normal sown condition. These genotypes could be used as donor parents for spot blotch resistance in breeding program or could be released as a variety after evaluating the agronomical traits and quality parameters.