Assessment of wheat genotypes for spot blotch (Bipolaris sorokiniana Sacc.) resistance under artificial epiphytotic conditions in the inner terai of Nepal

Abstract

Spot blotch, caused by (Bipolaris sorokiniana Sacc.) is a significant fungal disease leading to economic losses in wheat (Triticum aestivum), especially in regions with low soil fertility and warm, humid climates, such as the inner Terai of Nepal. A field experiment was conducted at the National Maize Research Program (NMRP), Rampur, Chitwan, during winter of 2021/022 with an aim of identifying wheat genotypes with spot blotch resistance under artificial epiphytotic conditions. Each genotype was sown in a single 2-meter long row alongside susceptible check genotypes (Agra and Morocco) at every 20th row. Aqueous spore suspension of B. sorokiniana was applied twice in border rows during the booting stage at 15-day intervals. Disease severity was assessed four times at five-day intervals using a double-digit scale based on the percentage blighted area on the flag and penultimate leaf, and the area under the disease progress curve (AUDPC) was calculated. The results categorized 43 genotypes as resistant, 127 as moderately resistants, 135 as moderately susceptible, 66 as susceptible, and 7 as highly susceptible based on AUDPC. Cluster analysis identified cluster 3 comprising 17 genotypes as superior in terms of disease resistance as well as agronomic parameters. NRN-34 emerged as the top-ranked genotype within this cluster, followed by NAL-73, NAL-94, NAL-12, NRN-34, NAL-57, NAL-43, NAL-82, and NAL-35, exhibiting lower AUDPC values and higher yield-attributing character values. This study will aid breeders in developing spot blotch-resistant and high-yielding wheat varieties by incorporating the identified promising genotypes into further breeding programs.