Assessment of Rapeseed-mustard (Brassica spp.) Genotypes for Resistance to Sclerotinia Rot Caused by Sclerotinia sclerotiorum (Lib.) de Bary

Abstract

Oilseed Brassicas are highly susceptible to Sclerotinia stem rot caused by Sclerotinia sclerotiorum (Lib.) de Bary, a globally destructive pathogen responsible for severe yield and quality losses. The present study aimed to evaluate rapeseed-mustard genotypes for resistance under artificial epiphytotic conditions using epidemiological disease parameters. Field experiments were conducted during two consecutive Rabi seasons (2022-23 and 2023-24) at the TCA Dholi Research Farm, Bihar, to screen eighteen genotypes obtained from AICRP on Rapeseed-Mustard against Sclerotinia rot. Artificial inoculation (Cotton swab) was performed at flowering using a virulent isolate of S. sclerotiorum, and disease development was assessed using Percent Disease Index (PDI), Area Under Disease Progress Curve (AUDPC), and apparent infection rate (r-value). Pooled analysis revealed that there was considerable variability among genotypes; none exhibited resistant or moderately resistant reactions. Twelve genotypes were categorized as moderately susceptible with comparatively lower disease progression, while five genotypes were susceptible and one genotype (NPC 16) was highly susceptible. Moderately susceptible genotypes such as DRMRIS 20-5, DRMRDR 2156, DRMRDR 2119, and DRMRIS 20-1 recorded lower pooled PDI (25-33%), reduced AUDPC values (330-489), and moderate r-values, indicating slower lesion expansion and partial resistance. In contrast, susceptible genotypes including NRCHB 101 and Rohini exhibited high PDI (̴ 55%), elevated AUDPC (>800), and rapid disease progression. The r-value ranged from 0.02 to 0.18, reflecting seasonal variation in epidemic development.