Host-pathogen interaction in Brassica juncea recombinant inbred lines for powdery mildew resistance using BLUP and GGE biplot analysis

Abstract

Powdery mildew, caused by the obligate biotrophic fungus Erysiphe cruciferarum, substantially reduces Indian mustard [Brassica juncea (L.) Czern] productivity, with yield losses reaching 90% under favourable conditions. A population of 259 F₈ recombinant inbred lines (RILs) from the cross RDV 29 (resistant) × RSEJ 775 (susceptible) was assessed for powdery mildew resistance using a 0-5 ordinal disease severity scale across six environments, at three locations viz., New Delhi, Nagpur, and Gujarat over two consecutive seasons (2023-24 and 2024-25), under natural epiphytotic conditions. Combined analysis of variance showed highly significant effects of genotype (F = 17.21), location (F = 466.91), and year (F = 26.88). The genotype×location interaction was significant (F = 5.99; P < 0.001), whereas the genotype×year interaction was not, confirming that resistance rankings were stable across seasons. Broad-sense heritability was moderate (H² = 0.47), with a genetic advance of 42.3%, indicating primarily additive gene action. The Best Linear Unbiased Prediction (BLUP) analysis identified 10 elite RILs with breeding values equivalent to those of the resistant parent and consistent resistance across environments. GGE biplot analysis explained 80.84% of the total GGE variation and detected no crossover genotype×environment interaction among resistant genotypes, supporting their broad adaptability. The Gujarat location was the most representative environment for screening for resistance, whereas the Nagpur location had the highest discriminative ability. This is the first report on host-pathogen interactions involving RILs generated from a newly identified and only powdery mildew resistance source identified in B. juncea from India.