Inheritance pattern and allelic relationships of white rust resistance genes in Indian mustard (Brassica juncea L. Czern. & Coss.)

Abstract

White rust, caused by Albugo candida (Pers.) Kuntze, is one of the most destructive diseases of Indian mustard, causes
significant yield losses in susceptible cultivars. The present study was undertaken to elucidate the inheritance and
allelic relationships of white rust resistance genes using susceptible × resistant and resistant × resistant crosses
evaluated across three environments (E1, E2 and E3). Four susceptible cultivars (Varuna, NRCHB 101, NRCDR 2 and
Giriraj) were crossed with resistant donors BIO-YSR, DRMRIJ 12-28, Heera, and GSL-1. Segregation analyses were
performed in F1, F2, BC1 and BC2 generations using chi-square tests. All resistant donors and F1 progenies exhibited
complete resistance, indicating dominance of resistance over susceptibility. In most crosses, F2 populations segregated
close to the expected 3:1 (resistant:susceptible) ratio, while BC1 generations conformed to a 1:1 ratio and BC2 populations
were uniformly resistant. These results consistently demonstrated that white rust resistance in BIO-YSR, DRMRIJ 12-28,
Heera, and GSL-1 is controlled by a single dominant gene. To investigate allelic relationships, the resistant × resistant
cross BIO-YSR × GSL-1 was evaluated across all environments. The F2 populations segregated in a 15:1 ratio, indicating
duplicate dominant gene action and confirming that the resistance genes in BIO-YSR and GSL-1 are non-allelic and
independently inherited. The consistent expression of resistance across environments highlights the stability of these
genes. The identification of distinct dominant resistance genes provides valuable opportunities for gene pyramiding
and marker-assisted breeding aimed at developing Indian mustard cultivars with durable and broad-spectrum resistance
to white rust.