Variation in Mustard Aphid (Lipaphis erysimi) Infestation and Resistance Levels Across Diverse Rapeseed-Mustard Genotypes

The present study evaluated 89 rapeseed-mustard genotypes for their resistance against mustard aphid during the Rabi season of 2023–24 at CCSHAU, Hisar, Haryana to understand the role of phenological and genotypic variations influencing aphid resistance. Screening targeted three key crop stages: aphid appearance, full flowering, and siliqua formation to measure aphid infestation levels using standardized indices. Aphid infestation was consistently higher in B. juncea (7.81 aphids/10 cm twig) compared to B. napus (1.88 aphids) during early stages of crop growth. At the aphid appearance stage, 60 genotypes were resistant (ARI = 1), 28 moderately resistant (ARI 1–2), and one tolerant. During the full flowering stage, resistant genotypes number declined slightly to 54 while, 32 remained moderately resistant. At full flowering, infestation in Brassica juncea (17.08 aphids/10 cm twig) remained higher than in B. napus (1.88 aphids/10 cm twig). The full siliqua formation stage saw higher aphid infestations, with four genotypes categorized as susceptible and eight as tolerant. However, by the full siliqua formation stage, the infestation levels between the B. juncea and B. napus (30.12 and 27.63 aphids) were nearly equal, indicating either a convergence in susceptibility at later crop stages or some sort of developmental asynchrony. The differential response of B. napus and B. juncea genotypes across crop growth stages, points to potential avenues for breeding programs to improve resistance in rapeseed-mustard crops.