Biophysical and biochemical mechanism of plant resistance in Brassica juncea (L.) Czern & Cross against Lipaphis erysimi (Kalt.) (Homoptera: Aphididae)

The mustard aphid ( Lipaphis erysimi Kaltenbach) is a major limiting factor in the production of rapeseed-mustard, causing significant yield and quality losses. Host plant resistance offers a sustainable and eco-friendly alternative to chemical control within integrated pest management (IPM) frameworks. The present investigation was carried out during the Rabi seasons of 2023–24 and 2024–25 to evaluate the resistance potential of diverse Brassica juncea genotypes against L. erysimi . Resistance was assessed using the Aphid Population Index (API), Aphid Damage Index (ADI), and Aphid Resistance Index (ARI). Among the genotypes evaluated, TARAMIRA and LACMA-SP523N5 were the most susceptible, while KRANTI, PM-25, and PDL-1 showed the highest levels of resistance. Significant correlations were observed between aphid resistance and key biochemical markers, including elevated levels of glucosinolates, total phenols, tannins, and antioxidant enzymes such as peroxidase, phenylalanine ammonia-lyase (PAL), and tyrosine ammonia-lyase (TAL). Conversely, increased total sugar content was associated with greater aphid susceptibility. Morphological traits such as stem thickness and surface wax deposition, particularly in PM-25, also contributed to aphid deterrence. These findings demonstrate that a combination of biochemical and morphological traits underpins resistance to L. erysimi in mustard. The identified resistant genotypes and associated defense mechanisms provide valuable insights for breeding programs aimed at developing aphid-resistant Brassica cultivars, contributing to sustainable pest management in oilseed crops.