Physical basis of host plant resistance in rapeseed and mustard against mustard aphid, Lipaphis erysimi (Kaltenbach)

Rapeseed-mustard ( Brassica spp.) is a vital oilseed crop in India, frequently affected by the mustard aphid, Lipaphis erysimi (Kaltenbach), a major sap-sucking pest that causes substantial yield losses. Considering the drawbacks of chemical control, host plant resistance offers a sustainable alternative. The present study was conducted under protected conditions to assess the physical basis of resistance in ten rapeseed-mustard genotypes against L. erysimi . Significant genotypic variations were observed in aphid population, percentage of infested siliques, and aphid multiplication rate across crop stages. PM 25, PM 26, and DRMR 150 − 35 consistently recorded lower aphid infestations and were categorized as resistant, whereas IC 491023 and YST 151 were highly susceptible. Among the physical traits, surface wax content showed a strong negative correlation with aphid population, suggesting its critical role in resistance. PM 25 exhibited the highest wax content (7.30%), contributing to its superior resistance. The findings indicate that physical traits like surface wax act as a first line of defense by hindering aphid colonization and feeding. This study highlights the potential of integrating such traits into breeding programs, with PM 25 emerging as a promising genotype for developing aphid-resistant varieties.