Phenology and morphological traits of wild crucifers impacting host selection and population build up by mustard aphid [Lipaphis erysimi (Kaltenbach)]

The current study aimed to decipher the role of various pheno-morphological traits in imparting resistance against mustard aphid Lipaphis erysimi (Kaltenbach) on diverse wild crucifer genotypes. The findings revealed significant variation in the phenology, morphological traits, aphid preference, population build-up, multiplication rate and resistance indices on the test wild crucifers. Genotypes exhibiting a higher number of siliquae on the main shoot but fewer seeds per siliqua demonstrated lower susceptibility to mustard aphid. Furthermore, those with fewer siliquae but a higher seed count per siliqua showed moderate aphid preference. Additionally, taller plants with more branches were associated with higher aphid multiplication rate and greater nymph recovery, indicating greater suitability for aphid establishment. However, shorter plants with fewer branches exhibited lower aphid multiplication rate and reduced nymph recovery. Among the qualitative traits examined, petal color score emerged as the most influential factor, showing a significant and negative association with host preference and overall aphid multiplication rate. There were exceptions where genotypes with lower petal color scores still exhibited greater aphid multiplication rate and host preference. The crucifer species like Lepidium sativum, Sisimbrium spp. Eruca sativa (IC60468), Brassica fruticulosa (Spain), Brassica tournefortii (RBT 2003), Crambe abyssinica (EC694071, EC694090, EC694125) were found with least aphid preference coupled with lower population build-up and multiplication rate. These findings underscore the complexity of aphid-plant interactions and importance of plant phenology and morphological traits for resistance against mustard aphid, and their deployment in a Brassica juncea improvement program.