Deciphering Defense Mechanisms and Genetic Determinants of Insect Resistance in Brassica Species

Brassica crops (genus Brassica) represent globally important vegetables and oilseeds yet are continuously threatened by insect pests that reduce yield and quality. While classical physiological and chemical defence mechanisms such as the glucosinolate–myrosinase system have been well documented, recent advances in genomics and molecular biology are beginning to unravel the genetic basis of insect resistance in Brassica species. Notably, emerging evidence highlights the central role of jasmonic acid (JA) signalling and the transcription factor MYC2 as a master regulator of inducible defence responses, where stress-induced degradation of JAZ repressors releases MYC2 to activate downstream defence genes and secondary metabolite biosynthesis. This review synthesizes the current understanding of defence mechanisms in Brassica against herbivores, highlights identified resistance genes and their functional roles, and examines the knowledge gaps that hinder progress in molecular breeding. We then explore future molecular approaches including high-throughput omics, gene editing, and resistance gene mining that hold promise for designing durable insect-resistant Brassica cultivars. Recognising the scarcity of major insect-resistance loci relative to pathogen resistance, we argue for integrated strategies combining classical breeding, biotechnology, and ecological management to accelerate the development of resilient Brassica germplasm.