Secondary genepool of Australian Cajanus species contains sources of resistance to Helicoverpa armigera (Hübner)

Abstract

AbstractA narrow genetic base in cultivated pigeonpea (Cajanus cajan (L.) Millsp.) limits the host plant resistance (HPR) to the devastating pest Helicoverpa armigera (Hübner). Earlier research on pod borer resistance in wild Cajanus relatives has mainly explored the tertiary genepool, making breeding for resistance difficult because of linkage drag. Previous investigations on a wide range of Australian native germplasm from the secondary and tertiary gene pools revealed resistance in the secondary gene pool, associated with total phenolic content (TPC). This study reports the application of the extreme phenotype genome‐wide association (XP‐GWAS) to associate single nucleotide polymorphisms (SNPs) with resistance traits. Mapping of 19 accessions, including 12 wild accessions to a reference pigeonpea genome have identified a total of 16,489 and 16,227 nonsynonymous SNPs for the resistance and TPC traits, respectively. These SNPs were subjected to functional analysis, and KEGG pathway analysis revealed the presence of candidate genes coding for the crucial enzymes in five defence‐related pathways that could be contributing to resistance. These pathways involve ‘Jasmonic acid synthesis’ (palmitoyl‐CoA hydrolase, phospholipase A1 and phospholipase A2), ‘insect hormone biosynthesis’ (aldehyde dehydrogenase) ‘Steroid biosynthesis’ (squalene monooxygenase, farnesyl transferase and lanosterol synthase), ‘Cutin, suberine and wax synthesis’ (O‐acyltransferase) and ‘Brassinosteroid biosynthesis’ (Det2). Analysis of SNPs associated with the TPC trait led to the identification of a divergent pathway of ‘secondary metabolite synthesis’ (flavonoid 3′ hydroxylase, l‐rhamnosyltransferase) in wild Cajanus species consistent with a high concentration of isoorientin and the possible presence of its derivative maysin; a strong insecticidal compound in leaves.