Lupeol a predisposing factor in grey mould (Amphobotrys ricini [N.F. Buchw.]) Hennebert disease pathogenesis in castor (Ricinus communis L.)

To understand the castor wax layer's multifaceted contribution to Amphobotrys ricini pathogenesis, the hydrophobic components of cuticular wax were analysed from waxy and non-waxy castor genotypes. Gas chromatography–mass spectrometry (GC–MS) technology enabled the stable detection and quantitative determination of various fatty acids and terpenoids. The investigation revealed a significant presence of triterpenoid compound ‘lupeol’, accounting for approximately 53.6% of the wax composition in the waxy genotype (DCH-519), which was absent in non-waxy genotype (ICS-324). On exposure to lupeol, about 93.3% of conidia germinated leading to rapid mycelium growth and sporulation of A. ricini. SEM analysis of waxy and non-waxy genotypes infected with A. ricini confirmed faster germination and production of longer germ tubes on waxy genotype compared with non-waxy genotype, which may likely due to early recognition of the suitable host in the presence of lupeol, ultimately aiding in speedy germination and growth of the pathogen setting pace for pathogenesis.