Bloom and whitefly resistance in Castor bean (Ricinus communis L.): a genetic and linkage analysis

Castor bean (Ricinus communis L.), is a commercially significant oilseed crop, valued for its high oil content and diverse applications. The Castor whitefly (Trialeurodes ricini Misra) is a multivoltine tropical pest that causes substantial yield losses, particularly during rabi and summer season. Morphological markers in castor are abundant, with bloom type being associated with whitefly resistance. This study investigated the relationship between bloom type and whitefly resistance by screening 29 genotypes with varying bloom types. The results demonstrated that double and triple bloom types are highly susceptible to whiteflies, whereas zero and single bloom types exhibited high resistance. The F₁ generations from crosses among different bloom types displayed susceptibility to whiteflies, except for the cross between zero and single bloom, which exhibited a single bloom phenotype. In the cross between bloom and no bloom (DPC 9 × TMV 5) monogenic dominant nature for bloom was observed. Genetic characterization of whitefly resistance in this cross indicated a monogenic recessive nature for whitefly resistance. It is suggested that bloom and whitefly resistance may be tightly linked in a repulsion phase or may involve the pleiotropic effect of a single gene. These findings were further corroborated by the cross between M 619-1 × SKI 215. Additionally, the study demonstrated monogenic incomplete dominance of triple bloom over zero bloom and monogenic complete dominance of triple bloom over double bloom.