The inheritance of seed resistance to Callosobruchus maculatus F. in cowpea (Vigna unguiculata L. Walp.). I. Analyses of parental, F₁, F₂, F₃ and backcross seed generations

Abstract

Bioassays for bruchid emergence on cowpea seeds were conducted on the parent, hybrid F1, F2, F3, and backcross seed generations of five crosses between susceptible cowpea lines and the resistant accession TVu 2027. The study was repeated with reciprocal F1 hybrid seeds, and reciprocal backcross hybrid seeds. For the latter, the mean day of bruchid emergence was also measured. F3 seed from individual F2 plants of one reciprocal cross were also bioassayed. Trypsin inhibitor determinations were made on the parental, reciprocal F1 and reciprocal and non-reciprocal F3 seed generations. The results indicated: (1) that the expression of resistance is mainly determined by the maternal genotype; (2) that resistance may be inherited as a major gene effect, with resistance recessive, and with the presence of modifier genes of different effects in different crosses; (3) that a cytoplasmic effect appears to be absent; (4) that a paternal or embryo genotypic effect on seed resistance can be detected in a certain backcross combination; (5) that trypsin inhibitors are partly associated with expression of resistance, but are uncorrelated in F2 segregation, and appear to be quantitatively inherited and variable between crosses. Thus additional mechanisms so far undetected may also be implicated in the expression of seed resistance to bruchids.