Genetic Effects on the Timing of Le dav 2 Induced Necrosis of Cotton

Cotton ( Gossypium spp.) embryos carrying the Le dav 2 allele in combination with the Le 1 allele at the Le 1 locus and/or the Le 2 allele at the Le 2 locus undergo a hybrid lethality reaction, which causes progressive necrosis and death between germination up to 21 d postgermination. Timing of the necrosis is thought to be controlled by the cumulative dosage of alleles Le 1 and Le 2 interacting with Le dav 2 , but there have been no studies to identify the exact genetic relationship between the alleles Le 1 , Le 2 , and Le dav 2 in terms of timing of necrosis induced by the Le dav 2 complementary lethality system. The objectives of this study were to determine: (i) if the timing of necrosis is under genetic control of the loci Le l and Le 2 , and (ii) if the mechanism of timing or mode of gene action is consistent across genotypes. Five cultivars ( Le 1 Le 1 Le 2 Le 2 ) were used as sources of Le 1 and Le 2 alleles. Seedlings from reciprocal crosses of (cultivar ✕ le 1 le 1 le 2 le 2 ) F 1 plants and an le 1 le 1 Le dav 2 Le dav 2 tester were scored for the presence and timing of the lethal reaction. Frequency histograms were used to phenotypicaily group seedlings according to the time of death. Observed frequencies of the phenotypic groups were tested against frequencies expected for digenic segregation. Results indicated that increased dosage of alleles Le 1 and Le 2 with Le dav 2 hastens necrosis, but variation among cultivars indicated that Le 1 ‐ Le dav 2 and Le 2 ‐ Le dav 2 interactions may not always be distinctly different. Three possible explanations for these differences are: (i) that additional loci are involved, (ii) that allelic action is modified by background genotypic differences, and/or (iii) that the Le 1 and Le 2 loci are polymorphic.