The genetics of blackarm resistance - V. Dwarf-bunched and its relationship to B1
In theF2 of a cross between two American Upland (G. hirsutum) types, Uganda B31 and the Sudan variety 514, a number of markedly dwarfed, ‘bunched-up’ plants appeared. Investigation showed that normality as opposed to ‘Dwarf-bunched’ depends on the presence of either of two duplicate genes, one dominant and the other giving an intermediate heterozygote. These genes have been calledDa andDb, the former deriving from 514 and the latter from Uganda B31. 514 is ofDaDadbdb genotype, Uganda B31 isdadaDbDb, Dwarf-bunched isdadadbdb, and the heterozygotedadaDbdb shows considerable variability with a range from dwarf to normal.
The genedb occurs in Gambia Native (G. hirsutum var.punctatum) and in the American Upland varieties Uganda SP84, XA129 and Deltapine, but it was not present in all Upland varieties examined.
The geneda is closely linked with (or possibly identical with) the blackarm-resistance geneB1. SinceG. barbadense types are ofDaDaDbDb composition,B1 can be utilized in conferring blackarm resistance on this group. Its use within, theG. hirsutum group is fraught with the danger of producing, Dwarf-bunched types as the end-product.
Volume 100, 2021
Continuous Article Publishing mode
Click here for Editorial Note on CAP Mode