Published online by Cambridge University Press: 27 March 2009
Populations derived from a diallel set of crosses involving five inbred Upland varieties were tested for bacterial blight resistance at Wad Medani in the Sudan and at Namulonge in Uganda. Four of the varieties carried a known B gene for resistance; no B gene was present in the fifth, which was used as a susceptible parent. The importance of genotype/environment interaction was emphasized and it was found that the B genes did not maintain the same dominance relationships at the two sites.
The Reba gene, B9L, segregated as a gene or ‘effective factor’ of large effect but Mendelian segregation was not discernible in hybrid populations not involving Reba. Most of the genetic variance was accounted for by additivity and dominance. Although statistical analysis failed to reveal epistasis there was a strong interaction in the B2 × B6 cross.
At Namulonge, where it was possible to test for leaf and boll resistance, the proportion of dominant and recessive alleles was the same for both phases of the disease.