Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Shootfly (Atherigona soccata Rondani) is a major pest of sorghum (Sorghum bicolor (L.) Moench) in Asia and Africa. In ten sets of Design II matings that involved 71 inbred sorghum lines representing several groups of breeding material, general combining ability (GCA) variances were larger than specific combining ability (SCA) variances for the percentage of plants with shootfly deadhearts (DH%) in all but one set. Significant SCA variances in three sets indicated the presence of non-additive gene action. DH percentages for parents, F(,1)s and F(,2)s were consistent with partial dominance for susceptibility in both sets in which susceptible male-sterile lines were mated with resistant lines. Three matings studied via generation-means analysis also revealed dominant or additive x additive gene action. Reciprocal differences were significant in both sets of Design II matings that included reciprocals. When the ten sets were grown in four environments that ranged from 59% to 98% DH on the susceptible check, genotype x environment interactions indicated that resistance to shootfly should be evaluated in more than one environment;Trichomes on the abaxial leaf lamina, inherited via a single genetic locus, reduced both egg laying and DH%. In nine experiments, each involving lines from one of four matings, the difference in DH% between trichomed and trichomeless derived lines ranged from 17 to 93% (generally 40-60%) of the difference between resistant and susceptible parents, indicating that a significant portion of the shootfly resistance in these matings was contributed by trichomes, by pleitrophic effects of the same locus, or by factors closely linked with trichomes. Though heritability of trichome density was 0.75 (single plot basis) in one mating, the correlation between trichome density and DH% was small and non-significant in the two matings studied. Heritability of DH% was ca. 30% in these two matings when calculated by regression of F(,4) on F(,3) line means (two replications). However, in these same matings heritabilities within trichomed, segregating and trichomeless groups of lines were considerably lower;No evidence of transgressive segregation for resistance was found among five resistant x susceptible, one susceptible x susceptible, and six resistant x resistant matings;A strategy to incorporate shootfly resistance into improved varieties by pedigree breeding methods is proposed.



Digital Repository @ Iowa State University,

Copyright Owner

Paul Thomas Gibson



Proquest ID


File Format


File Size

290 pages