Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

R. E. Atkins


Seed composition from S[subscript]1 families of C0, C2, C3, C4, and half-sib families of C1, C2, C3, and C4, together with 60 individual S[subscript]1 families chosen randomly from C0 and C4 of sorghum (Sorghum bicolor (L.) Moench) population IAP2B were evaluated in five Iowa environments;Four cycles of gridded mass selection of individual-panicle grain weight shifted the mean for grain yield favorably, and the range among S[subscript]1 families was extended. Increased values in C4 also were observed for seeds/panicle, 100-seed weight, days to midbloom, and plant height, but panicles/plant decreased. Genotypic variance among S[subscript]1 families increased from C0 to C4 for grain yield and days to midbloom. Estimates of inbreeding depression were significant (p < 0.05 or 0.01) for grain yield (-18.2%), panicles/plant (-13.7%), plant height (-11.5%), and 100-seed weight (-8.4%). Appreciable nonadditive gene action was expressed for those traits. Seeds/panicle and days to midbloom displayed additive gene action;Heritability estimates for grain yield increased from C0 to C4, but they decreased for panicles/plant. Expected gain/year for grain yield by using S[subscript]1 family selection increased from C0 (2.0% of the mean) to C4 (3.2%). Estimates for C0 vs C4 showed a decrease for panicles/plant (from 4.5% to 3.6% of the mean);Correlation coefficients indicated that selection for individual-panicle grain weight also influenced other characters. Correlations changed substantially in a positive direction from C0 to C4 for grain yield vs seeds/panicle, grain yield vs panicles/plant, and seeds/panicle vs panicles/plant, but they changed in a negative manner for grain yield vs 100-seed weight;Parameters estimated for the S[subscript]1 families and cycle composites indicated that IAP2B(M) should prove useful for developing female parents with a wide array of gene combinations. The higher estimates of genotypic variance and heritability for grain yield in C4, as well as the larger estimates of expected gain from S[subscript]1 family selection, indicated that further improvement of the population should be expected with additional cycles of recurrent selection.



Digital Repository @ Iowa State University,

Copyright Owner

Anthony J. Maves



Proquest ID


File Format


File Size

111 pages