Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Recurrent selection for three cycles, based on S(,1) lines, was completed in separate programs in the maize (Zea mays L.) variety, Iowa Synthetic #1 (BS1), for resistance to mechanical stalk breakage and resistance to stalk rot after inoculation with Diplodia maydis. Improvements in stalk quality and correlated responses in yield and several agronomic ear and plant traits were evaluated. The materials used for this study included the original (BS1C0) and the improved population of each cycle (BS1MS and BS1SR populations for stalk-strength and stalk-rot selection, respectively), population crosses between each method of selection, crosses of each population with a poor stalk quality single cross, the original (C0) and final (C3) populations selfed once, C0 x C3, and random S1 lines from the C0 and each C3;Highly significant improvements were observed for all stalk-quality traits. Changes from the C0 to BS1MSC3 and BS1SRC3, respectively, were as follows: resistance to mechanical stalk breakage, 34.8 to 56.5 and 46.7 kg; artificial stalk-rot rating, 3.5 to 1.8 and 1.7; rind strength, 3.4 to 4.2 and 4.3 kg; field stalk-rotted plants, 25.4 to 5.0 and 7.6%; and field stalk-lodged plants, 13.3 to 6.0 and 2.5%. Observed values for the population crosses, testcrosses of the populations, and S(,1) lines indicated that the stalk-quality traits were controlled primarily by additive gene action;Grain yield was reduced from 70.8 q/ha in the C0 to 49.5 and 54.2 q/ha in the BS1MSC3 and BS1SRC3 populations, respectively. The yield reductions were caused by reductions in all yield components except kernel weight, which showed increases for both selection methods. Divergent responses were observed in maturity and plant traits because the BS1MS populations showed increases and the BS1SR populations showed decreases for most traits. No significant associations were observed between stalk quality and resistance to northern leaf blight and European corn borer. All correlated responses in agronomic traits were caused primarily by allelic frequency changes for these traits during selection for improved stalk quality;A comprehensive breeding program that includes recurrent selection of S(,1) lines by using an index of stalk-rot resistance, rind strength, yield, and maturity, with extraction of superior lines after each cycle of population improvement, was recommended. The gain will be less than for individual selection for stalk rot or stalk strength, but the improved population should allow extraction of more lines with good stalk quality and desirable agronomic performance.



Digital Repository @ Iowa State University,

Copyright Owner

Michael Jerome Martin



Proquest ID


File Format


File Size

296 pages