Comparisons of Effects of Intrapopulation vs. Interpopulation Selection in Maize1

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Abstract
The responses of two populations of maize(Zea maysL.), ‘Jarvis’ and ‘Indian Chief’, after 10 cycles of full‐sib family( F) selection and 10 cycles of reciprocal recurrent (R) selection are reported. Average F selection responses per cycle were 3.5 and 1.4% for the two population and 2.0% for the population cross. Average R selection responses per cycle were 2.4 and ‐0.3% for the two populations and 2.7% for the population cross. A change in response to selection following the 8th selection cycle was observed for both selection procedures. the nature of genetic changes within populations following selection wase valuated using a divergence measure obtained from diallel information. Total divergence was resolved into additive‐associated and dominance‐associated gene effects. A two‐fold greater divergence was obtained within Jarvis than within Indian Chief. for F selection, divergence resulted from a dditive‐associated effects for the first 8 cycles whereas for R selection, divergence resulted from additive‐associated effects in Jarvis and dominance‐associated effects primarily in Indian Chief. Ear number increased consistently with increased grain yield during 8 cycles of selection. With continued selection, ear number changed in some, but not all, populations and dominance played an increasingly more important role in both selection programs. Cumulative inbreeding depression and increased complexity of the genetic effects under selection were explanations for observed changes in response to continued selection. Maximum divergence occurred with R selection; however, the highest yielding cross was Jarvis (R) C10 X Indian Chief (F) C10.