Evaluation of endosperm hardness and correlated responses of agronomic traits after four cycles of recurrent selection in two synthetic populations of maize
Abstract
Evaluation of four cycles of S$\sb1$ recurrent selection for increased kernel endosperm hardness was conducted at four locations over 2 years in the synthetic maize populations HSyn73 and HSyn99. Endosperm hardness was measured using the Stenvert hardness test and kernel density. Evaluation of progress over cycles of selection was performed on S$\sb1$ testcross hybrids. Test weight per bushel, grain yield, percent grain moisture, percent stalk lodging, percent seedling emergence, and plant and ear height were also measured to determine possible correlated responses of these agronomic characters to selection for endosperm hardness. Selection for endosperm hardness was performed using visually selected ears for advancement to the next cycle. Visual selection for endosperm hardness may be inadequate to detect small increases in endosperm hardness. The Stenvert hardness test is a quantitative measure which accurately indicates the level of endosperm hardness. Evaluation of progress for increased endosperm hardness was highly significant for the Stenvert hardness test in population HSyn73 only. A positive linear effect for kernel density over cycles was also significant in population HSyn73. Population HSyn99 exhibited no significant response to selection of endosperm hardness. Significant variation was present for random lines within cycles of selection for most agronomic characters in both synthetics, indicating selection progress was still possible. Highly significant phenotypic and genotypic correlations were seen between kernel density and Stenvert hardness measure in HSyn73 (r = 0.681 and r = 0.912, respectively) and in HSyn99 (r = 0.725 and r = 0.959, respectively). Test weight per bushel was significantly correlated with both Stenvert hardness and kernel density for both populations. Grain yield expressed a significant negative phenotypic correlation with both endosperm hardness measures in both populations. Plant and ear height showed significant phenotypic and genotypic correlations in both populations, and also ear height with percent stalk lodging. Plant height was highly correlated with both percent grain moisture and percent stalk lodging in population HSyn73, possibly resulting from late maturing hybrids having tall stature with high ear placement. Selection for kernel endosperm hardness did not alter agronomic performance for most traits measured. However a decrease in grain yield indicates that selection pressure for yield should occur concurrently when selecting for endosperm hardness.
Degree
Ph.D.
Advisors
Zehr, Purdue University.
Subject Area
Agronomy
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