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Inbreeding depression rates of materials derived from two groups of maize inbred lines^*

Felix Manuel San Vicente^I; Arnel Roy Hallauer^II

^IFONAIAP-CENIAP, Apdo. Postal 4653, Maracay 2101, Venezuela
^IIDepartment of Agronomy, Iowa State University, Ames, IA 50011, USA. Journal papel No. J-15083 of the Iowa Agric. and home Economics Exp. Stn., Ames, IA 50011. Project No. 3082. Send correspondence to A.R.H.

ABSTRACT

The production of single-cross maize (Zea mays L.) hybrids requires the use of inbred lines that have dependable, stable performance. Inbred lines are usually developed by self-pollination, and inbreeding in maize is accompanied by a reduction in the mean phenotypic value for most traits. The objectives of this study were to compare inbreeding depression rates of materials derived from older (pre-1960) and newer (post-1970) maize lines to determine if rate of inbreeding depression and fit of data to a linear model changed between the two groups of lines. Each group included six lines with B14A, B37, L289, L317, M14, and WF9 included in the older group and B73, B75, B76, B77, B79, and B84 included in the newer group. Nineteen generations within each of the two inbred groups representing nine levels of inbreeding (0 to 100% homozygosity at 12.5% intervals) were evaluated in 10 environments to determine rates of inbreeding depression for 15 plant and ear traits. The rates of inbreeding depression were similar for the two groups of lines for nine of the 15 traits. The rate of inbreeding depression was lower for tassel-branch number, ear-leaf width, number of ears per plant, ear length, ear diameter, and cob diameter in time newer lines, suggesting either that the newer lines were segregating at fewer loci than the older lines or that the frequency of favorable alleles was greater than 0.5. The reduction in the phenotypic means was negatively and linearly correlated with the coefficient of inbreeding for all traits except days to anthesis. The linear model explained 89% or more of the variation among the inbreeding level means for nine traits for both groups of lines.

Keywords: inbreeding depression rates; maize inbred lines.

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* Part of a thesis presented by F.M. San Vicente in partial fulfillment of the requirements for the Doctoral degree