Determination of the genetic basis for responses to plant population density in maize

Martin Gonzalo, Purdue University

Abstract

Selection for adaptation to higher densities in maize has played a major role in the improvement of maize hybrids. Selection has increased yield per unit surface area, but not potential yield per plant; thus yield gain is primarily a result of tolerance to high density conditions. The goal of this research is to understand the genetic basis for maize response to density. Three different types of populations were used, and several new analytical tools were developed to address this goal. For the first population, a set of 8 segmental introgression lines (SILs) derived from the cross of inbred lines B73 and Tx303 and their hybrids to the unrelated parent Mo17 were planted at two population densities (50000 and 100000 plants ha-1). A mixed model framework was used to directly test for the interaction between density effects and genetic effects, and account for heteroscedasticity of variance across the density treatment. Some SILs were consistently different from the recurrent parent regardless of the density, while others differed from the recurrent parent in one density level but not in the other, providing evidence for both main effects and interaction between genetic loci and density. Furthermore, some segments responded differently to density depending upon the inbreeding level. A second population of 186 recombinant inbred lines (RILs) derived from the cross of inbred lines B73 x Moll was also planted at two densities. Loci significantly associated with maize plant responses to density were identified, and a significant number of epistatic interactions were observed. The third population tested reciprocal backcrosses of a subset of RILs to their parental lines to determine whether reciprocal effects were affected by density. Differences in kernel size of the reciprocal backcrosses had less impact on early vegetative growth at high density than at low density. In addition, mapping of loci responsible for differences in plant height at multiple growth stages and time to anthesis and silking between reciprocal backcrosses for confirmed the presence of loci with significant parent-of-origin effects. These differences between reciprocal backcrosses could possibly be attributed to density-induced DNA methylation of imprinted loci.

Degree

Ph.D.

Advisors

Vyn, Purdue University.

Subject Area

Genetics

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