Surveying genetic and phenotypic variation for response to density stress in maize wheat and barley.,

Abstract

Increasing plant population density can increase biomass and grain yield on a per area unit basis, however this relationship is curvilinear where eventually a high plant density will overwhelm the tolerance to density stress and yield per unit area will decrease. The main objective of this thesis is to gain an understanding of the genetic and morphological responses to density stress. In the first part of this thesis, we examined differential gene expression in seedlings of four barley genotypes and five maize genotypes grown at low and high densities. A microarray analysis approach was employed and identified 219 and 35 transcripts differentially expressed in barley and maize, respectively, with little gene expression patterns overlap among genotypes, indicating that these genotypes respond in very different ways and may have different mechanisms to deal with density stress. In the second part of this thesis, we examined multiple genotypes of maize, wheat, and barley planted at three different densities with the highest density being up to three times the normal density. A combined genotype analysis for each species showed that the highest plant density had the greatest biomass yield m-2 for wheat and maize while barley had no significant difference among the three densities for biomass yield m-2. For grain yield m-2, barley had the lowest yield at the highest plant density, wheat had no difference among the densities and maize had the greatest grain yield m-2 in the high plant density.