|Holland, Jim - Jim|
Submitted to: Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/13/2006
Publication Date: 5/24/2006
Citation: Gonzalo, M., Vyn, T., Holland, J.B., Mcintyre, L. 2006. Mapping density response in maize: a direct approach for testing genotype and treatment interaction. Genetics. Interpretive Summary: Much of the improvement in yield of corn over the last century has been due to greater tolerance of stress. One of the key stresses that modern corn tolerates better than older varieties is the stress due to dense plantings. We mapped genome regions that affect this response in corn inbreds and hybrids and found that different traits are associated with improved yield under low and high planting densities. In addition, genes that are important in inbreds were not important in hybrids, and vice versa. We developed new statistical methods to directly identify gene regions that control responses to stress and identify some key traits that are associated with yield gains under high density.
Technical Abstract: Corn improvement has been strongly linked to improvements in stress tolerance, particularly to increased inter-plant competition. As a result, modern hybrids are able to produce kernels at high plant population densities. Identification of the genetic factors responsible for response to stress in corn requires direct testing of QTL by stress interaction, and evaluation of that response in multiple traits. In this paper, we take a broad view of the problem, and develop a general mixed-model approach suitable for use in situations with multiple fixed and random effects. This approach permits QTL detection, estimation of environmental effects, tests of changes in correlation among traits, and direct tests for the interaction between treatments and QTL. Aditionally, we show how to handle heteroscedascity of variances common in stress responses. We find positive evidence for interaction between QTL and density in cases where the approach of overlapping maps fails to find significant results. The relationships among traits varies with the densities and inbred/hybrid status, indicating that the physiological mechanisms underlying tolerance to stress are influenced by the density. Importantly, we find that a number of QTL are constitutively expressed across stress levels, while others depend upon stress levels.