Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2012
Publication Date: January 1, 2013
Citation: Washburn, J.D., Murray, S.C., Burson, B.L., Klein, R.R., Jessup, R.W. 2013. Targeted mapping of quantitative trait locus regions for rhizomatousness in chromosome SBI-01 and analysis of overwintering in a Sorghum bicolor x S. propinquum population. Molecular Breeding. 31:153-162. Interpretive Summary: Major advancements in science hinge on the identification of genes controlling plant and animal traits that are critically important to agriculture. Genes are tiny packets of genetic blueprint material that are found inside the cells of all plants and animals and control all of the physical characteristics of these organisms. Our work focuses on improving major grain and biofuel crops and, with gene sequences, the genetic blueprint will be visible and this information can make improving the plants more efficient. This study details the efforts to find major genes involved in perennialism in sorghum, which is a trait that is of importance in sustainable agriculture and in biofuel production. Identifying those portions of chromosomes that contain genes for winter survival in sorghum will permit more efficient identification and understanding of the function of these genes, and will allow scientists to understand those key features of the genetic blueprint that make sorghum's physical appearance differ from that of other cereals. Information will be primarily used by fellow scientists but the work should ultimately result in better adapted, higher producing crop varieties available to American farmers.
Technical Abstract: While rhizome formation is intimately associated with perennialism and the derived benefit of sustainability, the introduction of this trait into temperate-zone adapted sorghum (Sorghum bicolor (L.) Moench) cultivars warrants precise knowledge of the genetics conditioning this trait in order to minimize the risk of weediness while maximizing the productivity of perennial sorghum. As an incremental step towards dissecting the genetics of perennialism, a segregating F4 heterogeneous inbred family derived from a cross between S. bicolor and S. propinquum was phenotyped in both field and greenhouse environments for traits related to over-wintering and rhizome formation. An unseasonably cold winter in 2011 provided high selection pressure and hence, 74.8% of the population did not survive. This severe selection pressure for cold tolerance allowed the resolution of two previously unidentified over-wintering QTL and more powerful correlation models than previously reported. Conflicting with previous reports, a maximum of 33% of over-wintering variation could be explained by above-ground shoot formation from rhizomes; however, every over-wintering plant exhibited rhizome growth. Thus, while rhizome formation is required for over-wintering, other factors also determine survival in this interspecific cross. The fine mapping of a previously reported rhizome QTL on sorghum chromosome SbI-01 was conducted by targeting this genomic region with additional simple sequence repeat (SSR) markers. Fine-mapping reduced the 2-LOD rhizome QTL interval from 59 Mb to 14.5 Mb, which represents a 75% reduction in physical distance and a 53% reduction in the number of putative genes in the locus.