Title: Genotypic and phenotypic characterization of isogenic doubled haploid exotic introgression lines in maize Authors
Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 2011
Publication Date: February 17, 2012
Citation: Brenner, E., Blanco, M.H., Gardner, C.A., Lubberstedt, T. 2012. Genotypic and phenotypic characterization of isogenic doubled haploid exotic introgression lines in maize. Molecular Breeding. 30:1001-1016. Available: http://www.springerlink.com/content/g6l3662104697881/?MUD=MP. Interpretive Summary: Exotic maize germplasm is potentially a source of unique genes that may not be present in Corn Belt germplasm currently used by US breeders. In this study, cell wall digestibility (CWD) was studied by analyzing digestible neutral detergent fiber (DNDF) of corn stover. DNDF is an important indicator of silage nutritional quality and is associated with improved ethanol potential. Fifty double haploid (DH) inbreds were studied that were derived from 31 exotic races backcrossed once to an adapted corn belt inbred (25% exotic and 75% adapted). Five adapted check inbreds known to have good DNDF and silage quality were included for comparative purposes. The 50 DH inbreds were analyzed using 199 single nucleotide polymorphic (SNP) molecular markers distributed throughout the ten chromosomes of maize and covered 92.9% of the adapted parent genome. On average, 11.8% of the SNP markers were derived from the exotic parent, which is probably an underestimate. If a SNP is monomorphic (identical in both parents), it is not possible to identify parental origin. Promising lines derived from some exotic populations were identified with favorable DNDF, and were equal in quality to the five high forage quality checks. However, some of these promising lines for DNDF also carried undesirable traits such as late maturity, high ear placement, and greater stalk lodging, but these traits were not correlated to DNDF. The results from this research indicated that unique genes present in exotic races can be useful for improving DNDF, and may be useful to plant breeders to improve ethanol and forage quality. Since the DNDF quality traits were not correlated to the unfavorable agronomic traits (late maturity, ear height, lodging) it should be possible to develop germplasm from exotic sources with good DNDF and agronomic traits.
Technical Abstract: We characterized the genotypic and phenotypic variation for cell wall digestibility (CWD) and other agronomic traits of 50 backcross 1 generation doubled haploids (BC1DH) lines developed from the Germplasm Enhancement of Maize (GEM) project. These lines consisted of 31 exotic, unadapted maize races introgressed into PHZ51 and PHB47, temperate inbred lines with expired Plant Variety Protection. The 50 BC1DH lines and 5 check lines were genotyped with 199 single nucleotide polymorphism (SNP) markers distributed across the genome. We identified, on average, 11.8% of markers with exotic donor parent alleles. This, however, may underestimate donor introgressions, since we cannot discriminate monomorphic alleles from donor and recurrent parents. The potential roles of natural selection and the double haploid (DH) process in favoring selection of the recurrent parent genome are discussed. Although the proportion of the recurrent parent genome was underestimated, donor fragments evaluated across BC1DH lines covered 92.9% of the recurrent parent genome. The evaluation of BC1DH lines for cell wall digestibility revealed promising lines with CWD not differing significantly from forage quality lines used as checks. The introgression of donor genome, however, was generally associated with higher ears, lodging, and late flowering. Even with limited power, our association analysis revealed quantitative trait polymorphisms (QTPs) associated with CWD, flowering and lodging.