Submitted to: Molecular Breeding
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/8/2006
Publication Date: 10/5/2006
Citation: Xiong, Y., Fei, S., Brummer, E.C., Mooore, K.J., Barker, R.E., Jung, G., Curley, J., Warnke, S.E. 2006. Qtl analysis of fiber components and crude protein in an annual x perennial ryegrass population. Molecular Breeding. 18: 327-340. Interpretive Summary: Ryegrasses (Lolium spp.) are cool-season grasses used for both turf and pasture in the U.S. Knowledge of genes controlling differences between annual and perennial specific physical plant types would help in understanding genetic relationships among species and perhaps assist breeders in forage and turfgrass improvement programs. Forage quality is one of the complex quantitative traits that limit geographic distribution of ryegrass. Quantitative trait loci (QTLs), a term used for identifying multiple genes controlling a genetic trait, for fiber components, crude protein, and related characteristics over two years were analyzed using a turf-type perennial (Lolium perenne L.) x forage-type annual (or Italian) (Lolium multiflorum Lam.) hybrid mapping population. Sixty-three QTLs were identified for four forage quality traits on chromosome regions containing specific markers already known to differ between ryegrass types. For example, QTLs were detected on linkage groups (LG) 2, 6, and 7 for neutral detergent fiber (NDF), LGs 1, 2, and 7 for acid detergent fiber (ADF), LGs 6 and 7 for acid detergent lignin (ADL) and LG 2 for crude protein (CP). ADF and NDF were positively correlated and QTLs found in common on LGs 2, 6, and 7. These co-located QTLs provide evidence for the high phenotypic correlation between the two traits. These QTLs for fiber components were co-located with lignin biosynthesis genes and will provide potential markers for marker-assisted selection to improve forage quality in future ryegrass breeding programs.
Technical Abstract: Annual (Lolium multiflorum Lam.) and perennial (Lolium perenne L.) ryegrass are two common forage species in temperate regions. Improving the digestibility of forage by decreasing fiber content is a major goal in forage crop breeding programs. An annual X perennial ryegrass population was used to map quantitative trait loci (QTL) for fiber components-neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL), and crude protein (CP). Samples were harvested three times, in August and September 2003, and August 2004, respectively. Simple interval mapping was used to detect QTL from both male and female parental maps previously developed from the population. Fiber components were all positively correlated with each other and negatively with CP. The largest correlation were between NDF and ADF with r = 0.86, 0.72, and 0.82 from each of three harvests. All four traits showed intermediate broad-sense heritability ranging from 0.31 to 0.68. A total of 63 QTLs were detected for four traits measured over the three harvests from both female and male maps. Coincident QTLs were detected on linkage groups (LGs) 2, 6, and 7 for NDF, LGs 1, 2, and 7 for ADF, LGs 6 and 7 for ADL, and LG 2 for CP, respectively. Coincident QTLs were also detected on LGs 2, 6, and 7 for NDF and ADF, providing the genetic evidence of high phenotypic correlation. The QTLs on LGs 2, 6, and 7 for fiber components were co-located on the same LG with several lignin biosynthetic genes from perennial ryegrass.