Genetic Mapping of Grass-Legume Mixture Compatibility QTLs in Intermediate Wheatgrass.

Due to increased environmental stewardship and fertilizer prices, there is increased interest in using legume mixes in perennial croplands. In order to understand the genetics of grass-legume mixture performance, this study compares Quantitative Trait Loci (QTL’s) controlling the growth of intermediate wheatgrass (Thinopyrum intermedium) when grown in monoculture, polyculture with alfalfa (Medicago sativa), and polyculture with crested wheatgrass (Agropyron desertorum). For the study we evaluated 192 full-sib intermediate wheatgrass progeny from a biparental cross of M26 x M35, in 3 clonally replicated field plots for each treatment. Phenotypic traits measured were plant growth (Zadok’s phenology scale, height, and tiller count), forage mass, and forage nutritive value (NDF, ADF, ADL, CP, IVTD, and NEg). A linkage map comprised of 3568 single nucleotide polymorphisms in 21 linkage groups corresponding to 21 homologous chromosome pairs of both parents was used to identify quantitative trait loci (QTLs) based on trait averages for each genotype in each treatment. Forage nutritive values were determined using NIRS and validated with wet chemistry. All phenotypic data was analyzed in SAS and mapped using mapQTL software. Progeny grown in noncompetitive monoculture outperformed the clones grown in polycultures with greater plant growth and forage mass (0.56 kg/plant); whereas, the alfalfa polyculture had greater forage mass (0.05 kg/plant) than the grass polyculture (0.03 kg/plant). In contrast, the grass polyculture had greater lignin (8.5 %) content than the alfalfa polyculture (8.27%) and the greatest crude protein content of all the environments (6.7%, 5.04%, and 8.5% for the monoculture, legume polyculture, and grass polyculture, respectively). Although some QTLs were detectable in all three management systems, a relatively high frequency of QTLs were uniquely present or absent in one of the management systems. These results provide evidence of genes that have significant breeding value in specific management systems.