Genetic analysis of yield and quality in full-sib families of perennial ryegrass (Lolium perenne L.) under two cutting managements

The objective was to evaluate the genetic variability for total annual dry matter (DM) yield and three quality traits (digestible organic matter in dry matter (DOMD), water-soluble carbohydrate (WSC) and crude protein (CP)) in two ryegrass populations (maturity groups) using partially inbred full-sib (FS) families under simulated grazing (frequent cutting) and conservation management. Near Infrared Spectroscopy was used for estimation of the quality traits. The estimates of broad sense heritability were relatively high for all traits. Estimates derived from combined analysis over years and management ranged from 0.44 to 0.67 (DM yield); 0.60 to 0.72 (DOMD); 0.53 to 0.58 (WSC) and 0.38 to 0.65 (CP) The higher value was always associated with the mid-season population. Interpretation of heritability values was restricted because the experimental design (measurement of FS families grown as dense swards, no measurement of individual plants) did not allow estimation of non-additive genetic variance. Consequently, these estimates may be greater than the narrow sense values. Genotype X environment interactions (management and years) were present for DM yield and to a lesser extent for DOMD and WSC, but absent for CP. The genetic correlation between WSC and DOMD was highly positive (0.62 to 0.87), while the relationship of CP with both DM yield (-0.57 to -1.14) and WSC (-0.16 to -0.87) was negative. These results were consistent over years, management and maturity groups. None of the phenotypic or genotypic correlation estimates for DOMD with CP were significant. The remaining two pair-wise correlations were inconsistent over the two maturity groups. The correlation of DOMD with DM yield was negative for the late (-0.59) but uncorrelated for the mid-season population (-0.01). WSC and DM yield was positively correlated for the mid-season (0.45) but uncorrelated for the late-maturity group (0.06). The values quoted refer to combined analysis over years and maturity populations.