Genetic control of mineral concentration and yield in perennial ryegrass (Lolium perenne L.), with special emphasis on minerals related to grass tetany

Abstract

Grass tetany is a common metabolic disorder of ruminants in southern Australia. To investigate the genetic control of mineral concentrations leading to this disorder, replicate populations of perennial ryegrass half-sib families were grown at Hamilton and Timboon in southern Australia. Variation in herbage yield, and Mg, P, K, Ca, Na, Cl, S, Mn, Fe, Cu, Zn, and K/(Mg+Ca) (tetany ratio) concentrations in the herbage of these families was measured in the early spring of 1994. Large environmental effects on herbage mineral concentration were detected, with location differences accounting for 60–80% of the total variance. Both the mean and range for mineral concentration were similar for each population. As expected, Mg, Ca, and K were significantly correlated with tetany ratio; however, the concentrations of other minerals were not consistently associated with tetany ratio. Tetany ratio and Mg showed a negative genetic correlation in both groups. The genetic correlation for tetany ratio with K or Ca was less repeatable across groups. Significant family variance components (σ²_f) were detected for yield, Mg, Ca, K, and tetany ratio, and narrow-sense heritabilities for these traits were moderate to high (h² = 0·46–0·81). However, family location interactions were also significant, with σ²_fl often >σ²_f. A large proportion of the family location interaction for K and Mg concentration was associated with non-rank family changes indicating that family selection for low K or high Mg concentration would be effective across environments. However, family × location effects for Ca and tetany ratio were associated with substantial rank changes across locations. Selection for increased Mg concentration would appear the most suitable strategy for reducing the tetany ratio of perennial ryegrass, with possibly different cultivars required for the environments represented by Hamilton and Timboon.