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

Grass tetany is a common metabolic disorder of ruminants in southern Austra lia. To investigate the genetic control of mineral concentrations leading t o this disorder, replicate populations of perennial ryegrass half-sib famil ies 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 erects 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 significa ntly correlated with tetany ratio; however, the concentrations of other min erals were not consistently associated with tetany ratio. Tetany ratio and Mg showed a negative genetic correlation in both groups. The genetic correl ation for tetany ratio with K or Ca was less repeatable across groups. Sign ificant family variance components (sigma(f)(2)) were detected for yield, M g, Ca, K, and tetany ratio, and narrow-sense heritabilities for these trait s were moderate to high (h(2) = 0.46-0.81). However, family x location inte ractions were also significant, with sigma(fl)(2) often >sigma(f)(2). A lar ge proportion of the family x location interaction for K and Mg concentrati on was associated with non-rank family changes indicating that family selec tion for low K or high Mg concentration would be effective across environme nts. However, family x location erects for Ca and tetany ratio were associa ted 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 requi red for the environments represented by Hamilton and Timboon.