Inheritance of nutritive quality of summer herbage in Phalaris tuberosa L

Abstract

Nutritive quality was measured in a genetically diverse population consisting of 55 full-sib families in 16 half-sib groups. The families were grown as pure grass swards and grazed heavily at intervals during the second winter and spring. In early summer, the families differed significantly in crude protein and crude fibre contents and in in vitro digestibility. The heritabilities of these characters were 53.5, 43.0 and 60.4% respectively on a full-sib family mean basis. Phenotypic variances were such that the predicted response to selection for higher protein content was substantial, whereas those for lower fibre and higher digestibility were small. At later harvests environmental variation increased markedly, and family differences, though large, were not significant.

The predicted increase in protein concentration in early summer of one percentage unit for each generation of family selection at an intensity of 10% would be accompanied by a decrease in seedling size and a delay in flowering unless countered by opposing selection pressure. Two methods for suppressing the undesirable correlated response in flowering time were found to be equally effective, and a new method was formulated to minimize the number of protein determinations required in subsequent generations.

Techniques for sampling mature herbage for nutritional value assessment are discussed.