The genetic relationship between the digestibility of leaf, stem and whole plant in Setaria

Abstract

The genetic interrelationships of in vitro dry matter digestibility of whole plant (DMD_WP), leaf (DMD_L), stem (DMD_S) and terminal two leaf (DMD_2L) fractions were investigated in 4-week regrowth of 21 tetraploid clones of Setaria anceps and 14 hexaploid clones of Setaria trinervia.

There were significant differences between genotypes of more than eight digestibility units for all fractions, and for all fractions significant positive correlations were obtained between genotype performance at successive harvests.

Genotypic and phenotypic correlations between leaf and stem digestibility were mainly positive, but generally low. Genetic correlations for DMD_L–DMD_WP and DMD_S–DMD_WP mostly exceeded 0.7 and for DMD_2L–DMD_L 0.6. Markedly lower values were obtained for the DMD_2L–DMD_WP comparison. Genotypic correlations for DMD_WP-percentage leaf were greater than 0.4 at one harvest.

It is concluded that selection for high DMD_WP should result in improvement for both leaf and stem digestibility, providing selection was within populations at the same ploidy level. There appears to be little justification for basing selection on the terminal two-leaf fraction, in view of the relatively inconsistent ranking of genotypes in the two successive harvests, and the relatively low genetic correlations between digestibility of this fraction and that of the whole plant.