Relationship between the first and second crops and estimation of genetic parameters of the second crop on the nutritive value of timothy (Phleum pratense L.)

Improvement of the nutritive value of timothy (Phleum pratense L.) through breeding should result in enhanced livestock productivity. This study investigated the extent of genotype × crop interaction (G × C) between the first and second crops, and the extent of genotype × year interaction (G × Y) and narrow-sense heritability (h _N²) of the second crop of the nutritive value of timothy. Twenty-six clones were used to evaluate these interactions in 2007 and 2008, and 17 clones and their half-sib progeny were used to evaluate the h _N² in 2010 in Kunneppu, Japan by analyzing their nutritive value. The content of water-soluble carbohydrate (WSC) was significantly correlated between the two crops in 12 clones with many internode elongation stems (IES) in the second crop and the 2 years, with non-significant effects of G × C in these clones and G × Y. However, the low-digestible fiber (Ob) content and the ratio of Ob to organic cell wall showed weak to medium correlations between the two crops, regardless of IES ratio or the elapsed time of 2 years, with significant effects shown for the two interactions. The h _N² of the three traits was medium to high. These results suggest that, in the second crop, selections for WSC content through the first crop in genotypes with many IES in the second crop, and under multiple environments in other traits are potentially useful; and that recurrent selection which utilizes an additive genetic variance is likely to be effective for the three traits.