Genotypic evaluation of introduced white clover (Trifolium repens L.) germplasm in New Zealand

Optimal evaluation and use of introduced germplasm for species improvement is an ongoing challenge. Research was conducted to survey a select set of introduced white clover (Trifolium repens L.) germplasm from broad geographic origins to assess their genetic potential, based on F-1 crosses to elite New Zealand cultivars. The bulk progeny generated from test crosses to Grasslands cultivars Demand, Sustain and Kopu II were evaluated at Palmerston North under rotational grazing by sheep. The replicated trial consisted of the 26 germplasm accessions, three cultivars used as maternal parents, and 78F(1) bulk progeny breeding lines. Three morphological traits and estimated seasonal dry matter yield were measured over four years. Significant (P<0.05) genotypic variation was observed for all these traits among the parents and F-1 progeny lines. F-1 progeny lines with traits values greater than the cultivars were identified. Significant (P<0.05) genotype-by-season (sigma(2)(gs)) and genotype-by-year (sigma(2)(gy)) interactions were estimated for dry matter yield. Principle component analysis of the F-1 progeny-by-trait BLUP matrix identified 16 elite progeny lines with mean seasonal dry matter yield equal to or higher than the cultivars. Half of the lines had Demand as the cultivar parent, while only three had Kopu II as a parent. Fourteen of these progeny lines were derived from crosses to Australasian adapted germplasm. This study indicated that choice of adapted cultivar with which to cross is important, and introduced germplasm from Australasia is a valuable source of adaptive variation in these F-1 progeny. More complex approaches may be needed to identify and use adaptive allelic variation from germplasm sources beyond Australasia.