Response to selection for seed yield in six white clover cultivars

Abstract

The successful commercialisation of agronomically superior white clover (Trifolium repens) cultivars is dependent on their seed production potential. Field trials were established in 2000 and repeated in 2003 to determine the impact of selection for increased seed yield. The seed yield of the pre-release cultivar (the base population prior to selection for seed yield and cultivar release, representing generation 0) was compared with the field Nucleus generation of the released cultivar (second generation after selection for seed yield, representing generation 2) and the Basic seed generation (the fourth generation after selection for seed yield, representing generation 4), in six recent cultivars (Grasslands Kopu II, Grasslands Challenge, NuSiral, Grasslands Sustain, Grasslands Demand and Grasslands Prestige). The Nucleus and Basic generations had consistently higher seed yield than the pre-release generation for all cultivars. These increases in seed yield were associated with increases in inflorescence density (inflorescences/m2) and to a lesser extent with increased seed yield/inflorescence. Changes were also evident in flowering pattern with four of the six cultivars having a sharper flowering peak following selection. This improved uniformity was also evident through reduced variability in leaf size of the Nucleus generation compared to the pre-release generation. Grasslands Kopu II had the highest seed yields which were associated with moderately high inflorescence density in combination with high seed yield/ inflorescence. The selection strategy used in the final phase of the development of these cultivars has proven successful in increasing seed yield through refining flowering pattern and production while maintaining the morphology and uniformity of the new cultivar. Keywords: cultivars, genetic improvement, seed production, Trifolium repens, white clover