Forage yield and persistency of T. repens x T. nigrescens hybrids when sown with a perennial ryegrass companion

Introgression of reproductive traits from ball clover (Trifolium nigrescens Viv.) into white clover (Trifolium repens L.) is one breeding strategy to improve seed yields of T. repens that must be achieved without sacrificing agronomic performance and persistency. The yield and persistency of hybrids between white clover and the annual, profuse flowering species T. nigrescens were compared under a cutting regime over three harvest years. The hybrids included the F1 and the backcross (BC) 1, 2 and 3 generations produced using T. repens as the recurrent parent. Parental species and hybrids were sown with a perennial ryegrass companion; clover and perennial ryegrass dry-matter (DM) yield and the proportion of clover present were measured over the growing season. In the third harvest year, a portion of each plot was grazed. Differences were observed between T. nigrescens, the F1 and the backcross hybrids and T. repens. In the first and second harvest years, clover DM yield, the proportion of clover present and total DM yield of the backcross hybrids were similar to T. repens, whereas that of the T. nigrescens and the F1 hybrid were negligible. No significant difference in perennial ryegrass production was observed between the parental species and the hybrids when grown, respectively, in combination with these species and hybrids. In the third harvest year, clover DM yield and the proportion of clover present with the BC3 was lower than with T. repens. Throughout the growing season the DM production of T. repens and the backcross hybrids was similar. In the third harvest year, under cutting, DM yield of T. repens was greatest and that of the BC3 lowest, but under grazing, the yields of the BC1 and BC3 were greater than T. repens and the BC2. The implication of these results for the future development of these hybrids is discussed.