Modified synthetic varieties: a breeding method for forage crops to exploit specific combining ability.

摘要

Hybrid varieties have not become commercially successful in perennial and self-incompatible forage crops because of their severe inbreeding depression and/or ineffectiveness in commercial seed production. Here, a modified synthetic variety (MSV), a breeding method for forage crops is proposed, where specific combining ability (SCA) is exploited in a way different from that in hybrids. As Syn-l seeds from only two of its parental clones are used to produce its Syn-2, its performance in Syn-2 partially depends on the SCA between the two seed parents. The inbreeding coefficient of MSVs can be as low as that of conventional synthetic varieties sold today. To evaluate its advantages, 15 modified synthetic strains (MSSs) of timothy were developed from a set of Syn-l seeds of a conventional synthetic strain (CSS) having six parental clones. An MSS (Syn-2) showed a yield level equivalent to and a disease score significantly lower than the CSS (Syn-1) in a field test. The diallel crossing analysis implied that the SCA effects are influential for yield, and that MSV or other SCA-exploiting breeding methods have the potential to improve the yield level of timothy effectively..