Symbiotic competence of Trifolium subterraneum lines of low oestrogenic isoflavone content

Abstract

Twenty-nine lines of subterranean clover (Trifolium subterraneum), mostly selected for low levels of oestrogenic isoflavones, were inoculated with seven effective strains of Rhizobium trifolii. They were grown at two different root temperatures and their performances compared with those of the subterraneum clover cultivar, Tallarook. Ten criteria were used to assess symbiotic competence. No line was inferior to Tallarook in all ten criteria, but one line was inferior in nine of the ten, three in seven of the ten and fifteen others were poorer than Tallarook in one to six criteria. Of the ten lines whose symbiotic performances were as good as or better than Tallarook, a number also had low isoflavone levels, but there was no evidence to suggest that symbiotic competence was related to isoflavone content. It is concluded that it will be necessary to exercise caution in the agronomic or breeding use of lines Which are not consistently symbiotically competent.