Effect of temperature on competition amongst strains of <i>Rhizobium trifolii</i> for nodulation of two white clover varieties

Abstract

SUMMARY The effect of temperature and soil type on the relative success in nodulating cultivars of white clover ( Trifolium repens ) by mixtures of antibiotic‐resistant mutants of Rhizobium trifolii was studied. Under aseptic test‐tube culture, 75 str nodulated the plants 5 days earlier than 33 spc at the lowest temperature, but the temperature × Rhizobium strain interaction was not significant. 33 spc was more effective than 75 str at 25°C and, although no significant difference was found between the two mutant strains at the lower temperatures, die temperature × Rhizobium strain interaction was highly significant. In soil, when inoculated with mixed inoculum, cv. S100 was more uniformly nodulated by 75 str (81%) than S184 (49%). Success in nodulation could be altered by temperature and the temperature × bacterial strain interaction was significant. In the mixed inoculum treatments, 75 str was most compatible with S100 at 12°C, whereas 33 spc was most compatible with SI84 at 25°C; the bacterial strain × variety × temperature interaction was highly significant. The results are discussed from the point of view of improving symbiotic nitrogen fixation by selecting effective strains of Rhizobium which are compatible with the particular host cultivar, which are competitive with the indigenous population and whose optimum temperatures for nodulation and competitiveness are similar to the soil temperature at the times of inoculation.