Symbiotic variation of rhizobium trifolii with S.100 nomark white clover (<i>Trifolium repens</i> L.)

Abstract

Abstract The symbiotic effectiveness of 134 isolates of Rhizobium trifolii was investigated with S.Ioo Nomark as the tester variety; 70 were from sites of over 1000 ft. and 64 from lower elevations. The variation in mean time of primary nodulation for each isolate ranged from 5–6 to 13.9 days after inoculation. There was no significant difference between mountain and lowland isolates, and this factor was not correlated with the eventual growth of the plants. Mean nodule number per isolate varied from 4.4 to 29.5 and this was negatively correlated with symbiotic effectiveness as measured by visual grades of growth. Approximately 60% of the isolates from mountain soils were either ineffective or intermediate, compared with 33% of the lowland isolates. Bacterial strain variation is discussed in comparison with variation due to the host genotype.