Variation in symbiotic effectiveness in subterranean clover (Trifolium subterraneum L.)

(1) The symbiotic effectiveness of 15 varieties and of four tetraploid lines of subterranean clover were examined in association with several strains of nodule bacteria.(2) Relatively- small but significant differences in yield occurred between host' varieties, and the varietal order of response depended somewhat on the bacterial strain, but not enough to shorn- any well-defined variety-strain specificity. (3) Hybridization between varieties increased yields slightly in F2, less in F3, and the effect disappeared in F4. (4) With one doubtful exception all attempts to alter effectiveness by selection or breeding within hybrid material failed.
RESP-4466