Ecological studies of root-nodule bacteria introduced into field environments. I. A survey of field performance of clover inoculants by gel immune diffusion serology

Abstract

A gel immune diffusion procedure for identifying strains of rhizobia has been used to follow the persistence of two strains of Rhizobium trifolii introduced simultaneously into soil by clover seed inoculation. Isolations of rhizobia were obtained from nodulated clover at intervals between 3 and 42 months after sowing. Of 456 isolates examined, 53.3% were recognized as inoculum strains but one strain, TA1, was recovered more than 11 times as frequently as the other, UNZ29. At one place, the inoculum was recovered 30 months after sowing but at another it had disappeared after 18 months. There was a significant trend for the proportion of recoverable inoculum strains to diminish with Iapse of time between sowing and isolation. Even in places where natural populations of Rh. Trifolii were small or undetectable, there was no evidence to suggest that the strains introduced as seed inoculant were likely to become permanently established as a large proportion of the nodule bacteria in the soil.