Selection of strains of Rhizobium japonicum with exceptional nodule efficiency grown in culture medium with asparagine

Abstract

Five laboratory experiments were conducted with Rhizobium japonicum to elaborate a laboratory test for selecting strains with exceptional nodule efficiency. Exceptional strains grown at 30°C, during 7 to 8 days in liquid medium containing 400 of DL-asparagine were inhibited by more than 60% when compared with the same strain grown in medium containing 100 ppm of DL-asparagine. Normal strains were inhibited much less or not at all in the presence of 400 ppm of DL-asparagine. Thirty four strains were tested and of these 11 were classified as exceptional by the asparagine test. Nine of these strains were known before to produce exceptionally efficient nodules. All strains classified as normal were known as such from greenhouse tests. Sorological tests demonstrated that the 11 exceptional strains originated from only 2 sources. Two strains, originally from Australia, seemed sorologically identical, and the remaining 9, although with varying titers, all gave at least some cross agglutination indicating their relationship with inoculants originally imported from the U.S.A.