Groundnut nitrogen fixation by three serologically and morphologically distinct rhizobia

Abstract

Three cowpea miscellany rhizobia, a commercial strain (TAL 309) and two field isolates from Sudan (Wad Medani and Kadugli strains), were chosen for detailed studies because they could be separated by serological or morphological characteristics. The strains were screened in the greenhouse on three groundnut ( Arachis hypogaea L.) cultivars, “Ashford” and “MH383” (both Virginia types), and “Barberton” (a Spanish type). Whenever the TAL 309 strain was included in inoculum mixtures, it consistently occupied the majority of nodules with all three groundnut cultivars. Although significant differences were found in top dry-matter weights, color ratings, nitrogenase activities, and total nodule number among the three cultivars tested, there were no host-genotype-by-strain interactions either in growth measurements or in nodule occupancy. Correlation matrices indicated that several of the measures made could serve as reliable indicators of rhizobial efficiency. Both top dry-matter weight and plant color, and top dry-matter weight and C 2H 2 reduction were related at the 0.001 level of probability.