Cross-inoculation groups of rhizobia strains from <i>Arachis hypogaea</i>, <i>Stylosanthes guyanensis</i> and <i>Aeschynomene americana</i> species

Abstract

The genus Arachis, Stylosanthes and Aeschynomene which belong to the Aeschynomeneae tribe are nodulated by several different types of rhizobia. These bacteria form a highly heterogeneous inoculation group which is commonly known as tropical rhizobia. Two experiments were performed in greenhouse with Leonard jars under sterile conditions to evaluate the specificity host range of rhizobia isolated from root nodules of the Aeschynomeneae tribe, as well as its symbiotic efficiency. Twenty rhizobia strains isolated from Arachis hipogaea (cv. BR1), Stylosanthes guyanensis and Aeschynomene americana cultivated in soil samples from the north-east region of Brazil were tested. The isolates were used as inoculant for cowpea (Vigna unguiculata), Macropitilium atropurpureum and peanut (Arachis hypogaea). In a second experiment twenty rhizobia strains were tested in A. hypogaea, S. guyanensis, A. americana, V. unguiculata and M. artropurpureum species. Peanut and Macropitilium atropurpureum were capable of nodulating with all isolates tested but differences were found regarding symbiotic efficiency. On the other hand, only 8 of the isolates were capable of nodulating cowpea. These results  suggest that rhizobial isolates from the Aeschynomene tribe display differences in the host range and should form different inoculation groups.