COMPETITIVENESS OF NATIVE BRADYRHIZOBIUM-JAPONICUM STRAINS IN 2 DIFFERENT SOIL TYPES

Interstrain competitiveness is a key factor affecting the performance of rhizobium inoculant. In the present study five native strains of Br adyrhizobium japonicum, namely SSF 4, SSF 5, SSF 6, SSF 7 and SSF 8, w ere assessed for their competitiveness in nodulating soybean using ser ological methods. The strains were inoculated individually or with the type strain USDA 110 at a 1:1 ratio. Nodule occupancy determined by i mmunofluorescence and dot immunoblot assay revealed that under in vitr o conditions SSF 8 is more competitive than USDA 110 whereas the other s were less competitive. The competitive ability of these strains was also estimated in pot culture in the field. In red soil both SSF 8 and USDA 110 were equally competitive whereas in black soil SSF 8 compete d better than USDA 110 and produced more nodules. In a black soil fiel d trial using a randomized block design, USDA 110 or SSF 8, when inocu lated alone, occupied the majority of the nodules and enhanced nodule dry weight and shoot biomass. SSF 8 was more competitive when the stra ins were co-inoculated.