COMPETITIVE ABILITY OF RHIZOBIUM-MELILOTI STRAINS FROM PAKISTAN AND NEPAL FOR NODULATION IN 3 ALFALFA ACCESSIONS

Twenty strains of Rhizobium meliloti Dang. originating from Pakistan a nd Nepal were examined for their competitive ability with a streptomyc in-resistant mutant of commercially available strain 102F51a. Seedling s of three alfalfa (Medicago saliva L. and M. falcata L.) accessions ( Anik, Spredor 2, and Punyal) were grown in agar medium in glass test t ubes. The seedlings were inoculated with 20 individual rhizobial strai ns, and each strain combined with an equal proportion of a streptomyci n-resistant mutant of commercial strain 102F51a. After 10 weeks, plant s were harvested, dried, and weighed. Nodules were counted, and the ba cteroids from the nodules were cultured on yeast-extract mannitol agar medium with and without streptomycin to determine nodule occupancy (p roportion of the nodules on a plant occupied by the particular Pakista ni-Nepali strain). Punyal and Spredor 2 seedlings had a higher total d ry weight and formed greater numbers of nodules than Anik. Inoculated plants had greater dry weights than those in the -N treatment and lowe r dry weights than plants in the +N treatment. Plants inoculated with the 20 rhizobial strains differed in number of nodules and plant dry w eight; however, plants inoculated with single strains did not differ i n dry weight from plants inoculated with their respective strain combi nation with 102F51a. Ten rhizobial strains for Punyal, nine for Spredo r 2, and seven for Anik had greater nodule occupancy than plants inocu lated with commercial strain 102F51a. Consequently, these rhizobial st rains may be beneficial for inoculum production in Pakistan and Nepal.