Symbiotic effectiveness of spontaneous antibiotic-resistant mutants of Rhizobium sp Cicer nodulating chickpea (Cicer arietinum)

Spontaneous streptomycin-resistant mutants were isolated from two fast grow ing gum-producing strains Ca85 and Ca401 and from two moderately growing st rains Ca181 and Ca534 of Rhizobium sp. Cicer. The nodulation ability and sy mbiotic effectiveness of the mutants relative to parent strains were evalua ted on chickpea (Cicer arietinum) grown in sterilized chillum jars. Some mu tants of strains Ca85 and Ca401 showed Nod(-) phenotype whereas some mutant s of strains Ca181 and Ca534 showed Nod(+) fix(-) phenotype. Other mutants also showed decreased nodule number and reduction in nitrogenase activity a s well as in shoot dry weight as compared to inoculation with parental stra ins. The results showed that acquisition of streptomycin resistance in Rhiz obium sp. Cicer strains is associated with decreased symbiotic effectivenes s in chickpea, suggesting that antibiotic-resistant mutants first should be analyzed for symbiotic effectiveness before using these mutants for ecolog ical studies or nodulation competitiveness.