Symbiotic Effectiveness, Rhizosphere Competence and Nodule Occupancy of Chickpea Root Nodule Bacteria from Soils in Kununurra Western Australia and Narrabri New South Wales Australia.

Root nodule bacterial isolates from field-grown chickpea were evaluated in glasshouse and field experiments based on infectivity, relative symbiotic effectiveness, nodule occupancy, plant yield and survivability in the soil rhizosphere for their use as inoculants to enhance chickpea production in Western Australia. Compared to the Australian commercial chickpea inoculant strain Mesorhizobium ciceri sv. ciceri CC1192, 10 new strains were 'fast' growers, averaging 72 h to grow in culture at 28 °C. The relative symbiotic effectiveness (RSE%) of the new strains in field experiments determined by shoot weight ranged from 77 to 111% in the Desi genotype (var. Kyabra) and 83 to 102% in Kabuli (var. Kimberley Large). Kyabra yielded greater output (2.4-3 t/ha) than Kimberley Large (1.2-1.8 t/ha), with mean 100 seed weights of 23 and 59 g, respectively. The rhizobial strains living in the rhizosphere presented a higher competitive ability for nodule occupancy than those in the bulk soil. Tukey's multiple comparisons test showed no significant differences between the nodule occupancy ability of the introduced strains (i.e., 3/4, 6/7, N5, N300, K66, K188 and CC1192) in either Kyabra or Kimberley Large (p = 0.7321), but the strain competitiveness with each cultivar differed (p < 0.0001) for some of the test strains. Strains N5, N300, K72 and 6/7 were the top contenders that matched or beat CC1192 in nitrogen fixation traits. These findings show that new rhizobial strains derived from naturalized soil populations exhibited better adaptability to local soil conditions than CC1192.