Ecological studies of root nodule bacteria introduced into field environments part 4 symbiotic properties of rhizobium japonicum and competitive success in nodulation of 2 glycine max cultivars by effective and ineffective strains

Diatloff, A.; Brockwell, J.

Australian Journal of Experimental Agriculture and Animal Husbandry 16(81): 514-521


Accession: 005210752

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R. japonicum strain evaluation experiments with soybean (G. max) confirmed that strain CB1809 was ineffective in N fixation with the related cultivars 'Hardee' and 'Geduld' but was highly effective with 'Hampton'. There were no major symbiotic differences between the cultivars with other strains. Three strains including CB1809 were used, singly, in pairs, or all together, as inocula for 'Hardee' and 'Hampton' in competition studies in the field. The ratio of strains recovered from nodules was used as an index of competitive success. A few nodules contained more than 1 strain. There was a marked host .times. strain interaction in nodulating competitiveness related to symbiotic effectiveness, the order of competitive success being CB1809 > CC709 > CB1795 for 'Hampton' and CC709 > CB1795 > CB1809 for 'Hardee'. With 'Hardee', strain CB1809, although unsuccessful itself in forming nodules in the presence of the other inocula, appeared to suppress nodule formation by those strains. Nodulation by CB1795 in the presence of CB1809 was suppressed to such an extent that plant growth was retarded and not different from that of uninoculated control plants, although CB1795 alone nodulated 'Hardee' abundantly and effectively. There was no evidence that naturally-occurring ineffective R. japonicum posed any competitive threat to the nodulating ability of effective inoculant strains.