I carried out glasshouse and laboratory work at Murdoch University, with Zimbabwean isolates of soyabean root nodule bacteria that I collected from soils with a history of inoculation in Zimbabwe. I worked with a total of 137 soyabean root nodule bacteria isolates that were revealed by molecular methods to be drawn from the four species, Bradyrhizobium diazoefficiens, B. elkanii, B. japonicum and B. ottawaense. Although sites had been inoculated with B. diazoefficiens, they were dominated by the indigenous B. elkanii. Indigenous rhizobia are expected to exhibit greater environmental fitness in Zimbabwean soils than the exotic strains.
In 2015, I returned to full time employment in Zimbabwe where I work at the Soil Productivity Research Laboratory, involved with rhizobia inoculant production and promotion, soil testing and fertilizer recommendations, and integrated soil fertility management research. In 2016-2017, I selected the best two isolates from each of the four Bradyrhizobium species identified in glasshouse work at Murdoch as potential inoculant candidates and assessed their capacity for elite nitrogen fixation under field conditions at three sites in Zimbabwe. Results show that the best strains from each of the four species elicit high nitrogen fixation with a broad range (three) of commercial soyabean varieties available in Zimbabwe. We found that indigenous rhizobia, particularly B. elkanii were superior to the inoculant strains with respect to nodulation under field conditions. Based on biomass accumulation and nitrogen uptake, we recommend strains from the B. japonicum and B. diazoefficiens species for use in inoculant production.
I have previously reported on all this work and I am now working on publishing my research in peer-reviewed journals and submitting the thesis for examination.
Mazvita Chiduwa, Murdoch University, Australia, supervised by Julie Ardley, John Howieson, Paul Mapfumo, Graham O’Hara and Ravi Tiwari