Chickpeas are notoriously fussy about their choice in rhizobia partner, but a new research effort is looking to find a better match to enhance and expand chickpea production.
With investment from the Grains Research and Development Corporation (GRDC), three regional Nitrogen Fixation Program (NFP) projects are focusing on extending the adaptation and reliability of pulse crops, including chickpeas, through releasing more-robust inoculant strains and improving inoculation practices.
The NFP brings together research teams from Legume Rhizobium Sciences at Murdoch University, Curtin University, the WA Department of Primary Industries and Regional Development, the South Australian Research and Development Institute, the University of Adelaide and the New South Wales Department of Primary Industries.
Chickpea nitrogen fixation efficiency is reported to be lower than other pulses, and nodulation is reduced in acidic WA soils. The inoculant strain (Group N), Mesorhizobium ciceri, originally from Israel and introduced as the inoculant in the 1970s, forms an association specifically with chickpea. This inoculant strain has not been updated for 40 years.
The Murdoch University NFP team, led by Dr Ron Yates, is taking a two-pronged approach to learn about the genetics of rhizobia specific for chickpeas, using this knowledge to find a better strain to enhance and expand chickpea production.
Dr Yvette Hill from Murdoch University has undertaken environmental surveys to assess the status of variability of chickpea rhizobia in WA, more recently extending to Queensland and NSW.
"Nitrogen fixed by rhizobia is fundamental to sustainable farming practices and healthy productive pulse crops provide many benefits in cropping sequences, not only in the provision of nitrogen but as a disease and weed break," Dr Hill says.
"There are thousands of strains of rhizobia that can nodulate and potentially fix nitrogen with each pulse host. However, the amount of nitrogen fixed can vary substantially, depending on the compatibility of legume host and rhizobial strain."
Inoculant rhizobia strains are members of a number of bacterial genera, categorised into inoculant groups based on the legumes they nodulate. Some groups are quite promiscuous and can form symbiotic relationships with several different pulses.
"We know that Mesorhizobium are particularly adept at genetic change but we needed to learn just to what extent," Dr Hill says.
To this end, Dr Hill has conducted surveys of Mesorhizobium species nodulating chickpea across WA, Queensland and NSW cropping environments using genome sequencing techniques to track genetic differences.
"We're finding a range of differences as these bacteria are able to exchange the sections of their DNA that encode the ability to symbiotically fix nitrogen.
"We have been able to identify strains evolved in Australian soils that may be superior to the present Group N strain used to inoculate chickpeas and they are now being evaluated in field trials in WA, SA and NSW."
Potential new rhizobia strains need to be tested for their compatibility with any new chickpea varieties and in target production environments.
A number of these newly evolved Mesorhizobium strains that had been collected from WA acidic soils during the surveys are being trialled at Goomalling with the chickpea variety CBA Captain, after showing promising results from an acidic soil establishment trial conducted at Northam during 2020-21.
Further testing of new chickpea rhizobia strains will be required to determine their compatibility with farming system practices and new cultivars being developed.
Dr Hill has set up several field trials at South Burracoppin in acidic soils where chickpeas have not previously been grown. Treatments include inoculated chickpeas, uninoculated chickpeas and wheat. The influence of these treatments is being monitored for changes in the evolution of chickpea-nodulating strains over time. Dr Hill is planning to extend this research for the next decade.
"Essentially, it is a more-controlled version of the evolution of the strain we are seeing across Australia but will give us greater understanding of how inoculant strains influence the population of nodulating bacteria in our soils," Dr Hill says.
Any new rhizobia strains will be captured and stored in the purpose-built International Legume Inoculant Genebank supported by GRDC at Murdoch University.
Nitrogen fixation was in the spotlight last week at the Australian Nitrogen Fixation Conference, held in Fremantle from November 6-8 and sponsored by GRDC.
