Increasing the performance of legume-rhizobia symbiosis

Field survey results suggested an on-going need for rhizobia inoculation in New Zealand pastures ( Spatial patchiness in the size and effectiveness of soil rhizobia populations suggests that often these populations are insufficient or are performing poorly in terms of delivering BNF and feed quality benefits that farmers expect, and that New Zealand needs for on-going productivity, profitability and sustainability of farming systems.

Funding from MBIE and DairyNZ was used to develop state-of-the art methodologies and re-establish New Zealand’s capability in rhizobial research. For many decades there has been little rhizobia research in New Zealand (NZ) relating to the pastoral sector. Grasslanz Technology Limited was brought into the programme as a commercialisation partner and mentor, with the role of advising science on commercialisation needs and engaging potential industry partners.

A key goal of this Legume-Rhizobia programme was to harness the diversity of rhizobia already naturalised in New Zealand soils to provide the new commercial inoculants for the pastoral sector which match modern clover cultivars. Successful rhizobia inoculants must: -

  • Have the ability to effectively form a symbiotic partnership with the legume host and effectively fix N.
  • Compete well against naturalised soil rhizobia for nodule occupancy.

Following establishment of a collection of more than 500 white clover isolates, the programme identified strains that had greater symbiotic effectiveness and competitiveness than the current commercial strain. Initial field trials have confirmed the promising performance of new strains (i.e. 12-38% increases in clover biomass compared to control in field trials).

New formulation techniques have been developed that can sustain rhizobia viability for much longer periods than current commercial seed treatment processes. Improvements to seed coating have increased storage viability from the current 1–2 weeks to 16–20 weeks at 20°C. A new granule formulation increases storage viability even further, out to 6 months at 20°C. Preliminary work on microencapsulation of peat/rhizobia inoculum is also underway. These breakthroughs show that a step-change is now possible in rhizobia storage and thereby delivery of benefits on-farm.

Associated work has revealed the importance of the clover host genetics on effective rhizobia symbiosis. More importantly, quantitative genetic analysis of the interaction has identified that a significant proportion of the interaction is driven by plant genetic factors that can be exploited by plant breeders to develop clover cultivars for enhanced rhizobia interaction. Furthering the genetic analysis by incorporating clover DNA profiles has enabled development of a Genomic Selection prediction tool that is the first available for breeding plants with enhanced symbiotic performance. This development along with enhanced rhizobia strains has major beneficial implications for developing more sustainable pastoral agriculture with reduced nitrogen inputs.

For more information on the research please contact Shengjing Shi

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