Survival of white clover rhizobium isolate S11N9 in different delivery systems: assessment of potential for commercialisation

New Zealand pastoral farmers benefit from N2 fixed by the white clover-rhizobium symbiosis, but rhizobia isolates vary widely in their N-fixation ability. Rhizobium leguminosarum S11N9, isolated in NZ, outperforms the current commercial isolate TA1 in laboratory, glasshouse, and field trials. This study investigated production and shelf-life of S11N9 to establish its feasibility as a potential new rhizobium inoculant for white clover. Freeze dried and peat inoculants were prepared for both the S11N9 and TA1 rhizobia. s. Peat inoculants were subsequently formulated into granules and seed coatings using AgResearch technologies. Both isolates produced similar fermentation yields. S11N9 stored as freeze-dried powder at 4 oC survived longer than TA1 (12 vs. 10 months, respectively). Similarly, S11N9 peat inoculant had a longer shelf-life than TA1 when stored at 4 °C (44.7 vs. 21.7 months, respectively) and 20 °C (17.2 vs 9.1 months, respectively). Seeds coated with S11N9 had higher initial loadings than TA1 (107 vs 106 rhizobia/g seeds, respectively) but both declined on seeds stored at 20 °C at a similar rate. Both isolates were stable in peat granules for two months at 20 °C but TA1 dropped below target specifications after three months. Results suggest that isolate S11N9 is a promising alternative to TA1 and has high potential to be developed as a commercial inoculant for white clover.