Native soil origin influences the symbiotic N fixation effectiveness of chickpea mesorhizobia grown in Australian soils

Experiments conducted under controlled conditions can be poor predictors of the field performance of rhizobial inoculants. In this study, five field experiments were conducted over 2 years to evaluate the symbiotic performance of 12 previously identified strains isolated from Australia and Myanmar soils that had potential to improve chickpea productivity through symbiotic N₂ fixation. Strains collected from Australian soils had more than double the survival on seed and up to three times the nodulation at some experimental sites, compared with strains isolated from Myanmar soils. Generally, the newly isolated strains did not perform better than the current Australian commercial strain, Mesorhizobium ciceri CC1192. Although Myanmar strains had poor nodulation of chickpea plants (below nodule rating 1 in most cases) under Australian field conditions, the plant traits related to growth and symbiosis, such as shoot dry weight (SDW), yield and N fixation, were improved and sometimes equal to the plants inoculated with the Australian strains. Partial correlations showed that plants inoculated with Myanmar strains had greater associations with N fixation measurements (7 plant traits) than nodule number (1 trait), while a symbiotic effectiveness measure of the ratio between N fixation and nodule mass indicated that Myanmar strains are more than 75% more symbiotically efficient compared with the Australian strains. Better seed and soil survival of the Myanmar strains may increase plant nodulation and may lead to a highly effective inoculant strain. This study is one of the first to report increased symbiotic efficiency of N fixation of novel strains compared to a widely utilised commercial chickpea-nodulating strain, on a per nodule basis.