Ecological relationships between resident and inoculant rhizobia in pulse crop
Nitrogen is a key nutrient which influences plant growth and function. Some plants interact with rhizosphere microbes to assimilate atmospheric nitrogen in a plant –usable form. Legume-rhizobium symbiosis is an example for a symbiotic interaction where atmospheric nitrogen (N2) is converted enzymatically to ammonia/ ammonium (NH3/ NH4+) by rhizobial bacteria. Moreover, rhizobia and legumes co-evolved together with a strong mutualistic stability. Rhizobial nitrogen fixation is limited due to several biotic and abiotic factors. High temperature, low moisture content and soil acidity are some of the limiting abiotic factors where as competition between ineffective indigenous populations and introduced rhizobial strains is one of the major biotic factor which limit legume nitrogen fixation significantly. Since the studies on inter-strain interactions are lacking to date, there is a need to understand the various functions of inter-strain interactions of rhizobia associated with legume hosts.
The proposed work will look at the inter-strain competition of Rhizobium leguminosarum bv. viciae with respect to Pisum sativum L. (field pea) symbiosis. P. sativum L. (Field pea) is known to be one of the largest legume crops in Australia, with an average annual production of 0.3 million tonnes and thus it contributes significantly to N-fixation within Australia. This project will address how these interactions affect the overall nitrogen fixation efficiency of field pea and whether the host plants have discrimination of carbon and oxygen across rhizobia which might affect their fitness and mutualistic stability. Ultimately this study will provide new insights of rhizobial interactions on legume symbiosis by filling the research gap highlighted above.
A/professor Jeff Powell, Dr. Catriona Macdonald and A/Professor Pauline Mele