The poor availability of nitrogen is one of the principal factors limiting global biomass. Legumes are vital components of agricultural systems because of their ability to associate symbiotically with root nodule bacteria (RNB) and subsequently fix atmospheric nitrogen to a form that can be utilised by the plant partner. Furthermore, this symbiotic relationship provides available soil nitrogen for subsequent non-leguminous crops. This RNB-legume interaction is affected by a number of environmental factors. Progressive acidification of agricultural soils is one of the big challenges in agriculture as soil acidity negatively impacts legume productivity. One genus of RNB, Sinorhizobium, is particularly acid-sensitive causing a major reduction in Medicago productivity in acidic soils. Due to the importance of Medic pasture production, alternative strains have been captured, and are still being captured, from the genetic pool that display superior acid tolerance characteristics. This presentation will focus on the acid-tolerant species S. medicae (previously known as S. meliloti) and in particular on the previously used commercial inoculant WSM419
