Identification of strains of Rhizobium leguminosarum

Agriculture in New Zealand relies heavily on mixed pastoral crops. Legumes, such as white clover in particular, are extremely important due to their symbiotic relationship with Rhizobium spp. Many of these pastoral areas can be subject to dry conditions and drought. For Rhizobium spp. it is important to understand what effect desiccating stress can have and whether there is natural variation in the ability of individual strains to tolerate such stress. This could inform the development of better commercial inoculants and enable them to persist better in dry soils. Numerous researchers have investigated the nodulation ability and nitrogen fixation efficacy of R. leguminosarum bv. trifolii when in symbiosis with Trifolium repens (white clover). However, little research has focused on the ability of R. leguminosarum to live in soil as a saprophyte. This study aimed to investigate variation in desiccation tolerance of individual strains of R. leguminosarum bv. trifolli and to determine if it was possible to identify strains with higher tolerance to this stress. Twenty-four strains of R. leguminosarum were randomly selected from a collection obtained from sites that different in their annual soil moisture deficit (SMD). Twelve strains were chosen from three sites with high annual SMD (>100 days; dry sites) and 12 from three sites with low SMD (