Selection of rhizobial strains differing in their nodulation kinetics under low temperature in four temperate legume species

Background

Winter climate change including frequent freeze-thaw episodes and shallow snow cover will have major impacts on the spring regrowth of perennial crops. Non-bloating perennial forage legume species including sainfoin, birdsfoot trefoil, red clover, and alsike clover have been bred for their adaptation to harsh winter conditions. In parallel, the selection of cold-tolerant rhizobial strains could allow earlier symbiotic nitrogen (N) fixation to hasten spring regrowth of legumes.

Methods

To identify strains forming nodules rapidly and showing high N-fixing potential, 60 rhizobial strains in association with four temperate legume species were evaluated over 11 weeks under spring soil temperatures for kinetics of nodule formation, nitrogenase activity, and host yield.

Results

Strains differed in their capacity to form efficient nodules on legume hosts over time. Strains showing higher nitrogenase activity were arctic strain N10 with sainfoin and strain L2 with birdsfoot trefoil. For clovers, nitrogenase activity was similar for control and inoculated plants, likely due to formation of effective nodules in controls by endophyte rhizobia present in seeds.

Conclusions

Selection based on nodulation kinetics at low temperature, nitrogenase activity, and yield was effective to identify performant rhizobial strains for legume crops. The use of cold-tolerant strains could help mitigate winter climatic changes.