Isolation and characterisation of endophytic actinobacteria and their effect on the early growth and nodulation of lucerne (Medicago sativa L.).

Background and aims: Endophytic actinobacteria are known to benefit their hosts by improving plant growth and by reducing the severity of soil borne diseases. In this study, their role in enhancing the growth of lucerne and their interaction with its rhizobial symbiosis is examined. Comparison is made between endophytic actinobacteria isolated from wheat plants and isolates from the roots and nodules of four different legume species: lucerne (Medicago sativa L.), field pea (Pisum sativum L.), subterranean clover (Trifolium subterraneum L.) and burr medic (Medicago polymorpha L.). Methods: Two hundred and twenty five isolates of actinobacteria were recovered from the legumes. Five selected legume isolates were compared to five wheat isolates for their effects on rhizobial growth on agar and on the early nodulation and growth of lucerne plants inoculated with Sinorhizobium meliloti strain RRI 128. Results: Co-inoculation with lucerne isolates Streptomyces spp. LuP30 and LuP47B, increased lucerne shoot dry weight at 7 weeks after inoculation by 25 to 35 %, and shoot nitrogen content by 22 to 28 % respectively, compared to plants treated with Sinorhizobium meliloti RRI 128 alone. Conclusions: This study shows that some endophytic actinobacteria have the potential to enhance the lucerne – rhizobia symbiosis.