Effectiveness of Ensifer meliloti as beneficial microorganism depends on barley’s genotype and specific environmental factors

Abstract Background and aims Inoculation with plant beneficial microorganism (BM) may enhance plants’ resilience, their growth and decrease the susceptibility to pathogens and diseases. Good example of a beneficial microorganism is Ensifer meliloti ( Sinorhizobium meliloti ) Rm2011, a N -acyl homoserine lactones producing bacterium known for its beneficial effects on different plants in greenhouse or in vitro settings. Aim of this study was to transfer these findings to field conditions, a crucial step in development of applications for sustainable agriculture. Methods In this report, we present results from a four-year-long field experiment, in which genetically diverse spring barley ( Hordeum vulgare ) lines were inoculated with E. meliloti . The susceptibility of barley to naturally occurring leaf pathogens and diseases (e. g. leaf rust, mildew, chlorosis and necrosis) was monitored throughout the vegetative season. In addition, during the growth season, environmental parameters like air and soil temperatures, humidity and rainfall were recorded. Results We demonstrate that barley responsiveness to inoculation with BM, referred to here as primability , depends on its genetic background. Both primable and non-primable barley lines were identified. Our results indicate moreover that upon field conditions, air temperature and air humidity, modulate the potential responsiveness of barley to E. meliloti in primable lines. Conclusion This study shows that a plant protective application based on inoculation with E. meliloti should consider multifactorial interactions among the plant genotype, the pathogen and the beneficial microorganism. Furthermore, the environment can have an influence on the effectiveness of the inoculation.