Mutually beneficial legume symbioses with soil microbes and their potential for plant production

Abstract

Legumes develop different mutually beneficial symbioses with soil microbes, such as arbuscular mycorrhizal (AM) fungi, nodule bacteria and plant growth promoting bacteria. Symbioses supply the plants with nutrients (predominantly with nitrogen and phosphorus), protect them from pathogens and abiotic stresses and improve soil microbial biodiversity and fertility. The synergistic activity of beneficial soil microbes (BSM) on the plants has great importance for the use of multi-component symbiotic systems in low-input sustainable environmentally-friendly agrotechnologies. However, the complex nature of the AM symbiosis when in a multi-component symbiosis (plant-fungus-bacteria) creates complications for the fungus to produce AM fungal propagules and poses questions (a) about the effectiveness of the fungus per se in interactions with the plants, without associates, and (b) about the necessity of using sterile/axenic conditions for the production of the AM fungi based inoculants because of any mixing and competition by microbes from the inoculants with the local soil microbial consortia. The legume genes controlling interactions with BSM (including genes responsible for effectiveness of such interactions) should be considered as a united genetic system. The plant genome is more stable than that of microbes and therefore crop plants should select beneficial microbes and control the effectiveness of the whole plant-microbe system in the field for the benefit of the crop and therefore of human beings. There is clearly a need to breed legume crops with improved performance under sustainable conditions involving interactions with BSM and optimising the use of agrochemicals.