Tripartite Relationships in Legume Crops Are Plant-Microorganism-Specific and Strongly Influenced by Salinity

This study investigated the effects of specific strains of two arbuscular mycorrhizae fungi (AMF) (Rhizophagus irregularis and Claroideoglomus claroideum) and of two plant growth-promoting bacteria (PGPB) (Rhizobium leguminosarum and Burkholderia spp.), supplied either individually or as combination of a mixture of both arbuscular mycorrhizae fungi with each bacteria on root morphology, growth and fresh grain yield in pea (Pisum sativum L.) plants. Inoculated and non-inoculated pea plants were subjected to two levels of salinity (0 and 50 mM) by the addition of sodium chloride into tap water. Prior to fresh grain harvesting the morphology of root system was analyzed and the dry matter of roots and shoots were individually measured in randomly selected plants. Fresh pods were individually harvested per each plant; fresh (green) grains were separately counted and weighted per each pod at each individual plant, and the average grain weight was calculated by dividing total grain weight of plant with the respective number of green grains. The raise of salinity in the irrigation water strongly diminished the growth of pea plants by significantly reducing weight, length, surface area and root volume of pea plants. The relationships of pea plants with beneficiary fungi and bacteria were specific to each microorganism and highly depended on the environment. We found that under saline conditions, Rhizophagus irregularis provided a better vegetative growth and a higher yield than Claroideoglomus claroideum. Although, single application of Burkolderia spp. provides a better vegetative growth than single application of Rhizobium leguminosarum the best results, in terms of growth and harvested yield, were still obtained by combined application of AM fungi with Rhizobium leguminosarum. This combination was able to sustain the average grain weight at the level of non-saline plants and provided a significantly higher yield than the control plants