Diversity and nodulation effectiveness of rhizobia and mycorrhizal presence in climbing dry beans grown in Prespa lakes plain, Greece

Genetic characterization at the species and symbiovar level of indigenous rhizobial isolates nodulating Phaseolus vulgaris in Greece

Phaseolus vulgaris (L.), commonly known as bean or common bean, is considered a promiscuous legume host since it forms nodules with diverse rhizobial species and symbiovars. Most of the common bean nodulating rhizobia are mainly affiliated to the genus Rhizobium, though strains belonging to Ensifer, Pararhizobium, Mesorhizobium, Bradyrhizobium, and Burkholderia have also been reported. This is the first report on the characterization of bean-nodulating rhizobia at the species and symbiovar level in Greece. The goals of this research were to isolate and characterize rhizobia nodulating local common bean genotypes grown in five different edaphoclimatic regions of Greece with no rhizobial inoculation history. The genetic diversity of the rhizobial isolates was assessed by BOX-PCR and the phylogenetic affiliation was assessed by multilocus sequence analysis (MLSA) of housekeeping and symbiosis-related genes. A total of fifty fast-growing rhizobial strains were isolated and representative isolates with distinct BOX-PCR fingerpriniting patterns were subjected to phylogenetic analysis. The strains were closely related to R. anhuiense, R. azibense, R. hidalgonense, R. sophoriradicis, and to a putative new genospecies which is provisionally named as Rhizobium sp. I. Most strains belonged to symbiovar phaseoli carrying the α-, γ-a and γ-b alleles of nodC gene, while some of them belonged to symbiovar gallicum. To the best of our knowledge, it is the first time that strains assigned to R. sophoriradicis and harbored the γ-b allele were found in European soils. All strains were able to re-nodulate their original host, indicating that they are true microsymbionts of common bean.

The Inhibitory Effect of Endophyte-Infected Tall Fescue on White Clover Can Be Alleviated by Glomus mosseae Instead of Rhizobia

In artificial ecosystems, mixed planting of gramineous and leguminous plants can have obvious advantages and is very common. Due to their improved growth performances and stress tolerance, endophyte-infected grasses are considered to be ideal plant species for grasslands. However, endophytic fungi can inhibit the growth of neighboring nonhost leguminous plants. In this study, we chose endophyte-infected and endophyte-free tall fescue (Lolium arundinaceum Darbyshire ex. Schreb.) and clover (Trifolium repens) as the experimental materials to explore whether arbuscular mycorrhizal fungi and rhizobium can alleviate the inhibitory effect of endophyte infection on clover. The results showed that endophytic fungi significantly reduced clover biomass. Arbuscular mycorrhizal fungi inoculation significantly increased the biomass of clover in both endophyte-infected tall fescue/clover and endophyte-free tall fescue/clover systems but the beneficial contribution of arbuscular mycorrhizal fungi was more obvious in the endophyte-infected tall fescue/clover system. Rhizobia inoculation could alleviate the detrimental effect of tall fescue on the growth of clover but did not alleviate the detrimental effect of endophyte infection on the growth of clover.