Vigna spp. Root-Nodules Harbor Potentially Pathogenic Fungi Controlled By Co-habiting Bacteria

This study aimed to isolate, identify, and evaluate the pathogenicity of nodule-borne fungi of asymptomatic Vigna spp. plants, grown in soils from preserved tropical dry forests (Caatinga) areas and identify the occurrence of co-habiting bacteria from these plants, and which have potential to control the co-occurring pathogenic fungi. Fungi and bacteria were isolated from three Vigna species (V. unguiculata, V. radiata, and V. mungo), grown in soil samples collected in five preserved Caatinga areas (Northeastern, Brazil). All fungi and selected bacteria were phylogenetically characterized by the sequencing of ITS1-5.8S-ITS2, and the 16S rRNA gene, respectively. The pathogenicity of fungi in cowpea seeds germination was evaluated throughout the inoculation experiment in Petri dishes and pots containing sterile substrate. The potential of nodule-borne bacteria to control pathogenic fungi in cowpea was assessed in a pot experiment with a sterilized substrate by the co-inoculation of fungi and bacteria isolated from the respective individual plants and soils. The 23 fungal isolates recovered were classified within the genera Fusarium, Macrophomina, Aspergillus, Cladosporium, and Nigrospora. The inoculation of fungi in cowpea seeds reduced the emergence of seeds in Petri dishes and pots. Twenty-four bacteria (Agrobacterium sp., Bradyrhizobium sp., Bacillus sp., Enterobacter sp., Pseudomonas sp., Paraburkholderia sp., and Rhizobium sp.) inhibited the harmful effects of Macrophomina sp. and Fusarium sp., increasing the germination and emergency of potted cowpea plants, highlighting the strains Agrobacterium sp. ESA 686 and Pseudomonas sp. ESA 732 that controlled, respectively, the Fusarium sp. ESA 771 and Macrophomina sp. ESA 786 by 100 and 84.6% of efficiency.