Impact of antagonistic endophytic bacteria on productivity of some economically important legumes

Abstract

Understanding the interactions within and between endophytes and their hosts is still obscure. Investigating endophytic bacterial plant growth-promoting (PGP) traits and co-inoculation effects on legumes' performance is a candidate. Endophytic bacteria were isolated from Vicia sativa root nodules. Such endophytes were screened for their PGP traits, hydrolytic enzymes, and antifungal activities. Sterilized Vicia faba and Pisum sativum seedlings were co-inoculated separately with seven different endophytic bacterial combinations before being planted under sterilized conditions. Later on, several growth-related traits were measured. Eleven endophytes (six rhizobia, two non-rhizobia, and three actinomycetes) could be isolated, and all of them were indole-acetic-acid (IAA) producers, while seven isolates could solubilize phosphorus, whereas three, five, five, and four isolates could produce protease, cellulase, amylase, and chitinase, respectively. Besides, some of these isolates possessed powerful antifungal abilities against six soil-borne pathogenic fungi. Co-inoculation of tested plants with endophytic bacterial mixes (Rhizobia_mix+Actino_mix+non-Rhizobia_mix), (Rhizobia_mix+Actino_mix), or (Rhizobia_mix+non-Rhizobia_mix) significantly improved the studied growth parameters (shoot, root fresh and dry weights, length and yield traits) compared to controls, whereas co-inoculated plants with (Rhizobia_alone), (non-Rhizobia_mix), or (Actino_mix) significantly recorded lower growth parameters. Five efficient endophytes were identified: Rhizobium leguminosarum bv. Viciae, Rhizobium pusense, Brevibacterium frigoritolerans, Streptomyces variabilis, and Streptomyces tendae. Such results suggested that these isolates could be utilized as biocontrols and biofertilizers to improve legumes productivity. Also, co-inoculation with different endophytic mixes is better than single inoculation, a strategy that should be commercially exploited.

Keywords: Antifungal activity; Co-inoculation; Endophytes-legumes interactions; PGP; Plant biomass.