Interactions Between Micromonospora and Arbuscular Mycorrhizal Fungi

Abstract

Micromonospora is a Gram-positive bacterium that can be isolated from nitrogen-fixing root nodules from healthy leguminous plants and promotes plant growth. Selected strains of Micromonospora isolated in our laboratory from alfalfa root nodules showed in vitro antifungal activity against several pathogenic fungi. Moreover, root inoculation of tomato plants with these Micromonospora strains effectively reduced leaf infection by the fungal pathogen Botrytis cinerea, despite temporal and spatial separation between the inoculation of both microorganisms. Although Micromonospora improves plant growth and has antifungal activity against plant pathogens, the interaction between Micromonospora and AM fungi has not been studied before. Thus, the aim of the study was to work on the understanding of this interaction. The results obtained allow us to conclude that Micromonospora strains ALFpr18c and ALFb5 did not adversely affect the colonization and development of the AM fungi R. irregularis and F. mosseae on plant root. Micromonospora strain ALFpr18c increased the beneficial effect of the AM fungi on shoot dry weight of alfalfa and tomato when the AM fungi were established first on the roots. Therefore, it is possible to use Micromonospora ALFpr18c combined with AM fungi to improve plant growth. Micromonospora strains should be considered excellent plant probiotic bacteria as they combine plant growth-promoting activity with both direct antifungal activity against plant pathogens and the ability to prime plant immunity and did not adversely affect the colonization and development of the AM fungi.