Can Potato Plants Be Colonized with the Fungi Metarhizium and Beauveria under Their Natural Load in Agrosystems?

Maksim Tyurin,Viktor V Glupov,Natalia Smirnova,Tatyana Alikina,Olga Yaroslavtseva,Oksana G Tomilova,Vadim Yu Kryukov,Marsel R Kabilov

doi:10.3390/microorganisms9071373

Abstract

Beauveria and Metarhizium fungi are facultative plant endophytes that provide plant growth-stimulating, immunomodulatory, and other beneficial effects. However, little is known about the level of plant colonization by these fungi under natural conditions. We assessed the endophytic colonization of potatoes (Solanum tuberosum) with entomopathogenic fungi at their natural load in soils (102–104 colony-forming units per g). Microbiological analyses of soils and plant organs, as well as a metagenomic analysis of potato roots and leaves, were conducted in three locations in Western Siberia, consisting of conventional agrosystems and kitchen gardens. The fungi were isolated at a relatively high frequency from unsterilized roots (up to 53% of Metarhizium-positive plants). However, the fungi were sparsely isolated from the internal tissues of roots, stems, and leaves (3%). Among the genus Metarhizium, two species, M. robertsii and M. brunneum, were detected in plants as well as in soils, and the first species was predominant. A metagenomic analysis of internal potato tissues showed a low relative abundance of Beauveria and Metarhizium (<0.3%), and the communities were represented primarily by phytopathogens. We suggest that colonization of the internal tissues of potatoes occurs sporadically under a natural load of entomopathogenic fungi in soils. The lack of stable colonization of potato plants with Beauveria and Metarhizium may be due to competition with phytopathogens.

Highlights

Entomopathogenic fungi from the genera Beauveria and Metarhizium are natural regulators of insect populations and are environmentally friendly agents used for pest control [1].The primary reservoirs of these fungi are the soil and plant rhizosphere
We showed in previous work [14] that treating potato tubers pre-planting with Beauveria bassiana and Metarhizium robertsii conidia led to a decrease in Rhizoctonia disease and stimulation of plant growth under field conditions
The colony-forming units (CFUs) count of the fungi was lower in the soils of the conventional agrosystem than in the kitchen gardens, and, in most assays, Metarhizium was more abundant than Beauveria

Summary

Introduction

The primary reservoirs of these fungi are the soil and plant rhizosphere. Many studies have shown the successful colonization of plants after their inoculation with Beauveria and Metarhizium fungi or after the introduction of these fungi into the soil, as recently reviewed by Vega [3] and Bamisile and coauthors [4]. Few studies have focused on quantitative analyses of plant colonization under the natural load of fungi in ecosystems. It seems that natural endophytic colonization of grasses and trees by entomopathogenic fungi occurs infrequently (e.g., [5,6,7])

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