Resilience of the Natural Phyllosphere Microbiota of the Grapevine to Chemical and Biological Pesticides

Abstract

The phyllosphere is colonized by complex microbial communities, which are adapted to the harsh habitat. Although the role and ecology of nonpathogenic microorganisms of the phyllosphere are only partially understood, leaf microbiota could have a beneficial role in plant growth and health. Pesticides and biocontrol agents are frequently applied to grapevines, but the impact on nontarget microorganisms of the phyllosphere has been marginally considered. In this study, we investigated the effect of a chemical fungicide (penconazole) and a biological control agent (Lysobacter capsici AZ78) on the leaf microbiota of the grapevine at three locations. Amplicons of the 16S rRNA gene and of the internal transcribed spacer were sequenced for bacterial and fungal identification, respectively. Pyrosequencing analysis revealed that the richness and diversity of bacterial and fungal populations were only minimally affected by the chemical and biological treatments tested, and they mainly differed according to grapevine locations. Indigenous microbial communities of the phyllosphere are adapted to environmental and biotic factors in the areas where the grapevines are grown, and they are resilient to the treatments tested. The biocontrol properties of phyllosphere communities against downy mildew differed among grapevine locations and were not affected by treatments, suggesting that biocontrol communities could be improved with agronomic practices to enrich beneficial populations in vineyards. Plants support a complex micro-ecosystem, and they host distinct bacterial communities on and inside various plant organs (1). The aerial part of plants (phyllosphere) is normally colonized by a variety of bacteria, filamentous fungi and yeasts (2). Microbial phyllosphere communities are complex and composed by many uncultured microorganisms (2, 3), which are adapted to the harsh environmental conditions (4, 5). In particular, microbial epiphytes of the phyllosphere are exposed to the atmosphere and must deal with direct UV radiation, wide fluctuations in temperature, low water availability, and limited access to nutrients (2,6). Therefore, the composition of phyllosphere communities could be affected by environmental factors, such as UV radiation, air pollution, and nitrogen fertilization, as well as by biotic factors, such as plant species and invading microorganisms (6-8). Moreover, the phyllosphere is an open system and microbes can invade plant leaves by migration from the atmosphere, soil, other plants, insects, and animals (9).The phyllosphere has been less intensively studied than the rhizosphere and has received considerable attention in recent years (1). The interest in phyllosphere microbiology was initially driven by investigations into plant pathogens, but most phyllosphere-colonizing microorganisms live as commensals and/or mutualistic symbionts on their host plants (2,4,6). Phyllosphere communities are involved in functional processes as large in scale as the carbon cycle, nitrogen fixation, and degradation of organic pollu...

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