Effect of azoxystrobin on tobacco leaf microbial composition and diversity

Abstract

Azoxystrobin, a quinone outside inhibitor fungicide, reduced tobacco target spot caused by <i>Rhizoctonia solani</i> by 62%, but also affected the composition and diversity of other microbes on the surface and interior of treated tobacco leaves. High-throughput sequencing showed that the dominant bacteria prior to azoxystrobin treatment were <i>Methylobacterium</i> on healthy leaves and <i>Pseudomonas</i> on diseased leaves, and the dominant fungi were <i>Thanatephorous</i> (teleomorph of <i>Rhizoctonia</i>) and <i>Symmetrospora</i> on healthy leaves and <i>Thanatephorous</i> on diseased leaves. Both bacterial and fungal diversity significantly increased 1 to 18 days post treatment (dpt) with azoxystrobin for healthy and diseased leaves. For bacteria on healthy leaves, the relative abundance of <i>Pseudomonas</i>, <i>Sphingomonas, Unidentified-Rhizobiaceae</i> and <i>Massilia</i> declined, while <i>Methylobacterium</i> and <i>Aureimonas</i> increased. On diseased leaves, the relative abundance of <i>Sphingomonas</i> and <i>Unidentified-Rhizobiaceae</i> declined, while <i>Methylobacterium, Pseudomonas</i> and <i>Pantoea</i> increased. For fungi on healthy leaves, the relative abundance of <i>Thanatephorous</i> declined, while <i>Symmetrospora</i>, <i>Sampaiozyma</i>, <i>Plectosphaerella</i>, <i>Cladosporium</i> and <i>Cercospora</i> increased. On diseased leaves, the relative abundance of <i>Thanatephorous</i> declined, while <i>Symmetrospora</i>, <i>Sampaiozyma</i>, <i>Plectosphaerella</i>, <i>Cladosporium</i>, <i>Phoma</i>, <i>Pantospora</i> and <i>Fusarium</i>, increased. Compared to healthy leaves, azoxystrobin treatment of diseased leaves resulted in greater reductions in <i>Thanatephorous</i>, <i>Sphingomonas</i> and <i>Unidentified-Rhizobiaceae</i>, a greater increase in <i>Methylobacterium</i>, and similar changes in <i>Phoma, Fusarium</i>, <i>Plectosphaerella</i> and <i>Cladosporium</i>. Azoxystrobin had a semi-selective effect altering the microbial diversity of the tobacco leaf microbiome, which could be due to factors, such as differences among bacterial and fungal species in sensitivity to quinone outside inhibitors, ability to use nutrients and niches as certain microbes are affected, and metabolic responses to azoxystrobin.