Impact of Azoxystrobin and Rhizoctonia solani on Soil and Rhizosphere Microbiomes of Table Beet in New York

Table beet production in New York relies on azoxystrobin applied in-furrow to control root disease caused by the fungal pathogen, Rhizoctonia solani. Field trials were conducted in each of two years to evaluate the effect of azoxystrobin and post-emergent R. solani inoculation on microbial communities in bulk soil and the table beet rhizosphere. Soil samples were collected at the 2 to 4 leaf stage and root maturity from plots receiving in-furrow azoxystrobin, post-emergent R. solani inoculum, in-furrow azoxystrobin and post-emergent R. solani inoculum, or nontreated controls. Illumina sequencing of the 16S rRNA gene and the internal transcribed spacer region found treatment had no effect on alpha or beta diversity of the microbial communities. Sample type (rhizosphere and bulk soil) was the most important factor of community composition. The most abundant bacterial and fungal phyla were Proteobacteria and Ascomycota. Relative abundance in the bacterial community was not affected by treatment, sample type, or sampling time. Relative abundance of the fungal class, Saccharamycetes, was increased in the table beet rhizosphere. Alpha diversity was negatively correlated with Rhizoctonia incidence and severity in one year. There were few consistent relationships between Rhizoctonia incidence and severity and microbial taxa abundance. The abundance of Acidobacteria and Bacteroidota was negatively correlated with R. solani, and both phyla were enriched in the table beet rhizosphere. The identification of these and other microbial taxa associated with low Rhizoctonia incidence and severity may inform studies into microbiome-mediated management of R. solani and other soilborne plant pathogens.