Rhizosphere soil microbial communities under foxtail millet continuous and rotational cropping systems and their feedback effects on foxtail millet downy mildew suppression

Foxtail millet downy mildew caused by obligate parasitic Oomycetes Sclerospora graminicola (Sac.) Schrot greatly reduces the foxtail millet yield. The purpose of this study was to find the specific bacterial and fungal populations that might be involved in the suppression of foxtail millet downy mildew. Bacterial and fungal communities in foxtail millet rhizosphere soils under two different cropping systems were compared, with high-throughput Illumina sequencing technology. Compared with foxtail millet continuous cropping system, the foxtail millet-soybean-potato (Si-Gm-St) rotational cropping system showed the lower foxtail millet disease incidence (3.00%) and higher yield (3892.00 kg ha(-1)). The Bacteria/fungi value of foxtail millet rhizosphere soil in Si-Gm-St rotational cropping system was higher than that in foxtail millet continuous cropping system. The enzyme activities of phosphatase, urease and sucrase showed the same trend. Lower abundance of pathogenic microorganisms and higher abundance of plant growth-promoting microorganisms were observed under the Si-Gm-St rotational cropping system. There was a significant negative correlation between the relative abundances of Nocardioides, Devosia, Neorhizobium and Pseudomonas and foxtail millet downy mildew incidence, but an extremely significant positive correlation between the relative abundances of Fusarium, Cylindrocarpon, Ilyonectria, Thermoascus, Myrothecium and the disease incidence (P < 0.01). Different foxtail millet cropping systems were found to occupy different rhizosphere bacterial and fungal communities, and high bacterial diversity and low fungal diversity might be associated with the effective mitigation of downy mildew.