Streptomyces pactum Act12 controls tomato yellow leaf curl virus disease and alters rhizosphere microbial communities

Abstract

Actinomycetes comprise a large group of biocontrol bacteria, yet no studies have reported on their effects against plant virus diseases. Here, we evaluated the control effects and the possible mechanisms of Streptomyces pactum Act12 against tomato yellow leaf curl virus disease (TYLCD) through field and pot experiments. We also analyzed changes in plant growth and rhizosphere microbial community composition following the application of Act12. The pre-inoculation of soil with the Act12 agent enhanced the activities of peroxidase and chitinase while upregulating the expression of genes related to plant systemic resistance (PR-1 and SIPI-II) and specific TYLCD resistance (SIPer1 and SIVRSLip) in tomato leaves under field conditions. The effects of Act12 at inducing a decline in TYLCD severity and promoting plant growth were deemed satisfactory in all three field experiments. In the pot experiments, Act12 induced a decline in the viral DNA level and an enhancing of peroxidase, polyphenoloxidase, and phenylalanine ammonia lyase activities in tomato leaves. Additionally, Act12 treatment reduced the accumulation of H2O2 and O·−2, increased the levels of salicylic and jasmonic acids, and upregulated the expression of genes related to plant resistance and RNA interference in tomato leaves. Applying Act12 also increased the diversity of bacteria and the abundance of potential beneficial microbes (e.g., Trichoderma and Bacillus) in the root-zone and root-surface soils, resulting in modular differentiation of co-occurrence networks. In conclusion, applying the S. pactum Act12 agent reduced TYLCD severity and promoted plant growth in tomato. Whether the changes of resistance-related gene expression and rhizosphere microbial community composition contribute to TYLCV resistance needs to be further investigated.