Combined application of resistance inducer and Trichoderma control two tobacco soil-borne diseases by regulating the field soil microbial composition

Tobacco black shank (TBS) and tobacco root black rot (TRBR) are two of the most devastating tobacco soil-borne diseases that threaten sustainable tobacco planting. This study investigated the effects of Trichoderma sp. and a resistance inducer (RI) extracted from traditional Chinese medicine, individually or in combination, on the control of TBS and TRBR. The results showed that the application of Trichoderma sp. and RI, individually or in combination, significantly controlled the two soil-borne diseases by significantly affecting the bacterial, but not fungal, Shannon and Simpson diversity indexes. The disease indexes of TBS and TRBR in integrated application management were the lowest, resulting in the highest potassium contents in the tobacco leaves. The control efficacies of TBS and TRBR in the integrated application treatment were 71.52 ± 1.43% and 68.33 ± 0.69%, respectively. The integrated treatment altered the composition of the rhizosphere soil microbial community. The bacterial community, but not the fungal community, of the control treatment was separated from those of other treatments. The relative abundance of bacteria involved in chemoheterotrophy and fermentation in the control treatment increased, whereas that of bacteria involved in nitrification and aerobic ammonia oxidation decreased compared with the other treatments. Importantly, the application of Trichoderma sp. and RI, individually or in combination, clearly increased the relative abundance of saprotrophic fungi in contrast to the control treatment, while decreasing that of pathotrophic fungi. Our study suggests that a suitable integrated application of bioagents and RI has synergistic effects on the suppression of two tobacco soil-borne diseases by altering the rhizosphere microbiome composition in the field.