Thiophanate-methyl and its major metabolite carbendazim weaken rhizobacteria-mediated defense responses in cucumbers against Fusarium wilt

This study is led by Dr Xiaohu Wu (State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences). The effect of fungicides on the plant rhizosphere microbiome is a subject of ongoing debate, but whether any alteration in the rhizosphere microbiome could affect plant health is an issue that has not been thoroughly discussed. To address this deficiency, the rhizosphere microbiome of wilt disease–resistant and disease-susceptible cucumber cultivars were analyzed to determine whether (and which) plant-associated microorganisms have a role in disease resistance. Then, whether the fungicides thiophanate-methyl and carbendazim affect the rhizosphere microbiome were assessed, which may contribute to the plant’s immune.

Based on results acquired with both radicle-inoculation and soil-inoculation methods, cultivars Longyuanxiuchun (LYXC) and Shuyan2 (SY2) were identified as being disease resistant, whereas Zhongnong6 (ZN6) and Zhongnong38 (ZN38) were susceptible. The microbiome structure differed substantially between the resistant and susceptible plants, with LYXC and SY2 each having a significantly greater Shannon index than Zhongnong38. These results revealed that the disease-resistant cucumber cultivars recruited more beneficial bacteria, i.e., Bacillus, in their rhizosphere soil; as such, Bacillus was identified as a keystone genus in the microbial co-occurrence network. Thus, the presence of Bacillus may help cucumbers defend against fungal pathogens of the rhizosphere. Bacillus subtilis strain LD15, which was isolated from LYXC rhizosphere soil, could suppress the growth of pathogen growth in vitro and reduce disease severity in pot experiments. Moreover, evidence also confirmed the accumulation of LD1 in the rhizosphere soil of resistant cucumber cultivars. For LYXC, application of thiophanate-methyl or carbendazim altered the microbiome structure, decreased bacterial diversity, and reduced the abundance of Bacillus species. Finally, pot experiments verified that fungicide application decreased the proportion of LD15 in rhizosphere soil. From a microbial perspective, thiophanate-methyl and carbendazim may weaken the rhizobacteria-mediated defense response of cucumbers against cucumber Fusarium wilt. Our findings reveal a role for the rhizosphere microbiome in protecting plants from pathogens and constitute a reference for assessing the ecotoxicological risk of pesticides to non-target soil microorganisms.

See the article:

Thiophanate-methyl and its major metabolite carbendazim weaken rhizobacteria-mediated defense responses in cucumbers against Fusarium wilt

https://link.springer.com/article/10.1007/s42994-024-00181-5