Screening,Identification,and in Vitro Antagonistic Mechanism Analysis of Strains against Phytophthora nicotianae

ZHANG Zhigao; WANG Chuang; YIN Dong; HUANG Xumin; ZHANG Huifen; XU Xinghui; HE Wenqing; ZHANG Hong

doi:10.15933/j.cnki.1004-3268.2026.05.009

Abstract：To screen strains with antagonistic activity against Phytophthora nicotianae and to develop microbial resources for the biological control of tobacco black shank,antagonistic strains were isolated using dilution plating and dual-culture assays.Dominant antagonistic strains were identified based on morphological characteristics,16S rRNA gene,and the sequences of 31 housekeeping genes.Their antimicrobial capacity was further evaluated via broad-spectrum inhibition assays and determination of antibacterial activity in sterile fermentation filtrate.The control efficacy of sterile fermentation filtrates against P.nicotianae was assessed by measuring lesion length on detached leaves.Whole-genome sequencing of the antagonistic strain was performed using next-generation sequencing technology,and the genomic data were analyzed with KEGG database and antiSMASH software.Active antimicrobial compounds were identified by ultra-performance liquid chromatography coupled with high-resolution mass spectrometry(UPLC-MS).Results indicated that a strain of Bacillus cereus YC5 with antagonistic activity against P.nicotianae was successfully isolated and screened.Dual-culture assays demonstrated that strain YC5 exhibited a 74.22％inhibition rate against P.nicotianae,along with antifungal activity against multiple plant pathogenic fungi including the causal agents of tobacco Fusarium wilt and wheat crown rot.In vitro leaf tests confirmed that the sterile fermentation filtrate of YC5 significantly suppressed lesion expansion,demonstrating remarkable antifungal efficacy.Genomic analysis revealed that YC5 possessed a genome size of 5 859 938 bp with 34.779％GC content.Among the 5 824 predicted genes,3 813 were annotated in the KEGG database.antiSMASH predicted 14 secondary metabolite biosynthetic gene clusters,and UPLC-MS identified various upregulated antimicrobial compounds.These findings demonstrated that YC5 exerted its biocontrol activity primarily through the production of diverse antimicrobial substances,which effectively suppressed the growth of P.nicotianae and other phytopathogens,thereby providing protective effects for plants.In summary,strain YC5 has the ability to synthesize multiple antibacterial compounds,and has antagonistic effects on Phytophthora nicotianae and various plant pathogenic fungi.