Differential Potential of Resistance Mechanisms to the Fungicide Metalaxyl in Peppers.

Metalaxyl is one of the main fungicides used to control pepper blight caused by . Metalaxyl resistance of , caused by the long-term intense use of this fungicide, has become one of the most serious challenges facing pest management. To reveal the potential resistance mechanism of to fungicide metalaxyl, a metalaxyl-resistant mutant strain SD1-9 was obtained under laboratory conditions. The pathogenicity test showed that mutant strain SD1-9 had different pathogenicity to different host plants with or without the treatment of metalaxyl compared with that of the wild type SD1. Comparative transcriptome sequencing of mutant strain SD1-9 and wild type SD1 led to the identification of 3845 differentially expressed genes, among them, 517 genes were upregulated, while 3328 genes were down-regulated in SD1-9 compared to that in the SD1. The expression levels of 10 genes were further verified by real-time RT-PCR. KEGG analysis showed that the differentially expressed genes were enriched in the peroxisome, endocytosis, alanine and tyrosine metabolism. The expression of the candidate gene XLOC_020226 during 10 life history stages was further studied, the results showed that expression level reached a maximum at the zoospores stage and basically showed a gradually increasing trend with increasing infection time in pepper leaves in SD1-9 strain, while its expression gradually increased in the SD1 strain throughout the 10 stages, indicated that XLOC_020226 may be related to the growth and pathogenicity of . In summary, transcriptome analysis of plant pathogen strains with different metalaxyl resistance not only provided database of the genes involved in the metalaxyl resistance of , but also allowed us to gain novel insights into the potential resistance mechanism of to metalaxyl in peppers.