Differential Potential of Phytophthora capsici Resistance Mechanisms to the Fungicide Metalaxyl in Peppers

Abstract

Metalaxyl is one of the main fungicides used to control pepper blight caused by Phytophthora capsici. Metalaxyl resistance of P. capsici, 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 P. capsici 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 P. capsici. In summary, transcriptome analysis of plant pathogen P. capsici strains with different metalaxyl resistance not only provided database of the genes involved in the metalaxyl resistance of P. capsici, but also allowed us to gain novel insights into the potential resistance mechanism of P. capsici to metalaxyl in peppers.Microorganisms 2020, 8, 278 2 of 17 and has a single site of action on pathogens, Phytophthora can develop resistance as they are susceptible to mutations [3][4][5]. Metalaxyl resistance is mainly found in Phytophthora species such as P. capsici, P. infestans, and P. parasitica. A metalaxyl-resistant strain of P. infestans was discovered in the Netherlands in 1980 [6]. Subsequently, European and American countries reported metalaxyl-resistant strains of P. capsici [7][8][9]. China also reported resistant P. capsici in the 1960s [10]. To date, metalaxyl-resistant strains of P. capsici have been successively found in Anhui, Gansu, and Yunnan Provinces [10][11][12][13].There are some studies on the resistance mechanism of Phytophthora to metalaxyl. Chen et al.[14] revealed two evolutionary pathways of resistance involving the RPA190 gene. The results of their research indicate that changes in the activity of Phytophthora RNA polymerase are important resistance mechanisms. Similar results were also confirmed in P. infestans. The diversity of the RNA polymerase I large subunit sequence of P. infestans plays a key role in its resistance to metalaxyl [15]. The biolog...

Use of metalaxyl against some soil plant pathogens of the class Peronosporomycetes - A review and two case studies

“…This gene, which encodes a large subunit of the RNA polymerase I, seems to be under positive selection. The RNA polymerase activity is significantly inhibited by metalaxyl in sensi-tive strains in comparison to those resistant to this compound, in which only slight inhibition was recorded (Wang et al 2020;. Similar conclusions were also reached by Chen et al (2018).…”

NLR Genes Related Transcript Sets in Potato Cultivars Bearing Genetic Material of Wild Mexican Solanum Species

“…One of the aims of this study was to compile a set of new candidate R genes (File S2) for further investigation. Association of a candidate R gene with the cultivar specific resistance against some pathogen provides opportunity for further study and inclusion in potato breeding programs or other biotechnological approaches for plant improvement (e.g., [3,[79][80][81][82][83][84][85]). Further investigation of candidate R genes may be conducted with the aid of reverse genetics (suppression or increased expression of a targeted gene under testing combined with phenotype evaluation).…”

“…Further detailed investigation of these mRNAs could reveal new NLRs that are potentially useful for the further improvement of S. tuberosum commercial cultivars. P. infestans is rapidly evolving [84] and may gain the resistance to fungicides [85], and some new strains are rather dangerous [86], which makes molecular breeding quite pertinent [87]. The transcriptomic approach has proved itself as a useful tool to reveal new potential R genes for further introgression.…”

HD-ZIP Gene Family: Potential Roles in Improving Plant Growth and Regulating Stress-Responsive Mechanisms in Plants

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