Abstract
The potential for oxathiapiprolin resistance in Phytophthora capsici was evaluated. The baseline sensitivities of 175 isolates to oxathiapiprolin were initially determinated and found to conform to a unimodal curve with a mean EC50 value of 5.61 × 10-4 μg/ml. Twelve stable oxathiapiprolin-resistant mutants were generated by fungicide adaptation in two sensitive isolates, LP3 and HNJZ10. The fitness of the LP3-mutants was found to be similar to or better than that of the parental isolate LP3, while the HNJZ10-mutants were found to have lost the capacity to produce zoospores. Taken together these results suggest that the risk of P. capsici developing resistance to oxathiapiprolin is moderate. Comparison of the PcORP1 genes in the LP3-mutants and wild-type parental isolate, which encode the target protein of oxathiapiprolin, revealed that a heterozygous mutation caused the amino acid substitution G769W. Transformation and expression of the mutated PcORP1-769W allele in the sensitive wild-type isolate BYA5 confirmed that the mutation in PcORP1 was responsible for the observed oxathiapiprolin resistance. Finally diagnostic tests including As-PCR and CAPs were developed to detect the oxathiapiprolin resistance resulting from the G769W point mutation in field populations of P. capsici.
Highlights
Phytophthora capsici is a highly dynamic and destructive plant oomycete pathogen that causes root, fruit, and foliar diseases in a variety of important vegetable crops including pepper, tomato, eggplant, snap, and lima beans, and all cucurbits (Granke et al, 2012; Lamour et al, 2012), which can lead to devastating crop losses under conducive environmental conditions (Hausbeck and Lamour, 2004; Lamour et al, 2012)
The EC50 values of the 175 P. capsici isolates tested ranged from 3.19 × 10−4 to 9.86 × 10−4 μg/ml oxathiapiprolin, and produced a unimodal distribution with a mean of 5.61 × 10−4 μg/ml (Figure 1)
There has only been one other report describing the sensitivity of P. capsici to oxathiapiprolin that only focused on a limited number of isolates (Ji and Csinos, 2015), so the current study of 175 field isolates from 28 provinces throughout China has provided valuable data regarding the sensitivity of wild populations of this pathogen
Summary
Phytophthora capsici is a highly dynamic and destructive plant oomycete pathogen that causes root, fruit, and foliar diseases in a variety of important vegetable crops including pepper, tomato, eggplant, snap, and lima beans, and all cucurbits (Granke et al, 2012; Lamour et al, 2012), which can lead to devastating crop losses under conducive environmental conditions (Hausbeck and Lamour, 2004; Lamour et al, 2012). Oxathiapiprolin has been shown to have substantial activity against a range of plant pathogenic oomycetes, including Pseudoperonospora cubensis, Phytophthora nicotianae, and P. capsici (Ji et al, 2014; Cohen, 2015; Ji and Csinos, 2015), and the results of binding assays and affinity chromatography have shown that the molecular target of oxathiapiprolin is the oxysterol binding protein (OSBP; Andreassi et al, 2013; Pasteris et al, 2016), which is a member of the OSBP-related proteins (ORPs) family. Since the target protein of oxathiapiprolin in P. capsici genome has only been annotated with the protein Id: 564296 (PHYCAscaffold_14:545241–548188), and because the function of this protein in P. capsici or any other oomycetes remains unknown, the current study refers to this protein as PcORP1
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