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Development of Fungicide Cross Resistance in Helminthosporium solani Populations from California

M G Cunha1, D M Rizzo1

  • 1Department of Plant Pathology, University of California, Davis 95616.

Plant Disease
|March 1, 2019
PubMed

Insights

Potato fungicide resistance is widespread in California Helminthosporium solani populations. Most isolates resistant to thiophanate-methyl also resist benomyl, linked to a specific β-tubulin gene mutation.

Area of Science:

  • Plant Pathology
  • Fungal Genetics
  • Agricultural Science

Background:

  • Potato"s silver scurf pathogen, Helminthosporium solani, is prevalent in California.
  • Fungicide resistance, particularly to thiophanate-methyl, is a growing concern in agricultural settings.
  • Previous fungicide exposure in Tulelake, California, primarily involved thiophanate-methyl.

Purpose of the Study:

  • To investigate the fungicide resistance profiles of Helminthosporium solani populations in California.
  • To identify the genetic basis of thiophanate-methyl resistance in these isolates.
  • To develop a molecular diagnostic tool for detecting fungicide resistance.

Main Methods:

  • Fungicide sensitivity assays were performed on 238 H. solani isolates.
  • The β-tubulin gene was sequenced to identify mutations associated with resistance.
  • A polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) assay was developed and validated.

Main Results:

  • 182 out of 238 isolates were resistant to both thiophanate-methyl and benomyl; 56 were sensitive to both.
  • A specific mutation (glutamic acid to alanine at codon 198) in the β-tubulin gene was strongly associated with thiophanate-methyl resistance.
  • The PCR-RFLP assay accurately identified resistant and sensitive isolates with 100% correlation to phenotypic data.

Conclusions:

  • Widespread resistance to thiophanate-methyl and benomyl exists in California H. solani populations.
  • A specific β-tubulin mutation is a reliable marker for thiophanate-methyl resistance.
  • The developed PCR-RFLP assay provides an efficient tool for monitoring fungicide resistance in H. solani.
Keywords:
benzimidazolepotato tuber diseasesilver scurf

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