A High Multi-drug Resistance to Chemically Unrelated Oomycete Fungicides in Phytophthora infestans

Abstract

Mutants of Phytophthora infestans with high resistance to the amidocarbamates iprovalicarb and benthiavalicarb and to the cyanoimidazole cyazofamid were isolated after UV-mutagenesis and selection on media containing one of the above fungicides. In vitro fungitoxicity tests showed that all resistant strains presented a highly reduced sensitivity to both cyazofamid and to the amidocarbamates. Cross-resistance studies with other oomycete fungicides from different chemical groups showed that the mutation(s) for resistance to iprovalicarb (IPV), benthiavalicarb (BVC) and cyazofamid (CZF) also greatly reduced the sensitivity of mutant strains to the phenylamide metalaxyl, acetamide cymoxanil, morpholine dimethomorph, benzamide zoxamide and to chlorothalonil. A lower reduction of sensitivity of mutant strains to the strobilurins azoxystrobin, kresoxim-methyl, pyraclostrobin and trifloxystrobin, azolones famoxadone and fenamidone and to antimycin A was observed. A resistance correlation was not apparent for the dithiocarbamate propineb and phenylpyridinamine fluazinam. Studies of fitness parameters in the wild-type and mutant strains of P. infestans showed that most resistant isolates had significantly reduced sporulation and sporangial germination, but not in the differentiation of sporangia into zoospores. Pathogenicity tests on tomato seedlings showed that most resistant isolates were significantly less pathogenic compared to the wild-type parent strain. However, experiments on the stability of the resistant phenotypes did not show a reduction in resistance when the mutants were grown for more than eleven generations on inhibitor-free medium. This is believed to be the first report of high level multi-drug resistance in fungal pathogens to chemically unrelated fungicides inhibiting different sites of cellular pathway.

Reduced efficacy of fluazinam against Phytophthora infestans in the Netherlands

“…Also mutants of P. infestans resistant to a range of fungicides did not show a reduced sensitivity to fluazinam (Ziogas et al 2006). These surveys all used different fungitoxicity tests to determine whether changes in sensitivity had occurred.…”

Biocontrol of PGPR strain Bacillus amyloliquefaciens Ba168 against Phytophthora nicotianae on tobacco

“…Results show that the disease control efficacy of strain Ba168 is lower than MPA in two tobacco varieties, but higher than Dimethomorph preparations. Dimethomorph, Propamocarb, Azoxystrobin all have been applied in TBS control for many years, drug-resistant oomycetes emerge (80). Despite that, Dimethomorph is more effective than Propamocarb, Azoxystrobin when separately used (80).…”

“…Dimethomorph, Propamocarb, Azoxystrobin all have been applied in TBS control for many years, drug-resistant oomycetes emerge (80). Despite that, Dimethomorph is more effective than Propamocarb, Azoxystrobin when separately used (80). But, in this study, we show that Mixture of Propamocarb and Azoxystrobin is better than Dimethomorph used alone.…”

Baseline sensitivity and resistance risk assessmemt of Rhizoctonia cerealis to thifluzamide, a succinate dehydrogenase inhibitor

“…Fungicide-resistant mutants can survive in the environment in the pressure of the fungicide they are resistant to, but in most cases, this mutation change leads to a fitness penalty for the pathogen, resulting in the mutants being less aggressive and competitive in nature [36]. This can help to postpone the development of resistance in the natural populations in field.…”