Monitoring and characterization of Magnaporthe grisea isolates with decreased sensitivity to scytalone dehydratase inhibitors

Magnaporthe oryzae (Anamorph: Pyricularia oryzae), the causal agent of rice blast disease, is the major pathogen that reduces the yield of rice worldwide. Melanin biosynthesis inhibitors (MBIs) and strobilurins (QoIs) are common fungicides used to control the disease. One hundred and three M. oryzae isolates from different rice-production areas in Taiwan were evaluated for their molecular phylogeny and sensitivity to MBI and QoI fungicides. Molecular phylogenetic analysis showed that all M. oryzae isolates could be classified into nine genetic groups (A-I) based on the DNA polymorphism amplified by CNS1/MP primers. Predominant ones are groups A (72 isolates) and B (15 isolates). Fungicide tests showed that M. oryzae isolates were sensitive to MBIs (carpropamid and tricyclazole) and less sensitive to QoIs (kresoxim-methyl and azoxystrobin). Amplifying the cytochrome b (cyt b) gene revealed that isolates with low sensitivity to QoIs did not correspond with mutation at codon 129 or 143 in the cyt b gene.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Phylogenetic diversity and sensitivity to MBI and QoI fungicides of Magnaporthe oryzae in Taiwan

Hsieh

Chung²,

Chen³

2013

“…8,9) Studies on the mechanism of resistance and characterization of mutant STD proved that a single-point mutation resulted in a one-amino acid substitution (valine [GTG] 75 to methionine [ATG]: V75M) in STD. 10,11) Recently, new STD-inhibitors such as diclocymet 12) and fenoxanil 13) have been developed and registered as anti-blast chemi-cals in Japan.…”

Section: Reviewmentioning

confidence: 99%

Recent Topics on Action Mechanisms of Fungicides

Yamaguchi

Fujimura

2005

When the rice blast pathogen Magnaporthe oryzae recognizes J. Pestic. Sci., 30(2), 67-74 (2005) * To whom correspondence should be addressed. E-mail: yamaism@riken.jp © Pesticide Science Society of Japan Recent Topics on Action Mechanisms of FungicidesIsamu YAMAGUCHI* and Makoto FUJIMURA † Plant Science Center, Tsurumi, Yokohama,, Japan † Faculty of Life Science, University of Toyo, Itakura, Oura-gun, Gunma 374-0193, Japan (Received December 27, 2004) Plant diseases are damaging to crop production in a temperate and humid climate like that of Japan, which has resulted in the development of many excellent fungicides, but wide-spread use of site-specific fungicides can cause pathogens to develop resistance in the field. While all modern fungicides have been developed through extensive safety evaluation, there is deep public concern about their side effects on non-target organisms. Thus there is a growing interest in non-fungicidal disease-controlling agents since they are supposedly specific to target organisms and less likely to cause resistance. Review the surface characteristics of the host plants such as lipophilicity and hardness, its germinating hypha starts differentiating a special cell termed an appressorium to infect the plant. The formation of appressoria involves signal transduction and the expression of many genes. Then, appressorial cells mature by forming a layer of melanin on the innermost part of the cell wall, which affords high osmotic pressure generated inside the cell to penetrate the cuticle layer of the host plant. Thus if melanin biosynthesis is inhibited, the pathogen cannot exert its pathogenicity. In fact, melanin biosynthesis inhibitors (MBIs) are primarily not toxic to the vegetative growth of M. oryzae, but achieve outstanding control of the blast disease in vivo. Actually there are two types of melanin biosynthesis inhibitors; hydroxynaphthalene reductase inhibitors (MBI-R: fthalide, tricyclazole and pyroquilon) and scytalone dehydratase inhibitors (MBI-D: carpropamid, diclocymet and fenoxanil). The buff mutants of M. oryzae were shown to phenotypically resemble the MBI-R-treated wildtype strains and were essentially nonpathogenic to rice plant, which suggested that a melanin biosynthetic pathway is indispensable for the appressoria to obtain infectiosity. RIKEN 1)Carpropamid was developed as a novel potent controlling agent against the rice blast, 2) and enzyme kinetic data showed that carpropamid is a tight-binding competitive inhibitor of scytalone dehydratase (STD), a key enzyme in the biosynthesis of melanin. Its calculated Ki value was 140 pM, which is more than 10 5 times smaller than the Km for scytalone. 3,4) An X-ray analysis of the crystal structure of the STD complex with carpropamid identified interactions that determine the tight-binding 5) as shown in Fig. 1. Three types of interactions were considered important for the binding: (1) a strong hydrogen bond between N131 (Asn 131) and chlorine, (2) two hydrogen bonds mediated by water molecules (WTA) and (3) the i...

“…Isolates resistant to carpropamid were first reported in 2001 in Saga Prefecture, 4) and these isolates showed cross-resistances to other MBI-D fungicides. A single-point mutation in the SH gene (GenBank Accession Number AB004741), which causes the substitution of one amino acid in SH (valine 75 to methionine: V75M; R-mutation), was found in the carpropamid-resistant isolates.…”

mentioning

confidence: 99%

MBI-D resistance management of Pyricularia oryzae using an application program incorporating benomyl

Kimura

Fukuchi

2018

This study's objective was to evaluate the contributions of benomyl and a melanin biosynthesis dehydratase inhibitor (MBI-D) mixture to preventing the re-emergence of MBI-D-resistant Pyricularia oryzae in rice fields. In nursery boxes, applications of diclocymet or mixtures of diclocymet and tiadinil showed low leaf blast incidences, but MBI-D-resistant isolates were re-selected. However, a management program applying both benomyl and MBI-D-related products to nursery box plants prevented the re-emergence of MBI-D-resistant isolates more effectively than the application of only MBI-D-related products.