BACKGROUND Metyltetraprole is a new fungicide with a unique tetrazolinone‐moiety and a similar side chain to a known quinone outside inhibitor (QoI), pyraclostrobin. In this study we describe a unique bioactivity of metyltetraprole on QoI‐resistant strains of Zymoseptoria tritici and Pyrenophora teres . RESULTS Metyltetraprole exhibited potent antifungal activity against Ascomycetes; it was especially effective against Z. tritici and P. teres in seedling pot tests. Metyltetraprole was also effective in field tests with QoI‐resistant mutants. Antifungal activity tests using field strains of Z. tritici and P. teres showed that the performance of metyltetraprole was unaltered by QoI, succinate dehydrogenase inhibitor (SDHI), and sterol 14α‐demethylation inhibitor (DMI) resistance. However, the mitochondrial activity test indicated that the compound inhibits the respiratory chain via complex III. CONCLUSION Metyltetraprole is a novel fungicide that is highly effective against a wide range of fungal diseases, including important cereal diseases. Although metyltetraprole most likely inhibits the respiratory chain via complex III, it remains effective against QoI resistant strains. Therefore, metyltetraprole is considered as a novel fungicidal agent for controlling diseases affecting cereal crops and overcoming pathogen resistance to existing fungicides. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

BACKGROUND Metyltetraprole is a novel quinol oxidation site of Complex III inhibitor (QoI) fungicide that inhibits mitochondrial electron transport at the Qo site of the cytochrome bc1 complex. Previous reports have demonstrated that it is also active against the QoI‐resistant (QoI‐R) isolates of Zymoseptoria tritici and Pyrenophora teres with the mutations G143A and F129L in their cytochrome b gene, respectively. Further studies on cross‐resistance between metyltetraprole and existing QoIs were performed using an increased number of isolates of Z. tritici, P. teres, Ramularia collo‐cygni, Pyrenophora tritici‐repentis, and several other plant pathogenic fungi. RESULTS Differences in the EC50 values between the wild‐type and QoI‐R isolates with the mutations G143A or F129L were always smaller for metyltetraprole compared to those for the existing QoIs, and they were never greater than five in terms of resistance factor. The 2‐year field experiments showed that the metyltetraprole treatment did not increase the percentage of QoI‐R isolates likely to harbor the G143A mutation in a Z. tritici population. CONCLUSION The unique behavior of metyltetraprole against the existing QoI‐R isolates was confirmed for all tested pathogen species. Our results provide important information to establish a fungicide resistance management strategy using metyltetraprole in combination or alternation with other fungicides. © 2019 Society of Chemical Industry

Nonhost resistance of Arabidopsis thaliana against the hemibiotrophic fungus Colletotrichum tropicale requires PEN2-dependent preinvasive resistance and CYP71A12 and CYP71A13-dependent postinvasive resistance, which both rely on tryptophan (Trp) metabolism. We here revealed that CYP71A12, CYP71A13 and PAD3 are critical for Arabidopsis’ postinvasive basal resistance toward the necrotrophic Alternaria brassicicola. Consistent with this, gene expression and metabolite analyses suggested that the invasion by A. brassicicola triggered the CYP71A12-dependent production of indole-3-carboxylic acid derivatives and the PAD3 and CYP71A13-dependent production of camalexin. We next addressed the activation of the CYP71A12 and PAD3-dependent postinvasive resistance. We found that bak1-5 mutation significantly reduced postinvasive resistance against A. brassicicola, indicating that pattern recognition contributes to activation of this second defense-layer. However, the bak1-5 mutation had no detectable effects on the Trp-metabolism triggered by the fungal penetration. Together with this, further comparative gene expression analyses suggested that pathogen invasion in Arabidopsis activates (1) CYP71A12 and PAD3-related antifungal metabolism that is not hampered by bak1-5, and (2) a bak1-5 sensitive immune pathway that activates the expression of antimicrobial proteins.

20Robust nonhost resistance of Arabidopsis thaliana against the nonadapted 21 hemibiotrophic fungus Colletotrichum tropicale requires PEN2-dependent preinvasive 22Key words: Arabidopsis thaliana, Disease resistance, Metabolism, Plant-pathogen 41 interaction, Plant immunity 42 43The resistance of an entire plant species against all isolates of particular pathogens is 44 called nonhost resistance [1]. Arabidopsis thaliana exhibits nonhost resistance against a 45 nonadapted powdery mildew pathogen Blumeria graminis f. sp. hordei called Bgh. The 46 four PENETRATION genes, PEN1, PEN2, PEN3 and PEN4, have been reported in 47Arabidopsis to control entry of Bgh through activation of vesicle secretion, biosynthesis 48 of putatively antifungal metabolites, and their transport toward pathogen invasion sites, 49 respectively [2,3,4,5,6,7,8,9,10]. 50Colletotrichum tropicale (hereafter Ctro), formally called C. gleosporioides, is a 51 hemibiotrophic fungal pathogen that causes anthracnose on its host mulberry; however, 52 it is not able to infect the nonhost Arabidopsis. Entry control by Arabidopsis against 53Ctro involves PEN2 and PEN3 [11,12], whereas PEN1 is not essential for this unlike 54 the case of Bgh [13]. Nonhost resistance toward Ctro also needs EDR1 (ENHANCED 55 DISEASE RESISTANCE 1) [14], whereas the edr1 mutants exhibit enhanced resistance 56 toward the adapted powdery mildew Golovinomyces cichoracearum (formerly named 57 Erysiphe cichoracearum) [15], suggesting the presence of diverse plant strategies for 58 controlling the entry attempts of pathogens showing distinct infection modes. 59 Importantly, even the pen2 edr1 mutant is still not fully susceptible to Ctro [16], 60 because of strong postinvasive resistance activated once Ctro enters epidermal cells of 61 this mutant, which is defective in the preinvasive resistance that controls pathogen 62 entry. We reported previously that Arabidopsis cyp79B2 cyp79B3 double mutant is fully 63 susceptible to the nonadapted pathogen Ctro [16]. CYP79B2 and CYP79B3 are key 64 enzymes for the biosynthesis of tryptophan (Trp)-derived antimicrobial metabolites. 65 CYP79B2/CYP79B3 convert Trp into indole-3-acetaldoxime (IAOx) [17], and this 66 precursor is then converted into several compounds for antimicrobial immunity, such as 67 4 PEN2 substrates indole-glucosinolates (IGs), PAD3 (PHYTOALEXIN-DEFICIENT3)-68 dependent camalexin, and 4-hydroxy-ICN (4-OH-ICN), whose biosynthesis requires 69 CYP82C2 [18,19,20]. The cyp79B2 cyp79B3 mutant is defective in preinvasive 70 resistance against Ctro because CYP79B2 and CYP79B3 are indispensable for 71 production of IGs, which are substrates metabolized by PEN2 to (unidentified) 72 compounds with presumed antifungal activity [5]. However, contrary with the pen2 73 mutant, the cyp79B2 cyp79B3 plants were also defective in postinvasive resistance to 74Ctro [16]. We have shown that the pen2 pad3 mutant is partially defective in 75 postinvasive resistance to Ctro, indicating that the Arabidopsis phytoalexin, camalexin, 76 is a critical fact...

Arabidopsis thaliana exhibits durable 'non-host' resistance against the hemibiotrophic fungal pathogen Colletotrichum tropicale that infects mulberry plants. Arabidopsis non-host resistance comprises two layers of defense: preinvasive and postinvasive resistance. The EDR1 protein kinase contributes to Arabidopsis preinvasive resistance against C. tropicale by inducing the expression of plant defensin (PDF) genes. Here we report that the expressions of multiple PDF genes were strongly induced in Arabidopsis upon invasion by C. tropicale. Invasion by a necrotrophic pathogen, Alternaria brassicicola, also induced PDF expression. Importantly, PDF expression triggered upon invasion by both pathogens was inhibited in edr1 mutants, indicating the requirement of EDR1 for PDF expression in postinvasive resistance by Arabidopsis. Analysis of ora59 mutants also revealed that this gene is critical for induced PDF expression following pathogen invasion. Furthermore, inoculation assays of A. brassicicola indicated that ORA59 is involved in postinvasive resistance against the pathogen, suggesting invasion-triggered PDF expression contributes to postinvasive resistance in Arabidopsis.