Fungicide Sensitivity Profile of Pyrenophora teres f. teres in Field Population

Comparison and Analysis of Resistance Differences in Alternaria alternata from Fungicides with Three Different Mechanisms

The pathogen Alternaria alternata infects a variety of plants and crops, notably poplars, and results in large financial losses. Using twelve chemical fungicides for fungicide sensitivity tests (FSTs) on A. alternata, the result showed that prochloraz (PCZ), mancozeb (MZ), and fludioxonil (FLU) have potent inhibitory effects against the pathogen through different mechanisms. To investigate how the pathogen responded to fungicide-induced stress, transcriptome and physiological investigations were carried out after treatments with three fungicides at their corresponding 50% effective concentration (EC50) doses. The MZ treatment produced a distinct genetic response; FLU treatment produced the greatest number of differentially expressed genes (DEGs), followed by PCZ. DEGs from FLU treatment were mostly engaged in ribosome biosynthesis, those from MZ treatment in lipid and carbohydrate metabolism, and those from PCZ treatment in carbohydrate metabolism, according to Gene Ontology (GO) analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that FLU and PCZ treatments were associated with ribosome biogenesis, whereas MZ treatment was linked to the pyruvate metabolic pathway. Collinear trend analysis indicates that MZ exhibits a unique pattern, with FLU treatment causing the most significant overexpression of genes, followed by PCZ. The six categories of 88 elevated DEGs associated with fungal resistance include tyrosinase, ATP-binding cassette (ABC) transporters, major facilitator superfamily (MFS) transporters, antioxidant and cellular resilience genes, as well as genes involved in cell wall and membrane biosynthesis. Notably, the pathways involved in the synthesis of melanin and ergosterol exhibited the strongest response to FLU. The results of a correlation analysis between physiological indices and resistance-related genes indicated that melanin content, malondialdehyde (MDA) content, and tyrosinase activity were positively correlated with the majority of resistance-related DEGs, whereas soluble protein content, superoxide dismutase (SOD) activity, and catalase (CAT) activity were negatively correlated, which is consistent with the observed trends in the measured physiological indicators. Taken together, this study provides a theoretical basis for developing more effective fungicides and chemical control strategies against A. alternata.

Sensitivity to the Demethylation Inhibitor Difenoconazole Among Baseline Populations of Various Penicillium spp. Causing Blue Mold of Apples and Pears

Difenoconazole (DIF), a demethylation inhibitor fungicide, was registered in 2016 for the control of postharvest diseases of pome fruits. In this study, 162 isolates from P. expansum (n = 31) and 13 other "non-expansum" Penicillium spp., i.e., P. solitum (n = 52), P. roqueforti (n = 32), P. commune (n = 15), P. paneum (n = 9), P. psychrosexuale (n = 8), P. crustosum (n = 5), P. carneum (n = 3), P. palitans (n = 2), along with one isolate each of P. citrinum, P. griseofulvum, P. raistrickii, P. ribium, and P. viridicatum, were collected from multiple packinghouses in the U.S. Pacific Northwest. In vitro sensitivity assays showed similar sensitivities of spores and mycelia across species with the mean EC50 values ranging from 0.01 for P. psychrosexuale (n = 8) to 1.33 μg mL-1 for P. palitans (n = 2), whereas the mean EC50s were 0.03, 0.12, 0.19, and 0.51 μg mL-1 for P. expansum (n = 31), P. paneum (n = 9), P. solitum (n = 52), and P. crustosum (n = 5), respectively. The recommended rate of DIF controlled P. expansum and P. roqueforti isolates but not all isolates of four other Penicillium spp. on Fuji apples after five months at 1.5 °C. The mixture of DIF + fludioxonil (FDL) (AcademyTM) controlled all the dual-sensitive isolates (DIFSFDLS) and DIF single-resistant (DIFR) isolates among the six species tested but not the FDLR and dual DIFRFDLR isolates. Notable polymorphism was detected in the CYP51 gene of the "non-expansum" species with four mutations located at four residues. Although the isolates analyzed in this study had not previously been exposed to DIF, the findings indicate variable sensitivity levels among the Penicillium spp.

Sensitivity Analysis of Pyrenophora tritici-repentis to Quinone-Outside Inhibitor and 14α-Demethylase Inhibitor Fungicides in Latvia

Tan spot caused by Pyrenophora tritici-repentis is a severe threat to wheat production in all major wheat-growing regions. Sustainable tan spot control can be achieved by an integrated approach, including responsible management of fungicide sprays. The data about the sensitivity of P. tritici-repentis to various fungicides in the Baltic Sea region are rare. In this study, we described the variation of P. tritici-repentis sensitivity to four fungicide active ingredients to detect the formation of resistance to the most commonly used quinone-outside inhibitor (QoI) and 14α-demethylase inhibitor (DMI) fungicides in the pathogen's population in Latvia. The effect of prothioconazole, mefentrifluconazole, pyraclostrobin, and azoxystrobin on 93 P. tritici-repentis strains from various hosts was tested in vitro by assessing mycelium linear growth inhibition at three different active ingredient concentrations (0 0.01, 0.1 and 0.5 mg L-1). Pathogen sensitivity significantly (p < 0.001) varied between the fungicide active ingredients and strains. The prothioconazole (concentration 0.5 mg L-1) had the most significant effect, with a median mycelial growth inhibition of 70.34%, followed by pyraclostrobin (47.02%), azoxystrobin (24.24%), and mefentrifluconazole (11.11%). Mutation G143A was detected in cytb gene sequences and confirmed the resistance formation in Latvia's P. tritici-repentis population, while F129L and G137R mutations were absent. This study provided insight into P. tritici-repentis population's sensitivity to active ingredients of DMI and OoI fungicide groups, helping to fill the knowledge gap about the pathogen fungicide sensitivity in this region.