During the different stages of its development, wheat is possible infected by many plant pathogens. One of the most common is Zymoseptoria tritici, the causal agent of the disease called Septoria Tritici Blotch (STB). The most common strategy in the Z. tritici disease management is treating plants with fungicides. Unfortunately, this plant pathogen as many others evolved resistance towards some of the most commonly used fungicidal classes. The aim of this study was to detect the resistance of Z. tritici to strobilurin fungicide azoxystrobin. During the April 2017, around 300 plant samples were collected from 11 geographical regions in the Czech Republic. From those plant samples, 52 monosporic Z. tritici isolates were obtained and tested for the presence of the resistance. The fungicide resistance was measured and detected by laboratory agar dilution biotest and molecular methods as a CAPS marker (Cleaved Amplified Polymorphic Sequences) and qPCR (Quantitative Polymerase Chain Reaction). By agar dilution biotest, resistance to azoxystrobin was confirmed in 54% of total 52 analysed isolates. By CAPS marker analysis, the presence of G143A mutant allele of the mitochondrial cytochrome b gene, linked to the fungicide resistance, was confirmed in all selected isolates marked as resistant in the biotest. The DNA of one infected leaf sample collected from the field marked as 17Zt212 was isolated and tested by the qPCR method. In the field sample (17Zt212), the 4% of the Z. tritici population was found to be resistant to fungicide azoxystrobin.

Frogeye leaf spot, caused by Cercospora sojina Hara, is a foliar disease affecting soybean (Glycine max (L.) Merr.), often managed by applications of quinone outside inhibitor (QoI) fungicides. In 2013 and 2014, symptomatic leaf samples were collected from Mississippi soybean fields leading to the collection of 634 mono-conidial C. sojina isolates. In vitro bioassays were performed to evaluate the sensitivity of 14 isolates plus a baseline. Resistant and sensitive isolates were characterized by determining the effective fungicide concentrations at which 50% of conidial germination was inhibited (EC50). Additionally, the molecular mechanism of resistance was determined for all 634 isolates. Greater than 93% of C. sojina isolates collected in Mississippi carried the G143A amino acid substitution indicating a shift to a QoI-resistant population throughout Mississippi soybean fields. Greenhouse studies confirmed that due to this amino acid substitution, symptoms caused by QoI-resistant isolates developed in spite of a QoI fungicide application.

<p>Frogeye leaf spot (FLS) is a foliar disease in soybean (<i>Glycine max</i> (L.) Merr.) caused by the fungal pathogen <i>Cercospora sojina</i> Hara. FLS is commonly found in hot and humid regions of the southern United States but has become more common in the North Central states. Foliar application of quinone outside inhibitor (QoI) fungicides has been one of the major tools used in the management of this disease, but QoI-resistant <i>C. sojina</i> isolates have been already confirmed in 21 states, including Indiana. We hypothesized that resistant populations of <i>C. sojina</i> to QoIs fungicides are widespread in Indiana and that sexual reproduction is occurring within <i>C. sojina</i> populations, likely contributing to the dissemination of fungicide resistance. The main objectives of this research were to determine the distribution of QoI-resistant <i>C. sojina</i> isolates on soybean from Indiana and to evaluate <i>C. sojina </i>populations for potential sexual reproduction. In the summer of 2019 and 2020, 406 isolates of <i>C. sojina </i>were collected from 32 counties across Indiana and screened for QoI-fungicide resistance using a PCR-RFLP method. An i<i>n vitro </i>fungicide sensitivity test was performed on a subset of isolates to evaluate the sensitivity of <i>C. sojina</i> isolates to azoxystrobin, pyraclostrobin, picoxystrobin, and prothioconazole. A discriminatory dose of picoxystrobin (QoI) and prothioconazole (demethylation inhibitor- DMI) were established at 1 μg/ml and 10 μg/ml, respectively, to distinguish between QoI-resistant and sensitive isolates and to identify a reduction in sensitivity to DMI fungicides, respectively. Discriminatory doses were estimated by testing five concentrations (0.001, 0.01, 0.1, 1, and 10 µg/ml) of each fungicide. QoI-resistant isolates were found in 29 out of the 32 counties. Two hundred and fifty-one (251) out of the 406 isolates (61.8%) were confirmed as QoI-resistant. Partial nucleotide sequences of the cyt <i>b</i> gene from four resistant and four sensitive <i>C. sojina</i> isolates corroborated the presence and absence of the G143A mutation, respectively. Results from the sensitivity assays with azoxystrobin and pyraclostrobin discriminatory doses supported the findings from the PCR-RFLP assay as all QoI-resistant mutants were inhibited less than 50% when exposed to these doses. Results from this study indicated that QoI-resistant <i>C. sojina</i> isolates are spread throughout Indiana and that prothioconazole (DMI) could be a potential supplemental or alternative fungicide to control FLS. Additionally, mating type distribution was determined in 43 <i>C. sojina</i> populations for assessment of potential sexual reproduction. Fifteen (15) populations did not deviate significantly from the expected 1:1 ratio, suggesting potential for cryptic sexual reproduction in these populations, but further research on genetic diversity is required to verify these results. </p> <p> </p>