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BACKGROUND: Stem‐end rot caused by Lasiodiplodia theobromae is one of the most important diseases of papaya in northeastern Brazil. It can be controlled effectively by demethylation inhibitor (DMI) fungicides, but the occurrence of DMI resistance may decrease fungicide efficacy. RESULTS: Detached fruit studies revealed that isolates with EC50 values of 6.07 and 6.28 μg mL−1 were not controlled effectively, but reduced virulence and ability to grow at temperatures ranging from 12 to 32 °C suggesting fitness penalties were observed. Cross‐resistance was observed only between difenoconazole and propiconazole. The entire cytochrome P450 sterol 14α‐demethylase (LtCYP51) gene and its flanking regions were cloned. The gene was 1746 bp in length and contained three introns. The predicted protein contained 525 amino acids. Phylogenetic tree analysis showed that the LtCYP51 belongs to the CYP51B clade. No amino acid variation was found between sensitive and resistant isolates; however, the gene was constitutively more highly expressed in resistant isolates. CONCLUSION: Resistance to DMI fungicides in L. theobromae is based on LtCYP51 gene overexpression and fitness penalties may be present in difenoconazole‐resistant isolates. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Stem-end rot caused by Lasiodiplodia theobromae is one of the most devastating diseases of papaya in northeastern Brazil. It is most effectively controlled by applications of fungicides, including site-specific fungicides at risk for resistance development. This study investigated the molecular mechanisms of reduced sensitivity to the QoI fungicide azoxystrobin and resistance to the MBC fungicide thiophanate-methyl in L. theobromae from Brazilian orchards. The EC 50 values for azoxystrobin in sixty-four isolates ranged from 0.36 μg/ml to 364.24 μg/ml and the frequency distribution of EC 50 values formed a multimodal curve, indicating reduced sensitivity to azoxystrobin. In detached fruit assays reduced sensitive isolates were not controlled as effectively as sensitive isolates at lowest label rate. Partial fragments were obtained from target genes β- tubulin (751 bp) and Cytb (687 bp) of isolates resistant to thiophanate-methyl and reduced sensitivity to azoxystrobin. Sequence analysis of the β- tubulin fragment revealed a mutation corresponding to E 198 K in all thiophanate-methyl-resistant isolates, while reduced sensitivity to axoxystrobin was not attributable to Cytb gene alterations. The target gene-based mechanism conferring resistance to thiophanate-methyl will likely be stable even if selection pressure subsides. However, the mechanism conferring reduced sensitivity to azoxystrobin is not based on target gene modifications and thus may not be as stable as other genotypes with mutations in Cytb gene. Unlabelled Image • Reduced sensitivity to azoxystrobin in Lasiodiplodia theobromae from papaya was observed. • Reduced sensitivity to azoxystrobin was not attributable to Cytb gene alterations. • Resistance to thiophanate-methyl was associated with E 198 K mutation in β-tubulin gene. • No-cross-resistance was found between azoxystrobin and thiophanate-methyl. [ABSTRACT FROM AUTHOR]

Glomerella leaf spot (GLS) and bitter rot (BR), caused by Colletotrichum spp., are major diseases on apple in southern Brazil. Among integrated pest management tools for disease management in commercial orchards, fungicides remain an important component. This study aimed to identify Colletotrichum spp. from cultivar Eva in Paraná state orchards; evaluate their in vitro sensitivity to cyprodinil, tebuconazole, iprodione, and fluazinam; and determine the baseline in vitro sensitivity of these isolates to benzovindiflupyr and natamycin. Most isolates belonged to Colletotrichum melonis and C. nymphaeae of the C. acutatum species complex. The two species varied in sensitivity to fluazinam and tebuconazole, but no variability was found for any other fungicide. The lowest 50% effective concentration (EC 50 ) values of Colletotrichum spp. were observed for cyprodinil (mean EC 50 < 0.02) and benzovindiflupyr (mean EC 50 < 0.05); EC 50 values were intermediate for fluazinam (mean EC 50 < 0.33) and tebuconazole (mean EC 50 < 0.14), and they were highest for natamycin (mean EC 50 < 5.56) and iprodione (mean EC 50 > 12). Cyprodinil and fluazinam are registered for use in Brazil for apple disease management but not specifically for GLS and BR. Tebuconazole is one of the few products registered for Colletotrichum spp. control in apples. In conclusion, flowers and fruitlets can serve as sources of inoculum for GLS and BR disease; C. acutatum was the predominant species complex in these tissues; cyprodinil and fluazinam applications may suppress GLS and BR; and benzovindiflupyr and natamycin warrant further investigation for GLS and BR disease control of apple due to comparably high in vitro sensitivity.