IDENTIFICATION OF METHYL-THIOPHANATE RESISTANCE IN FIELD STRAINS OF FUSICLADIUM ERIOBOTRYAE, THE CAUSAL AGENT OF LOQUAT SCAB

Benzimidazoles, and specifically methyl-thiophanate, have been broadly used in the last two decades in Spain to control loquat (Eriobotrya japonica Lind.) scab caused by Fusicladium eriobotryae (Cavara) Sac. However, to date no study has been conducted to identify resistant isolates to this fungicide. For this purpose, 249 isolates of F. eriobotryae collected from the main loquat producing areas in Spain (Andalucía and Comunidad Valenciana) were grown in culture medium amended with methyl-thiophanate (0.5 µg/ml). After one month of incubation, the relative growth compared with that obtained in a non-amended medium (control) was calculated; 33 isolates were resistant to methyl-thiophanate (>30% growth relative to the control). In addition, the resistance to methyl-thiophanate in F. eriobotryae was characterized by mutations in the β-tubulin gene. DNA of representative susceptible and resistant isolates was extracted and a partial sequence of the β-tubulin gene was obtained. Resistant isolates showed the presence of only one non-synonymous mutation in the codons 198, 200 or 240 of this gene, which has been previously reported as characteristic of methyl-thiophanate resistance in other plant pathogens. These mutations could be used to develop a screening protocol to identify isolates of F. eriobotryae resistant to methyl-thiophanate.