Resistance of Monilinia fructicola to thiophanate-methyl in Croatia
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Resistance of Monilinia fructicola to thiophanate-methyl in Croatia Dario Ivić & Tina Fazinić & Adrijana Novak & Lorena Šajbić & Miloš Stepanović & Tanja Gotlin Čuljak & Tihomir Miličević
Accepted: 7 October 2020 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2020
Abstract Croatian isolates of Monilinia fructicola, M. laxa and M. fructigena have been collected from peach, nectarine, sweet cherry, plum and apricot fruits and assessed for their sensitivity to thiophanate-methyl. Out of 66 isolates collected, 34 were identified as M. fructicola (52%), 22 as M. fructigena (33%) and 10 as M. laxa (15%). Mycelial radial growth on water agar amended with thiophanate-methyl was measured to determine half maximal effective concentration values (EC50). All isolates of M. laxa and M. fructigena showed as sensitive, with EC50 values lower than 1 µg ml− 1 in 31 from 32 isolates. In M. fructicola, 19 isolates (56%) were sensitive, nine (26%) were resistant (EC50 2–30 µg ml− 1), and six (18%) were highly resistant (EC50 > 30 µg ml− 1). Positive allele-specific PCR with primer pair HRR/HRF, detecting resistant point mutations in β-tubulin gene, was recorded in 15 out of 16 highly resistant, resistant and less sensitive M. fructicola isolates. Among all species, PCR assay coincided with agar assay in 95% of cases. Highly resistant M. fructicola isolates AL 24/19 and VR 8/18 caused typical D. Ivić (*) : T. Fazinić : A. Novak : L. Šajbić Croatian Agency for Agriculture and Food, Centre for Plant Protection, Gorice 68b, 10000 Zagreb, Croatia e-mail: [email protected] M. Stepanović Institute of Pesticides and Environmental Protection, Banatska 31b, 11080 Beograd-Zemun, Serbia T. G. Čuljak : T. Miličević Faculty of Agriculture, University of Zagreb, Svetošimunska cesta 25, 10000 Zagreb, Croatia
brown rot on nectarine fruits inoculated with conidia suspended in 5 or 10 µg ml− 1 of thiophanate-methyl. Four sensitive isolates of all three species did not develop on inoculated fruits. Besides implications for brown rot management, the finding of M. fructicola strains resistant to thiophanate-methyl may indicate that this species could be adapting to fungicides more rapidly than M. laxa or M. fructigena. As resistant M. fructicola isolates were also found in orchards where benzimidazoles have never been used, there is a possibility they originate from already benzimidazole-resistant strains which entered and established in Croatia. Keywords Monilinia . Brown rot . Benzimidazoles . Fungicide sensitivity
Brown rot is among the most important diseases of stone fruits worldwide. Up to the beginning of the 20th century, it was considered that Monilinia laxa (Aderh. & Ruhland) Honey and Monilinia fructigena (Aderh. & Ruhland) Honey are the only causal agents of brown rot in Europe. In 2002, a new species M. polystroma was described (Van Leeuwen et al. 2002) and later reported from some European countries (Petróczy and Palkovics 2009; Vasić et al. 2016). Monilinia fructicola (G. Winter) Honey, the fourth Monilinia species causing b
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