Fitness and Competitive Ability of <i>Botrytis cinerea</i> Field Isolates with Dual Resistance to SDHI and QoI Fungicides, Associated with Several <i>sdh</i>B and the <i>cyt</i>b G143A Mutations

Respiration inhibitors such as the succinate dehydrogenase inhibitors (SDHIs) and the quinone outside inhibitors (QoIs) are fungicide classes with increasing relevance in gray mold control. However, recent studies have shown that dual resistance to both fungicide classes is a common trait in Botrytis cinerea populations from several hosts throughout the world. Resistance of B. cinerea to SDHIs is associated with several mutations in the sdhB, sdhC, and sdhD genes, while resistance to QoIs, in most cases, is associated with the G143A mutation in the cytb gene. The objective of the current study was to investigate the fitness and the competitive ability of B. cinerea field strains possessing one of the H272Y/R/L, N230I, or P225F sdhB substitutions and the G143A mutation of cytb. Fitness parameters measured were (i) mycelial growth and conidia germination in vitro, (ii) aggressiveness and sporulation capacity in vivo, (iii) sclerotia production in vitro and sclerotia viability under different storage conditions, and (iv) sensitivity to oxidative stress imposed by diquat treatments. The competitive ability of the resistant isolates was measured in the absence and presence of the SDHI fungicides boscalid and fluopyram selection pressure. The measurements of individual fitness components showed that the H272R/G143A isolates had the lower differences compared with the sensitive isolates. In contrast, the groups of H272Y/L/G143A, N230I/G143A, and P225F/G143A isolates showed reduced fitness values compared with the sensitive isolates. Isolates possessing only the cytb G143A substitution did not show any fitness cost. The competition experiments showed that, in the absence of fungicide selection pressure, after four disease cycles on apple fruit, the sensitive isolates dominated in the population in all the mixtures tested. In contrast, when the competition experiment was conducted under the selection pressure of boscalid, a gradual decrease in the frequency of sensitive isolates was observed, whereas the frequency of H272L and P225F isolates was increased. When the competition experiment was conducted in the presence of fluopyram, the sensitive isolates were eliminated even after the first disease cycle and the P225F mutants dominated in the population. Such results suggest that the sdhB mutations may have adverse effects on the mutants. The observed dominance of sensitive isolates in the competition experiments conducted in the absence of fungicides suggest that the application of SDHIs in alternation schemes may delay the selection or reduce the frequency of SDHI-resistant mutants. </jats:p

Sensitivity and efficacy of the succinate dehydrogenase inhibitor fluxapyroxad, against raspberry spur blight fungus Didymella applanata

Didymella applanata, the causal agent of raspberry spur blight, is a destructive plant pathogen that can cause serious reductions in total yield. The use of fungicides plays a crucial role in successful control of the pathogen. The sensitivity of 94 isolates (66 collected during 2013 and 28 in 2017) of D. applanata to the succinate dehydrogenase inhibitor, fluxapyroxad, was evaluated in this study. In addition, the efficacy of fluxapyroxad in raspberry spur blight control in the field was determined. The isolates tested in this study showed different sensitivity to fluxapyroxad in vitro. The EC50 values of total number of isolates tested were ranged from 0.82 to 5.92 mu gml(-1). The ranges of EC50 values for the isolates varied between the localities where the isolates originated from and also the year of isolation. The mean EC50 values in the group of isolates obtained in 2013 were 1.95 mu gml(-1)+/- 0.81 (0.82 to 4.05 mu gml(-1)), while the EC50 values for those isolated in 2017 were ranged from 1.16 to 5.78 mu gml(-1) (mean=3.24 mu gml(-1)+/- 1.38). The efficacy trials were conducted during 2017 and 2018 in a commercial raspberry field at two locations in western part of Serbia. Applied in both concentration rates 0.02 and 0.03% of the formulated product (0.006 and 0.009% of a.i.), fluxapyroxad showed a very high efficacy in spur blight control in practical condition

Detection and characterization of fungicide resistant phenotypes of Botrytis cinerea in lettuce crops in Greece

The development of resistance to chemical control agents needs continuous monitoring in Botrytis cinerea. 790 isolates from lettuce and other vegetable crops were collected from six widely separated sites in Greece and tested for their sensitivity to 11 fungicides from nine unrelated chemical groups. 44 of the isolates exhibited multiple resistance to fenhexamid (hydroxyanilides), azoxystrobin and pyraclostrobin (QoI's), boscalid (SDHI's), cyprodinil and pyrimethanil (anilinopyrimidines), fludioxonil (phenylpyrroles), carbendazim (benzimidazoles) and iprodione (dicarboximides). Thirty per cent of such phenotypes were detected in an experimental glasshouse with lettuce crops, the third year after commencing fungicide applications. The average resistance factor (R-f) for mycelial growth to fenhexamid, pyraclostrobin, boscalid, cyprodinil and fludioxonil, was over 40, 1,000, 100, 700 and 50, respectively. Some strains with high resistance to anilinopyrimidines (14 %) or moderate to fludioxonil (7 %) were detected even in isolates collected from vegetable crops prior to commercial use of these fungicides in Greece. Isolates with fludioxonil moderate resistance and fenhexamid high resistance, were detected for the first time in Greece. The results suggested the high risk in chemical control of grey mould due to development of resistance to most fungicides with site-specific modes of action. Isolates with resistance to fluazinam (phenylpyridinamines) and to chlorothalonil (phthalonitriles) were not found. The inclusion of appropriate multi-site inhibitors like chlorothalonil in fungicide anti-resistance strategies was indispensable