Petar Vukša

Toxicity of copper hydroxide, dithianon, fluazinam, tebuconazole and pyraclostrobin to Didymella applanata isolates from Serbia

A study of the in vitro sensitivity of 10 isolates of Didymella applanata to copper hydroxide, dithianon, fluazinam, tebuconazole and pyraclostrobin, was conducted. The isolates were derived from diseased raspberry canes sampled during 2013 at five localities in western part of Serbia, known as the main raspberry growing region of the country. Prior to sensitivity testing experimental conditions for radial growth assay were optimized. The results showed that the temperature of 22°C, oatmeal agar medium and 12/12 hrs light/ darkness light regimen provided the best conditions for sensitivity tests. Most of D. applanata isolates were sensitive to the tested fungicides. The narrowest range of EC50 values was recorded for tebuconazole (1.42–2.66 mg L−1). The widest range of EC50 values was obtained for pyraclostrobin, ranging from 0.17 mg L−1 to 55.33 mg L−1. The EC50 values for the studied isolates were 39.48–51.19 mg L−1 for copper hydroxide, 12.12–18.73 mg L−1 for dithianon and 5.72–42.56 mg L−1 for fluazinam. According to resistance factor values, all D. applanata isolates were sensitive to copper hydroxide, dithianon and tebuconazole. Among tested isolates, six were highly resistant to pyraclostrobin (RFs in the range of 207.1–325.5) and two moderately resistant to fluazinam (RFs were 3 and 7.4), respectively.

VKOR variant and sex are the main influencing factors on bromadiolone tolerance of the house mouse (Mus musculus L.).

BACKGROUND After reports of management problems in practice, a survey was conducted to determine the presence of bromadiolone-resistant animals in different house mouse (Mus musculus L.) populations in Serbia. A 21 day no-choice feeding test was carried out to examine the resistance of house mice to bromadiolone. Eighty house mice collected from four locations (ten males and ten females per location) were tested for bromadiolone tolerance. Surviving animals and their F1 offspring were screened for mutations. The influence of VKOR variant, zygosity and sex on bromadiolone tolerance was analysed. RESULTS Bait intake and changes in body weight revealed different animal responses regarding susceptibility or resistance. Leu128Ser, Tyr139Cys and a new Ala21Thr polymorphism were detected in wild-born survivors and their F1 generation. However, not every individual with the polymorphisms Leu128Ser and Tyr139Cys survived the feeding test. VKOR variants and sex caused variations in bromadiolone tolerance. CONCLUSION For the first time it was shown that the VKOR variant, along with sex, is responsible for bromadiolone tolerance in house mice. Other factors influencing bromadiolone tolerance, including sex-specific factors, cannot be excluded. The tolerance levels of VKOR variants should be determined in further studies in order to evaluate the effectiveness of bromadiolone in sustainable management.

Toxicity of mancozeb, chlorothalonil, captan, fluopyram, boscalid, and difenoconazole to Didymella applanata isolates from Serbia

Field isolates of Didymella applanata, the causal agent of spur blight of raspberry, were evaluated in vitro for their sensitivity to mancozeb, chlorothalonil, captan, fluopyram, boscalid and difenoconazole. A total of 10 isolates, collected during 2013 at five localities in the major raspberry growing region in Serbia, and characterized as copper hydroxide, dithianon, and tebuconazole (sensitive), pyraclostrobin (sensitive or highly resistant) and fluazinam (sensitive or moderately resistant), were used in this study. The EC50 values for the isolates ranged from 1.33 to 2.88 mg L−1 for mancozeb, from 3.18 to 6.65 mg L−1 for chlorothalonil, from 15.75 to 24.69 mg L−1 for captan and from 1.80 to 8.20 mg L−1 for fluopyram. The narrowest range of EC50 values was recorded for difenoconazole (0.23–0.49 mg L−1), whereas the widest range was obtained for boscalid (4.49–49.25 mg L−1). The calculated resistance factors showed that all D. applanata isolates were sensitive to mancozeb, chlorothalonil, captan, and difenoconazole. Four isolates were moderately resistant to boscalid, while three of them were also moderately resistant to fluopyram. This finding of moderately resistant isolates to these SDHI fungicides indicates a possible cross-resistance which should be clarified in further investigations.

Is low efficacy of fungicides always a consequence of fungicide resistance development in pathogen populations

Efficacy of four fungicides with different modes of action (vinclozolin, pyrimethanil, benomyl and fenhexamid) in control of B. cinerea in raspberry, was investigated in the paper. The trials were conducted at two localities in commercial raspberry plantations. In the case of unsatisfactory fungicide efficacy, qualitative and/or quantitative test of the susceptibility of the isolates to particular fungicide was performed, to determine whether the low efficacy is a consequence of resistance development in the pathogen population. At both localities, pyrimethanil and fenhexamid demonstrated the highest efficacy (73.2-89.6%), while the efficacy of vinclozolin was statistically significantly lower (48.7-63.4%) at both localities. However, qualitative and quantitative test of susceptibility to vinclozolin showed that all the isolates were susceptible to vinclozolin and that the reason for unsatisfactory efficacy should be primarily sought in inadequate fungicide application.

Different toxicity of the strobilurin fungicides kresoxim-methyl and trifloxistrobin to Venturia inaequalis isolates from Serbia

Sensitivity of monosporial isolates of V. inaequalis, originated from apple orchards previously exposed (commercial and experimental) and those originated from location where fungicides had never been used (wild type), to strobilurin fungicides kresoxim-methyl and trifloxistrobin was investigated in this study. The experiments were carried out in laboratory using in vitro and in vivo methods. Mycelia growth inhibition on PDA medium with kresoxim-methyl and trifloxistrobin was monitored and sensitivity parameters (EC50 values) were determined using probit analysis. The isolates sensitivity in vivo was tested on apple seedlings using inoculation method. The EC50 values were ranging from 0.066–2.033 and 0.011–0.323 µg mL−1 for kresoxim-methyl and trifloxistrobin, respectively. The wild type of isolates showed a normal susceptibility to kresoxim-methyl and trifloxistrobin, while isolates originated from experimental and commercial orchard where those fungicides had been used extensively, showed significantly lower sensitivity to the both strobilurin fungicides. The isolate that showed the resistance to kresoxim-methyl and trifloxistrobin in vitro test, also showed reduced sensitivity in vivo test and could not been controlled satisfactory by fungicide concentrations that are commercially used, as well as by double higher, after apple seedlings inoculation.