Sensitivity to Fungicides and Esential Oils in Czech Isolates of Phytophthora infestans

Abstract A total of 235 Phytophthora infestans isolates were collected from five regions of the Czech Republic during the growing seasons 2012–2014 and 2016 and examined using the in vitro amended agar method for their sensitivity to metalaxyl-M (MFX), propamocarb-HCl (PCH), and dimethomorph (DMM). A majority of the isolates (50%) were sensitive to MFX. Resistant isolates were found in all four years of the survey; they represented 30% of the samples. The EC50 values of PCH in inhibiting mycelial growth of 65% of the overall isolates were higher than 100 μg ml−1, which indicates the occurrence of insensitivity to PCH in the Czech P. infestans populations. DMM was very effective, and the mycelial growth of all isolates tested was completely suppressed at the concentration of 0.1 μg ml−1. Furthermore, the efficacy of 12 plant essential oils was tested against 20 isolates of P. infestans using the in vitro amended agar method. Essential oils of Cymbopogon winterianus, Litsea cubeba, Mentha spicata, Pelargonium graveolens, Syzygium aromaticum, and Thymus vulgaris were observed to have the highest antifungal activity against P. infestans, with minimal inhibitory concentrations less than or equal to 1 μl ml−1.