Efficiency of detecting resting spores of Synchytrium endobioticum (potato wart disease) in infested sites of Ukraine and Georgia

Aim. To determine the occurrence and persistence of Synchytrium endobioticum, resting spore contamination in a small survey of (known infested) potato plots in Ukraine and Georgia; to compare the detection efficiency for resting spores (winter sporangia) of S. endobioticum using an extraction method, routinely applied in Ukraine, based on the use of sodium iodide (NaI) and an extraction method largely based on EPPO Standard PM 7/28(2) (2017), using kaolin and calcium chloride (CaCl2) for extraction. Methods. The examination of fields, aimed at detecting of S. endobioticum in 22 infested plots in Georgia, was conducted following the standard European Plant Protection Organisation (EPPO) phytosanitary procedure PM 3/59(3) (2017), and in Ukraine in 11 plots according to the Ukrainian Standard ‘Methodological recommendations on sampling during quarantine inspection and evaluation’ (Omeluta V P et al, 1996). Resting spores were extracted using kaolin and CaCl2 (following largely EPPO Standard PM 7/28(2) 2017), and floatation in a solution of NaI (Zelya et al, 2005), respectively. The content of soil organic matter (SOM), collected in potato wart infested plots in Ukraine and Georgia, was determined according to the ‘Method of laboratory determination of the content of organic matter’, largely following the method of Tyurin to determine total soil organic carbon (Jankauskas B et al, 2006). The persistence or decline of potato wart in infested plots was evaluated, based on our own observations and the data of the national phytosanitary services (https://dpss.gov.ua; http://agr.georgia.gov). The results of the study were subjected to statistical analysis, using Statistica 5 software. Results. It was found that under a low up to high level of organic matter in soil samples (2.0–2.7 and 3.1–3.9 %, respectively) and a moderate to high level of inoculum in soil (3–15 up to 41–65 resting spores/g soil, respectively) there were no significant differences in the efficiency of two extraction methods under consideration: the floatation in a solution of NaI and the application of kaolin and CaCl2. However, at a low number of resting spores present in soil (1–2 resting spores/g soil), the efficiency of the method using NaI decreased statistically significant by 20–30 % as opposed to the method using kaolin/CaCl2. A relatively high level of soil contamination with resting spores was found in 11 investigated plots of 4 Ukrainian regions: 41–46 resting spores/g soil in the Ivano-Frankivsk Region, 49 in the Lviv Region, 40–65 in the Zakarpattia and 52–65 Chernivtsi Regions. The majority of the 22 investigated Georgian plots showed a low inoculum level (1–7 resting spores/g soil) and only in one village their level amounted to 15 resting spores/g soil (Uchguli village, Mestia municipality). Conclusions. The method applying sodium iodide was found to be comparable to the method applying kaolin and CaCl2 under conditions of moderate to high inoculum levels (15–65 resting spores/g soil) but the latter method was more efficient under conditions of high content of organic matter and very low inoculum level (