The current state of the population of the golden potato cyst nematode Globodera rostochiensis (Nematoda, Heteroderidae) in the northwest of Ukraine

The golden potato cyst nematode (GPCN) Globodera rostochiensis (Wollenweber, 1923) Skarbilovich, 1959 is a highly specific parasite of the roots of the nightshade plants (Solanaceae). Thus, the state of the pest population demands constant monitoring and control of distribution and numbers. The distribution of G. rostochiensis in Volyn region of Ukraine was studied in 2008-2018 using the data of the state institution the Volyn Regional Phytosanitary Laboratory. The present article gives the analysis of the study results. The disease foci were detected by visual aboveground inspection of potato plantings, also by manually collecting soil samples before planting the potatoes and after harvesting, and consequently analyzing theme. The initial (pre-planting) and conclusive (after harvest) population density of GPCN in the soil was determined by the number of cysts and the mean number of larvae and eggs in cysts obtained from 100 cm(3) of soil. Cysts were isolated from soil samples by the standard funnel flotation method. The dead and living larvae were identified visually by the shape of the body and the state of internal organs. According to the results of assessing pre-planting and post-harvest nematode numbers in soil, the reproduction coefficient P-f/P-i was calculated. In Volyn region, G. rostochiensis was first observed in 1968 on farmland and since then, the parasite has spread. Pest foci were recorded in 15 districts of the region in 303 settlements on the area of 946.123 hectares. It was however found that during the latest decade, the area of soils affected by G. rostochiensis in Volyn region decreased by 147.647 hectares. The largest infected areas (over 100 ha) were located in Kovel, Rozhyshche and Manevistky districts, the least infected area was observed in Ivanychi district of the region. The pest was not found in Lutsk district. The highest infection rate was recorded in Rozhyshche district. The highest ratio of viable cysts was observed in the soils of Volodymyr-Volynsky and Rozhyshche districts. The soils of the southern districts (located in the natural zone of forests and steppe) of the region demonstrated 1.5 times higher infection rates compared to soils of the northern districts (in the natural zone of mixed forests). The soils of the southern districts also harboured stable and strong pest populations. The pre-planting soil infection rates proved to directly depend on the reproduction coefficient of GPCN. If the values of P-i, initial infection rate, were lower than 1,000 larvae and eggs per 100 cm(3), the reproduction coefficient was 1.18. Increase in the pre-planting infection rate to 2,000 eggs and larvae per 100 cm(3) did not affect the reproduction coefficient. At approximately 5,000 eggs and larvae per 100 cm(3) the reproduction coefficient exceeded 2, which should be considered in developing the pest control measures.