Sodininkystė ir daržininkystė - Sodininkystės ir daržininkystės institutas

This lesion is often sharply delineated by leaf veins, and thus assumes a distinctlyangular shape (Weit et al., 1987). Apart from the leaf wetness essential forinfection, the factors determining disease progress are: rate of foliage growthand physiological age of the host. The fungus is easily carried by wind currents,rain splash, farm implements. It is favored by cool to moderately warmtemperatures, downy mildew is most aggressive when heavy dews, fog andfrequent rains occur (Khetmalas, Memane, 2003). Until now, there has beenlimited knowledge on the epidemiology, spread and intensity, destructivity ofPseudoperonospora cubensis in Lithuania.This study was undertaken to determine the effects of temperature, amountof precipitation and relative humidity on spread and intensity of P. cubensis.Materials and methods. Cucumber (cultivar Trakø pagerinti) plants weregrown from seeds in the field of Lithuanian Institute of Horticulture in2004-2005 to examine spread and intensity of Pseudoperonospora cubensis undernatural growing conditions. Seeds were sown on June 4-6 in a double rowbeds. Plot size 50 m 2 , each plot consisted of 20 plants in a double-row bed(25 x 25 cm within beds, 1 m between beds). Cucumbers were cultivated accordingto generally accepted technologies in LIH (Bobinas, 1999). Data on diseasewere recorded at 3 day intervals, starting with the appearance of disease,following a scale of 0-5, where 0 – no sporulation, 1– leaves are damaged till1%, 2 – leaves are damaged from 1-5%, 3 – leaves are damaged from 5-20%,4 – leaves are damaged from 20-40%, 5 – leaves are damaged > 40% anddisease intensity was calculated by formula (Þemës ûkio augalø kenkëjai…,2002):∑ a ⋅b⋅100R=N ⋅ KR – sporulation intensity, a·b – sum of plants damaged with same point,N – total number of plants, K – the best point of damage. In addition, theexperiment was replicated twice. Regression analysis was used to analyze spreadand intensity of disease (Tarakanovas, 2003).Data on mean air temperatures, amount of precipitation and relativehumidity were obtained from Metos D (Fig. 1-2) and their role was determinedon the development of disease.Results. Meteorological conditions for plant development and diseaseappearance in 2004-2005 were quite favorable. The mean air temperature,relative humidity (RH), and rain significantly affected downy mildewdevelopment. In 2004 the first symptoms of disease was assessed on August 6,because the biggest amount of precipitation (17.8 mm) fell from the last decadeof July and first days of August (Fig. 3). The mean air temperature during thisperiod was 17.2-18.5°C; the spread of disease was 10.8% and disease intensity1.2%. Disease progress was the highest on August 9-12, the spread of diseaseincreased from 20.7% to 81.3% and disease intensity increased from 8.4% to39.6%. On these days the mean day temperature was 20.8-23.2°C, the meannight temperature was 15-16.4°C and RH was 80-95% (Fig. 3). Following187