Abstract: The investigation on the population fluctuation of main pathogens Pythium spp.and Fusarium oxysporum f.sp.cucumerinum in the rhizosphere of four cucumber varieties showed that there was a significant difference in the population number of pathogens for different cucumber varieties and for different growth stages of the same variety,which was in accordance with the regular disease incidence pattern.The population number of Pythium spp. was significantly higher at cucumber creeping stage than at its other growth stages,while that of Fusarium oxysporum f.sp.cucumerinum was the highest at cucumber principal-fruiting stage.There was a closer positive relationship between two test pathogens and their antagonistic bacteria,with the correlation coefficient being 0.95 and 0.81,respectively.

Key words: Wetland, Carex lasiocarpa population, Aboveground biomass, Plant height, Sheath height, Fractal dimension