Development of Populations of Softrot Bacteria on Witloof Chicory Leaves during Root Production in the Field

During a 4.-year field experiment at ihe Experimental Slatton for Arable Farming in Lelystad, the Netherlands, witloof chicory plants, grown for root production, were surveyed for Ihe presence of epiphylic or saprophytic populations of the softrot bacteria (Enriniu carotovora and Pseudomonus marginalia) on their leaves. Isolates of pectolytic bacteria collected frotn the leaves were identified and the influence of environmental variables was assessed testing the hypothesis of an increase of the number of isolates on plants in the field. A significant linear correlation (R- = 0,47, n = 20, P = 0.002)" was found for the regression of the number of pectolytic isolates on titne (tnonth) and temperature (monthly average). The average monthly growth rate of the softrot bacteria was significantly greater than zero during the field seasoti, indicating an increase of the populations of softrot bacteria. The ratio between the number of Envinia and Pseudomonus isolates changed during the growing season from a predominance of pseudomonads frorn May until July to ati equal ratio from Atigust until harvest. The number of isolates of Erwinia carotovora was negatively correlated with total global radiation. The increase in the number of Ecc later in the growing season was attributed to protection from high radiation levels and adverse temperatures in the tmicroclimate under the canopy,