A Study of Environmental Factors that Affect Survival of Pumpkin Isolates of Verticillium dahliae

Abstract

V. dahliae is a destructive soilborne pathogen to many economically important crops worldwide. Knowledge of environmental influences, including temperature, source, and availability of nutrients and pH, on disease development is central to devising control strategies. The effects of root decoction media, pH, and temperature on radial growth and microsclerotia production in 32 Verticillium dahliae (Kleb.) isolates from Trinidad were investigated. There were significant differences (P ≤ 0.05) in colony diameters and growth rates for isolates grown on different media. The highest growth occurred on 5% nutsedge root extract agar (NREA) and the least amount of growth was obtained on 1% pumpkin root extract agar (PREA). Production of microsclerotia was significantly higher on 5% PREA, 5% NREA, and potato dextrose agar (PDA). Growth tests on PDA formulated to different pH levels revealed that the most growth occurred at pH 5.2, but this was not significantly different from colony diameters obtained at pH 4.2, 6.2, and 7.2. pH, however, had a pronounced effect on production of microsclerotia. The optimum temperature for radial growth and formation of microsclerotia in V. dahliae in vitro was found to be 25 ± 1 °C. The effects of isolates and temperature on incidence and symptom severity in susceptible pumpkin plants were also tested under controlled conditions. There was no significant difference in symptom severity when inoculated plants were grown at 25 ± 1 °C and at 30 ± 1 °C. The pathogen was recovered from infected plants grown at 35 ± 1 °C, although growth is completely inhibited at this temperature in vitro. There was no significant difference among isolates in their pathogenic response at the four different temperatures tested.