Epidemiology and development of forecasting model for powdery mildew (Oidium erysbhoides) in jujube (Zizbhus mauritiana ) for Delhi

Abstract

An experiment was conducted during 1999-2001 at New Delhi to study the effect of temperature and hours of high relative humidity on powdery mildew infection caused by Oidium erysiphoides Fr. in jujube (Ziziphus mauritiana L). Growth of the fungus in terms of conidia germination and germ-tube elongation was favoured at 8-34 degree Celcius. Maximum response was recorded at 26.2 degree Celcius. Relative humidity = 90% was found to favour highest germination as well as germ-tube growth. Minimum 5 hr period was required for conidia germination and to start penetration on fruits. Infection index on fruits was highest (0.96) at temperature 24-26 degree Celcius, while lower index (0.1- 0.15) was at temperature 10-34 degree Celcius. Relative humidity response at 26 degree Celcius expressed in terms of fruit infection index was a typical sigmoid function. Infection index was increased from about 0.17 to 0.90 with the increase in hour of relative humidity from 5 to 24. Data of temperature and relative humidity responses were used to simulate the effect of relative humidity hours (hr) at different temperatures (t) and explained through a multiple regression model, infection index (y) = 0.077 + 0.00583 t* h-0.000003 t² * h²-0.083 h- 0.00076 t² + 0.001 h² (R²= 0.88). Model was validated with the data generated through orchard inoculation. Therefore, the model could be used to assess risk of powdery mildew in jujube based on the occurrence of temperature and relative humidity during the fruit development stage.