Effect of temperature and relative humidity on conidial germination of the causal agent of cucumber powdery mildew

This study was conducted in the plant protection department, faculty of agriculture and botany department, faculty of art and Science in AL. Gubba. Omar AL-Mukhtar University during season 2019-2020. The effects of relative humidity (RH) and temperature on conidial Germination of E. cichoracearum were studied in controlled environments to define conditions that affect the disease development of cucumbers in AL.Gabel, AL-Akhder region. Libya. Gradients of RH (20–90%) at constant temperatures (20–30°C) were generated in single growth chambers to determine their effect on mildew development on mature cucumber plants, temperature from 5 to 35 are evaluated their effect of Temperatures of 30°C and above were deleterious for spore germination, germ tube elongation, and disease development Lesion growth and rate of disease progression were significantly higher at 20°C than at 25°C. Low RH levels (20–40%) reduced spore germination and lesion growth, accelerated host tissue death, and reduced disease progress. Intermediate RH levels (50–70%) increased spore germination and optimized disease development, provided temperatures were maintained within favorable limits. High RH levels (80–90%) were favorable for spore germination but continued exposure to these conditions led to a limited lesion growth and disease progress. Short daily periods (two or three daily exposures of at least 2 h) of high temperatures (35°C) suppressed disease development by 70–92%.