Factors associated with occurrence of target leaf spot of cucumber
Target leaf spot, caused by Corynespora cassiicola, is a severe disease affecting cucumber cultivation. Most Japanese cultivars are susceptible to this disease. Additionally, the pathogen often has fungicide resistance making it difficult to control. We investigated factors associated with the occurrence of cucumber target leaf spot in order to predict and prevent the disease. The pathogen can grow at 10-35°C on potato dextrose agar medium. The optimum temperature for mycelial growth was approximately 30°C. Conidia of the pathogen germinated well at 25-35°C. Optimum temperatures for pathogen infection on cucumber leaves were approximately 25-30°C. Slight infection was observed at 10 and 35°C. More than 18 h of leaf-wetness duration at 20-30°C was necessary for obvious infection of the pathogen. Disease symptoms were enhanced by extension of the wetness duration. Symptoms especially became severe after more than 30 h of wetness. The results of inoculation tests showed that the number and/or area of lesions varied among cucumber cultivars. Some cultivars showed reduced symptoms in both the number and area of lesions compared with a susceptible control cultivar. These cultivars appeared to be resistant on pathogen infection and development. The findings we obtained from this study are useful for prediction and control of cucumber target leaf spot.
Araki, N., Ozaki, R. and Usami, T. (2021). Factors associated with occurrence of target leaf spot of cucumber. Acta Hortic. 1312, 431-438
Corynespora cassiicola, Cucumis sativus, cultivar, environmental factor, plant disease