Articles
Environmental effects on the sporulation of Corynespora cassiicola in cucumber leaf spots
Article number
1378_41
Pages
309 – 316
Language
English
Abstract
Target leaf spot caused by Corynespora cassiicola, a destructive greenhouse disease, affects cucumber cultivation in Japan.
In greenhouses, conidia formed on diseased plants from earlier crops often survive for long periods, thereby causing primary disease occurrence during subsequent cropping seasons.
Leaf spots produce numerous conidia and disperse the disease.
An earlier study elucidated the optimum temperatures and necessary leaf wetness durations for C. cassiicola infection.
The present study assesses the relation between physical conditions and pathogen sporulation in leaf spots.
Findings indicate that conidia formation occurs mainly at 20-30°C, with optimal sporulation at 28-30°C. Earlier, we reported the optimal temperatures for conidial germination, hyphal growth, and infection as 25-30°C. Results of this study indicated that conidial formation occurs within a similar temperature range.
In contrast, few conidia formed at 35°C, whereas C. cassiicola grows and germinates well at this temperature.
Free water induces sporulation: water sprayed on leaves led to profuse conidia formation on leaf spots.
Relative humidity (RH) of 100% induced significant sporulation on leaf spots, even when no free water was present.
However, the conidia were significantly fewer under conditions of RH less than 100%. The conidia per lesion area at early stages of lesion formation (5 days after inoculation) were more numerous than at a later stage, indicating that small but fresh lesions can be an infection source.
These findings are useful for evaluating the risk of disease occurrence.
In greenhouses, conidia formed on diseased plants from earlier crops often survive for long periods, thereby causing primary disease occurrence during subsequent cropping seasons.
Leaf spots produce numerous conidia and disperse the disease.
An earlier study elucidated the optimum temperatures and necessary leaf wetness durations for C. cassiicola infection.
The present study assesses the relation between physical conditions and pathogen sporulation in leaf spots.
Findings indicate that conidia formation occurs mainly at 20-30°C, with optimal sporulation at 28-30°C. Earlier, we reported the optimal temperatures for conidial germination, hyphal growth, and infection as 25-30°C. Results of this study indicated that conidial formation occurs within a similar temperature range.
In contrast, few conidia formed at 35°C, whereas C. cassiicola grows and germinates well at this temperature.
Free water induces sporulation: water sprayed on leaves led to profuse conidia formation on leaf spots.
Relative humidity (RH) of 100% induced significant sporulation on leaf spots, even when no free water was present.
However, the conidia were significantly fewer under conditions of RH less than 100%. The conidia per lesion area at early stages of lesion formation (5 days after inoculation) were more numerous than at a later stage, indicating that small but fresh lesions can be an infection source.
These findings are useful for evaluating the risk of disease occurrence.
Authors
Y. Sonoke, T. Usami
Keywords
Cucumis sativus, humidity, plant disease, sporulation, temperature
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