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First Report of Downy Mildew Caused by Pseudoperonospora cubensis on Chayote (Sechium edule) in Taiwan

Chayote (Sechium edule) is cultivated on more than 500 ha in Taiwan for its edible shoots and fruit. In August 2005 and later, 40 to 75% of the chayote plants cultivated in the Taichung District Agricultural Improvement Station in Puli developed pale yellow, irregular spots on the upper leaf surfaces with corresponding sporulation on the lower leaf surfaces. The lesions eventually became necrotic and spread over the entire leaf surface, leading to defoliation. Pseudoperonospora cubensis, which was previously reported as the cause of downy mildew on squash (Cucurbita moschata), muskmelon (Cucumis melo), cucumber (Cucumis sativus), and sponge gourd (Luffa cylindrica) in Taiwan, was identified (1). Sporangiophores were 182 to 410 μm long, 4.8 to 7.2 μm wide, and dichotomously branched. Sporangia were grayish, ovoid to ellipsoidal, 18.2 to 38.6 μm long, and 13.5 to 25.2 μm wide. Biflagellate zoospores were 9.5 to 12.6 μm in diameter. Pathogenicity tests were conducted four times with six 2-week-old plants in each trial. A sporangial suspension (1 × 10⁵ spores per ml) prepared from infected leaves (5 to 6 weeks after infection) was sprayed on all leaves until runoff. The plants were then covered with polythene bags and incubated for 48 h at 18 ± 1°C in a growth chamber. Control plants were sprayed with sterile water. Characteristic symptoms developed on all inoculated plants after 20 days, while control plants remained symptomless. Microscopic observation of leaf tissues of symptomatic plants confirmed the presence of P. cubensis. To our knowledge, this is the first report of P. cubensis causing downy mildew on chayote in Taiwan.

References: (1) S. T. Hsu et al. List of Plant Diseases in Taiwan. The Phytopathological Society of the Republic of China, 2002.