First Report of Leaf and Stem Downy Blight of Longan Seedlings Caused by Peronophythora litchii in Taiwan

摘要

Fruit downy blight caused by Peronophythora litchii Chen ex Ko et al. is an important disease of litchi (Litchi chinensis Sonn.) in Taiwan, especially in rainy seasons. Previous records indicate litchi as the only natural host of P. litchii, but this pathogen was found on seedlings of longan (Euphoria longana Lamarck) in 2000. Young seedlings of longan that had emerged in a litchi orchard near Caotun, Nantou County, showed symptoms of droopy leaves and leaf blight. Water-soaked lesions appeared on young leaves, which turned into brown, round or irregular lesions (about 3 to 5 cm long). Diseased leaves withered and collapsed eventually. Dark brown lesions were found on stems of some infected seedlings but none of the infected seedlings were killed. Also, no symptoms were found on mature leaves. The pathogen produced numerous sporangia on sporangiophores on diseased leaves under humid conditions.