First report of leaf spot caused by Bipolaris setariae on cassava in China.

Cassava (Manihot esculenta Crantz) is an important food crop in tropical regions of China. Seventy percent of the cassava output is used for starch and ethanol production and it has become the base of food and bioenergy industries. In July 2009, a new leaf spot disease was found on cv. HuaNan205 from a cassava plantation in Danzhou, Hainan Province. Disease occurred on 50% or less of the plants. Initial symptoms were elliptical, chlorotic, and water-immersion lesions of 2 to 4 mm in diameter. These lesions became dry and yellow due to the progress of the disease. A brown halo was around the lesions, and in wet conditions, a dark gray mildew often appeared in the middle of the lesion. Diseased leaves turned yellow and the plants eventually became defoliated. The pathogen was isolated and pathogenicity was established by following Koch's postulates. Young, healthy, and fully expanded green leaves of Cassava cv. HuaNan205 were surface sterilized and then inoculated by spraying them with a suspension of conid...