First Report of Pythium cylindrosporum Causing Black Leg on Geraniums in China

Geranium has been widely used in garden landscaping for its rich colors, long florescence, and easy reproduction. During the fall season of 2014 and 2015, the geranium seedlings in a nursery garden in the northern suburbs of Kunming City, Yunnan Province, showed symptoms of black leg. Five cultivars of geranium（Pelargonium×hortorum）, including ‘Horizon’ and ‘Divas’ suffered, showing a maximum morbidity rate of 50%. The basal stems of the plant turned black and were water-soaked, and its leaves turned yellow from the bottom up. As the disease progressed, the affected plants wilted and collapsed. The diseased basal stem tissue was rinsed under running water, blotted dry, and cut into 0.5-cm pieces. The pieces were plated on the semiselective medium for oomycetes (17 g/liter corn meal agar amended with nystatin 15 mg/liter, ampicillin 250 mg/liter, rifampicin 10 mg/liter, and miconazole 1 mg/liter) (Morita and Tojo, 2007) and incubated at 25 °C for 3 days. Colonies resembling Pythium sp. were transferred to ...