First Report of Black Spot in Dendrobium officinale Caused by A. alternata in Zhejiang Province,China

Dendrobium officinale has been used as one of the most valuable medicinal herbs in China．Zhejiang Province produces 80% world yield of D. officinale with 2.749 ton and $57 million per year (Pan et al., 2016). In 2001, growers in Lin’an city, Zhejiang Province,reported sporadic occurrence of black spot symptoms on D. officinale plants. The same symptoms occurred in about 60% of D. officinale greenhouses in Zhejiang province in 2014. Symptoms on leaves initially appeared as small lesions (1 to 7 mm diam.), circular, light to dark brown. The spots gradually enlarged in size with brownish-red borders. Severely affected plants have defoliated earlier. Small pieces of symptomatic leaf tissues were surface sterilized with 1.5% sodium hypochlorite for 2 min, plated on 2% potato dextrose agar (PDA), and incubated at 25°C in the dark for 7 day. A total of 13 single spore isolates namely ZJA-1 to ZJA-13 from 15 leaf samples were transferred onto potato carrot agar (PCA) plates (Simmons, 2007). After 5 days, olive-gr...