First report of Penicillium oxalicum causing Blue Mould on Gastrodia elata Bl. in Jilin Province, China.

Gastrodia elata Bl. is a saprophytic perennial herb in the Orchidaceae. It is commonly called "tian ma" in Chinese and mainly distributed in eastern Asia, such as China, Japan, Korea, and India. Its tuber extracts are clinically used to treat headache, dizziness, epilepsy, infantile convulsion, and tetany (Zeng et al. 2018; Zhan et al. 2016). During March to late-May 2018, blue mold symptoms were observed on decayed G. elata in Jingyu County, Jilin Province, China. The decayed area of the tubers was dark brown to black, and tissue was soft and watery. The lesions expanded gradually, and bluish green sporulation formed on the surfaces of tubers. Severe blue mold led to death of G. elata. To isolate the causal organism, tissues were excised from diseased and healthy tubers (each about 5 mm2), surface sterilized by soaking in 75 per cent ethyl alcohol for 1 min and 10 per cent sodium hypochlorite for 5 min, rinsed three times in sterilized distilled water, plated on potato dextrose agar (PDA)medium, and incubated at 27°C. Fungal isolates were obtained from infected tissues by the single-spore isolation method. Colonies on PDA were velutinous, plane or nearly plane. Mycelia were initially white or pale-green and cottony. Then they produced blue green pigments in 3 to 5 days. After culturing 5 days, conidia were examined microscopically. Conidia were colorless, unicellular, and kidney-shaped. Conidia measured approximately 3.5 to 4.5 × 2.5 to 3.0 ?m. The morphological characteristics of the fungus were similar to Penicillium oxalicum. The universal primer pair ITS4 and ITS5 was used to amplify and sequence the ribosomal DNA internal transcribed spacer (rDNA-ITS)region by polymerase chain reaction assay from extracted genomic DNA TM1. The ITS sequence (586-bp segment)of TM1 was deposited in GenBank (accession no. KY674515)and revealed 99 per cent similarity with the ITS rDNA sequence of P. oxalicum strain BGPUP4 (KP780809), confirming the morphological identification (Singh and Chauhan 2017). Pathogenicity tests were conducted by spraying conidial suspension (1 × 106 conidia/ml)on the sterilized surface of three healthy G. elata tubers. Another three tubers were sprayed with sterilized distilled potato dextrose broth as a control. All inoculated tubers were covered with sterilized plastic bags and maintained in the dark at 25°C. Symptoms appeared on the inoculated tubers after 7 days, which were the same as those on the original infected tubers. However, the control tubers were asymptomatic. The same pathogen fungus as the inoculated isolate was successfully reisolated from inoculated tubers using the same isolation method described for G. elata but not from any of the control tubers. To the best of our knowledge, this is the first report of P. oxalicum causing blue mold on G. elata in Jilin Province, China.