S. Y. Yang,
S. C. Su,
G. Fan, and
J. Wang, Laboratory for Silviculture and Conservation Ministry, Beijing Forestry University, Bejing, 100083, China; and
P. S. Leng, Department of Landscape, Beijing Agricultural College, Beijing, 102206, China
In the 1990s, pistachio (Pistacia vera L. ‘Kerman’ and ‘Peters’) was introduced in China. They are found in many orchards in Beijing and Gansu and Hebei provinces, northern China. In 2009, a new disease was observed on leaves, stems, and fruits in pistachio orchards in Gansu Province. Disease incidence in 8- to 12-year-old orchards was 30%. Yield losses reached 25%. Symptoms began as discrete, sunken, black spots, approximately 10 mm in diameter, followed by circular lesions that eventually coalesced with tissue death recorded and orange fructifications developed on lesions. Pieces of diseased leaves, stems, and fruits were surfaced sterilized and placed on 2% potato dextrose agar (PDA) at 25°C. A fungus was consistently isolated. After 10 days, cultures on PDA showed aerial, white mycelium that turned gray to grayish black with a salmon-to-orange conidial mass at 25°C and a 12-h photoperiod. Brown, 80 to 120 μm long setae were observed in the acervulus. Conidia were hyaline, fusiform to nearly straight, and averaged 12 to 18 × 3 to 5 μm. On the basis of morphological characteristics, the fungus was identified as Colletotrichum gloeosporioides (Penz.) Sacc. (2). On PDA, 0.5 μg/ml of benomyl was applied for the sensitivity test (3). Benomyl completely inhibited the growth of the fungus. Mycelial DNA was extracted, PCR amplified using ITS1 and ITS4 primers for the ribosomal DNA internal transcribed spacers 1 and 2, and sequenced. The DNA sequence was recorded in GenBank as No. HQ631378. The DNA sequence was blasted showing 99% identity with Accession Nos. GQ144454 and GU004376, for C. gloeosporioides. Pathogenicity tests were conducted under greenhouse conditions at 25°C. Three replicates of 2-year-old ‘Kerman’ plants were inoculated with mycelial PDA plugs placed on 0.5-cm2 stem wounds and then wrapped with Parafilm. Controls were inoculated with PDA plugs without the fungus. After 3 weeks, stem cankers were observed on inoculated plants. Control plants remained healthy. Pathogenicity was also tested on injured leaves and fruits. A 10-μl drop of a spore suspension of 104 conidia/ml was applied on ‘Kerman’ and ‘Peters’ leaves and ‘Kerman’ fruits and placed on plates with a wet filter paper at 25°C. Small, black lesions were observed at 2 days after inoculation. At 7 days, necrotic lesions covered the entire surface. C. gloeosporioides was reisolated from necrotic lesions. Controls did not develop symptoms. C. acutatum has been reported on pistachio in Australia (1), but to our knowledge, this is the first report of anthracnose caused by C. gloeosporioides on pistachio.
References: (1) G. J. Ash and V. M. Lanoiselet. Australas. Plant Pathol. 30:365, 2001. (2) J. Y. Lu. Plant Pathogenic Mycology. China Agricultural Press, Beijing, 2001. (3) N. A. R. Peres et al. Plant Dis. 86:620, 2002.