ABSTRACT
An anthracnose disease was observed on stems of high-bush blueberry plants (Vaccinium corymbosum L.) in Liaoning Province, China in 2012. The typical symptoms consist of sudden wilting and dieback of stems during the growing season. Dark brown lesions originate from infected buds and kill portions of the stems. Lesions have grayish white centers, with the necrotic areas becoming 6 to 8 cm in length. Disinfected stem pieces were placed on potato dextrose agar (PDA) and incubated at 28°C for 5 to 7 days, after which the emerging colonies were transferred to fresh PDA. All isolates initially produced white growth, but turned pink after 7 days before becoming blackish green. The average colony diameter was 65.5 to 75.0 mm after 7 days. Conidia were aseptate, hyaline, fusiform to ellipsoid, 8.5 to 16.5 × 2.5 to 4.0 µm in size and single celled with two to seven oil globules. Setae were not found on the acervuli. These characteristics matched published descriptions of Colletotrichum acutatum (1) (teleomorph Glomerella acutata). Pathogenicity test was confirmed in 15 2-year-old healthy potted plants of cv. Berkeley. Stems of 10 plants were punctured with flamed needles and sprayed with 5 ml of conidial suspension (106 conidia per ml in sterile distilled water) of isolate LNSW1. Five control plants were inoculated with sterile distilled water. Seven days after inoculation, eight of the 10 blueberry plants exhibited stem lesions, leaf chlorosis, followed by branch dieback 15 days post-inoculation. The symptoms were similar to those observed on diseased plants in the field, and no lesions were observed on control plants. The pathogen was reisolated from the margin of lesions and identified by colony growth characteristics on PDA. PCR amplification of one isolate (LNSW1) was carried out by utilizing the universal rDNA-ITS primer pair ITS1/ITS4. The sequence (557 bp) of isolate LNSW1 (GenBank Accession No. JX392857) showed 99% identity to G. acutata (AB443950) and C. acutatum (AJ749672) in a BLAST search. An approximately 490-bp fragment was amplified from LNSW1 by the species-specific primer pair CaInt2/ITS4 (2). The pathogen was identified as G. acutata (asexual stage: C. acutatum J.H. Simmonds) on the basis of morphological characters, rDNA-ITS sequence analysis, and a PCR product with species-specific primers. To our knowledge, this is the first report of C. acutatum in high-bush blueberry plants in China. References: (1) C. Lei et al. Fungal Diversity 12:183, 2009. (2) S. Sreenivasaprasad et al. Plant Pathol. 45:650, 1996.
ABSTRACT
Blueberry (Vaccinium spp.) is becoming increasingly popular in China as a nutritional berry crop. With the expansion of blueberry production, many diseases have become widespread in different regions of China. In August of 2012, stem and leaf spots symptomatic of anthracnose were sporadically observed on highbush blueberries in a field located in Liaoning, China, where approximately 15% of plants were diseased. Symptoms first appeared as yellow to reddish, irregularly-shaped lesions on leaves and stems. The lesions then expanded, becoming dark brown in the center and surrounded by a reddish halo. Leaf and stem tissues (5 × 5 mm) were cut from the lesion margins and surface-disinfected in 70% ethanol for 30 s, followed by three rinses with sterile water before placing on potato dextrose agar (PDA). Plates were incubated at 28°C. Colonies were initially white, becoming grayish-white to gray with yellow spore masses. Conidia were one-celled, hyaline, and cylindrical with rounded ends, measuring 15.0 to 25.0 × 4.0 to 7.5 µm. No teleomorph was observed. The fungus was tentatively identified as Colletotrichum gloeosporioides (PenZ.) PenZ & Sacc. (teleomorph Glomerella cingulata (Stoneman) Spauld. & H. Schrenk) based on morphological characteristics of the colony and conidia (1). Genomic DNA was extracted from isolate XCG1 and the internal transcribed spacer (ITS) region of the ribosomal DNA (ITS1-5.8S-ITS2) was amplified with primer pairs ITS1 and ITS4. BLAST searches showed 99% identity with C. gloeosporioides isolates in GenBank (Accession No. AF272779). The sequence of isolate XCG1 (C. gloeosporioides) was deposited into GenBank (JX878503). Pathogenicity tests were conducted on 2-year-old potted blueberries, cv. Berkeley. Stems and leaves of 10 potted blueberry plants were wounded with a sterilized needle and sprayed with a suspension of 105 conidia per ml of sterilized water. Five healthy potted plants were inoculated with sterilized water as control. Dark brown lesions surrounded by reddish halos developed on all inoculated leaves and stems after 7 days, and the pathogen was reisolated from lesions of 50% of inoculated plants as described above. The colony and conidial morphology were identical to the original isolate XCG1. No symptoms developed on the control plants. The causal agent of anthracnose on blueberry was identified as C. gloeosporioides on the basis of morphological and molecular characteristics, and its pathogenicity was confirmed with Koch's postulates. Worldwide, it has been reported that blueberry anthracnose might be caused by C. acutatum and C. gloeosporioides (2). However, we did not isolate C. acutatum during this study. To our knowledge, this is the first report of stem and leaf anthracnose of blueberry caused by C. gloeosporioides in China. References: (1) J. M. E. Mourde. No 315. CMI Descriptions of Pathogenic Fungi and Bacteria. Kew, Surrey, UK, 1971. (2) N. Verma, et al. Plant Pathol. 55:442, 2006.
