First Report of Anthracnose Caused by Colletotrichum kahawae and Colletotrichum horii on Tea-Oil Tree in China

S Wei, H Yuan, T Lei, S Chen - Plant Disease, 2023 - Am Phytopath Society
S Wei, H Yuan, T Lei, S Chen
Plant Disease, 2023Am Phytopath Society
Tea-oil tree (Camellia oleifera Abel) is an important economic woody plant in southern
China. The buds, fruits, and leaves of tea oil tree are all susceptible to anthracnose, causing
the wilt or even fall of the plant. Every year, the disease incidence of anthracnose reached
20 to 40% in diseased fields. In 2020, leaves with anthracnose were collected from the main
producing areas of tea-oil tree in Yunnan Province and Guizhou Province, China. To isolate
the pathogen, several fragments of diseased tissues (5× 5mm) were disinfected in 75 …
Tea-oil tree (Camellia oleifera Abel) is an important economic woody plant in southern China. The buds, fruits, and leaves of tea oil tree are all susceptible to anthracnose, causing the wilt or even fall of the plant. Every year, the disease incidence of anthracnose reached 20 to 40% in diseased fields. In 2020, leaves with anthracnose were collected from the main producing areas of tea-oil tree in Yunnan Province and Guizhou Province, China. To isolate the pathogen, several fragments of diseased tissues (5× 5mm) were disinfected in 75% alcohol for 40 s and then rinsed three times in sterilized water. Then, tissues were placed on PDA medium and incubated at 26 C for 5 days. Fungal isolates with morphology characteristics similar to Colletotrichum spp. were consistently recovered from diseased tissues. Eighteen fungal isolates were obtained. Among them, three representative single-spore isolates (C2, gy15, Ch) were picked for further analysis. The isolates C2 and gy15 on the PDA were gray-white in the initial stage and later became olive-green and spread to the edge. Abundant orange-red conidial masses were present on the colony surface. Conidia were cylindrical and with blunt circles at both ends, with a size of 9.9 to 21.8× 4.0 to 6.8 µm (n= 50). The hyphae of isolate Ch on PDA were thin, cotton-like, gray to gray-black; the center of the back of the colony was brown, and the color of the colony became darker, and concentric rings could be produced. The conidia were cylindrical, with blunt circles at both ends, with a size of 6.3 to 15.0× 3.2 to 7.0 µm (n= 50). To further identify the pathogens, the internal transcribed spacer (ITS) region of ribosomal DNA, actin (ACT), chitin synthase (CHS), b-tubulin (TUB2), calmodulin (CAL), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were amplified (Weir et al. 2012; Yang et al. 2009). The resulting sequences were deposited under the GenBank accession numbers OK148894, OM397909, OM249943, OL422149, OM184266, and OM718003 for C2; OK148975, OM397910, OM249944, OL422150, OM184267, OM718004 for gy15; and OK148976, OM397911, OM249945, OL422151, OM184268, and OM718005 for Ch. A BLAST search showed that the sequences of isolates C2 and gy15 had 99.57 to 100% similarity to the type strain of Colletotrichum kahawae ICMP12952. The sequences of isolate Ch had 99.03 to 100% similarity to the type strain of Colletotrichum horii ICMP 17968. Further, a phylogenetic tree based on the combined ITS, ACT, CHS, TUB, CAL, and GAPDH sequence using the neighbor-joining algorithm revealed that the isolates were C. kahawae and C. horii. Pathogenicity assays were conducted on healthy leaves collected from 1-year-old tea-oil tree. The experiments were repeated twice. The leaves were surface sterilized with 75% ethanol. After drying, they were placed in a plastic box prelaid with sterilized absorbent paper. The leaf surface was slightly pierced with a sterile needle, and each stab wound was inoculated with 10 µl of conidial suspension (1× 106 conidia/ml). All inoculated leaves were placed in a moist chamber at 25 C with 80% relative humidity. After 10 days, inoculated leaves showed similar symptoms as observed in the field, whereas controls remained symptomless. C. kahawae and C. horii were reisolated from the diseased leaves and were identified by sequencing. C. kahawae is widespread on coffee in Africa (Waller et al. 1993). C. horii has been associated with fruit and stem diseases of Diospyros kaki from China, Japan, and New Zealand (Weir et al. 2010). To our knowledge, this is the first report of C. kahawae and C. horii causing anthracnose of tea-oil tree.
The American Phytopathological Society
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