Macadamia ternifolia F. Muell. (Proteaceae) is a high-value commodity commonly known as small-fruited Queensland nut or Gympie nut. Currently, China has the largest macadamia nut-growing area globally. In June 2023, a severe anthracnose disease of M. ternifolia was found in three counties and cities, including Mangshi, Yingjiang, and Puer, Yunnan, China. Symptoms on fruit were circular or irregular, brown to black, water-soaked, and sunken lesions. On leaves, irregular spots usually originated from the leaf margins. As the lesions matured, fruits and leaves dropped. A visual survey was conducted on 150 trees from five plantations (each 3.6 ha and 1500 plants/ha), and the average incidence rate of anthracnose was 57%. A total of nine infected leaves were randomly sampled from five plantations, respectively. Pathogens were isolated using a single-spore isolation method (Choi et al. 1999). Nine cultures were obtainted, and seven of the nine isolates resembling Colletotrichum sp.. Colonies of three isolates were cottony, white to light gray with aerial mycelium on the upper side and pink on the back (isolates MIQ04, MIA03 and MIA05). Conidia were unicellular, hyaline, aseptate, and cylindrical with rounded or acute ends, measuring 11.8 to 17.74 × 4 .72 to 6.6 μm, setae were dark brown, slightly curved, with a size of 190 to 210 μm. These morphological characteristics were consistent with published descriptions of the C. gloeosporioides complex (Weir et al. 2012). For molecular identification, The ribosomal internal transcribed spacer (ITS), beta-tubulin (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), chitin synthase (CHS-1), histone-3 (HIS3), glutamine synthetase (GS), calmodulin (CAL), and the Apn2-Mat1-2 intergenic spacer along with the partial mating type Mat1-2 gene (ApMat) were amplified and sequenced based on previous studies (Liu et al., 2022; Ma et al., 2025). The sequences were deposited in GenBank (Accession: ITS: PO465190-PQ465192, TUB2: PQ566707-PQ566709, GAPDH: PQ65393 1-PQ653933, ACT: PQ653922-PQ653924, CHS-1: XXX, H3:XXX, GS:XXX, CAL: PQ653928-PQ653930 and ApMat: PQ653925-PQ653927). Multilocus phylogenetic tree were developed by Maximum Likelihood (ML) and Bayesian methods, which showed that the three isolates clustered together with the Colletotrichum jiangxiense with 100% and 98% bootstrap support. For the pathogenicity test, nine healthy plants were inoculated with 20 μl of conidial suspension (1 × 106 conidia/ml) at 25℃ and 90% relative humidity, and three leaves were inoculated per plant. Three healthy plants were inoculated with 20 μl sterile distilled water as a control group, totaling 3 replicates. After 5 days, the inoculated leaves showed tawny, necrotic lesions, whereas the controls remained asymptomatic. The same fungal pathogen was re-isolated from inoculated leaves and no pathogen was isolated from the control group. The identity was confirmed by morphological and molecular analysis, fulfilling Koch’s postulates. The species C. jiangxiense has been previously reported to cause severe anthracnose on avocado and chili in China (Yang et al., 2021; Zhang et al., 2023), and Avocado in Mexico (Ayvar-Serna et al., 2021). To our knowledge, this is the first report of C. jiangxiense causing anthracnose on M. ternifolia in China, causing severe yield losses per year. Taken together, the results provide important information for epidemiological studies and management of this disease.
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