First Report of Anthracnose Caused by Colletotrichum boninense on Spotted Laurel in China

Spotted laurel (Aucuba japonica 'Variegata') is an evergreen shrub native to China, Korea and Japan, prized for its foliage of green and golden yellow mottled foliage (Fang and Hu 1990). In November 2020, about 50% of spotted laurel in Jiangxi Academy of Forestry (28°44'10''N, 115°49'1.62"E) at Jiangxi province were observed to have anthracnose-like symptoms. The typical symptoms were tended to coalesce to form initially dark brown specks on the leaves, which developed to nearly circular spots of the diameter no more than 1.2 cm and might join to large irregular spots. The spots were grayish white at the center, purple brown at the border and surrounded by a yellow halo. To isolate and identify the pathogen, 15 leaves with typical symptoms were sampled. Isolation and morphological analysis were performed following the method of Ding et al. (2021). Among 40 fungal isolates, 33 showed the same morphological characters. The colony on PDA was umbonate pink-gray in the center surrounding by white margin, the reverse was greyish-cream. The average mycelial growth rate was ca. 0.8 mm per day at 25±1°C on PDA. The conidia were hyaline, aseptate, straight, apex round and base round, mean ± SD = 16.50±3.75 μm × 7.50±2.50 μm. For further confirmation of the identity, six genes, including ITS, GAPDH, ACT, TUB2, CAL and CHS-1 (Damm et al. 2012) were amplified and sequenced. The sequences of rDNA-ITS, GAPDH, ACT, TUB2, CAL and CHS-1 of 1SJ5 were deposited in GenBank as: OM988385, ON009367-ON009371. Phylogenetic analysis based on the above six genes showed that isolates formed a single clade with the strains of Colletotrichum boninense. Pathogenicity tests of isolate 1SJ5 were carried out on the leaves in the field. The mycelial plugs of isolate 1SJ5 were applied on punctured leaves of A. japonica using a sterile needle in field. Inoculation with only a PDA plug served as controls. 14 -21 days, symptoms like those observed in the field, developed on the inoculated plants but not on the controls. The fungus was re-isolated from the margins of the leaf spots and identified by morphological and molecular characters. C. boninense has been reported as causing anthracnose on a broad range of hosts including strawberry (Bi et al. 2017), Eucalyptus robusta (Zhang and Zhu 2018), Alcantarea imperialis (Meneses et al. 2019), and so on. To our knowledge, this is the first report of leaf anthracnose on A. japonica caused by C. boninense in China and our findings will be useful for its management.