First Report of Anthracnose caused by Colletotrichum siamense and C. gloeosporiodes on Cornus hongkongensis in China.

In summer 2021, severe anthracnose symptoms were found on the leaves of C. hongkongensis in Nanchang Institute of Technology (28°41'32.61"N, 116°1'53.75"E), with an incidence estimated at 25% to 55%. The lesion occurred mostly on young leaves with irregular reddish-brown with yellowish halos (Figure 1 A, B and C). Samples were collected and isolated. After the pathogenicity tests in the greenhouse, isolates of C. siamense and C. gloeosporiodes were selected for field experiment. To confirm pathogenicity, mycelial plugs of isolate SL13 and SH15 were applied on punctured leaves of C. hongkongensis using a sterile needle in field. Inoculation with only a PDA plug served as controls. All the leaves were covered with plastic bags for 48 h maintain high relative humidity. Seven days later, symptoms similar to those observed in the field developed on all leaves inoculated with isolated SL13 and SH15 (Figure 1 E and F), while the controls remained symptomless. Conidia of isolate SL13 and SH15 hyaline, were usually aseptate, sometimes becoming 1-septate with age, smooth-walled and cylindrical with both ends obtusely rounded, which were measured 13.68-17.41 × 4.38-6.09 µm (n = 30) (Figure1 J) and 11.01-16.15 × 3.520-5.09 µm (n=30) (Figure 1 K), respectively. Sequences were deposited in GenBank with accession numbers of OL658843 and OL858837 for ITS, OL677435 and OL961567 for ACT, OL961569 and OL961568 for GAPDH, OL677434 and OL677437 for TUB2, OL677436 and OL961570 for CHS1, respectively. Based on the phylogenetic tree analysis using IQ-TREE, isolate SL13 and SH15 was clustered with C. siamense and C. gloeosporiodes, respectively. C. siamense has been reported to cause anthracnose on C. hongkongensis (Wang et al., 2021). To our knowledge, the first report of C. gloeosporiodes and Colletotrichum siamense causing anthracnose on C. hongkongensis in China.