First Report of Leaf Blight of Ginkgo biloba L. Caused by Neopestalotiopsis clavispora G.F. Atk. in Sichuan, China.

ABSTRACT

Ginkgo (Ginkgo biloba L.), the oldest existing tree species in the world, is an important ornamental and medicinal plant, widely planted in China. In October 2022, a new leaf blight disease was observed in Chengdu city (30°05'to 31°26'N, 102°54'to 104°53'E). Disease incidence averaged 82.5% across five foci. The typical symptomatology begins when leaf margins turn yellow and small black spots appear at the edge of the leaf, chlorotic areas turn brown, dry and deformed. Gradually, the necrotic lesions spreads to the middle of the leaf and eventually the whole leaf falls off. Infected tissues from ten leaves were cut into small pieces (5 × 5 mm); surface sterilized for 30 s in 3% sodium hypochlorite; 60 s in 75% ethanol; rinsed three times in sterile water; placed onto potato dextrose agar (PDA) amended with streptomycin sulfate (50 µg/mL); and incubated at 25°C for 3 to 8 days. A hyphae was removed from the edge of the fungal colony and placed onto potato dextrose agar (PDA) plates. After incubation at 25℃ with a 12-hour light/dark cycle for 8 days, the colony diameter reached 77.5 to 81.5 mm. Colonies grown on PDA were white, cotton, flocculent, undulating on the surface, dense in aerial hyphae and light yellow on the back. Black pycnidia formed superficially, scattered over the PDA, following two weeks of incubation. Pycnidia contained sticky black conidia. The spores were were spindle shaped, with five cells, and four septations measuring 20.9 to 34.8 µm × 6.8 to 8.8 µm (avg. 28.4 × 7.6 µm; n=40). The three median cells were versicolored, typically two dark brown cells and one light brown cell, whereas the basal and apical cells were hyaline. Conidia had a single basal appendage (2.87 to 4.1 µm long; n = 40) and two to three apical appendages (18.3 to 29.1 µm long; n = 40). Based on colony and conidial morphology, the isolate was identified as N. clavispora (Maharachchikumbura et al. 2014). The partial sequence of the internal transcribed spacer (ITS), ß-tubulin gene (TUB2), and translation elongation factor subunit 1-a gene (TEF1) were amplified and sequenced using the universal primer pairs ITS1/ITS4(Zhang et al. 2022), BT2A/BT2B (Li Yuan et al. 2022), and EF1-526F/EF1-1567R (Maharachchikumbura et al. 2012), respectively. Sequences of representative isolate LQYX were deposited in GenBank (ITS OQ152504, TUB OQ168328, and TEF1 OQ168329). BLAST results indicated that the ITS, TUB, and TEF1-α sequences showed 99 to 100% identity with N. clavispora sequences at NCBI (GenBank MG729689, MG740735, and MG740758). Identification was confirmed by Bayesian inference using Mr. Bayes. Next, inoculations were conducted on leaves of ten G. biloba in the field to verify the pathogenicity of LQYX. Ten healthy leaves of each plant were surface sterilized with 75% ethanol, and the wound was rubbed out on the leaf edge on the sterilized sanding paper. A conidia suspension (1 × 107 ml-1) was sprayed on the leaves, aseptic water was used as the control, and the transparent plastic bag was used to maintain relative humidity. After 14 days (26 ℃, 14 hours light / 10 hours dark), the inoculated leaves had similar symptoms as the original diseased plants, whereas controls were asymptomatic. The N. clavispora was re-isolated from the infected leaves and identified by morphological characteristics and DNA sequence analysis. The pathogenicity test was repeated three times with similar results, confirming Koch's postulates. To our knowledge, this is the first report of leaf blight of G. biloba caused by N. clavispora in China, which has greatly affected the appearance of the city and should be further studied. This report can help identify this disease and further develop effective control measures.