Dalbergia odorifera T. Chen is a national second-grade protected and one of the four famous trees in China, with high medicinal and economic value. Leaf spot disease in this plant can cause the leaves to dry up, perforate or even fall off, which affects the growth and development, and also has a great influence on its products. In May 2019, the leaf spot of Dalbergia odorifera T. Chen was found and observed in Chengmai County (N19°40′, E110°0′), Hainan Province, China, and the symptomatic leaves were brought back to the laboratory for research; According to our survey at that time, the incidence of the disease was between 10% and 15%. A sterile stainless-steel scalpel was used to cut the tissues at the junction of the leaf lesions and placed on a clean bench, soaked in alcohol (75 %) for 30 s, and rinsed thrice with sterile water. Then it was inserted obliquely onto lactic acid-containing potato dextrose agar (PDA) and incubated at 28 °C for 5 days. The growing prominent colonies were singled out and re-inoculated on PDA and SNA plates. Preliminary identification was based on morphological characteristics, followed by molecular identification of strains by evaluating genes for translation elongation factor-1α(TEF-1α), beta-tubulin, mitochondrial small subunit (mtSSU)( Duan et al. 2019; Cao et al.2019; Stenglein et al.2010), and histone H3 (Jacobs, et al. 2010) . Through morphological observation, the isolate was identified as Fusarium fujikuroi. At the initial stage of growth on PDA, the strain produced a large number of white hyphae, followed by pink and purple-brown hyphae in the center of the colony which spread to the surrounding area. The microspores were abundant, colorless, elliptic or clavate, without septum or at 1-2 septate, and the size was about 3.3 to 13.5 × 1.2 to 3.2 µm. After nine days of culturing on SNA medium, few, large conidia were observed, typically sickle-like, with 3-4 septa with a size of about 20 to 40.2 × 2.3 to 4.4 μm. The identity of the strains was determined by comparing the gene sequences of TEF-1α, mtSSU, beta-tubulin and histone H3 by NCBI BLAST. The results showed that TEF-1 α (MN958396), mtSSU (MN958394), β - tubulin (MN958395), and histone H3 (MN958397) from the target strain (jxht0302) had 100% sequence homology with F. fujikuroi (GenBank, accession numbers KF604040.1, MF984420.1, XM023575231.1, and MF356523.1 respectively). Next, the infection of D. odorifera T. Chen seedlings with and without injury was studied using a fungus block, with PDA as a control. Two days after inoculation with injury, obvious lesions were observed on the leaves, which appeared at least 5 days post- inoculation without injury, with no lesions in the control group. F. fujikuroi could be re-isolated from the leaves with lesions, but not from the control group. F. fujikuroi causes Black Rot of Macleaya cordata and maize ear rot (Yull et al.2019; Duan et al. 2019). As far as we know, this is the first report of F. fujikuroi causing leaf spot disease of D. odorifera T. Chen. Given the importance of D. odorifera T. Chen products, this disease needs more attention to tackle it.
First report of Fusarium fujikuroi in the Lao PDR