First Report of Diaporthe tectonendophytica Causing Leaf Spot on Dalbergia odorifera in Guangxi, China.

ABSTRACT

Dalbergia odorifera T. Chen (Family Fabaceae) is a national level II protected plant in China, with extremely high economic value and medical properties (Zhao et al. 2020). In June 2023, an unknown leaf spot was found in a garden land of Pingxiang city, Guangxi, China, and approximately 80% of the plants covered an area of 500 m2 displayed similar symptoms. The spots were grey to white, 4~6 mm in diameter (n=30) with black pycnida on the spots surface (Fig S1, A-D). Multiple disease spots were observed on a single leaf. The pycnida on the lesion were picked and mashed, to make a conidia suspension using sterile water. The conidial solution was then spread onto a potato dextrose agar (PDA) plate containing streptomycin, with 10 mg of streptomycin per 100 mL, and incubated for 3 days at 28°C with a 12 hour photoperiod. Three isolates (GXPX01, GXPX02 and GXPX03) were obtained by re-culturing the colonies on fresh PDA plates. The colony on PDA were white with aerial mycelia (Fig S1, E-F). Black conidiomata developed at 28°C with a 12 hour photoperiod in 20 days (Fig S1, G-H). Alpha conidia were 4.2~6.4 µm × 1.8~2.6 µm (average =5.1 × 2.3 µm, n = 30), mostly bi-guttulate, hyaline, ellipsoid, apex bluntly rounded, base obtuse to subtruncate, smooth (Fig S1, I). Beta conidia were 15.1~33.5 µm × 1~1.8 µm (average = 24.5 × 1.5 µm, n = 30), filiform, hyaline, curved or hamate, aseptate, base subtruncate (Fig S1, J). Morphological characteristics of the three isolates matched those of Diaporthe spp.(Gomes et al. 2013). The rDNA internal transcribed spacer (ITS) region, the translation elongation factor 1-α (TEF1), the calmodulin (CAL), the histone H3 (HIS) and the ß-tubulin (TUB2) genes of the three isolates were amplified using the primer pairs ITS4/ITS5, EF1-728F/EF1-986R, CAL-228F/CAL2Rd, CYLH3F/H3-1B, and T1 /CYLTUB1R, respectively (Crous et al. 2004, Sun et al. 2021). The sequences were all deposited in GenBank (accession numbers OR437511 to OR437513 for ITS, OR454965 to OR454967 for TEF1, OR454968 to OR454970 for CAL, OR454971 to OR454973 for TUB2, OR454974 to OR454976 for H3). Sequences had 98.36% to 100% homology with the corresponding sequences of known Diaporthe tectonendophytica strains MFLUCC 13-0471 in the NCBI database. Phylogenetic analysis was based on combined ITS, TEF1, TUB2 and CAL sequences data using MEGA 11 software to construct phylogenetic tree with Maximum Likelihood (Doilom et al. 2017). In the phylogenetic tree, the combined sequences attributed the three isolates to the D. tectonendophytica (Fig S2). The pathogenicity was tested on leaves of 1.5-year-old D. odorifera seedlings. Three leaves were wounded with a sterile needle and individually inoculated with a 5 mm mycelial disk of PDA culture from each isolate. Sterile PDA disks inoculated leaves as a control. The test was repeated three times. The inoculated plants were placed in a greenhouse at 25℃ and 90% humidity, with a photoperiod of 12 hours. Five days after inoculation, necrotic lesions appeared on inoculated leaves and symptoms from all three isolates were the same as those form natural infections ( Fig S1, K-N), whereas all the control remained symptomless (Fig S1, P). The pathogen was reisolated from the inoculated leaves and again identified as D. tectonendophytica, with the same methodology used for the initial identification. D. tectonendophytica was reported to cause plant diseases, such as stem gray blight of red-fleshed dragon fruit (Hylocereus polyrhizus) (Rahim et al. 2021), leaf spots disease on Elaeagnus conferta and Pometia pinnata (Sun et al. 2021). To our knowledge, this is the first report of D. ctonendophytica causing leaf spot disease on D. odorifera.