First Report of Pseudopestalotiopsis theae Causing Leaf Spot of Date Palm (Phoenix dactylifera) in China

Date palm (Phoenix dactylifera L.) is a popular landscape tree in Fujian province, in South China. In November 2018 and June 2019, a leaf spot disease was observed on date palm in Fuzhou city. A survey of date palm plants grown in four different locations revealed that the disease incidence was almost 20%. The spots were brown with a yellow margin, 1 to 20 mm in diameter, and oval to irregular. In later stages, the spots gradually expanded and coalesced, became dry and died. For isolation, small pieces (0.5 cm2) were cut from leaf spots obtained from seven trees and disinfested with 70% alcohol. Leaf pieces were then placed onto 2% potato dextrose agar (PDA) and incubated at 25±2°C for 3 to 4 days. One fungus was consistently isolated from fifteen leaves. Fungal colonies were white with undulating margins and a light cream on the reverse side. Black globose to oblate conidiomata were irregularly distributed throughout ten-day-old colonies. The conidiogenous cells were septate, colorless, smooth-walled, straight to slightly curved, ampulliform or subcylindrical, and 6.0 to 13.5 × 1.3 to 3.0 μm [(n=50); x̄ ± SD = 9.5 ± 2× 2 ± 0.5μm]. Conidia were fusiform and five-celled with constrictions at the septa, measuring 18.5 to 31.5 × 5.0 to 7.5 μm [(n=50); x̄ ± SD = 25.5 ± 2 × 6.5± 0.2μm]. The three median cells were light to dark brown and the two end cells were colorless. Apical cells had 2 to 4 appendages ranging from 10.2 to 22.5 μm long. Basal cells had one appendage ranging from 3.5 to 5.5 μm long. The internal transcribed spacer (ITS) region of the ribosomal DNA and translation elongation factor 1-alpha (TEF1-α) gene of fungus were amplified using primers ITS1/ITS4 and EF1728F/EF1986R, respectively. Amplified products (ITS: MN294700 and TEF1-α: MN970514) showed 99% sequence identity to Pestalotiopsis sp., and Pseudoestalotiopsis theae sequences in GenBank. A comparison of MRC12 sequences with the type culture sequences (ITS: JQ683727 and TEF1-a: JQ683743) also showed high similarity, where ITS sequences exhibited only a three-nucleotide difference at the start of the sequences. No differences, however, were found between the TEF1-α sequences. On the basis of morphology and molecular characteristics, the fungus was identified as Ps. theae (Sawada) Maharachch., K.D. Hyde & Crous Steyaert (Maharachchikumbura et al. 2014). To confirm pathogenicity, five disinfested leaves on three healthy five-year-old date palm plants in a nursery (average temperature 26°C), were punctured 3 to 5 times with a sterilized needle, and then 10 to 15 mL conidial suspension (105 conidia/mL in sterilized distilled water) was sprayed over punctured areas of the leaves. For the control treatment, punctured leaves were sprayed with sterilized distilled water. All inoculated leaves plus the control were covered with plastic bags. After 10 days, brown leaf spots similar in appearance to those observed in the field appeared on all wounded leaves, and Ps. theae was successfully re-isolated; the control leaves remained asymptomatic. Previously, Ps. theae was reported on oil palm (Elaeis guineensis Jacq.) from Sierra Leone and Thailand (Turner, 1971; Suwannarach et al. 2013). To our knowledge, this is the first report of Ps. theae on date palm in China. This report expands the host range Ps. theae to date palm and underscores the potential threat of an emerging leaf spot pathogen on Phoenix species. References Maharachchikumbura, K.D., et al. 2014. Stud. Mycol. 79: 121-186. Suwannarach, N., et al. 2013. J. Gen. Plant Pathol. 79: 277-279. Turner, P.D. 1971. Phytopathol. 14: 1-58.

Keywords: Date Palm; Pseudopestalotiopsis theae; conidia; conidiomata.