Red Foliage Blight of × Taxodiomeria peizhongii Caused by Neopestalotiopsis clavispora Newly Reported in China.

Abstract

× Taxodiomeria peizhongii Z.J. Ye, J.J. Zhang & S.H. Pan is a hybrid of Taxodium mucronatum and Cryptomeria fortunei. It can adapt to various site conditions and has a good saline-alkali tolerance, which is a unique tree species in eastern China. In August 2020, a red foliage blight with an incidence of 70% (105/150 plants) was found on the leaves of × T. peizhongii in a nursery, Shanghai, China (121°21'12"E, 31°41'56"N). It developed from apical leaves of branches downwards. The infected leaves became reddish brown and withered. Fresh specimens were collected from 3 infected trees. Small samples (3-4 mm2) from lesion margins were sterilized, plated on potato dextrose agar (PDA) and incubated at 25°C. Nine isolates of the same fungus were obtained. Three representative isolates (DFS1-3, DFS1-8, and DFS1-9) were used for morphological and molecular studies and deposited in the China's Forestry Culture Collection Center (cfcc57401 to cfcc57403). The colonies of three isolates on PDA grew fast, covering the entire plate with white cottony mycelia in 7 days. Acervuli of DFS1-3 were 618-996 × 586-945 µm (n = 50). Conidiogenous cells were 4.4-9.8 µm (n = 50) long. Conidia were 5-celled, clavate to fusiform, smooth, 19-24 × 6.4-8.8 µm (n = 50). The 3 median cells were dark brown to olivaceous, central cell was darker than other 2 cells, and the basal and apical cells were hyaline. All conidia developed one basal appendage (3.4-8 µm long; n = 50), and 2-3 apical appendages (15-30 µm long; n = 50), filiform. The morphological characters of DFS1-8 and DFS1-9 were almost identical to DFS1-3. Based on morphological studies, the isolates were Neopestalotiopsis sp.. The DNA of 3 isolates was extracted. The internal transcribed spacer region (ITS), β-tubulin 2 (TUB2) and translation elongation factor 1-alpha (TEF1-α) loci were amplified using the primer pairs ITS1/ITS4, T1/Bt-2b, EF1-728F/EF-2. BLAST result showed that ITS of the three isolates were identical to Pestalotiopsis sp. at a high level (greater than 99%), and TUB2, TEF1-α were highly similar with Neopestalotiopsis sp. (greater than 99%). The sequences were deposited in GenBank [Accession Nos. OM188301 and OM222696 to OM222697 for DFS1-3; OM188303 and OM222698 to OM222699 for DFS1-8; OM188302 and OM222700 to OM222701 for DFS1-9]. A maximum likelihood and Bayesian posterior probability analyses using IQtree v. 1.6.8 and Mr. Bayes v. 3.2.6 with the concatenated sequences (ITS, TUB2, TEF1-α) clustered 3 isolates together with N. clavispora including type isolate (MFLUCC 12-0281). Based on the morphology and phylogeny, the fungus was N. clavispora. To confirm pathogenicity, 9 healthy 2-yr-old seedlings, and 10 leaves per seedling were wounded with a sterile needle and inoculated with conidial suspension (106 conidia/mL). Three control plants were sprayed with sterile water. Seedlings were covered with plastic bags after inoculation and kept in a greenhouse at 25 ± 2°C and RH 80%. Seven days after inoculation, all inoculated leaves were reddish brown and withered like those observed in the field, whereas the control plants remained symptomless. N. clavispora was successfully reisolated from the infected tissues. This pathogen has been reported to cause leaf blight on many other hosts, such as Ligustrum lucidum and macadamia, but in recent years, the disease has also been reported on flowers, such as Anthurium. It has not been reported on Taxodium and Cryptomeria. This is the first report of N. clavispora infecting × T. peizhongii in the world. These data will help select appropriate fungicides for managing this newly emerging disease.