Research Article |
Corresponding author: Guoping Wang ( gpwang@mail.hzau.edu.cn ) Academic editor: Nattawut Boonyuen
© 2021 Xianhong Wang, Yashuang Guo, Yamin Du, Ziling Yang, Xinzhong Huang, Ni Hong, Wenxing Xu, Guoping Wang.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wang X, Guo Y, Du Y, Yang Z, Huang X, Hong N, Xu W, Wang G (2021) Characterization of Diaporthe species associated with peach constriction canker, with two novel species from China. MycoKeys 80: 77-90. https://doi.org/10.3897/mycokeys.80.63816
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Species of Diaporthe infect a wide range of plants and live in vivo as endophytes, saprobes or pathogens. However, those in peach plants are poorly characterized. In this study, 52 Diaporthe strains were isolated from peach branches with buds, showing constriction canker symptoms. Phylogenetic analyses were conducted using five gene regions: internal transcribed spacer of the ribosomal DNA (ITS), translation elongation factor 1-α (TEF), ß-tubulin (TUB), histone (HIS), and calmodulin (CAL). These results coupled with morphology revealed seven species of Diaporthe, including five known species (D. caryae, D. cercidis, D. eres, D. hongkongensis, and D. unshiuensis). In addition, two novel species D. jinxiu and D. zaofenghuang are introduced. Except for the previously reported D. eres, this study represents the first characterization of Diaporthe species associated with peach constriction canker in China, and contributes useful data for practicable disease management.
Constriction canker, Diaporthe, multi-gene phylogeny, Prunus persica, taxonomy, two new taxa
The genus Diaporthe (asexual morph Phomopsis) was established by Nitschke in 1870 and predates its sexual morph established in 1905, thus Diaporthe is used for this genus (
Peach (Prunus persica L.) originated from China, where it has been cultivated for more than 3,000 years (Faust and Timon 2010). In the past ten years, the national annual production of peach and nectarine was 10–15 million tons, accounting for 50% of global production (http://www.fao.org/faostat/en/#data/QC). In recent years, peach constriction canker has been frequently observed in peach orchards in Fujian province, one of the important peach-cultivation areas in China. This disease can cause flower bud necrosis, no flowering, and even kill the shoots, resulting in a severe economic loss for growers. Peach constriction canker was firstly observed in 1934 in New Jersey, USA (
The infected peach branches with buds showing constriction canker symptoms were collected in Fujian province of China in 2017–2018. The collected samples were subjected to fungal isolation following the protocol described by
Fungal morphology was determined by culturing a 5-d-old mycelial disc (5 mm in diameter) on a petri dish containing PDA and oatmeal agar (OA) (
Genomic DNA was extracted from pure culture using modified cetyltrimethyl-ammonium bromide (CTAB) protocol (
The PCR amplicons were purified and sequenced at the Sangon Biotech (Shanghai, China) Company. Consensus sequences were obtained using DNAMAN (v. 9.0, Lynnon Biosoft), and deposited in GenBank (Suppl. material
Sequences generated in this study were blasted against the NCBI GenBank nucleotide database to determine the closest relatives. Alignment of different gene regions of isolates obtained in this study, their relatives and the ones of the type species (Suppl. material
Phylogenetic analyses were conducted based on the concatenated five loci. Bayesian inference (BI) was used to construct phylogenies using MrBayes v. 3.1.2 (
Additionally, maximum parsimony analyses (MP) were performed on the multi-locus alignment using PAUP (Phylogenetic Analysis Using Parsimony) v. 4.0b10 (
In the surveyed orchards, this disease caused flower-bud necrosis, little or no flowering (Fig.
The strains mentioned above together with 49 reference isolates of previously described species (Suppl. material
A phylogenetic tree generated by Bayesian analysis based on combined ITS, TEF, CAL, HIS, and TUB sequence. Diaporthella corylina (CBS121124) was selected as the outgroup. Bayesian posterior probability (PP ≥ 0.90), MP bootstrap support values (MP ≥ 50%) and RAxML bootstrap support values (ML ≥ 50%) are shown at the nodes (PP/ML/MP). The branches of the new Diaporthe species are marked with red stars B, C are partial phylogenetic taxa highlighting D. zaofenghuang and D. jinxiu together with their closely related species, respectively.
Named for the host variety (Prunus persica cv. Jinxiu), from which the species was isolated.
Sexual morph: not observed. Asexual morph on alfalfa stems after 15 days. Pycnidial conidiomata small, covered by pale yellow discharged conidial masses at maturity, 385–810 μm diam. Conidiophore hyaline, cylindrical, smooth, phialidic, unbranched, straight or slightly curved, 16–21 × 2–2.5 μm. Conidiogenous cells phialidic, cylindrical. Alpha conidia hyaline, aseptate, ellipsoidal, biguttulate, rounded at each end, 5.8–7.1 × 2.7–4.0 µm (mean = 6.4 ± 0.4 × 3.5 ± 0.3 μm, n = 50). Beta and gamma conidia not observed.
Culture characteristics. Cultures incubated on PDA at 25 °C in cycle of light/darkness, growth rate 11.5 mm per day. On PDA medium, colonies were sparse and villous, flourishing at edge of colony. On OA medium, colonies dense with neat edges, with yellow pigment in the center.
China, Fujian Province, Sanming City, on buds of Prunus persica cv. Zaofenghuang, 23 March 2017, Y. S. Guo (holotype
In the phylogenetic, multi-locus tree, D. jinxiu forms a distinct clade with maximum support (1/100/99) and is most closely related to D. rhoina, but with smaller pycnidial conidiomata than the later (D. jinxiu = 386–807 μm vs D. rhoina = 500–2500 μm) (
Named after the host species (Prunus persica cv. Zaofenghuang) from which the species was isolated.
Sexual morph not observed. Asexual morph on alfalfa stems. Pycnidial conidiomata conical, yellowish translucent conidial drops exuded from ostioles, 650–1430 μm diam. Conidiophores fasciculate, hyaline, long cylindrical, straight or slightly curved, apex pointed, 13.7–20.9 × 1.8–2.7 μm. Conidiogenous cells phialidic, cylindrical. Alpha conidia hyaline, aseptate, ellipsoidal, biguttulate, rounded at one end, slightly apex at another end, 5.3–7.5 × 2.9–3.7 µm (mean = 6.0 ± 0.6 × 3.1 ± 0.3 μm, n = 50). Beta and gamma conidia not observed.
Cultures incubated on PDA at 25 °C in cycle of light/darkness, growth rate 8.5 mm per day. Colonies initially white on surface, producing black pigment from center of medium and expanding outwardly after 5–7 d. On PDA, edge of colony petal-like, irregular; on OA, edge relatively flat.
China, Fujian Province, Sanming City, on buds of Prunus persica cv. Zaofenghuang, 23 March 2017, Y. S. Guo (holotype
Two isolates representing D. zaofenghuang form a well-supported clade (1/100/100) and appear to be most closely related to D. penetriteum. Diaporthe zaofenghuang can be distinguished from D. penetriteum based on ITS, HIS, and TUB loci (10/578 in ITS, 45/520 in HIS, and 7/525 in TUB). Morphologically, D. zaofenghuang differs from D. penetriteum in having larger conidiomata (D. zaofenghuang = 653–1433 μm vs D. penetriteum = 180–490 μm) and alpha conidia (D. zaofenghuang = 6.0 ± 0.6×3.1 ± 0.3 μm vs D. penetriteum = 5.0 ± 0.3 × 2.2 ± 0.2 μm). Additionally, D. penetriteum produces two types of conidia, but D. zaofenghuang produces only alpha conidia (
In this study, phylogenetic analyses based on the five combined loci (ITS, TEF, CAL, HIS, and TUB) coupled with morphology revealed seven Diaporthe species (viz. D. caryae, D. cercidis, D. eres, D. hongkongensis, D. jinxiu, D. unshiuensis, and D. zaofenghuang) associated with peach constriction canker. Of these species, two novel species D. jinxiu and D. zaofenghuang in distinct clades were described. Diapothe jinxiu has smaller conidiomata as compared to its closest relative D. rhoina. However, it is not possible to have more morphological comparisons at this stage because limited biological information is available for this species (
Based on molecular data, several Diaporthe species associated with peach diseases in other countries have been identified and characterized, including D. amygdali, which is responsible for apical dead shoot, twig and shoot blight in peach and nectarine in Uruguay (
Previous studies have revealed that species of Diaporthe are highly divergent and closely linked to sampling areas, such as 19 species of Diaporthe infecting pears cultivated in 15 provinces of China (
This work was financially supported by the earmarked fund for the China Agriculture Research System (CARS-28) and the Key National Project (no. 2018YFD0201406). The authors would like to thank Dr. Xiang Li, Canadian Food Inspection Agency, for helping to improve the English in the manuscript.
GenBank accession numbers of isolates included in this study
Data type: GenBank accession numbers
Explanation note: GenBank accession numbers of sequences obtained from this study.
List of Diaporthe species used to phylogenetic analysis in this study, with details about host, country, and GenBank accession numbers
Data type: GenBank accession numbers
Explanation note: GenBank accession numbers of sequences downloaded from GenBank.