|ZHOU, XUE - Northwest Agricultural & Forestry University|
|AOKI, TAKAYUKI - National Institute Of Agrobiological Sciences (NIAS)|
|SMITH, JASON - University Of Florida|
|KASSON, MATTHEW - West Virginia University|
|CAO, ZHI-MIN - Northwest Agricultural & Forestry University|
Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2016
Publication Date: 8/1/2016
Citation: Zhou, X., O'Donnell, K., Aoki, T., Smith, J.A., Kasson, M.T., Cao, Z.-M. 2016. Two novel Fusarium species that cause canker disease of prickly ash (Zanthoxylum bungeanum) in northern China form a novel clade with Fusarium torreyae. Mycologia. 108(4):668-681.
Interpretive Summary: The present study was conducted to identify the pathogen(s) responsible for canker disease of Chinese prickely ash or Sichuan pepper, Zanthoxylum bungeanum, in northern China. This economically important tree is highly prized for Sichuan pepper, a common peppery spice used in Asian cuisine, and for its seeds, which are used in traditional Chinese medicine. Symptoms of the Sichuan pepper disease include branch and stem cankers, branch death, and occasionally tree death. To identify the pathogen(s), 38 strains of the filamentous mold Fusarium were isolated from symptomatic tree tissue in five provinces, from Gansu in the northwest to Shandong in the northeast. The isolates were identified by sequencing portions of four genes and then comparing the sequences with those in the web-accessible databases GenBank and FUSARIUM-ID. Based on the results of these queries, the DNA sequences were analyzed phylogenetically to accurately place the isolates within Fusarium. The latter analysis revealed that two closely related and novel Fusarium species accounted for most of the isolates. When isolates of the two novel species were inoculated on healthy Sichuan pepper trees, they induced cankers, thereby establishing that they were responsible for the canker disease. Given the importance of these pathogens, they were formally described as the novel species F. zanthoxylum and F. bungeanum. These two pathogens are most closely related to F. torreyae, which currently threatens extinction of the critically endangered Florida torreya tree (Torreya taxifolia) in Florida and Georgia. Results of this study will be of interest to plant pathologists, fungal biologists, foresters, silviculturists, and plant breeders.
Technical Abstract: Canker disease of prickly ash (Zanthoxylum bungeanum) has caused a decline in the production of this economically important spice in northern China in the past 25 y. To identify the etiological agent, 38 fungal isolates were recovered from symptomatic tissues from trees in five provinces in China. These isolates were identified by conducting BLASTN queries of NCBI GenBank and phylogenetic analyses of DNA sequence data from the nuclear ribosomal internal transcribed spacer region (ITS rDNA), a portion of the translation elongation factor 1-a (TEF1) gene, and genes encoding RNA polymerase II largest (RPB1) and second largest (RPB2) subunits. Results of these analyses suggested that 30/38 isolates belonged to two novel fusaria most closely related to the Florida torreya (Torreya taxifolia Arn.) pathogen, Fusarium torreyae in Florida and Georgia. These three canker-inducing tree pathogens form a novel clade within Fusarium here designated the F. torreyae species complex (FTOSC). BLASTN queries of GenBank also revealed that 5/38 isolates recovered from cankers represented an undescribed phylogenetic species within the F. solani species complex (FSSC) designated FSSC 6. Stem inoculations of three fusaria on Z. bungeanum resulted in consistent canker symptoms from which these three fusaria were recovered. The two novel fusaria, however, induced significantly larger lesions than FSSC 6. Herein, the two novel prickly ash pathogens are formally described as F. zanthoxyli and F. continuum.