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First Report of Powdery Mildew Caused by Erysiphe cruciferarum on Centella asiatica in China.
Plant Disease ( IF 4.5 ) Pub Date : 2023-03-14 , DOI: 10.1094/pdis-12-22-2845-pdn
Xuetao Wang 1 , Qian Zhou 1 , QingQing Lan 1 , RongRong Mu 1 , JingYi Wang 1 , Liu Yang 2 , Lu Liu 3 , Su Xu 4 , Yongqiang Tian 5
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Centella asiatica belongs to the Umbelliferae family of perennial herbaceous plants, which are grown worldwide for use as health supplements, edible vegetables and traditional herbs, and are of vital medicinal and edible value in China. (Biswas et al. 2021). In October 2022, the investigation in the 800 m2 garden of Lanzhou (36°06' N,103°43' E) found that more than 80% of C. asiatica plants were infected by powdery mildew, and the leaf infection rate was 90%. The disease severely affects the actual value of C. asiatica. At the beginning of the disease, thin, radial, irregular white colonies appear on the leaves and gradually spread to the stems. The white colony then expands and thickens, covering the upper surface of the whole leaf, and gradually spreading to the lower parts of the stem and leaf. In severe cases, the leaves wither and die. A small portion of fungal spores was glued from the leaf surface with adhesive tape and placed in sterile water for microscopic examination (Zhang et al. 2022). The conidiophore is upright, cylindrical, composed of 3-4 cells, and its size is 72 to 110 × 8 to 10 μm. Conidial pedicels have 16 to 26 μm long cylindrical podocytes. Monoconidia are cylindrical or oval in shape, 16 to 37 μm long, width 11 to 18 μm (n=80). Conidia lack an obvious cellulose body. The bud tube is formed from the end of conidia, and papillary appressorium develops on the epiphytic mycelia. Based on these morphological characteristics, the pathogen was initially identified as Erysiphe cruciferarum (Braun et al. 2012). To validate the identity, the internal transcribed spacer (ITS) of the pathogen (JXC) rDNA was amplified by PCR and sequenced with PM6/ITS5 and PM5/ITS4 primers (Takamatsu et al. 2001). The resulting sequences were registered to GenBank (GenBank Accession OP935627 and OQ253404). At the same time, the ITS sequence size was 535 bp and 521 bp respectively. The ITS sequence of the JXC was 99% (527/534) identical to E.cruciferarum (KT588635) on Eschscholzia californica in Slovakia and 99% (527/534) identical to E.cruciferarum (KC878683) on Chinese Cabbage in China. The ITS sequences from GenBank were subjected to conduct maximum likelihood phylogenetic analysis by MEGA 7.0. The data indicate that strain JXC and E. cruciferarum are clustered on the same branch. The pathogenicity test was performed according to Koch's postulate. By gently pressing the infected leaves on five healthy potted C. asiatica. Meanwhile, five uninoculated plants were used as controls (Zhang et al. 2022). The plants were put into a greenhouse culture (25℃, 14 h light, 10 h dark, humidity ≥ 70%). After 12 days, the inoculated plants showed symptoms of powdery mildew, while the control group had no symptoms. The fungus on the inoculated plant was re-isolated, and identified as E. cruciferarum based on morphological observations and molecular identification. The powdery mildew caused by E.cruciferarum has been reported on Indian mustard in Korea and Chinese cabbage in China, respectively (Kim et al. 2009; Zhao et al. 2014). To our knowledge, this is the first report of C. asiatica powdery mildew caused by E.cruciferarum in China. This finding poses a potential threat to the quality and yield of C. asiatica plants, while providing a preventive basis for the cultivation of C. asiatica.
更新日期:2023-03-14
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