First Report of Fruit Decay on Pepper Caused by Diaporthe actinidiae in China

Abstract

HomePlant DiseaseVol. 100, No. 8First Report of Fruit Decay on Pepper Caused by Diaporthe actinidiae in China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Fruit Decay on Pepper Caused by Diaporthe actinidiae in ChinaC. Zhang, W. Z. Wang, Y. Z. Diao, and X. L. LiuC. ZhangSearch for more papers by this author, W. Z. WangSearch for more papers by this author, Y. Z. DiaoSearch for more papers by this author, and X. L. LiuSearch for more papers by this authorAffiliationsAuthors and Affiliations C. Zhang W. Z. Wang Y. Z. Diao X. L. Liu , Department of Plant Pathology, China Agricultural University, Beijing 100193, China. Published Online:13 May 2016https://doi.org/10.1094/PDIS-07-15-0835-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Pepper (Capsicum annuum L.) is an economically important vegetable crop worldwide (Valadez-Bustos et al. 2009). China is one of the main producers and exporters of chili and other peppers in the world (Valadez-Bustos et al. 2009). In August 2014, a previously unreported disease causing yield losses was observed on pepper cv. Chaotianjiao fruit in several fields of Jilin Province (43°71′ N, 125°54′ E). About 6 to 10% of plants were symptomatic and infected fruit had irregular, water-soaked lesions (c. 2.3 to 3.8 cm2) on the skin and extensive internal decay. Lesion margins on three fruits from different fields were cut into 5 mm pieces, surface-disinfested with 1% sodium hypochlorite for 1.5 min, and placed on 1.5% potato dextrose agar (PDA) amended with 0.02% streptomycin sulfate. A mycelial plug (5 mm diameter) from the growing edge of colonies cultured 3 days at 25°C of each isolate was transferred to PDA and incubated at 25°C for 14 days under a 12-h photoperiod. Three isolates from different fields (JL1-1, JL1-2, and JL1-3) were obtained by single-sporing. White aerial mycelial mats were formed on PDA at 25°C. After 7 days, entire colonies became tan to light brown, forming gray concentric rings. Black, spherical or bluntly conical pycnidia were produced on the colony surface 14 days after culturing. Alpha conidia were hyaline, unicellular, ellipsoidal to fusiform, and 4.4 to 7.8 × 1.9 to 2.7 μm (mean: 5.9 × 2.3 μm). Beta conidia were hyaline, unicellular, filiform to hamate, and 16.8 to 32.7 × 1.0 to 2.2 μm (mean: 24.9 × 1.7 μm). Based on these morphological characters, the fungus was identified as Diaporthe actinidiae N. F. Sommer & Beraha (Lee et al. 2001). The identification was confirmed molecularly by DNA extracted from the mycelium of the isolates, and the ITS region was amplified and sequenced using primers ITS4 and ITS5 (Mathew et al. 2015; Shu et al. 2014). BLASTn analysis showed that the sequence of 609 bp (Accession No. KT163360) had 98% homology with the sequence of D. actinidiae (KC145886). The D. actinidiae isolates (JL1-1, JL1-2, and JL1-3) were tested for pathogenicity both on pepper and eggplant by two different inoculation methods. For each isolate, 24 pepper cv. Chaotianjiao fruit were surface disinfested, and half of the fruit were stabbed by a micropipette tip. A mycelial plug (5 mm diameter) from a 4-day-old PDA culture was placed on the surface of six wounded and six unwounded fruit and covered with sterile absorbent cotton moistened with sterile distilled water. Six wounded and six unwounded fruit were also inoculated with 10 µl of a conidial suspension (1 × 106 conidia ml–1), respectively. Twelve fruit with or without wounding served as controls and treated with agar plugs or sterile distilled water, respectively. The fruit were placed in a moisture chamber with a 12-h photoperiod at 25°C. The test was performed twice. The inoculated fruit developed lesions at the inoculation points that were similar to those observed in the field after 4 or 7 days. The lesions then expanded to cover whole fruits with alpha and beta conidia observed on lesion surfaces after 7 or 10 days. Control plants were asymptomatic. The pathogen was only reisolated from the inoculated fruit. These isolates were confirmed to be D. actinidiae based on morphology and ITS sequence as described above. To our knowledge, this is the first report of D. actinidiae causing fruit decay on pepper in China and worldwide. D. actinidiae was mainly the causal organism of stem-end rot of kiwifruit as previously reported (Lee et al. 2001). Considering the economic importance of pepper in China and throughout the world, further study of fruit decay of pepper caused by D. actinidiae is warranted.