Cercosporin from Pseudocercosporella capsellae and its critical role in white leaf spot development

Gunasinghe, Niroshini and You, Ming Pei and Cawthray, Gregory R. and Barbetti, Martin J. (2016) Cercosporin from Pseudocercosporella capsellae and its critical role in white leaf spot development. Plant Disease, 100 (8). pp. 1521-1531. ISSN 0191-2917

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Abstract

Pseudocercosporella capsellae, the causative agent of white leaf spot disease in Brassicaceae, can produce a purple-pink pigment on artificial media resembling, but not previously confirmed, as the toxin cercosporin. Chemical extraction with ethyl acetate from growing hyphae followed by quantitative [thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC)] and qualitative methods showed an identical absorption spectrum, with similar retardation factor (Rf) values on TLC papers and an identical peak with the same retention time in HPLC as for a standard for cercosporin. We believe this is the first report to confirm that the purple-pink pigment produced by P. capsellae is cercosporin. Confocal microscopy detected green autofluorescence of cercosporin-producing hyphae, confirming the presence of cercosporin inside hyphae. The highly virulent UWA Wlra-7 isolate of P. capsellae produced the greatest quantity of cercosporin (10.69 mg g-1). The phytotoxicity and role of cercosporin in disease initiation across each of three Brassicaceae host species (Brassica juncea, B. napus and Raphanus raphanistrum) was also studied. Culture filtrates containing cercosporin were phytotoxic to all three host plant species, producing large, white lesions on highly sensitive B. juncea, only water-soaked areas on least sensitive R. raphanistrum, and intermediate lesions on B. napus. It is noteworthy that sensitivity to cercosporin of these three host species was analogous to their susceptibility to the pathogen, viz., B. juncea the most susceptible, R. raphanistrum the least susceptible and B. napus intermediate. The presence of cercosporin in the inoculum significantly increased disease severity on the highly cercosporin-sensitive B. juncea. We believe that this is the first study to demonstrate that P. capsellae produces cercosporin in liquid rather than agar media. Finally, this study highlights an important role of cercosporin as a pathogenicity factor in white leaf spot disease on Brassicaceae as evidenced by the ability of the cercosporin-rich culture filtrate to reproduce white leaf spot lesions on host plants and by the enhanced virulence of P. capsellae in the presence of cercosporin.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to submitted version in accordance with the copyright policy of the publisher.
Faculty / Department / School: No Faculty
Date Deposited: 01 Mar 2017 03:36
Last Modified: 27 Feb 2018 06:16
Uncontrolled Keywords: white leaf spot, cercosporin, Pseudocercosporella capsellae, oilseed rape, phytotoxin
Fields of Research : 07 Agricultural and Veterinary Sciences > 0703 Crop and Pasture Production > 070308 Crop and Pasture Protection (Pests, Diseases and Weeds)
Socio-Economic Objective: D Environment > 96 Environment > 9604 Control of Pests, Diseases and Exotic Species > 960403 Control of Animal Pests, Diseases and Exotic Species in Farmland, Arable Cropland and Permanent Cropland Environments
Identification Number or DOI: 10.1094/PDIS-10-15-1192-RE
URI: http://eprints.usq.edu.au/id/eprint/30695

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