Journal of Phytopathology. 2017;1–16. wileyonlinelibrary.com/journal/jph | 1 © 2017 Blackwell Verlag GmbH Received: 27 February 2017 | Accepted: 25 April 2017 DOI: 10.1111/jph.12589 ORIGINAL ARTICLE Potato bacterial wilt suppression and plant health improvement after application of different antioxidants Shahenda M. A. Farag 1,2 | Kamel M.A. Elhalag 1,3 | Mohamed H. Hagag 1,2 | Abdel Salam M. Khairy 1,2 | Heba M. Ibrahim 4 | Moheb T. Saker 4 | Nevein A. S. Messiha 1,3 1 Potato brown rot project, Ministry of Agriculture, Dokki, Giza, Egypt 2 Central Administration of Plant Quarantine, Dokki, Giza, Egypt 3 Bacterial Diseases Research Department, Plant pathology research institute, Agricultural Research Center (ARC), Giza, Egypt 4 Faculty of Agriculture, Physiology Department, Mansura University, Mansura, Dakahlia, Egypt Correspondence N. A. S. Messiha, Bacterial Diseases Research Department, Plant Pathology Research Institute, Agricultural Research Center (ARC), Giza, Egypt. Email: nevein_messiha@yahoo.com Funding information The Egyptian State Ministry for Scientific Research, Grant/Award Number: STDF2905 Abstract Bacterial wilt caused by Ralstonia solanacearum is a devastating disease that often threatens potato production and exportation. The potential of four antioxidants (sea- weed extract (SWE), yeast, chitosan and ascorbic acid (ASA)) in controlling the disease was evaluated in vitro, under glasshouse and field conditions. The field experiment was conducted in two naturally infested locations: Wardan, Giza (sandy soil), and Talia, Minufiya (silty clay soil). Only chitosan showed antibacterial properties against the pathogen in vitro. SWE, yeast and chitosan showed disease suppression under both glasshouse and field conditions. The disease suppression was accompanied by an in- crease in the ratio of soil copiotrophic to oligotrophic bacteria. The three antioxidants increased plant nitrogen content, decreased soil OM content and decreased C/N ratio. Disease suppression after chitosan application was clearly observed only in Wardan area, which was characterized by a higher soil alkalinity. A high percentage of antago- nistic fluorescent strains similar to Pseudomonas putida group were detected for chitosan-treated plants in Wardan area (sandy soil). ASA drastically decreased the count of the pathogen in soil, but was conducive to the pathogen in plant tissues. A remarkable increase in microbial (bacterial and fungal) soil and rhizosphere diversity as indicated by PCR-DGGE analysis for bacterial 16S rRNA and fungal 18S rRNA was recorded. In Talia area (silty clay soil), the soil microbial community was more stable and was in general resistant to the disease where the soils were characterized by high electrical conductivity. SWE, yeast and ASA significantly increased crop production in Talia area only. KEYWORDS Ralstonia solanacearum, seaweed extract, yeast, chitosan, ascorbic acid, biodiversity, crop production 1 | INTRODUCTION Potato is the third most important crop for human consumption after rice and wheat. Egypt is considered the top potato producer and exporter in Africa. In 2013, Egypt exported 427,907 ton to Europe, Russia and Arabic countries as compared to 738,594 ton exported by whole Africa (FAOSTAT, 2013). Potato brown rot disease (bacterial wilt) is one of the most important threats for potato production and international trading. It is a systemic bacterial disease caused by Ralstonia solanacearum race 3 biovar 2 phylotype II sequevar 1 (Prior & Fegan, 2005). In Egypt, potatoes are grown either in the traditional produc- tion fields in the Nile Delta or in the newly reclaimed areas, mainly in the desert. Since 1998 and according to FAO standards and EU