Salicylic acid can reduce infection symptoms cause

Authors: Robert Czajkowski Jan M van der Wolf Aleksandra Krolicka Zofia Ozymko Magdalena Narajczyk Natalia Kaczynska Ewa Lojkowska

Publish Date: 2014/11/13

Volume: 141, Issue: 3, Pages: 545-558

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Abstract

The potential for control of Dickeya solani infections in potato by elicitation of in vitro grown potato plants with salicylic acid SA was investigated by selective plating and confocal laser scanning macroscopy CLSM In replicated experiments potato plants grown on medium supplemented with 25 or 50 μM of SA were evaluated for the phytotoxic effects Potato plants grown on medium supplemented with SA and inoculated with GFPtagged D solani were investigated for blackleg development and colonization of potato plants by the bacteria Three days after inoculation colonization of roots by D solani was observed in 100  control plants grown on medium without SA but not in plants grown on medium supplemented with 50 μM SA After 14 days 100  of control plants showed severe disease symptoms whereas plants grown on medium supplemented with 50 μM SA and inoculated with bacteria did not express any symptoms After 14 days bacteria were found inside 100  stems of control plants in densities of ca 103–104 cfu g−1 and inside ca 10–15  stems of plants treated with 50 μM SA in densities similar to these in the control plants The GFPtagged bacteria were macroscopically detected on the surface of the roots of control plants but not on the surface of the plants treated with 50 μM SA 14 days after inoculation The implications of SA treatments on plant fitness and disease development are discussedBacterial diseases of potato blackleg and soft rot caused by pectinolytic Pectobacterium and Dickeya spp are responsible for major losses in seed and ware potato production in Europe and worldwide Pérombelon and Salmond 1995 Pérombelon 2002 Toth et al 2011 In Europe the Dickeya spp outbreaks have increased substantially since 2001 when the isolates of the new Dickeya species D solani have been found in potato for the first time Slawiak et al 2009ab This pathogen has never before been observed in the European climate zone or elsewhere van der Wolf et al 2014 Tsror et al 2009 Slawiak et al 2009 Laurila et al 2008 Since 2005 the presence of D solani has been reported in potato in many European countries including The Netherlands Finland Poland Germany Belgium France United Kingdom and Sweden as well as outside Europe in Israel and Georgia The species has become the predominant pathogen responsible for the blackleg incidences in Europe Toth et al 2011 Tsror et al 2011 van der Wolf et al 2014 D solani seems to be virulent in potato and possesses features allowing its easy spread and survival under the temperate climate in Europe Czajkowski et al 2009 2012aThe potential to control pectinolytic Dickeya spp in potato is limited Czajkowski et al 2012b Up to now only an integrative strategy combining the use of certified seed tubers descending from pathogenfree minitubers hygienic practices during harvesting and grading and avoidance of pathogen introduction during planting and in storage is partially efficient but has not resulted in a broad eradication of the pathogens from the potato production chain Perombelon and Kelman 1980 Toth et al 2011Reduction of Pectobacterium and Dickeya spp populations by treatment of potato tubers is ineffective and consequently rarely used in practical applications in fields van der Wolf and de Boer 2007 Both physical treatments including hot air and hot water UV radiation and solarization and utilization of chemical agents combining disinfectants and antibiotics contribute to reduction or eradication of only superficial bacterial populations whereas they will not affect bacteria located deeper inside the tubers Czajkowski et al 2012b Pectobacterium and Dickeya spp are vascular pathogens able to infect potato tubers internally Perombelon and Kelman 1980 Czajkowski et al 2009 2010 and due to the ability of inhabiting the inner tuber tissues they will not be affected by the superficial treatments thus the physical measures and chemical control agents will not effectively contribute to the control of Pectobacterium and Dickeya spp in potatoThe use of elicitors inducing natural resistance in plants against bacterial infections can be considered as a promising alternative to chemical and physical treatments It is well established that plants have evolved a range of different defence mechanisms to combat invasion and infections caused by bacterial pathogens Despite the presence of passive physical and chemical barriers different mechanisms are also activated specifically upon pathogen introduction and infection Kessmann et al 1994 The induced resistance IR may be restricted to the site of the pathogen entrance or it may spread systemically and develop also in other healthy distant parts of the plant Durrant and Dong 2004The two best characterized defence mechanisms in plants are induced systemic resistance ISR and systemic acquired resistance SAR Vallad and Goodman 2004 Activation of the ISR and SAR leads to similar phenotypic responses however the molecular and biochemical pathways that are activated in these defence mechanisms are different SAR is mainly induced by the exposure of roots or foliar tissues leaves and haulms to abiotic and biotic elicitors and depends on the salicylic acid signal molecule Ryals et al 1994 Activation of SAR leads to production and accumulation of specific pathogenesisrelated proteins PR proteins Métraux et al 2002 In contrast ISR is prompted by the presence of plantgrowth promoting rhizosphere bacteria in plant rhizospheres and is mediated by the plant hormones ethylene and jasmonic acid Van Loon et al 1998 Also ISR is not associated with production of PR proteins Heil and Bostock 2002Certain chemicals eg salicylic acid SA benzothiadiazole BTH acybenzolarSmethyl BION 26dichloroisonicotinic acid or βaminobutyric acid BABA can activate the SAR defence mechanism without the plant’s interaction with pathogens Gozzo 2003 Whereas ISR most often requires the presence of living microorganisms or their fragments eg pathogen proteins pathogen cell walls components for induction Pieterse et al 2001 ISR can also be enhanced by applying exogenous plant hormones jasmonic acid and ethylene or their derivatives Shoresh et al 2005 Pieterse et al 2000 For example Luzzatto et al 2007a demonstrated that calla lily Zantedeschia spp plants exposed to exogenous BION or methyl jasmonate elicitors produced high levels of antimicrobial phenolics It was also shown that elicitation of these plants with methyl jasmonate but not with BTH induces priming and consequently resistance against P carotovorum via induction of oxidoreductases LuzzattoKnaan et al 2014Although SA and its analogs have been extensively used in research on systemic resistance in different plants relatively little information can be found on its role in protection against the pectinolytic bacteria Palva et al 1994 reported that addition of the SA to the growth medium of axenicallygrowing tobacco seedlings causes almost complete resistance to infection by P carotovorum subsp carotovorum and to our knowledge there is no information available on the effect of SA on Dickeya spp particularly the D solani infections of potato

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