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Nonspecific toxins as components of a host-specific culture filtrate from Fusarium oxysporum f. sp. cubense race 1

Abstract:

Bananas and plantains (Musa spp.) are among the most important crops in the world providing staple food for hundreds of millions of people. However, banana production has been devastated by fungal infestations caused by Fusarium oxysporum f. sp. cubense (Foc). Despite the fact that there is very little known on the role of microbial metabolites in the molecular mechanism of Foc infections, it has been proposed that the toxins fusaric acid and beauvericin produced by Foc play an important role during pathogenesis. The aim of this contribution was to study the toxic components of culture filtrates (CF) of Foc and to isolate the extracellular microbial metabolites involved in the plant response. An in vitro bioassay was used to evaluate the production of phytotoxic metabolites as well as the specificity of culture from a strain of Foc belonging to VCG 01210 (race 1). A host-specific CF was obtained and the phytotoxic compounds characterized as fusaric acid, beauvericin and fumonisin B1. Despite the presence of these nonspecific toxins, a water-soluble extract from the CF induced protection to the main phytotoxic fraction, measured by lesion area. This hydrophilic fraction induced a fast and strong response of just jasmonic acid (JA)-dependent defence genes rather than salicylic acid (SA)- and ethylene (ET)-response genes in resistant cultivars. Extracellular proteins isolated from CF of Foc provide an important source for further investigations on the molecular basis of the interaction between Foc and banana.