In vitro Response of Fusarium oxysporum Isolates to Isothiocyanates Application

Some strains of Fusarium oxysporum are pathogenic to different plant species during their pre- and postharvest stages and are responsible for serious economic losses. Management of this fungus is usually with the aid of environmentally-harmful chemicals. However, other biodegradable compounds such as isothiocyanates (ITCs) have demonstrated their nematicidal, bactericidal and fungicidal potential. In this research, the in vitro fungitoxic effect of ITCs of allyl, benzyl, phenyl, phenylethyl and propyl at concentrations of 0, 0.1, 0.3, 0.5, 1.0, 1.5 and 2.0 μ L-1 was tested on various isolates of F. oxysporum obtained from gladiolus corms, jatropha seeds, mango leaves, papaya and coahuayote fruit. Daily mycelial growth and conidial germination of these five isolates was evaluated at different incubation period. To verify the fungistatic or fungicidal response, the ITCs were removed and the fungi were re-grown only in nutrient media. As average, conidia of F. oxysporum were more sensitive to the ITCs than mycelium. At the end of the incubation period, there were significant differences (P < 0.05) in mycelia growth of the ITC-treated fungi compared to the untreated ones. The F. oxysporum isolates that were the most sensitive to the benzyl ITC were those obtained from mango leaves and coahuayote fruit. The mango isolate was also very sensitive to phenylethyl ITC. At concentrations ranging from 1.0 to 2.0 μ L-1, the allyl ITC also suppressed the growth of F. oxysporum isolated from papaya and coahuayote fruit. Except for the phenyl ITC in the coahuayote fruit, conidial germination of F. oxysporum did not occur under the influence of the remaining ITCs, whilst in the control treatment germination reached 100%. As average, the concentration applied did not influence the growth of the fungi. Once the source of the ITCs was removed from the Petri plate re-growth and germination took place in all fungi. In conclusion, the ITCs tested differed in bioactivity and the mycelium and conidia of the different F. oxysporum isolates varied in their susceptibility and tolerance to these compounds.