Elicitation of Phytoalexin rishitin in Potato Tuber Slices Infected by Fusarium spp., Does it Consider a Factor of Pathogenicity?

Potato tubers, under storage conditions, suffer from Fusarium dry rot disease caused by Fusarium spp. leading to devastating losses of stored tubers.  Newly harvested tubers are resistance toward Fusarium infection, but disease becomes more vigorous by increasing storage period.  Inoculation of potato tuber slices of Desiree cv. (highly susceptible) or Spunta cv. (highly resistant) either by a weak pathogen (F. moniliforme) or severe pathogen (F. solani) and tracking accumulation of phytoalexin rishitin in inoculated tissues at different intervals from inoculation revealed that Desiree cv. accumulated high amounts of rishitin in a very short time in comparison to another three tested situations. Dipping of potato tuber slices of both cvs. in different concentrations of the known antibiotic chloramphenicol prior to inoculation with a weak pathogen (F. moniliforme) led to increased disease severity associated with accumulation huge amounts of rishitin in inoculated tissues. The correlation coefficient between disease severity and rishitin production was +0.83.  Moreover, the reaction of spunta cv. toward inoculation by a weak pathogen was changed from the state of resistance to very severe susceptibility.  Since chloramphenicol affects protein synthesis on 70S ribosome’s, it was postulated that it prevents synthesis of factor(s) take a part in cell death during infection. Mitochondria extracted from potato tuber tissues secret compound(s) decreased rishitin synthesis in potato tuber slices treated with mycelia extract of F. solani. Treatment of isolated mitochondria with this antibiotic led to the elimination of this factor(s) from their secretions. Results obtained revealed that the elicitation of phytoalexins may consider one of pathogenicity factor of such system.