In vitro analysis of defense mechanisms in the system Solanum tuberosum-Alternaria alternata

In a preliminary study on the interaction between an Alternaria alternata pathotype and Solanum tuberosum a series of parameters, indicative of active and passive defence processes, was investigated in vitro using tolerant (Chiquita) and susceptible (Superior) cultivars. Ion leakage experiments along with growth of suspension cultures and plating efficiencies in the presence of fungal culture filtrates suggest that toxin tolerance is a valuable character in distinguishing between resistant and susceptible genotypes. As far as active defence was concerned, although TLC patterns suggested the synthesis of different fluorescent compounds, probably phenolic acid, when fungal elicitors were applied to Chiquita or susceptible tissue,cultures, no consistent pattern suggesting a relationship with defence could be observed. On the other hand, peroxidase isozyme analysis after different dual culture periods showed the activation of ionically and covalently bound peroxidases in the presence of the pathogen only in cv. Chiquita.