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In a preliminary study on the interaction between an Alternaria alternata pathotype and Solatium tuberosum a series of parameters, indicative of active and passive defense 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 defense 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. [ABSTRACT FROM AUTHOR]

Hypersensitive browning, host cell death and phytoalexins (rishitin) synthesis in both callus cultures and cotyledons have been observed in a susceptible tomato cultivar following treatment with high molecular weight cell wall components from Phytophthora infestans race IB. The growth of the pathogen was restricted on both elicited differentiated and undifferentiated tomato tissues. Substance(s) released by germinating sporangia, but not by the mycelium, suppressed the hypersensitive reaction. [ABSTRACT FROM AUTHOR]