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Phytoalexin Nature of Heat-Induced Protection Against Bean Anthracnose. J. E. Rahe, Assistant Professor, Pestology Centre, Department of Biological Sciences, Simon Fraser University, Burnaby 2, British Columbia, Canada; Phytopathology 63:572-577. Accepted for publication 14 November 1972. DOI: 10.1094/Phyto-63-572.

Heat treatment of anthracnose-infected bean hypocotyls prevented the development of lesions and the large increases of phenylalanine ammonia-lyase (PAL) and total acetone-soluble phenolic substances associated with pathogenesis. Instead, smaller increases of PAL and total acetone-soluble phenolic substances occurred following heat treatment, as well as necrotic flecks within which infection hyphae were restricted. Phaseollin synthesis was stimulated in infected heat-treated plants to levels far in excess of those occurring in the normal susceptible interaction. Additional phenolic and/or fluorescing substances were detected chromatographically in extracts from infected hypocotyl tissue, but not from healthy tissue. Distinctive differences in the apparent quantities and/or times of appearance of these substances were observed in natural resistant and susceptible interactions. Comparisons of fluorescing and phenolic substances associated with natural resistant and susceptible interactions and with the heat-treated susceptible interaction suggested that the nature of host-parasite interaction is shifted from susceptibility to resistance by heat treatment. Differences in the levels of phaseollin which occurred in naturally resistant and heat-induced “resistant” responses are discussed in terms of differences in the numbers of cells occupied by infection hyphae at the time phaseollin synthesis was stimulated.