Multiple host-specific toxins of Alternaria mali and their effect on the permeability of host cells

Abstract

A very virulent isolate of Alternaria mali, the incitant of apple blotch, was found to produce two major host-specific toxins (HSTs) and five minor ones in liquid culture. The minor toxins were less active than the major ones, but were still specifically toxic to the plants which are susceptible to the pathogen. Examination of other isolates of A. mali indicated that although these lacked some of the seven HSTs, they were still pathogenic to susceptible plants. No HSTs were detected in dormant spores, but they were released by germinating spores. The released toxins had R F values which were identical to those of the two major HSTs from culture filtrates when compared by t.l.c. Susceptible leaves infiltrated with solutions of the HSTs lost more intracellular electrolytes than control leaves during the first 30 min of treatment. Inoculation with spores resulted in an increased loss of electrolytes from susceptible leaves during the first 4 h of incubation (pre-infection stage), and induced another enhanced loss of electrolytes at 10 h (penetration by infection hyphae). Loss of electrolytes from the resistant leaves was not affected by treatment with toxins or by inoculation with spores. Tenuazonic acid was not detected in dormant or germinating spores, and was thought not to be involved in the initial step of the infection process in nature.