Induction and expression of systemic resistance to the anthracnose disease in bean

Development of anthracnose symptoms in trifoliate leaves of Phaseolus vulgaris inoculated with Colletotrichum lindemuthianum was greatly restricted when the primary leaves had been inoculated with the same pathogen 1 week earlier. Penetration from appressoria was inhibited and hyphal growth in epidermal cells was sometimes decreased in preinoculated plants. The response of preinoculated plants also differed: wall appositions and encroachment of nuclei at attempted penetration sites occurred more frequently, and earlier cell death often followed successful penetration. Resistance in trifoliate leaves was also induced by injection of primary leaves with conidia or culture filtrates of the pathogen or a dialysis retentate of these filtrates. Resistance in epicotyls and primary leaves was induced by inoculation of the hypocotyl 1 week earlier. Inoculated cotyledons abscissed, and failed to alter the susceptibility of primary or trifoliate leaves to subsequent inoculation. The results are discussed in relation to a hypothesis to explain the process of induced systemic resistance.