Abstract
Races of Colletotrichum lindemuthianum formed appressoria on bean hypocotyls and penetrated epidermal cells regardless of the resistance or susceptibility of the cultivars used. Quantitative studies using a newly developed cell grading system showed that infections of resistant varieties were normally restricted to single cells which became necrotic soon after penetration. Two types of cellular response were distinguished; the type found depended on the fungal race used. In one incompatible combination studied in detail, hyphal growth slowed soon after penetrated cells became necrotic but continued for several days. Susceptible tissue remained visibly unaffected for 3 or more days while considerable fungal colonization took place. Necrosis then occurred and macroscopic brown lesions appeared. A dense deposit, “reaction material”, formed at the site of penetration in some cells of both resistant and susceptible tissue; hyphae developed no further. The results are discussed in relation to different hypotheses concerning processes of resistance.
Published Version
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