HEMIBIOTROPHIC INFECTION OF PISUM-SATIVUM BY COLLETOTRICHUM-TRUNCATUM

The infection of pea (Pisum sativum) by Colletotrichum truncatum was s tudied by light and electron microscopy. These investigations were fac ilitated by use of an Argenteum pea mutant, which has a readily detach able epidermis. Infection pegs emerging from appressoria penetrated ep idermal cells directly. Large intracellular primary hyphae formed a de nse stromatic mycelium confined within a single epidermal cell. Primar y mycelia gave rise to thinner secondary hyphae which radiated into su rrounding cells and caused extensive wall dissolution. Melanized scler otia developed in the centre of chlorotic water-soaked lesions. Acervu li were not observed. Epidermal cells survived initial penetration by primary hyphae, as shown by their ability to plasmolyse and accumulate Neutral red, but all infected cells were dead when the secondary hyph ae had formed. Six cultivars of pea were susceptible, but seven other legumes were resistant. A single isoform of polygalacturonase with a p I of 8.3 and apparent M(r) of 40000 was purified from culture filtrate s and the N-terminal amino acid sequence determined. The relevance of the results to the taxonomy of C. truncatum and the relationships betw een infection process and host range are discussed.