HISTOLOGICAL STUDY OF HOST–PARASITE RELATIONSHIPS BETWEEN SEPTORIA GLYCINES HEMMI AND SOYBEAN LEAVES AND PODS

Abstract

Histological studies of the host–parasite relationships between Septoria glycines Hemmi and soybean have revealed that penetration is stomatal without, the presence of an appressorium. Subsequent spread of the pathogen is intercellular in the mesophyll tissue and in the parenchyma sheath and phloem of the leaf veins. While the fungus does not show marked action in advance and requires to be in intimate contact with vital cells in order to progress through host tissue, its fruiting bodies are matured only in the holonecrotic region of the lesion. The fungus seems incapable of invading the plesionecrotic zone which borders the holonecrotic region; the role of this zone in limiting the pathogen to a discrete spot has been discussed.Colonization of the pericarp and seed is primarily intercellular, although intracellular hyphae may be found in the sclerenchyma of the subhilum region of the seed. Infection of the seed may occur directly at the point of contact of the seed with the wall, or by systemic invasion via the placenta and funiculus. This study establishes conclusively that S. glycines is seed-borne in the soybean.