Some Observations on the Relation between the Penetration Hypha and Haustorium of the Barley Mildew (Erysiphe graminis DC.) and the Host Cell (I)

Abstract

1. When the conidia of barley mildew, Erysiphe graminis hordei, germinated on the epidermal strips of onion scales, which were deprived of their soluble content by immersing in alcohol for a long time and by subsequent washing with running water, the germ tubes remained alive for a week. While on a living barley leaf of comparatively resistant varieties, penetration hypha was usually enveloped by a big callus during the process of penetration, and the germ tubes were killed within one or two days after inoculation. It is suggested that the germ tube is presumably killed by a certain substance or substances produced near the penetrated point in the barley cell, and not by the mechanical impediment of the callus. The degree of callus formation varies with the variety of barley, growth stage, rate of application of nitrogen and silica, etc.
2. After a few days after inoculation, it was occasionally observed that both living and dead haustoria existed in the same and one living epidermal cell. This fact indicates that when one or some haustoria die, the host cell or the other haustoria in the same cell will not always be injured immediately.
3. Long epidermal cells under the old pustule are usually colonized by so many haustoria, often reaching 70 or 80 in number. Among many living haustoria in such a host cell, which is evidently alive, dead ones are often observable.
4. When a detached, diseased barley leaf is kept in a moist Petri dish, the leaf turns yellow and ultimately dies except the pustule bearing part. The epidermal cells in such area left alive, surrounded by dead tissues on all sides, are nearly dead or apparently dead and yet some of them contain living haustoria. It may be said from these observations that the haustoria, at least a part of them, in the dying cell do not precede in death to the host cell.
5. The barley mildew developed a longer hypha without haustorial formation, on the bleached onion epidermis, floated on glucose solution or on a culture solution containig yeast-extract, than on the substratum floated on water.
6. Primordial haustoria, just beginning to develop finger-like processes, were formed, though very rarely, in the epidermal cells of buckwheat, but no hyphal development from the germ tubes was observed.