LIVING HAUSTORIA AND HYPHAE OF ERYSIPHE GRAMINIS F.SP. HORDEI WITH INTACT AND PARTLY DISSECTED HOST CELLS OF HORDEUM VULGARE

Erysiphe graminis DC f.sp. hordei Em. Marchal was grown on the inner epidermis of the coleoptile of barley (Hordeum vulgare L.) in mounts that permitted microscopic observation and treatment of living cells of both host and parasite. Growth rates of the mildew fungus on partially isolated single layers of epidermis from coleoptiles equaled rates on intact green leaves 48–72 h after inoculation when the colonies elongated by 14–17 μ/h. The colonies often grew at approximately normal rates for 3–6 h after the protoplasts of parasitized host cells were destroyed by dissection, with the single haustorium of the colony exposed to artificial ambient media. The most prolonged growth occurred when the contents of the host cell were replaced with solutions that were hypertonic with respect to the host (0.5–0.6 M sucrose). Haustoria in contact with hypertonic media were normal in uptake of neutral red, in apparent turgidity, and in the position of the haustorial sac closely affixed to the body of the haustorium. Removal of this single haustorium stopped hyphal growth immediately, but growth often resumed after 3–24 h and then continued for 5–24 h at rates [Formula: see text] to [Formula: see text] of the normal rate without formation of new haustoria. Microbial contamination prevented the assessment of the capabilities of mildew hyphae for growth over long periods after dissection of host cells. The results suggest, however, that haustoria exposed by the present techniques are functional and therefore might be used to investigate the nature of uptake and secretion by these structures, but that the haustorium is not essential for short periods of hyphal growth by E. graminis f.sp. hordei.