Some Observations on the Relation between the Penetration Hypha and Haustorium of the Barley Mildew and the Host Cell

Abstract

1. When conidia of barley powdery mildew are mounted in water under cover glass and the water is exchanged repeatedly, most of the conidia soon lose their protoplasmic and vacuolic structure and die becomig homogenously granular. Some of the conidia break at the shoulder part or burst violently from unrecognizable portion. The plug-like structure at the ends of conidia is sometimes off, causing the conidial contents to exude out.When conidial chains connected with conidiophores and hyphal cells are treated as above, the cells in the chains including conidiophores also immediately disorganize or burst to death. Hyphal pieces taken from the marginal part of pustule are often observed to break at the tip end, when immersed in water.2. When diseased barley leaves are sprayed with water, water drops of various size are detained by upper parts of the conidial chains standing closely to each other, and soon evaporate, leaving the upper disorganized conidia adhesive to each other, giving scabby appearance.Water spraying continued for a few days does not so much damage the lower conidia of the chains, conidiophores, and hyphal cells underneath that conidia formation will be recovered. Spraying for more than a week destroys almost completely those fungal cells, but the hyphae at the margin of the pustule survive and are observed to develop conidial chains at the periphery a few days later.3. Adhesion of conidia and conidial chains by spraying with water may be explained, as reported in a previous paper concerning the effect of lithium on the barley powdery mildew (1959), by breakage of the outer layer of the membrane of conidia swollen by water absorption and adhesive nature of the inner layer of the membrane.4. Water spray for a few days brings about yellowing or browning of the epidermal or internal cells of the host tissue under the pustule. When spraying is continued, the discolored part extends and the color becomes intense. Brown lines are often observed macroscopically along the vein. The cells which are discolored early and intensely are not always the epidermal cells containing haustoria nor the mesophyll cells in direct contact with the infected epidermal cells. Early and strong discoloration of stomatal cell is conspicuous, which are situated not only on the pustule-bearing surface but also on the opposite side. Mesophyll cells in the inner layer and the cells within and surrounding the vascular bundle are often discolored early.5. Previous to discoloration, yellow, viscous, small drops appear on the surface of mesophyll cells and gradually enlarge becoming brown. The membrane of the cells in contact with the stained drops become yellow or brown and the discoloration extends on the membrane. The mesophyll cells with its membrane discolored entirely are often observed to keep turgid condition. Discoloration of the contents of the mesophyll cells and death of them occur generally later. Colored substance in the drop must be exudate from the mesophyll cells.6. As stated in 4, many of the stomatal cells under the pustule sprayed with water die soon and accordingly the stream of sap in the leaf, moving from vascular bundles, through mesophyll cells and epidermal cells, to stomatal cells and into the atmosphere, must be disturbed. The substances translocated to the host tissue under the pustule from the surrounding tissue, are not or hardly utilized by the fungus which is killed or weakened by water spray, and cause excessive contents of the mesophyll cells under the colony. These conditions must bring about abnormal physiology of the mesophyll cells and may be one of the causes of their death.