Penetration Phenomena and Facultative Parasitism in Alternaria, Diplodia, and Other Fungi

Mechanical injury alone caused cells of wheat, sorghum, and broom corn to become markedly discolored near the points of injury; such discolored regions lacked callosities, auto-stained disks, red rings, and other infection phenomena. 2. The two hundred new diseases which resulted from the cross inoculations occurred under conditions very unlike field conditions. 3. All species of Alternaria placed on wheat coleoptiles induced the formation of callosities; all except three produced internal hyphae. 4. Alternaria infection of wheat coleoptiles is characterized by the formation of callosities by the host, and by the appearance of stained rings or disks around points of incipient infection. 5. Alternaria caused callosities to appear in seedling stems of wheat, oats, rye, barley, pop corn, sorghum, broom corn, cabbage, radish, turnip, tomato, Abutilon, soy bean, wax bean, watermelon, pumpkin, and muskmelon; Helminthosporium gramineum and Cephalosporium acremonium caused them to appear in field corn. 6. Diplodia zeae, Cephalosporium acremonium, Colletotrichum nigrum, and Acrothecium sp. induced wheat coleoptiles to produce callosities. 7. Detached and broken elongate callosities induced in wheat by Diplodia showed that elongate callosities sometimes project down into cell cavities, and that they are attached by one or both ends. 8. Different combinations of hosts and fungi resulted in the formation of different kinds of callosities. 9. Penetration hyphae usually entered vertical cell walls. 10. In tube cultures, epidermal cells of hosts below Alternaria inoculum often showed isolated groups or single brown cells; internal hyphae were not seen in most of such cells. 11. Alternaria spp. from asparagus and rose produced internal hyphae in swollen vertical cell walls of wheat; similar internal hyphae of Alternaria sp. from Abutilon occurred in vertical cell walls of cabbage, and some were produced in vertical cell walls of muskmelon by Alternaria sp. from iris. 12. Alternaria and Helminthosporium usually penetrated the hosts here considered within 1-5 days or not at all. 13. Sorghum and broom corn seedling stems infected with Alternaria often exhibited prominent red-brown, auto-stained, disk-shaped spots around incipient infection points. Auto-stained spots, yellow or gray in color, were seen in the epidermal cells of wheat, oats, tomato, cabbage, and soy bean seedling stems infected with Alternaria. 14. Infected regions of sorghum and broom corn always had a prominent red-brown color. The pigment was produced abundantly, and often diffused out of infected or mechanically injured seedlings and stained the rags surrounding them. 15. Rings of spores of two species of Alternaria and one of Helminthosporium on sorghum leaves caused red infection rings. 16. Species of Penicillium, Botrytis, Cephalothecium, and Epicoccum produced appressoria on wheat coleoptiles, but caused no infections. 17. Species of Syncephalastrum, Saprolegnia, Cunninghamella, Botrytis, Cephalothecium, Fusarium, Thielavia, Thielaviopsis, Pestalozzia, Chaetomium, Aspergillus, and Sterigmatocystis did not penetrate wheat coleoptiles. 18. Two species of Alternaria and one of Helminthosporium caused callosities to form in pumpkin hairs. 19. Soy bean seedling stems infected with Alternaria exhibited yellow, disk-shaped aggregations of droplets or granules at points of incipient infection. 20. Stomatal penetration by Alternaria occurred in a pea leaf and a tomato stem; no other cases were seen. 21. Alternaria penetration of onion bulb membranes consisted of hyphae of normal diameter passing through swollen vertical cell walls. 22. Since broth filtrates in which Alternaria and Helminthosporium had grown and liquid pressed from Alternaria mycelium caused no callosities or altered spots to appear in wheat coleoptiles, it is concluded that chemicals from these fungi do not cause such reactions, or that such chemicals do not enter wheat coleoptiles in the absence of mycelium.