Studies on the parasitism of sooty mould fungi

Abstract

The microscopic investigations were carried out on the morphological difference of external mycelium between the saprophytic and parasitic species of the sooty mould fungi belonging to the Meliolaceae (Perisporiaceae), Capnodiaceae, Microthyriaceae and Deuteromycetes. These results are as follows:
1. In the parasitic species belonging to Meliola, Meliolina, Irene, Irenina, Irenopsis and Amazonia of the Meliolaceae, to Balladyna of the Capnodiaceae, and to Asterina, Parasterina, Lembosia and Morenoella of the Microthyriaceae, the external mycelium is filamentous, straight walled, with hyphopodia or knot cells, and produces reticulate or velvety, small colonies scattering on the surface of the host plants.
2. In the saprophytic species belonging to Capnodium, Neocapnodium, Hypocapnodium, Capnophaeum, Scorias, Chaetoscorias, Chaetothyrium, Aithaloderma, Limacinia, Phaeosaccardinula and Triposporiopsis of the Capnodiaceae, to Perisporina, Dimerium, Dimerina and Phaeostigme of the Meliolaceae, and to Triposporium, Microxyphium and Caldariomyces of the Deuteromycetes, the external mycelium is dematioid, mucilaginous, without hyphopodia or knot cells, and produces membranous or velvety, large colonies covering over the upper surface of the host plants.
3. The presence or the absence of the hyphopodia or knot cells formed on the external mycelium are an important characteristic to distinguish the parasitic from saprophytic species. Almost all of the examined parasitic species have hyphopodia, and rarely knot cells. The hyphopodia are usually definite in shape as well as in arrangement in each species, but in Meliolina octospora these are very few in number, indefinite in arrangement, more or less irregular in shape.
4. The results of histological studies of the host tissue infected with parasitic sooty moulds reveal that nearly all the species produce the penetrating hyphae from the hyphopodia, and that the hyphae send haustoria into the epidermal or rarely subepidermal cells. But some species of the Meliolaceae do not produce the haustoria, and Meliolina octospora produce intercellular hyphae from the hyphopodia, and the hyphae send haustoria into the mesophyll cells. The saprophytic species do not produce the haustoria and also the infection hyphae from the external mycelium.
5. Very similar to powdery mildew fungi in parasitism, the parasitic sooty mould fungi are considered as obligate parasites, and saprophytic ones are considered as obligate saprophytes. These obligate parasites and saprophytes are heterogeneously contained in the Meliolaceae and Capnodiaceae respectively. As regards to the classification of these families from the parasitical point of view, the present author proposes that the obligate parasites having hyphopodia or knot cells on the external mycelium should belong to the Meliolaceae, and that the obligate saprophytes without hyphopodia or knot cells should belong to the Capnodiaceae, and that the Meliolaceae should be divided into the two subfamilies, the Melioleae and Meliolineae, according to the position where haustoria are produced, as the Erysiphaceae is divided into the two subfamilies, the Erysipheae and Phyllactinieae.