Morphology of hyphae in leaf tissues infected with java corn downy mildew fungus peronosclerospora maydis in relation to sporulation ability

Java corn downy mildew fungus, Peronosclerospora maydis (Racib.) C. G. Shaw [Sclerospora maydis (Racib.) Butl.], was inoculated to seedlings of corn, Zea mays L., at the 2.5-leaf stage and incubated at 25 C-20 C (daytime-night, 12 hr each) for 27days. Systemic symptoms appeared on the 6th-10th leaves of the plant thus treated. For anatomical study, the leaves used were the 8th, 9th and 10th leaves which were at the developing stage and the 11th leaf which had not emerged out of leaf whorl and showed inconspicuous symptoms. As for the 8th-10th leaves, samples were taken from sporulating area, non-sporulating area on lesion and border area between these 2 areas. As for the 11th leaf, no conidia were formed on the whole area and the tip part was sampled. Observations made after sectioning the samples embedded in paraffin revealed the presence of 3 kinds of hypha types, i.e., “crooked type”, “slender type” and “intermediate type”. In the samples taken from the leaf which had not emerged and also from the non-sporulating area, most of hyphae observed were of the slender type, intermingled with a few hyphae of the intermediate type, whereas no crooked type hyphae were found. In the sporulating area, however, most of the hyphae observed were of the crooked type, intermingled with a few hyphae of the intermediate type and very few of the slender type. In the border between these 2 areas, crooked and intermediate type hyphae were mostly observed with a few hyphae of the slender type. From these observations, it was concluded that the hyphae in leaf tissues seem to be of the slender type in non-sporulating areas located in the basal part of leaves at the developing stage as well in non-emerged leaves. These hyphae gradually change to the intermediate type and the crooked type along with the leaf development. After assuming the crooked type, the hyphae seem to be able to produce conidia.