Peer-review: Yes - Open Access: Yes|http://science.thomsonreuters.com/cgi-bin/jrnlst/jlresults.cgi?PC=MASTER&ISSN=0031-949X

In 1932 the writer observed at Quincy, Florida, several decayed maize ears somewhat similar to those attacked by Diplodia zeae[Stenocarpella maydis] or D. macro-spora, but differing in their sour fungoid odour and in having brown sclerotia on some of the outer husks. The affected ears are shrunken and often adhere to the husks, which are covered with a salmon-pink, later dull greyish mycelium attached to the sclerotia. In severe cases the mycelium is visible on the kernels and between the kernel rows, but sometimes only the base shows external signs of infection.
The fungus proved to be a species of Rhizoctonia able to infect healthy maize seedlings, especially when the mycelium and sclerotia were placed in the soil round the roots or in incisions in the stalks. Soil inoculation with pure cultures reduced seedling emergence to 31 per cent., as compared with 100 per cent. in uninoculated controls. In laboratory inoculations the roots and mesocotyl were rotted and sclerotia were formed in and on them. The highest incidence of infection on the ears of plants under field conditions was obtained by inserting the inoculum in the shank or into a wound in the ear tip. The Wheatley white dent variety was more susceptible than Cuban yellow flint corn, especially towards maturity. The kernel is apparently penetrated by the mycelium at its base, whence it passes into the endosperm and embryo.
The fungus is stated to differ from any of the species of Rhizoctonia previously described and is accordingly named R. zeae n.sp. The sclerotia usually arise from the branching and anastomosing of hyphal aggregations and measure 0.5 to 1 mrn. in diameter in culture and 0.1 to 0-5 mm. on the host, usually occurring singly but sometimes conglomerated; the hyphae are 4 to 10 µ in width, hyaline at first, reddish-brown in old cultures, and salmon-pink (later grey) on the host. Cultures maintained their viability for a year. On potato-dextrose agar the minimum, optimum, and maximum temperatures for development were 11° to 14°, 33°, and 40° to 4'2° C., respectively; the sclerotia resisted freezing for 15 days. The optimum hydrogen-ion concentration for growth was PH 6.8. with a minimum near PH 2.5 and a maximum about PH 10.0.

Text in English

Reprints Collection