Abstract
Abstract A description is provided for Ustilaginoidea virens . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Oryza sativa and Zea mays . DISEASE: False smut of rice appears as olive-green, velvety, globose masses, up to 1 cm diam. in some of the ears of the inflorescence. The spore ball, beneath the dark layer of mature spores, is orange-yellow, paling inwards until it is almost white, as it ages it becomes almost black. The glumes are closely applied to the lower part of the spore ball which is at first covered with a membrane. Infection, producing similar symptoms, has been reported on the male inflorescence of Zea mays (8: 716) and on wild species of Oryza . GEOGRAPHICAL DISTRIBUTION: Widespread in the tropics, in U.S.A. (California and S.E. states) and in Italy (CMI Map 347, ed. 2, 1968). Records not yet mapped are Australia (NT), Costa Rica, Dominican Republic and Laos. TRANSMISSION: There appears to be no evidence for seed transmission and the conidia are probably viable for a short time only. The air-borne conidia have a diurnal periodicity with peak at 22.00 hr, numbers being very low between 04.00 and 16.00 hr (46, 316). The ascospores of the reported perfect state may also be air-dispersed.
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