Description of spore stages of Puccinia sorghi in South Africa

Abstract

The life-cycle of Puccinia sorghi, a heteroecious fungus, consists of five well-defined spore stages. The uredinial and telial stages are completed on the primary maize host whereas pycnial and aecial stages occur on Oxalis comiculata (creeping sorrel), a perennial and widespread weed. Although the sexual phase of maize rust has been known to occur in South Africa for many years, accurate descriptions of spore stages are not readily available. Surface-sterilised discs of maize leaves containing telia were placed on water agar plates and inverted over O. comiculata plants covered with a settling tower. Removal of plants at different time intervals showed that 6 h of high humidity at 19–21°C were sufficient for germination of teliospores and infection of the alternate host by basidiospores. Both light and scanning electron microscopy of O corniculata leaf sections provided detailed descriptions of the pycnia, containing receptive hyphae and spermatia. and aecia with aeciospores. The frequent detection of aecial infections on O. comiculata in KwaZolu-Natal suggested that sexual recombination may play a rote in generating new variants of P. sorghi in South Africa. © 2004, Taylor & Francis Group, LLC.