Initial events in the colonization of dyer's woad by Puccinia thlaspeos

Abstract

The initial events involved in basidiospore germination and infection of dyer's woad by Puccinia thlaspeos were studied using scanning electron microscopy and the polymerase chain reaction. The presence of dew was shown to promote infection but was not necessary. Under the conditions of this study, infection of leaf tissue could sometimes be detected using the polymerase chain reaction as quickly as 3 h after inoculation, but 6 h was usually required. Basidiospores and germ tubes were both attached to the leaf surface by an extracellular matrix, and the germ tubes produced appressoria before penetration into the leaf tissue. Penetration was direct rather than through the stomates, and colonization occurred via the growth of intercellular hyphae and haustoria.Key words: biological control, mycoherbicide, noxious weed, Puccinia, dyer's woad.