Scanning electron microscopy of early infection of dyers woad, Isatis tinctoria by germlings of Puccinia thlaspeos

Abstract

Dyers Woad (Isatis tinctoria) is an introduced noxious weed of crop and rangeland in northern Utah. A native rust fungus (tentatively identified as Puccinia thlaspeos) is being investigated as a possible biological control agent of the weed. In order to effectively use the rust in a bio-control program, it is necessary to understand its epidemiology and characteristics.Weeds were inoculated by suspending previously infected weed leaf fragments over test plants. Teliospores on these fragments produced basidiospores which dropped onto the weed seedling leaf surfaces. Inoculated leaves were prepared for SEM by fixation in 2% cacodylate buffered glutaraldehyde, post fixed in 2% buffered osmium tetroxide and dehydrated through ethyl alcohol and critical point dried. Mounted specimens were sputter-coated with gold. Some tissues were freeze fractured in 100% alcohol and fragments were critical point dried, coated and mounted for SEM.