Persistent, systemic, asymptomatic infections of Albugo candida, an oomycete parasite, detected in three wild crucifer species

Field observations and published data suggested that the oomycete parasite Albugo candida (Pers.) Kuntze could exist as latent, asymptomatic, systemic infections. The wild crucifer species Lepidium campestre (L.) R.Br., Arabis lyrata L., and Erysimum menziesii ssp. eurekense R.A. Price were chosen as models to test this hypothesis. Detection of the parasite in asymptomatic host tissue was based on polymerase chain reaction amplification of ribosomal DNA internal transcribed spacer region I of A. candida using primers designed to discriminate between plant and parasite DNA template. Albugo candida was detected in high proportions of asymptomatic field plants (vegetative and reproductive), greenhouse grown vegetative rosettes, and laboratory germinated seedlings of each species. For example, A. candida appeared to be systemic in all 20 field plants and 10 inoculated rosettes of L, campestre. Albugo candida was present in uninoculated rosettes and seedlings (up to 98%) suggesting seed borne transmission of the pathogen. Although the parameters controlling symptom development are still unclear, presence of the pathogen appeared not to be sufficient for symptom expression. Persistent, asymptomatic, systemic infections that are vertically transmitted through seed suggest that A. candida may possibly form endophytic relationships with at least some of its crucifer hosts.