4 Rhizaria: Phytomyxea

Abstract

Phytomyxea comprises two orders: Plasmodiophorida and Phagomyxida. The group is characterized by a unique type of nuclear division, cruciform division, in which a persistent nucleolus aligns parallel to the spindle and perpendicularly to the metaphase plate of chromatin. Other major features of Phytomyxea are intracellular, biotrophic plasmodia as growth forms and heterokont, biflagellated zoospores. Members of Plasmodiophorida produce environmentally resistant resting spores, which have not been observed in Phagomyxida. Economically significant phytomyxids include the causal agents of clubroot on cabbage and other brassicaceous crops and powdery scab of potato. In addition, several Phytomyxea are vectors for pathogenic viruses on crop plants, including wheat and sugar beet.