PLASMODIOPHORALES 



Chapter V 

 Phylogeny and Relationships of the Plasmodiophorales 



Historical 



The phylooeny and relationships of the Plasmodio- 

 pliorales have been the subject of great interest and 

 discussion among mycologists and protozoologists 

 during the past half century because species of this 

 order possess certain developmental stages which 

 are similar to those of the Myxomycetes, Proteo- 

 myxa. and other Protozoa, and the simple fungi. Be- 

 cause of inadequate data relative to the order itself 

 as well as to the groups with which it appears to be 

 related, these discussions have been largely specu- 

 lative, and a review of the literature shows that but 

 few of the workers have agreed on the systematic 

 position of the Plasmodiophorales. 



Woronin ('78) stated that Plasmodiophoia stands 

 closest to the Myxomycetes but differs by the lack of 

 a true sporangium and by its parasitic mode of life. 

 In every other way. in iiis opinion, it resembles most 

 closely the myxochytridiales. De Bary ('84) de- 

 scribed P. Brassicae as a doubtful member of the 

 Myxomycetes, but Zopf ('84) established a sepa- 

 rate family, Plasmodiophoraceae, for Plasmodio- 

 phora and Tetramyjca under the zoosporic group of 

 the Monadineae next to the Gymnococcaceae. He 

 nonetheless included the Monadineae in the Myxo- 

 mycetes. and liis exclusion of the latter group from 

 the fungi in 1890 suggests that he did not regard the 

 Plasmodiophoraceae as true fungi. A year later Lan- 

 kester incorporated the Monadineae, Plasmodio- 

 phora and Tetramyxa in a new class, Proteomyxa, of 

 the protozoa. As noted elsewhere, Schroeter ('86) 

 ignored Zopf's family and created a new order, 

 Phytomyxini. with one family, Pliytomyxaceae, to 

 include Pla.imodiophorii, Phyiomfixa, and Soro- 

 sphaera and placed it next to the Myxogastres. In 

 1897 he placed the Phytomyxinae between the Acra- 

 siae and ^lyxogastres and pointed out that because 

 of its free spores P. Brassicae stands close to the 

 Acrasiae but differs principally from this group by 

 its true plasmodium. zoospore stage, and intramatri- 

 cal habit of life. Tubeuf and Smith ('97), however, 

 excluded Phi/tomi/jra from the Phytomyxinae and 

 described Plasmodiophora, Tetramiixa, and Soro- 

 sphaera as pathogenic slime-fungi. Schroeter's dis- 

 position and viewpoint was supported by Lotsy 

 ('07) and Pavillard ('10) who regarded Plasmo- 

 diophora as a myxomycete which has retrogressed 

 because of its parasitic mode of life. Pavillard in 

 particular stressed tlie presence of an initial flagel- 

 late stage as the chief indication of relationsliip be- 

 tween the two groups. 



This viewpoint was severely criticized by Maire 

 and Tison ('09). After a careful cytological study 

 of Sorosphaera, they refuted Pavillard's claim and 

 expressed the opinion that the Plasinodioiihoraceae 

 constitute an entirely distinct group, intermediate 



between the Sporozoa and Myxomycetes and derived 

 more or less directly from the Flagellata. They fur- 

 ther pointed out that although the type of nutrition 

 of the Plasmodiophoraceae is plant-like, while the 

 absence of cellulose and the presence of chitin in tlie 

 spore membrane are animal characteristics. Later 

 ('11), however, they emphasized the close resem- 

 blance of Lif/niera to Woronina polycystis and postu- 

 lated that this genus may have been derived from 

 Woronina-\i\ie ancestors through the disappearance 

 of sporangiosori. Maire and Tison thus concluded 

 that the origin of the Plasmodiophorales should be 

 sought in the neighborhood of the Cliytridiales.asthis 

 order was interpreted at that time. Winge ('13) like- 

 wise maintained that "the relationship of the Plas- 

 modiophoraceae with the holocarpic Chytridiaceae 

 is beyond doubt," and pointed out that certain species 

 of Synchytriiim, Asterocystis, Bhizomyia, Sorolpi- 

 diiim, Woronina, and Pyrrhosorus occupy intermedi- 

 ate positions and represent transition forms between 

 the two groups. Stevens ('13, '25) included the Plas- 

 modiophorales as the first order under the Myxomy- 

 cetes. Maire and Tison were supported by Schwartz 

 ('It) who stated that the differences between the 

 Plasmodiophoraceae and Myxomycetes are too great 

 to be accounted for by the former's parasitic mode 

 of life. Although he regarded the two groups as re- 

 lated, Schwartz, nonetheless, believed that the Plas- 

 modiophoraceae should form a separate order inter- 

 mediate between the Myxomycetes and Chytridiales. 

 Jahn ('14), Cavers ('1.5), and Pascher ('18) con- 

 curred in general with the views of Winge and 

 Schwartz. In reviewing Schwartz's paper, Jahn 

 stated that the Plasmodiophorales have little in com- 

 mon with the Myxomycetes and are closely related 

 cytologically with the Cliytridiales. He excluded the 

 order entirely from the ^lyxomycetes in 1928. Na- 

 waschin ('24) asserted that P. Brassicae has nothing 

 in common with the Myxomycetes as far as nuclear 

 structure is concerned and advocated its inclusion 

 among the non-amoeboid type of Protista. Cavers 

 ('15) stressed the relationship of the Plasmodiopho- 

 raceae and chytrids and believed that Sorolpidiiim 

 may possibly be a connecting link between this fam- 

 ily and the Synchyiriaceae. 



' The view that the Plasmodiophoraceae are closely 

 related to the Chytridiales has been rather widely 

 accepted. Gaumann ('26) and Gaumann and Dodge 

 ('28) included the Plasmodiophoraceae with the Wo- 

 roninaceae. Olpidiaceae. and Synchytriaceae in a 

 special group, the Archimycetes. apart from the 

 Phycomycetes. They accordingly linked the Plasmo- 

 diophorales with Fischer's earlier-named iNIyxochy- 

 tridiales. Kniep ('28) regarded them as fungi, and 

 wliile admitting that they may perhaps be included 

 in the Chytridiales, he said that the last word on 

 their exclusion from the Myxomycetes had not been 



