Spongospora

"What's in a name? . . . ." ~ Juliet

Molecular evidence has resulted in the renaming and classification of members of this genus. Dick (2001) recommended that the two formae speciales , Spongospora subterranea (Wallr.) Lagerheim f.sp. nasturtii Tomlinson and Spongospora subterranea (Wallr.) Lagerheim f.sp. subterranea Tomlinson, differ enough to be separate species. So for a while we had Spongospora subterranea (Wallr.) Lagerheim and Spongospora nasturtii M. W. Dick. Down et al (2002) supported this name change, as did Neuhauser et al (2010).

Additional molecular evidence led Hittorf et al (2020) to establish a new plasmodiophorid genus, Hillenburgia , and rename S. nasturtii as Hillenburgia nasturtii (Wallr.) Neuhauser, Hittorf, Kirchmair.

Personal Comments

We tried to get potatoes infected with powdery scab from several sources in the USA, but every time someone sent us potatoes, either the stages were too advanced, or the infection was common scab, not powdery scab. With that in mind, I wrote a letter to the late Roger Wastie at what was then the Scottish Crop Research Institute (SCRI) (now The James Hutton Institute ) in Invergowrie, Scotland, to see if he could help locate infected potatoes in Scotland. Roger arranged for us to visit two commercial growers who had ties to SCRI in July 1989. When I got there, it was one of the driest summers in Scotland's history, and Roger was afraid that there would not be much powdery scab. The dogma was that powdery scab is more prevelant in cool, damp growing seasons. The first grower we visited had fields that were being used for SCRI trials: Every plant we dug up had tubers with powdery scab! Likewise for the second grower. So I had plenty of material to prepare for electron microscopy before returning to the USA. So much for dogma.

Roger and I had an enjoyable day driving up past Aberdeen, talking to the growers, having lunch in a rural pub, and tea break in Stonehaven on the way back to Invergowrie outside of Dundee. Roger and his wife, Margaret, had me over for dinner one night before I returned to the USA. When I left, I asked Roger if he would help me arrange a sabbatical at SCRI in a few years. He agreed. In 1992 I contacted him again and he helped to arrange for me to be a visiting reseacher at SCRI in 1993-94 in a laboratory in Crop Genetics.

During my sabbatical at SCRI in Crop Genetics, I learned confocal scanning laser microscopy, and, in an unrelated project, collected root galls on potatoes caused by Spongospora . I prepared the galls in buffer for extraction of DNA with pulsed-field gel electrophoresis, which eventually led to a molecular karyotype of S. subterranea by graduate student Ron Bryan. Unrelated to science while at SCRI, I joined the Dundee University Scottish Country Dance Society, even wearing my kilt to dances, and to this day keeping in touch with some of my favorite dance partners. I also met my future wife in the lab where I worked in Crop Genetics. She came to the USA in the late summer of 1994 and is now an American citizen, adding to my overall enjoyment of retirement.

I would have liked to compare karyotypes of the Spongospora that causes powdery scab on potatoes to what at the time was named Spongospora subterranea (Wallr.) Lagerheim f.sp. nasturtii Tomlinson, the one that causes crook root of watercress. One source of crook root on watercress was at a commercial grower in Pennsylvania, the other I found in a fresh spring in one of our Ohio state parks near Athens. Although I found every stage of sporangial development (used some transmission electron micrographs in the review in The Mycota VII, Part A ) in the watercress from both sites, I was never able to observe sporogenic development, even with weekly samplings for an entire year from the local source. Given that molecular evidence has resulted in the renaming of the organism that infects watercress to Hillenburgia nasturtii , one might expect that the karyotypes would differ significantly.

Roger Wastie retired a few years after I left SCRI in 1994. Sadly, he passed away during a routine medical examination soon after his retirement. When my wife and I were in Fife on one of our holidays in Scotland to visit family and friends, we happened upon a quaint cemetery, and, to our surprise, came across Roger's memorial stone . I'll aways think of Roger out in the field , collecting potatoes.

Images of Spongospora & Hillenburgia

• Powdery scab of potato
• Spongospora sporogenic plasmodia, LMG
• Spongospora young sporogenic plasmodium, TEMG
• Spongospora transitional sporogenic plasmodium, TEMG
• Spongospora sporosorus (spore ball), LMG
• Spongospora sporosorus (spore ball), TEMG
• Spongospora sporangial plasmodia, LMG
• Young sporangial plasmodium of Spongospora , TEMG
• Sporangial lobes of Spongospora , TEMG
• Noncruciform divisions in sporangial lobes of Spongospora , TEMG
• Spongospora sporangial lobes with zoospores, TEMG
• Spongospora zoospore, TEMG
• Spongospora zoospore flagella, TEMG
• Spongospora zoospores, LMG
• Molecular karyotype for Spongospora
• Hillenburgia sporangial plasmodium on watercress, TEMG
• Cruciform divisions in Hillenburgia sporangial plasmodium on watercress, TEMG
• Cruciform division in Hillenburgia sporangial plasmodium on watercress, TEMG
• Hillenburgia on watercress cruciform division (anaphase), TEMG

Selected References for Spongospora

• Arnold, D. L., Flegmann, A. W. & J. M. Clarkson. 1994. Development and evaluation of a laboratory-based technique for screening somaclonal regenerants of watercress ( Rorippa nasturtium-aquatium ) for resistance to crook root disease ( Spongospora subterranea f.sp. nasturtii ). J. Phytopath. 141: 202-208.
• Braselton, J. P. 1992. Ultrastructural karyology of Spongospora subterranea (Plasmodiophoromycetes). Can. J. Bot. 70: 1228-1233.
• Ciaghi, S., Neuhauser, S. & A. Schwelm. 2018. Draft genome resource for the potato powdery scab pathogen Spongospora subterranea . MPMI 31: 1227–1229. Doi: 0.1094/MPMI-06-18-0163-A
• Clay, C. M. & J. A. Walsh. 1990. Ultrastructure of sporangial development in Spongospora subterranea f.sp. nasturtii infecting watercress. Mycol. Res. 94: 463-471.
• Dick, M. W. 2001. Straminipilous Fungi. Systematics of the Peronosporomycetes Including Accounts of the Marine Straminipilous Protists, the Plasmodiophorids and Similar Organisms, Kluwer Academic Publishers, Dordrecht, The Netherlands.
• Diriwächter, G. & D. G. Parbery. 1991. Infection of potato by Spongospora subterranea . Mycol. Res. 95: 762-764.
• Down, G. J., Grenville, L. J., & J. M. Clarkson. 2002. Phylogenetic analysis of Spongospora and implications for the taxonomic status of the plasmodiophorids. Mycol. Res. 106: 1060–1065.
• Hittorf, M. et al (2020). Revised taxonomy and expanded biodiversity of the Phytomyxea (Rhizaria, Endomyxa). J. Eukaryot. Microbiol. Doi: 10.1111/jeu.12817
• Kole, A. P. 1954. A contribution to the knowledge of Spongospora subterranea (Wallr.) Lagerh., the cause of powdery scab of potatoes. Tijdschr. Plantenziekten 60: 1-65. Doi: 10.1007/BF01998440
• Lahert, H. & J. A. Kavanagh. 1985. The fine structure of the cystosorus of Spongospora subterranea , the cause of powdery scab of potato. Can. J. Bot. 63: 2278-2282.
• Merz, U. 1992. The identification of freshly discharged secondary zoospores of Spongospora subterranea : pattern of movement and fine structure. Plant Pathology 41: 490-494.
• Merz, U. 2008. Powdery scab of potato—occurrence, life cycle and epidemiology. Am. J. Pot. Res. 85: 241–246.
• Merz, U. & R. E. Falloon. 2009. Review: powdery scab of potato—increased knowledge of pathogen biology and disease epidemiology for effective disease management. Potato Research 52: 17–37.
• Neuhauser, S., Bulman, S. & M. Kirchmair. 2010. Plasmodiophorids: The Challenge to Understand Soil-Borne, Obligate Biotrophs with a Multiphasic Life Cycle. Pp. 51-78. In: Gherbawy, Y. & Voight, K. (eds.), Molecular Identification of Fungi, Springer-Verlag, Berlin-Heidelberg.
• Strydom, R.F., Wilson, C.R., Tegg, R.S. et al. 2024. Advancements in Spongospora subterranea : Current Knowledge, Management Strategies, and Research Gaps. Potato Res. Doi: 10.1007/s11540-024-09701-8
• Tomlinson, J. A. 1958. Crook root of watercress. III. The causal organism Spongospora subterranea (Wallr.) Lagerh. f.sp. nasturtii f.sp.nov. Trans. Br. Mycol. Soc. 41: 491-498.