I am attempting to establish axenic cultures of L. major, E. Canadensis & E. nuttallii for the purpose of ecophysiological studies in the absence of algae. If anybody can offer a technique which works I would greatly appreciate it, thank you.
Not sure if this will help, but the attached paper include technique for obtaining axenic cultures of marine mollusks. Perhaps there is some technical overlap?
You could try asking John Eaton (now retired from Liverpool University, but still on the Editorial Panel of Aquatic Botany). When I was working with him on my own PhD back in the 70s he was doing a lot of culture work with elodeids I recall, and he may have some useful tips. The last email I have for him is
Dr. Elisabeth Gross at the Université de Lorraine in Metz, France, knows how to obtain axenic macrophytes for lab experimentation (e.g., Gross 2003). However, I do not know if she has ever grown Elodea spp. or Lagarosiphon specifically. Unfortunately Dr. Gross is not on RG, but you may try to contact her via the Aquatic Botany secretariat, as she too is on the Editorial Board of this journal.