Tetramyxa parasitica, een gal op Ruppia

Tetramyxa parasitica Goebel, a Plasmodiophoracean parasite, has been found on Ruppia spiralis L. ex Dum. in three places in the south-western part of the Netherlands, viz. in the Flaauwersinlaag and in the Weversinlaag on the island of Schouwen and in the „inlaag” near the Torenpolder on the island of Noord-Beveland. The parasite forms more or less spherical galls on the stems (fig. 1, b), the leaves and even on the inflorescences (fig. 1, a) of the host. The galls seem to be formed only under special ecological conditions. Although the localities on Schouwen were visited every month since June 1959 the galls were only found for the first time in 1962. Salinity may perhaps be a factor involved in the sporadic appearance of these galls. In 1962 the maximum salinity in the ponds was below 10‰ Cl’; in the preceding years it was considerably higher.