Ultrastructural Studies of Zoosporangium and Resting Sporangium of Synchytrium desmodii

The development of the zoosporangium and resting sporangium of Synchytrium desmodii , the causal agent of the wart disease of Desmodium is described. During zoosporangium development synaptonemal complexes are formed. (The presence of synaptonemal complexes is characteristic for pachytene of the first meiotic nuclear division.) Zoospore differentiation and maturation in zoo‐sporangia within the same sorus is asynchronous. Prosorus formation was not observed and it is suggested that previous descriptions of a prosorus in S. desmodii may have been based on observations of an empty collapsed zoosporangium. The resting sporangium of S. desmodii is ultrastructurally similar to that observed for S. endobioticum, S. mercuralis and S. anemones . The mature resting sporangium contains a single centrally located nucleus, a large amount of reserve material (lipid) and is surrounded by an extremely thick multilaminate wall which may be up to 15 μm in thickness. Germination studies of surface sterilized seeds of Desmodium and seeds contaminated with resting sporangia of S. desmodii did not lead to plants infected with S. desmodii and thus no conclusion can be made about whether the wart disease of Desmodium can be seed transmitted but only that resting sporangia of S. desmodii may be found on the surface of seeds harvested from naturally infected fields.