Studies on the Systemic Fungus, Puccinia suaveolens

The autoecious rust Puccinia suaveolens attacks the creeping thistle Cirsium arvense. Infection with uredospores first produces isolated uredc-pustules, usually with teleutospores. The mycelium later grows down into the roots and becomes systemic. In some of the root-buds the mycelium appears unchanged and bears uredosori; in others it undergoes a somatic segregation of mating type and bears spermogonia only. Teleutospore germination is so erratic that basidio-spore infection is responsible for only a small amount of the spermogonial infection observed. The spermogonial mycelium in the systemically infected shoots is heterothallic and there are two mating types. All the spermogonia on one shoot bear spermatia of only one mating type. Therefore segregation of mating type must take place at the base of the shoot or even in the roots. The multinucleate condition of the mycelium in both uredosoral and spermogonial shoots makes it impossible to observe segregation directly.