Strategies of pathogenicity in monokaryotic and dikaryotic phases of rust fungi, with special reference to vascular infection

Observations relating to the infection of vascular tissue of host plants by rust fungi are reviewed. In a substantial number of heteroecious and autoecious rusts, penetration of the vascular tissues is observed during monokaryotic but not dikaryotic phases of infection. It is also associated with the production of simple, filamentous intracellular structures, unlike the specialized, clavate haustoria of the uredinial and telial stages. The differing strategies of the monokaryon and dikaryon in the acquisition of host assimilate are discussed in the context of the distinct structural, physiological and biochemical features of their pathogenicity.