Life cycle and life strategy features of Puccinia glechomatis (Uredinales) favorable for extending the natural range of distribution

The objective of this study was to find features in microcyclic rust fungi (Uredinales) on wild host plants favorable for extension of the natural range of distribution. Puccinia glechomatis, a leptosporic rust fungus and its herbal host Glechoma hederacea (Lamiaceae), both natives to Eurasia and introduced in North America, were used for this study. Although the host has been known from North America since the beginning of the nineteenth century, the rust fungus was first observed there only in recent years. Favorable features were identified by studying the life cycle of the rust, including nuclear conditions and seasonal characteristics as well as its spread in North America. The life cycle was studied macroscopically by inoculation experiments, by various light microscope techniques, and by scanning electron microscopy. The spread of the pathogen and its host were reconstructed by evaluating host plant herbarium specimens and databases, literature, and field study data. The studies on P. glechomatis show that, generally for microcyclic rust fungi, establishment and potential for spread are based on several favorable features of both the host (e.g., synanthropic occurence and dispersal, genetic stability, regeneration of vegetative plant parts) and the rust fungus (asexual reproduction/genetic stability, homothallism, propagation with host plant, formation of both leptospores and thick-walled teliospores).