Intracellular structures of Puccinia Poarum on its alternate hosts

Abstract

A morphological and quantitative comparison has been made of the development of intracellular structures of the heteroecious rust, Puccinia poarum , in tissues of its pycnial-aecial host, Tussilago farfara and of its uredinial-telial host, Poapratensis . The relatively unspecialized intracellular hyphae of pycnial-aecial pustules differ from haustoria of uredinial-telial stages in their greater length, more irregular growth with occasional septation, and in their lack of a clear neck region or recognizable haustorium mother cell. Intracellular structures of P. poarum were found in epidermal, mesophyll and bundle sheath cells of both hosts, occurring in greater concentration in the bundle sheath than in the mesophyll. In Tussilago , infection of the vascular tissue was demonstrated. The frequency of penetration of mesophyll cells by haustoria in Poa was greater than that by intracellular hyphae in Tussilago . The volume of haustoria present in cells of the different types of infected tissue in Poa leaves was inversely related to host cell size, being highest in bundle sheath parenchyma cells and lowest in the epidermis. Haustoria in mesophyll cells increased in size and complexity throughout successive sub-stages of uredinial and telial development. The effects of infection of P. poarum on host tissue included reduced growth of Tussilago mesophyll cells adjacent to pycnia, increased volume of nuclei in infected cells of both hosts and a typically close association between nuclei of infected Poa cells and haustoria. These differences between monokaryotic intracellular hyphae and dikaryotic haustoria in growth habit, frequency of penetration of host cells, association with host nuclei and ability to infect vascular tissue suggest that the alternating phases of the rust life-cycle differ in their nutrition and physiology, requiring two types of intracellular structure.