Ontogeny of the uredium of Melampsora lini

Light microscopy and transmission and scanning electron microscopy were used to study the development of uredia of Melampsora lini. Uredia were produced 6–10 days after inoculation with urediospores of M. lini. Uredium ontogeny began with the formation of a uredium initial from a hyphal plexus in a substomatal cavity. The hyphae oriented vertically and expanded; the enlarged ends divided to form a palisade of uredial initial cells. These cells divided into basal and terminal cells. Each terminal cell divided transversely to form a peridial and an intercalary cell; the basal cell became the sporogenous cell. The intercalary cells disintegrated early in the expansion of the uredium and released their contents into the intercellular matrix. The sporogenous cell, usually swollen at one end, gave rise by budding to successive sympodially produced spore buds which elongated and divided transversely to form pedicels and immature spore cells. As the spores matured the pedicels shriveled and became separated from the urediospores. Elongated, often capitate, paraphyses formed throughout the uredium and functioned to rupture the peridium and epidermis which covered the immature uredium. The peridium and the intercalary cells formed only once during ontogeny of the uredium, this being associated with only the first generation of urediospores. The intercalary cells were disrupted during uredium ontogeny, and most of the peridial cell layer was sloughed off, along with the overlying epidermis, upon rupture of the latter. The paraphyses were permanent and remained in the uredium throughout its functional life. Successive generations of urediospores arose within the same uredium from spore buds produced sympodially from the original sporogenous cell but without forming additional peridial or intercalary cells.

Studies on aecial development in rust fungi: Puccinia polliniae

The leaves of Goldfussia dalhousiana become infected by Puccinia polliniae with the onset of rains in the Western Himalayas. Pale yellow dots appear on the leaves, developing into pustules and extending centrifugally. Pycnia develop on the upper surface and aecia on the lower. Protoaecia are differentiated into fertile and displacement zones. After dikaryotization, the basal cells elongate, become binucleate, and, by transverse conjugate division, produce the aeciospore mother cells. By transverse division, each of these form a large aeciospore and a small disjunctor cell towards the basal cell. The basal cells at the periphery, by transverse conjugate divisions, give peridial mother cells each of which by an oblique conjugate division cuts off an intercalary cell towards the outside and a peridial cell towards the inside. The peridial cells develop thick walls and the intercalary cells degenerate. The peridium has a dual origin and the aecia are of the aecidioid type. The aeciospores are circular to oval in shape, binucleate, and multiguttulate. They have radially striate thickened walls and two to three germ pores.