New Zealand Journal of Botany abstracts

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Ultrastructural studies of pathogenesis and uredinial development of Melampsora larici-populina and M. medusae on poplar and M. coleosporioides and M. epitea on willow

A. G. SPIERS

Soil Conservation Centre, Aokautere
Ministry of Works and Development
Private Bag, Palmerston North, New Zealand

D. H. HOPCROFT

Electron Microscope Unit
Applied Biochemistry Division, DSIR
Private Bag, Palmerston North, New Zealand

Abstract Light, transmission, and scanning electron microscopy were used to study pathogen- esis and uredinial development of Melampsora lar- ici-populina, M. medusae, M. coleosporioides, and M. epitea. Pathogenesis and uredinial development in each of the four Melampsora species were simi- lar. Hyphae ramified intercellularly throughout leaf tissue and haustoria were formed from mother cells which adhered closely to cell walls. Penetration pegs invaginated the host cell plasma membrane and extensive wall deposits formed occasionally. The haustorial neck was bridged with a dark-staining band located mid-way along the neck. The wall of the haustorial body was bilayered and its cyto- plasm was identical with that of intercellular hyphae. Haustoria in invaded cells were sur- rounded with ribosome-studded endoplasmic reticulum. Uredinia developed from' a layer of subepidermal initial cells which divided twice (sometimes three times) across the vertical axis to form three cells viz., a proximal peridial cell, a cen- tral intercalary cell, and a distal sporogenous cell. Intercalary cells formed electron-lucent inclusion bodies before disintegrating. Spore buds from spo- rogenous cells extended into positions formerly occupied by intercalary cells forming urediniospore initials. These initials divided unequally forming an immature urediniospore and a smaller pedicel cell. The urediniospore expanded and developed thickened echinulate walls. Successive uredinio- spores arose sympodially. Clavate, smooth-walled paraphyses were abundant in uredinia. These arose from cells in the base of the uredinium and like peridial cells were formed only with the first gen- eration of urediniospores. When ruptured the epi- dermis peeled back to reveal an intact lining of moribund peridial cells.

Keywords Poplar; willow; Melampsora rust; uredinia; haustoria; paraphyses

Received 10 May 1984; accepted 19 July 1984
New Zealand Journal of Botany, 1985, Vol. 23: 117-133
0028-825X/85/2301-0117$2.50/0 © Crown copyright 1985

PDF file of entire paper: medium quality (7508K); (scanned from paper original: notes about this process)

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