Video microscopy of spore development in Haptoglossa heteromorpha, a new species from cow dung

Abstract

Haptoglossa heteromorpha sp. nov. is an aplanosporic species isolated from Rhabditis nematodes found in cow dung samples from northeast England. Video microscopy was used to record sporangial development and spore release. The thalli were distinguishable from previously described Haptoglossa species because they produced one or more broad dome-shaped exit papillae. The thalli were also unusual in having a series of regularly spaced vacuolar regions which appeared to collapse several minutes before spore release. The aplanospores were released from sporangia in an explosive rush from the apex of the broad dome-shaped papillae. The spores initially aggregated together in an irregular clump but later dispersed. The aplanospores were found to be of two distinct sizes (3.5 and <10.5 μ diam), and the resulting infection cells were morphologically distinct, even though the sporangia that produced them were morphologically indistinguishable. Small infection cells were elongate with a wide bilobed base and a narrow tapered vacuolate apex, and there was a distinct pad-like protrusion on the ventral side of the spore. The large aplanospores produced typical Haptoglossa infection cells (gun cells) which had a broad vacuolate basal region and curved sharply to a beaked apex. This is the first record of an aplanosporic species of Haptoglossa consistently producing heteromorphic infection cells that are likely to have different mechanisms of infection.