Ascoma Morphology of Pseudopeziza Trifolii Forma Specialis Medicaginis-Sativae (Dermateaceae) on Alfalfa

Abstract

Ascomatal initials of Pseudopeziza trifolii f. sp. medicaginis-sativae consist of ascogonial coils forming on intracellular hyphae in parenchyma cells of living alfalfa leaflets. In some young ascomata, the ascogonial coils are surrounded by an aggregation of hyphae, while in other initials, such hyphae are sparse. Ascogenous hyphae and paraphyses develop and grow through the surrounding mycelium toward the host epidermis. Croziers proliferate from the binucleate ascogenous cells. Asci are eventually produced, with each mature ascus containing eight uninucleate ascospores. Ascosporogenesis is similar to that described in a number of Ascomycetes. Until the time of ascospore discharge, the hymenium of an ascoma is covered by hyphae in and under the infected host epidermis, and by periphysoids arising from these hyphae. The host epidermis ruptures when the ascoma is mature. A pseudoparenchymatous excipulum is present. Vegetative mycelium generally fills most of the host cells under the ascoma, and somatic hyphae appear to radiate outward from the ascoma to surrounding host cells. Septa in the hyphae have pores, with Woronin bodies in close proximity to the pores. Some pores have electron-dense plugs. The aggregation of hyphae observed throughout ascoma development is often referred to as a stroma; however, this aggregation is not always well developed, and it is not known whether or not it arises as a result of a sexual stimulus. Ascomata of this fungus can therefore be interpreted as either stromatic or nonstromatic.