The Development of Diaporthe phaseolorum Variety Sojae in Culture

Abstract

The development of the Phomopsis state of Diaporthephaseolorum var. sojae is described briefly. Both a and J conidia are produced from similar phialides. The isolate studied is homothallic but has trichogynes or trichogyne-like hyphae in early developmental stages. Perithecia develop from initials that include an ascogonial coil surrounded by enveloping hyphae. Perithecial initials ultimately differentiate into an outer peridium, a prominent centrum pseudoparenchyma layer, and paraphyses. Peridial and centrum hyphae in the apical region proliferate early in development to produce an elongate, periphysis-lined neck. The ascogenous system develops from the terminal portion of the ascogonial coil by septation of coil cells and subsequent production of short, ascogenous hyphae. The ascogenous hyphae proliferate to form a hemispherical basal hymenium. Asci are produced from croziers. The asci become detached from the hymenium and fill the centrum, compressing paraphyses and pseudoparenchyma. Development of D. phaseolorum var. sojae is believed to be a variation of the basic developmental pattern known in some other Pyrenomycetes. Data obtained from developmental studies of perithecia play an important role in current systematic concepts of pyrenomycetous fungi. The major source of this emphasis comes from Luttrell's comprehensive review (26) of perithecial development where developmental patterns were conceived as centrum types characteristic of various taxonomic groups. The present study is the third in a series of investigations of perithecial development in representative Pyrenomycetes. Previous studies on Hypoxylon serpens (Pers. : Fr.) Kickx (17) and Gelasinospora reticulospora (Greis & Greis-Dengler) Moreau & Moreau (18) revealed that perithecial development in these fungi could be viewed as a variation on the same basic ontogenetic pattern. Nonetheless, these two fungi belong to different families and represent the Xylaria and Sordaria perithecial centrum types, respectively. An additional centrum type believed to represent the Diaporthales has received little detailed study. The Diaporthe type centrum has traditionally been depicted as lacking paraphyses in the perithecium, although Luttrell himself has questioned the universality of this concept (27). More recently, studies in the genus Gnomonia by Fayret and Parguey-Leduc (10) and Huang and Luttrell (16) have provided evidence that paraphyses exist in fungi that are unquestionably members of the Diaporthales. There have been, however, no comprehensive developmental studies on Diaporthe, the type genus of the Diaporthales. The present study was therefore undertaken.