The genus Botryosphaeria


 

The name Botryosphaeria is applied to collections of ascomycetes in which the bitunicate asci are produced within stromatic, pseudothecial ascomata. The ascomata range from relatively simple uniloculate forms to large multiloculate structures, or aggregations of unilocular ascomata often united on a common basal stroma. They are ostiolate, and may be embedded in the host tissue or burst out and become partly superficial. The forms of the ascomata are variable within a species, which is undoubtedly a result of the conditions under which they were formed, the substrate on which they develop, nutrient quality and availability, and environmental conditions, such as temperature and water availability.

The centrum (that part of the ascoma in which the asci are produced) develops as a cavity within the stroma. Early in its development the pseudothecium contains numerous filaments, or pseudoparaphyses, connected to the roof and base. The pseudoparaphyses are quite wide and are frequently septate, and usually they are constricted at the septa. The asci develop amongst the pseudoparaphyses that dissolve or otherwise gradually disappear by the time the asci are fully mature. Asci are bitunicate, cylindrical or, more usually, clavate, often with an ill-defined stalk. A thinner region at the tip of the inner wall results in the typical apical cavity. Each ascus  contains eight ascospores arranged obliquely in a more or less biseriate manner. Ascospores are hyaline, one-celled, mostly oval, with the widest point at the middle and with a subobtuse base and apex. They are often inequilateral, and they can become brown and 1–2 septate with age. The ascospores do not have mucilagenous caps or appendages and this is the basic difference between Botryosphaeria and the closely related genus Guignardia.

Characters of the asci and ascospores are relatively stable within a species but dimensions, overlap considerably between species making them difficult to apply for species differentiation. For these reasons, species are differentiated largely on the morphological characters of the anamorphs.

 

Ascomata and conidiomata of B. parva on a grapevine stem.
Sectioned ascomata and conidiomata of B. parva.
Immature ascoma of B. lutea with asci developing amongst pseudoparaphyses.

Ascus of B. stevensii.

 


Differentiation of species

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The genus Botryosphaeria. Version 2 saved 30 March 2004
Alan J. L. Phillips, alp@fct.unl.pt
Centro de Recursos Microbiológicos, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
Page copyright © 2004 A. J. L. Phillips