Nothorhytisma nahuelitae . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Nothorhytisma nahuelitae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. DISEASE: Tarspot disease of southern beech. The symptoms and life cycle seem remarkably similar to those of Rhytisma acerinum . No serious damage seems to be done to infected trees. Like many South American members of the genus, Nothofagus pumilio is a deciduous tree. Unless the fungus is systemic, therefore, it seems likely that its life-cycle begins with the colonization of young leaves by air-dispersed ascospores in spring. Nothing is known of the appearance of young colonies, but stromata form during the summer and are followed by the conidial state in late summer. Ascomata form during winter on the dead fallen leaves, ripening during spring. The speed of development, and the stages during ripening are not known, but it is possible that the variability observed in the anatomy of ascomata before ascus production - the presence or absence of the extra layer above the lower wall - may represent two different points in the ripening process. HOSTS: Nothofagus pumilio (dead fallen leaf, living leaf). GEOGRAPHICAL DISTRIBUTION: SOUTH AMERICA: Argentina, Chile. TRANSMISSION: Presumably by air-borne ascospores released in humid conditions. The internal anatomy of the ascoma, and particularly the presence of mucus around the paraphyses, and the complex tissues at the periphery of the hymenium indicate that ascomata are likely to be able to shut again after the initial opening if conditions become dry, with the dark covering layer providing protection from uv light and desiccation. The widely-exposed hymenium suggests that ascospores are released by violent discharge, and are air-dispersed, probably in wet weather, following an increase in pressure within the ascoma generally and the ascus in particular, as a result of water uptake by the mucus around the paraphyses. Being colourless, thin-walled and without an obvious mucous sheath, the ascospores probably have little protection from UV light and desiccation after leaving the ascus (SHERWOOD 1981), and so are probably short-lived. Conidia may be water-dispersed.