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However, asci in some genera or species can occur in numbers of one (e.g. Monosporascus cannonballus), two, four, or multiples of four. In a few cases, the ascospores can bud off conidia that may fill the asci (e.g. Tympanis ) with hundreds of conidia, or the ascospores may fragment, e.g. some Cordyceps , also filling the asci with smaller cells.
The asci produce four ascospores each by sexual reproduction. Ascospores are forcibly released from the asci at the end of a rain event following a dry period and are splashed by water or carried by wind to host leaves and flower stems. [3] When the ascospores reach the host plant, the infection cycle begins.
As an ascomycete, Ceratocystis coerulescens produces ascospores encased as groups of eight in asci. The asci are protected by a perithecium, a flask-shaped ascocarp, in which the pathogen overwinters. Ascospores are the sexual spores and are far less common than the asexual spores known as conidia.
Large masses of yeast cells, asci or ascus-like cells, or conidia can also form macroscopic structures. For example. Pneumocystis species can colonize lung cavities (visible in x-rays), causing a form of pneumonia. [11] Asci of Ascosphaera fill honey bee larvae and pupae causing mummification with a chalk-like appearance, hence the name ...
The bitunicate asci are thick-walled, with an outer and inner layer. The outer and inner layer of the ascus wall are called exotunica and endotunica, and they separate during ascospore release. [6] The asci usually contains eight ascospores, while the shape and separation of the ascospores are more variating. [13]
An analysis of 939 asci in which the genotypes of all meiotic products (ascospores) could be determined found 11 asci with an exceptional segregation pattern. These included six asci in which there was one wild-type meiotic product but no expected reciprocal double-mutant (B5B3) product.
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Ascospores are considered important characters for determining species within the genus. They are either 2-celled (1-septate) or multi-celled (muriform) and are either hyaline or pigmented (green or brown), often with a characteristic halo (perispore) visible when viewed in a microscope. Asci contain eight, two or rarely one spore. [6] [8] [11 ...