Déterminisme de la reproduction sexuée du Phaeosphaeria (Leptosphaeria) nodorum agent de la septoriose du blé. II. Action de la température et de la lumière

Perithecial formation of Phaeosphaeria nodorum is obtained in vitro on sterilized wheat straws, under strict conditions of light and temperature. The absence of any reproductive form in the dark indicates photoinduction. The different parameters of light (duration, quality, and intensity) influence perithecial morphogenesis. A 12-h photoperiod, near ultraviolet light (300 nm < λ < 400 nm), and intensities of 400 and 600 μW/cm2 are the most favourable conditions for perithecial differentiation. The perithecial production occurs best at 10 °C, is markedly reduced at 14 °C, and absent above 14 °C. Light and temperature have a sequential influence on the successive stages of perithecial development. Whereas primordial formation is photoinhibited and cryostimulated, transformation to the early stage of perithecial development is photoinduced and not affected by temperatures of 10 and 18 °C. The subsequent stages up to ascogenesis are photostimulated and cryoinduced, and ascosporogenesis is photoindependent and cryostimulated. Key words: Phaeosphaeria, Leptosphaeria nodorum, perithecia, light, temperature.

Les organes de reproduction de l'ascomycète Phaeosphaeria (Leptosphaeria) nodorum et de sa forme asexuée Septoria nodorum

The reproductive organs of one of the pathogens responsible for the septoria diseases of wheat were studied from cultures. There are two types of pycnidia for the asexual stage (one belongs to Septoria nodorum Berk. (=Stagonospora nodorum (Berk.) Castellani & Germano); the other is microconidial) and pseudothecia for the teleomorph: Phaeosphaeria nodorum (E. Müller) Hedjaroude (=Leptosphaeria nodorum E. Müller). The latter are differentiated from glomerular primordia, and their development is typical of an ascolocular pyrenomycete, with a perilocular layer generating descending pseudoparaphyses and periphyses lining the ostiolar cavity. The asci, with a "Jack-in-the-box" dehiscence, are bitunicate. Key words: Phaeosphaeria nodorum, Leptosphaeria, ontogeny and structure, pseudothecia, pycnidia.

Déterminisme de la reproduction sexuée de Phaeosphaeria (Leptosphaeria) nodorum, agent de la septoriose du blé. I. Hétérothallisme et rôle des microspores

Recently identified conditions for in vitro perithecia formation made it possible to demonstrate the existence of previously suggested heterothallism in Phaeosphaeria nodorum. Of the 28 possible pairwise crosses between the eight cultures derived from the spores of a single ascus, 9 were fertile, whereas none of the cultures ever produced fertile perithecia on their own. This result is smaller than the one obtained in classical bipolar heterothallism and suggests the existence of another incompatibility mechanism. The growth and the colour of mycelia derived from eight single ascospores from the same ascus seem to cosegregate with the factor for heterothallism. The formation of microspores in colonies from single ascospores indicates that they may play a role in the formation of perithecia. Used for fertilization, these microspores showed that they were able to bring the complementary nucleus, thus enabling the differentiation of perithecia. However, they are able to germinate and do not behave strictly as spermatia. Key words: Phaeosphaeria, Leptosphaeria nodorum, heterothallism, microspores.