DETERMINISM OF SEXUAL REPRODUCTION OF PHAEOSPHAERIA (LEPTOSPHAERIA) NODORUM AS CAUSE OF WHEAT SEPTORIOSIS .2. INFLUENCE OF TEMPERATURE AND LIGHT

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 < lambda < 400 nm), and intensities of 400 and 600 muW/cm2 are the most favourable conditions for perithecial differentiation. The perithecial production occurs best at 10-degrees-C, is markedly reduced at 14-degrees-C, and absent above 14-degrees-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-degrees-C. The subsequent stages up to ascogenesis are photostimulated and cryoinduced, and ascosporogenesis is photoindependent and cryostimulated.