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Environmental Factors Regulating Sexual and Asexual Reproduction by Mycosphaerella ligulicola. R. E. McCoy, Former Graduate Student, Department of Plant Pathology, Cornell University, Ithaca, New York 14850, Present position of senior author: Assistant Professor (Plant Pathologist), Agricultural Research Center, University of Florida, Ft. Lauderdale 33314; R. K. Horst(2), and A. W. Dimock(3). (2)(3)Assistant Professor, and Professor, respectively, Department of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 62:1188-1195. Accepted for publication 28 April 1972. DOI: 10.1094/Phyto-62-1188.

Cardinal temperatures for formation of pycnidia and perithecia of Mycosphaerella ligulicola differed significantly. The temperature/pycnidium-development curve was nearly identical to that for linear growth of the fungus on potato-dextrose agar; i.e., minimum 3, optimum 26, maximum 30 C. Perithecia were not produced at temperatures greater than 24 C; the optimum was 21 C. The effect of temperature on asexual reproduction is compounded by its effect on spore number, size, and septation. Conidium size and per cent of septate conidia produced are inversely proportional to temperature; number of conidia produced is directly related to temperature. Light is required for reproduction by certain isolates, not by others. Isolates requiring light for sporulation are stimulated toward pycnidium formation by near-ultraviolet light at a daily photoperiod of 10 to 15 hr. Perithecium production appears to be stimulated when the proportion of far red light exceeds that in the near red portion of the spectrum at over-all irradiance levels of 450 µw/cm2. However, this effect was overridden at a higher light intensity, 1,500 µw/cm2, under which perithecia were produced at all light qualities tested. High moisture levels favor pycnidium formation, whereas dry conditions accelerate development of perithecia.

Additional keywords: Ascochyta chrysanthemi, chrysanthemum ray blight, Chrysanthemum morifolium.