Studies on the production of perithecial stromata by Cordyceps militaris in artificial culture

Abstract

Some nutritional and environmental factors which influence the production and maturation of perithecial stromata of Cordyceps militaris (Linnaeus) Link in artificial culture have been studied. The fungus grows vegetatively in defined media with a variety of carbon and nitrogen sources without added vitamins, and can use nitrate as sole nitrogen source, but forms stromata only under special nutritional conditions such as are provided by a medium of sterilized soaked rice grains. Illumination at more than 3 foot-candles is necessary for stromata to be initiated, and an intensity greater than a threshold value between 15 and 90 ft-c is necessary for production of mature perithecia. Temperatures above about 22 °C depress stroma development. So, too, does excessive aeration, which removes a gaseous or volatile stimulatory substance which is produced by the cultures. Media found suitable for stroma production include mineral salt solutions with either starch or sucrose associated with either haemoglobin or casein or peptone. Amino acids, used singly or in mixture, and glucose were not favorable. There was no evidence that fruiting required growth factors. The results support the view that stroma production is favored by media with carbon and nitrogen sources which cannot be assimilated until they have been hydrolyzed, and which consequently sustain favorably low concentrations of assimilable nutrients over a long period.