The Alternaria brassicae fungus manifests on every plant organ and in every stage of development of the plant. The abiotic factors have an important role during the fungus’s development and pathogenicity. The study must be done in order to establish its needs regarding certain abiotic factors such as: temperature, humidity, athmospheric pression and light. The study is necessary in order to get to know the moment when the firts infections appear. By knowing these elements, a prognosys can be made, and also a warning for the recommended treatment, in order to stop the disease. The Alternaria brassicae fungus is passed on from one year to another, through the seed which comes from sick plants. In terms of laboratory conditions, on crop environment potato-glucose agar, phytopathogenic fungus Alternaria brassicae was isolated on potato-glucose agar on oilseed tunip. The sick biological material, which was formed from leaves, and stems, which had specific disease symptoms, was put in a wet room, where, after 3 days, the mycelium formation was observed. On CGA environment, the Alternaria brassicae fungus formed light-grey colonies, with silky aspect, and dark-grey on the back. The optimum temperature which is necessary in order for the conidions to develop is between 28°C and 36°C degrees. The maximum value of temperature can be considered to be at 42°C. The formed colonies have a weak aspect, and fructifications weren’t even formed anymore. The conidions’s germination is possible at 4°C, 16 hours being necessary. The optimum temperature can be considered the de 28-32°C temperature interval, when 79-83% of conidions germinated. The maximum temperature was discovered to be 40°C and letal temperature was identified as being 42°C, when conidions did not germinate, not even when the Petri recipient was further set to an optimum temperature of 32°C. The Alternaria brassicae fungus’ colonies developed extremely well in the presence of light. As the relative atmospheric humidity value grows higher, the colonies’ development is very good, and the vegetative mass is extremely dense, think, of grey colour. Temperature, relative atmospheric humidity and light are important factors in the Alternaria brassicae fungus evolution. dense, think, of grey colour.

fungus; biology; conidions

Presentation: oral