In our country the most frequent causal agents of mint (Mentha piperita), diseases are parasitic fungi such as Puccinia menthe, Septoria menthe, Erysiphe biocellata, Fusarium sp., and Verticillium dahliae.

However, Verticillium dahliae - an agent causing mint wilting and dying has occurred regularly over the past few years, affecting mint exploitation period, so that mint is grown as a biennial plant. This was the reason for conducting closer investigations on some morphological, breeding and ecological features of the pathogen.

The starting material comprised samples of mint that showed symptoms of wilting. Samples were taken from the production field of the Institute for Medicinal Plants Research "Dr Josif Pančić" during 1997 where entire mint shrubs were observed to wilt and die. The disease manifests itself by gradual yellowing and then by plant dying from the top to its basis. Initially, individual mint plants were infected and thereafter the disease spread to all plants of a single shrub. Microscopic examinations of a mint stem cross-section evidenced vascular tissue necrosis but not microsclerotia presence.

Standard phytopathological method was used to isolate the pathogen (by surface disinfecting of a stem tissue fragment in 1% of NaOCl for 3 min.), whereby pure culture was obtained. Two weeks after artificial inoculation of mint plants carried out under glasshouse conditions, wilting symptoms were reproduced to be like those of natural infection.

Based on the symptoms manifested on mint plant, as well as morphological, breeding and other characteristics, pathogenic fungus Verticillium dahliae was evidenced.

On a potato-dextrose agar the examined isolate slowly forms whitish colony that soon becomes dark with whitish rims and a mass of microsclerotia disappearing when agar is kept for a longer time.

Verticillium dahliae has white-gray, septet mycelium, while conidiophores are fingerlike branched. Conidia are unicellular, non septet, transparent and the size of the examined isolate was 3,00- 4.71 x 4,71-7,2 mm. Conidia are formed individually or in a group on sterigmata tips. To study the effects of a culture medium on the parasite development, a number of media were employed; onion medium, carrot medium, oats medium, peas medium, potato-dextrose medium, beans medium and agar and water medium.

Also, the effects of substrate pH on the pathogen growth and development were studied medium acidity being adjusted to pH 5, 6, 7, 7.5 and 8.

Among ecological features, the effects of different temperatures (0°C, 5°C, 12°C, 18°C, 20°C, 25°C, 28°C, 33°C) on the development of the studied isolate were examined. The growth of colonies was estimated every three days during several weeks.

Studies of breeding and ecological features of the examined mint isolate evidenced that oats medium and potato-dextrose agar effected most favourably the isolate growth, while optimal temperature was at the interval of 20-25°C.

Key words: mint, Verticillium dahliae, wilt, breeding and ecological features.