St. John's wort (Hypericum perforatum L.) has not so far been commercially grown in Serbia. But, because of its increasing use as antidepressant medication there is great interest for commercial growing of this plant in our country. At the Institute for Medicinal Plant Research "Dr Josif Pančić", Belgrade, from 1997-1999 St. John's wort growing has been initiated.

In 1999, there were four types of St. John's wort plantations in the experimental field. Two years old plantations where established in fall 1997 and spring 1998, and one year old plantations where established in fall 1998 and spring 1999. The plants were grown on heavy soil (black marsh soil), with 48.6% of clay, 45.9% of powder, 5.5% of sand and content of humus (3.5%). The most grown population was that usually grown from the Institute's collection, originated from western Serbia. New plantations of 8 genotypes of St. John's wort originating form the different location of Serbia and Europe were established in 1999.

The diseases symptoms of St. John's wort started in the first year of planting (1998), but the disease became severe in 1999, when most of the plants has died out.

The first sign of disease in 1999, appeared when the plants were 15 to 25 cm high. Some plants died very young and some after flowering. The disease caused wilting of the plants top, yellowing and necrosis of leaves and death of some branches followed by whole plant. Some of the plants from one bush died out before flowering, some of them produced flowers, but all of them died out after flower harvest.

Infected plant has necrotic roots, stems and branches. In cross section there was vascular discoloration of roots and stems. Segments cut from symptomatic branches and necrotic root piece were disinfected in 0.5% sodium hypochlorite and placed on potato dextrose agar (PDA) at 25°C. Fusarium spp. was isolated from necrotic branches and roots. Cutting the end of colony on PDA, 8 pure cultures were isolated.

Ten-week-old St. Johne's wort plant, growing in potting mix. In 10 cm pots, were inoculated by injecting 10 ml of suspension of conidia 5-10 cm from both side of root zone. Plants were grown in a greenhouse at 90% relative humidity and 25 to 35°C. The first symptoms on inoculated plants appeared four weeks after inoculation on leaves with yellowing and later necrosis. From necrotic plant parts the same culture as with first isolation was re-isolated. Pathogenicity test was repeated and the results were similar.

By morphology studies of conidia and growing isolated cultures on Carnation Leaf Agar media (CLA) 8 isolates were identified as Fusarium oxysporum. This is the first report of Fusarium oxysporum causing St. John's wortwilt and root and crown rot in Serbia.