LEAF AND HEAD ROT OF CHINESE-CABBAGE - A NEW FIELD DISEASE CAUSED BY PYTHIUM-TRACHEIPHILUM MATTA

A new disease has arisen in field grown Chinese cabbage (Brassica camp estris ssp. pekinensis) in Denmark. The soil-borne causal agent was sh own to be Pythium tracheiphilum Matta, a little known pathogen of lett uce. Until now, outbreaks of the disease in Chinese cabbage were gener ally attributed to Phytophthora porri Foister, since symptoms of the d isease in the field resemble those caused by Ph. porri in Chinese cabb age in cold stores. In some severely affected crops harvest losses in 1994, directly attributable to P. tracheiphilum, were estimated to abo ut 50%, corresponding to a market value of up to $ US 20000 per ha. Ou tbreaks of the disease coincide with the heading of the crop, while ju venile plants or seedlings are apparently not attacked. It appears tha t the outer leaves are infected directly from the soil. Mainly above g round parts are affected and colonized by the pathogen, and indication s of infection via the root system have not been observed. This is the first record of P. tracheiphilum as a pathogen of Chinese cabbage.