Agronomic performance of partly clubroot-resistant spring oilseed turnip rape lines

In field experiment studies that tested the effects of three partly resista nt cultivars of spring oilseed turnip rape (Brassica campestris), multiplic ation of clubroot was moderate. When initial soil inoculum levels were 47-7 2% of infected test plants in the bioassay, only 2.1-10% of the plants were infected after harvest. The yield of partly resistant lines was 5-10% high er compared with that of the susceptible cultivar SW Kulta, which on averag e yielded 1.73 t/ha. The average disease severity index (DSI) after harvest in these trials was 12.7 for the nonresistant cultivar SW Kulta and ranged between 2.2 and 6.2 for the partly resistant lines. The study demonstrated that in fields where the soil infestation level gives a DSI of less than 1 0, or when less than 20% of the bait plants are infected in the bioassay, i t is possible to avoid the risk of severe yield losses from clubroot infect ions by integrating a partly resistant cultivar into the crop rotation.