Development of a new semiselective medium for detecting Alternaria brassicicola in cruciferous seeds

A semiselective medium (CW medium) was developed to detect seed-borne Alter naria brassicicola. The medium consists of 30 g galactose, 3 g calcium nitr ate, 1 g dipotassium hydrogenphosphate and magnesium sulfate, 20 g agar, as well as 100 ppm benomyl and chloramphenicol per liter. CW medium can effec tively suppress the growth of some common saprophytic seed-borne fungi, i.e ., Aspergillus spp., Cladosporium spp., Fusarium spp., Penicillium spp., an d Ulocladium spp. Identifying A. brassicicola on CW medium is based on the morphology and color of the colony. A colony of A. brassicicola is a darkis h brown to black color with black powdery fruiting structures after 7 days of incubating on the CW medium at 24 degrees C with 12 hours diurnal light. A. alternata is also capable of growing on this medium, but its colony is white and can be easily differentiated from A. brassicicola. The efficiency and sensitivity of CW medium have been confirmed by numerous international seed laboratories.