• Three seed treatments were shown to be effective in controlling black rot of rape. • Paenibacillus sp. reduced Xanthomonas campestris on rape seeds and reduced black rot. • Agapanthus caulescens (indigenous to South Africa) at 15 mg/ml reduced black rot. • Hot water seed soak at 50 °C for 30 min effectively controlled black rot.

Seed-borne pathogens found on brassica seeds can cause significant reduction in crop productivity and quality. In this study, seed health tests and germination of brassica seeds collected from several seed companies in South Africa, including a farm retained sample, were evaluated. Fungi detected from 13 seed samples using the agar plate method included Alternaria brassicicola, A. alternata, Aspergillus niger, A. glaucus and Penicillium spp. A. alternata, the most common fungal species isolated, was found in seven samples with an incidence ranging from 0.5-6.25%. Results of the pathogenicity tests of the Alternaria species showed that only the A. brassicicola isolate produced necrotic lesions on rape and cabbage seedling leaves. No seed-borne bacteria reported to be pathogenic to brassicas were detected from the seeds. Germination of seeds was evaluated according to the International Seed Testing Association rules. The highest seed germination was observed in a cauliflower seed sample at 97% and a rape seed sample recorded the lowest at 17%.