Vascular stem resistance to black rot in Brassica oleracea

The stem vascular system of several accessions of cultivated Brassica olera cea L. showed resistance to black rot caused by Xanthomonas campestris pv. campestris (Pammel) Dowson. Resistance prevented systemic spread of the pat hogen in the vascular system of stem. It was race nonspecific and effective at the early stage of seedling growth. A major dominant gene (Rs; resistan t in stem), responsible for expression of compete stem resistance in adult plants (more than six true leaves), was found in a Chinese kale line SR1. A t least one more dominant gene with additive interaction was necessary to p rovide complete resistance in seedlings. In progeny of a cross with a cabba ge line PI436606, kale SR1 stem resistance segregated independently of race -specific resistance from a PI436606. It can be considered as an alternativ e mechanism of plant defense, and a highly valuable feature for crops syste mically infected by black rot during propagation in commercial nurseries.