Variation for Black Rot Resistance in Tronchuda Regenerated from Epicotyl Segments

Abstract

Tronchuda (Brassica oleracea var. tronchuda Bailey syn. costata) regenerants with resistance to Xanthomonas campestris pathovar campestris Pammel (Dawson) were produced by culturing epicotyl segments of 3-week-old seedlings on Murashige and Skoog medium supplemented with 2 mg BAP and NAA at 0.1 mg·liter–1. Cultures were placed in darkness (1, 2, or 3 weeks) or in a 16-hour·day–1 light regime. Seedlings of all four cultivars were more susceptible (mean disease severity rating of 3.8 to 4.0; where 1 = trace and 4 = more than 2 cm2 diseased leaf tissue) than the respective regenerants. There were significant differences in disease severity of regenerants among and within the four cultivars. Dark incubation of cultured explants generated plants with higher disease resistance than evident with control plants. One week of dark incubation resulted in increased resistance in regenerants of `Penca de Chaves', `Portuguesa', and `Vilinda' (2.1, 2.3, and 2.7 mean disease severity, respectively), whereas 2 weeks of dark incubation increased resistance in regenerants of `Ana Maria' and `Vilinda' (2.1 and 2.7 mean disease severity, respectively). The genotype×plant treatment interaction was significant. Chemical names used: 6-benzylaminopurine (BAP); a-naphthaleneacetic acid (NAA).