Evaluation of physical and chemical disinfection methods of Brassica oleracea seeds naturally contaminated with Xanthomonas campestris pv. campestris

Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot of crucifers, is a seedborne pathogen that causes severe yield losses worldwide. Seed treatments represent the most effective strategies to control the pathogen. In this study several physical and chemical treatments were evaluated for their efficacy in containing the contamination of the seeds with Xcc, without compromising the germination. The experiments were carried out with a naturally contaminated seed batch, selected among four lots for its higher contamination with Xcc (9.5 x 10(1) cells/g of seed). The evaluation was performed under controlled conditions following a modified protocol from ISTA (2019), highlighting different degrees of effectiveness of the tested disinfection treatments. Seeds disinfected under laboratory conditions with hydrogen peroxide (3%) for 30 min showed the 100% containment of the level of contamination with Xcc with the germination rate at 95.3% after the treatment, if compared with the untreated control. The same treatment was tested at the operation site of the seed company to evaluate the applicability of the method under commercial conditions. Under practical conditions, reducing the length of the treatment to 15 min, the strict control of the temperature of the disinfecting bath, the drying temperature at 37 degrees C and the use of small quantities of seeds, between 50 and 300 g, were crucial to obtain disinfected and viable seed.