Thermotherapy for Xanthomonas campestris pv. campestris Control in Kale Organic Seeds

Among the vegetables produced in the organic system, there are the brassicas as the largest group in Brazil, and in brassicas, one of the most important pathogens is Xanthomonas campestris pv. campestris (Xcc), which causes black rot of crucifers. The importance of this bacterium is increased because it is transmitted by seeds. The objective of this research was to evaluate the effect of thermotherapy in kale seeds, produced in the organic system, on the physiological seed quality and on Xcc control. Sixteen treatments were evaluated [factorial scheme: four lots of kale seeds (10714, 10751, 10756 and 10789) and four treatments (control, seeds inoculated with Xcc, seeds inoculated and treated at 50 degrees C for 20 and 40 minutes)], in a completely randomized design, with four replicates. Germination, seed vigor (first count) and Xcc incidence were evaluated. Thermotherapy in kale seeds at 50 degrees C for 20 and 40 minutes of exposure reduces the infection of Xanthomonas campestris pv. campestris to 10% and 4%, respectively. However, in a seed lot with low initial seed vigor, the heat treatment reduces the germination rate and first count in the germination test. In seed lots with high initial vigor it can be recommended heat treatment at 50 degrees C for up to 40 minutes of exposure for control of Xcc in kale organic seeds.