Weeds are survival niches of Xanthomonas campestris pv. campestris in São Paulo state, Brazil

Abstract

Weeds play an important role in agricultural ecosystems, as they host pathogens such as Xanthomonas campestris pv. campestris (Xcc), causal agent of brassica black rot. For Brazilian conditions, there is little information about Xcc host species, which motivated this study. Asymptomatic and symptomatic weeds were collected during 2017 and 2018, in six brassica cultivation fields in the state of São Paulo, Brazil, to detect the presence Xcc in the phyllosphere and identify host weeds. The endophytic survival of Xcc strain 3098C was also evaluated in four experiments in a greenhouse, with 23 weed species from 14 botanical families. In the brassica fields, Xcc was recovered from the phyllosphere of 25 weed species, however the frequencies of recovery varied between the species evaluated. Plants of Bidens pilosa (hairy beggarticks), Coronopus didymus (lesser swinecress), Galinsoga parviflora (gallant soldier), Ipomoea nil (whiteedge morning-glory), Lepidium virginicum (virginia pepperweed), Raphanus raphanistrum (wild radish), Raphanus sativus (cultivated radish) and Sonchus oleraceus (common sowthistle) were identified as symptomatic hosts of Xcc. In the greenhouse, Xcc was recovered from all the weed species evaluated, however the average survival periods varied between 5 and 42 days. Based on the results, it is recommended to control Amaranthus spp., Bidens spp., Commelina spp., C. didymus, Cyperus spp., Emilia fosbergii, Euphorbia heterophylla, G. parviflora, Ipomoea spp., Leonurus sibiricus, L. virginicum, Nicandra physalodes, Portulaca oleracea, R. raphanistrum, R. sativus, Oxalis oxyptera, Solanum americanum and S. oleraceus in areas with brassica cultivation and a history of black rot.