Ricardo Marcelo Gonçalves

Alternative hosts of Curtobacterium flaccumfaciens pv. flaccumfaciens, causal agent of bean bacterial wilt

Alternative hosts are an important way of phytopathogenic bacteria survival between crop seasons, constituting a source of inoculum for the following crops. Bacterial wilt, caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), is one of the most important diseases for common bean, and little information is available about the host range of the bacterium. In this study, we assessed possible alternative hosts for Cff, especially those cultivated during winter, in rotation systems with common bean. Plants of barley, black oat, canola, radish, ryegrass, wheat and white oat, were assessed under field and greenhouse conditions. Cff colonized epiphytically all plant species and endophytically black oat, ryegrass, wheat and white oat plants assessed in the greenhouse assays. Under field conditions, Cff colonized all plant species by except radish. All bacterial strains re-isolated from the plants were pathogenic to common bean and identified as Cff by PCR with specific primers. Based on our results, the cultivation of bean crop in succession with barley, black oat, canola, ryegrass, wheat and white oat should not be recommended, mainly in areas with a history of bacterial wilt occurrence. In these cases, the better option for crop rotation during the winter is radish, a non-alternative host for Cff.

Resistance of Xanthomonas euvesicatoria strains from Brazilian pepper to copper and zinc sulfates

Bacterial spot, caused by Xanthomonas spp., is one of the major bacterial diseases in pepper (Capsicum annuum L.). The infection results in reduced crop yield, particularly during periods of high rainfall and temperature, due to the low efficiency of chemical control with copper bactericides. This study evaluated the copper and zinc sulfate sensitivity of 59 pathogenic strains of Xanthomonas euvesicatoria isolated from pepper plants produced in various regions throughout Brazil. Both the respective sulfates and a mixture thereof was evaluated at 50, 100, 200 and 400 μg.mL-1. All the evaluated strains were found to be resistant to zinc sulfate (100 μg.mL-1) and 86.4% were resistant to copper sulfate (200 μg.mL-1). The mixture of copper (200 μg.mL-1) and zinc (200 μg.mL-1) sulfates inhibited the growth of all strains of X. euvesicatoria. To our knowledge this is the first study to report the resistance of X. euvesicatoria strains from pepper plants to copper and zinc sulfates in Brazil.