Characterization of bacterial pathogens causing fruit soft rot and stem blight of bell pepper in Georgia, USA

Abstract

Bacterial soft rot is one of the major destructive diseases affecting crop production worldwide. In summer 2017, soft rot of fruit and stem blight was observed on bell pepper in commercial fields in south Georgia, USA. Bacteria were isolated from infected fruits and stems, and 5 isolates (MPS05, MPS06, PF01–2, PF04–3 and PF05–3) were characterized in the study. The isolates were identified as Pectobacterium carotovorum subsp. brasiliense (Pcb) and P. aroidearum (Pa) by morphological characteristics, biochemical and physiological tests, PCR amplification using Pcb-specific primers, and phylogenetic analysis of the 16S rDNA sequences. Pathogenicity tests on bell pepper seedlings indicated that isolates MPS05 (Pcb) and PF05–3 (Pa) were aggressive, causing plant tissue discoloration, lesions on leaves and stems, plant wilt and death. Inoculation of bell pepper fruit with MPS05 and PF05–3 at different concentrations (105, 106, 107 and 108 CFU/ml) resulted in fruit tissue maceration and complete fruit rot. To our knowledge, this study is the first report of disease caused by P. carotovorum subsp. brasiliense on pepper in the United States and the first report of P. aroidearum causing disease on pepper in the world.