Erwinia persicina as the new causal agent of lettuce soft rot

Abstract

Water-soaked large spots on leaves, severe rot on the head and tissue collapse symptoms were observed on field-grown lettuce (Lactuca sativa) in one of the most important lettuce growing areas in central Anatolia during 2018–2019. Bacteria were isolated from symptomatic lettuce plants. Pathogenicity tests were conducted on a curly lettuce variety, and the pathogenic strains were examined with biochemical tests, including antibiotic susceptibility, cultivar reactions, reactions to copper-based compounds and 16S rRNA gene sequencing. The isolated bacterial strains were Gram negative, oxidase negative, fermentative, positive for fermentation of sorbitol and negative for D-xylose, and the strain produced a water-soluble pink pigment on nutrient agar. Some of the strains were resistant to different antibiotics. All the strains were resistant to different levels of copper-based compounds. Sumarnas and Calorina were the most susceptible varieties, and Bachus was the least susceptible variety to infection. 16S rRNA sequencing confirmed that the causative bacterium of lettuce soft rot in this study was Erwinia persicina.