Archivio Journal of Plant Pathology

Abstract:

In June 2008, brown necrotic spots were observed on leaves and stems of Verbena x hybrida grown in Piedmont. The incidence of the disease was approximately 50%. Pale yellow, circular bacterial colonies developed on LB agar. Pathogenicity was determined by growing three strains (Ve1, Ve2, Ve3) in LB broth, diluting the suspensions to 107 CFU ml-1, and spraying the foliage of healthy Verbena x hybrida plants. Control plants were sprayed with sterile nutrient broth. After 5 days of incubation at 20±1°C, lesions identical to those observed in the field developed only on plants inoculated with strain Ve3. From these a bacterium identical to the inoculated strain was readily recovered. Strain Ve3 was subjected to API 20E system (bio- Mérieux, France) generating the 7digit code 1205373, identical to that reported by Mergaert et al. (1984) for the type strain (NCPPB 1578T) of Erwinia rhapontici. Growth occurred at 37°C. When the 16S rDNA gene sequence of strain Ve3 was compared by BLASTn with nucleotide sequences from GenBank, it showed 97% identity with the conparable sequence of E. rhapontici ATCC 29283. However, Ve3 strain did not produce the typical E. rhapontici pink bacterial colonies and a pink pigment on potato dextrose agar (Wise et al., 2008). Based on cultural, biochemical, nutritional and pathogenicity tests as well as on 16S rDNA sequence, the bacterium isolated from Verbena × hybrida seems to belong to an unknown Erwinia sp. This is apparently the first report of bacterial blight of Verbena × hybrida caused by an Erwinia sp. in Italy and in the world. Mergaert J., Verdonk L., Kersters K., Swings J., Boeufgras J.M., De Ley J.,1984. Numerical taxonomy of Erwinia species using API systems. Journal of General Microbiology 130: 1893-1910. Wise K.A., Zhao Y.F., Bradley C.A., 2008. First report of pink seed of pea caused by Erwinia rhapontici in North Dakota. Plant Disease 92: 315.