G. F. Wang and G. L. Xie , Institute of Biotechnology, Zhejiang University, Hangzhou
310029 ,China; P. Kawicha , Faculty of Natural Resources and Agro-Industry Kasetsart University,
Sakonnakhon Province, 47000, Thailand; B. Liu , Agricultural Bioresource Research Institute,
Fujian Academy of Agricultural Science, Fuzhou 350003,China; J.S.Huang, Institute of
Environmental and Plant Protection, Chinese Academy of Tropical Agricultural Sciences,
Danzhou 571737, China; Y. P. Duan, U.S. Dept. of Agriculture Agricultural Research Service U.S.
Horticultural Research Laboratory, 2001 South Rock Road Fort Pierce, FL 34945
Abstract
Bacterial wilt of mulberry (BWM) was first reported in the first half of 2008, in China. Five strains were identified as Enterobacter cloacae according to the traditional bacteria phenotype identification. This work is about the pathogenicity and further identification of other four BWM isolats, which can cause grafted mulberry (Nongsang ×
Heyebai) leave wilt and defoliation symptoms, were tested by In Vitro and In Vivo inoculation. Taxonomic and phylogenetic placement was investigated by analysis of the 16S rDNA regions and rpoB gene, which were amplified by PCR and directly sequenced. For comparison, two isolates R2-2 and R6-2 have been clearly identified as E. asburiae , and two isolates R11-2 and R18-2 should represent a novel species of the genus
Enterobacter sp.. BIOLOG tests and the Sherlock Microbial Identification System (MIDI) display profile variability that only Enterobacter genus level identification could be made in this disease. These data highlight a complex of Enterobacter strains was the causal of mulberry wilt in Zhejiang province.
Additional keywords: pathogenicity · 16S rDNA · ropB · FAME · BIOLOG
Mulberry ( Morus alba ) is an important sericulture plant widely grown in Japan, Egypt and the
Southeast Asia. It was reported that Pseudomonas syringae pv. mori (25), Pseudomonas solanacearum (9) (amended to Ralstoina solanacearum ) (33) and Erwinia carotovora (34) were the three most important bacterial disease of mulberry. During the summer-autumn in 2005-2006, a severe outbreak of a foliar decline disease was noted in the mulberry orchards at Hangzhou city,
Zhejiang province, China. The field symptoms and five pathogens identified to be Enterobacter cloacae were first described by Wang (35). Four other representative isolates undertaken further identification in this research shown that a Enterobacter complex is the pathogen of mulberry wilt disease.
Fourteen species of Enterobacter genus have been reported (11), among which E. cancerogenus (6), E. nimipressuralis (2), E. cloacae subsp. dissolvens (24), E.
pyrinus (4) and E. cloacae complex (22) were phytopathogens. According to the historical records, the woody bacterial diseases usually related with E. cancerogenus and E. nimipressuralis which poplar canker disease (6) and elms wetwood disease causing (3). Other species such as E. cloacae complex are always associated with internal yellow disease of papaya (18), internal decay of onion
(1) and rhizome rot of ginger plants (17).
Pathogenicity, biochemical and physiological features, carbon source utilization, fatty acid
* To whom correspondence should be addressed.
† e-mail:glxie@zju.edu.cn