First report of potato blackleg caused by biovar 3Dickeyasp. (Pectobacterium chrysanthemi) in Greece

Potato (Solanum tuberosum L.) is an important crop in China. In 2013, diseased potatoes exhibiting blackleg and soft rot symptoms were found in the winter potato growing areas of Huizhou city, Guangdong Province, China, with an incidence of approximately 20%. Initially, the stem bases of infected plants blackened and this symptom spread upward. Later, foliage of the diseased plants became yellow and the stem rotted with vascular discoloration. Twenty diseased plants with typical black leg symptoms were collected from a 10-ha potato field with approximately 60,000 potato plants per hectare. A bacterium with small, irregular, round, fluidal, white colonies was isolated from the vascular tissue of all diseased plants on nutrient agar at 26°C for 2 days. Ten strains were randomly selected for pathogenicity assays. Potato plants (cv. Favorita) at the five- to six-leaf stage were inoculated by injecting their stems with 1 ml of each strain in a bacterial suspension (3 × 108 CFU/ml). The inoculated potato plants were incubated at 16 to 21°C and 65 to 85% humidity, and exhibited the same symptoms as the diseased potato plants in the field by 3 to 5 days post inoculation (dpi). The bacterium was reisolated from the diseased tissue (stem) of the inoculated potato plants and produced characteristic pits on crystal violet pectate medium (1). The bacterium utilized a-methyl glucoside, glucose, lactose, maltose, cellobiose, raffinose, melibiose, and citrate, but not d-arabitol, sorbitol, or malonate. The bacteria also gave a positive reaction for catalase and production of reducing substances from sucrose, but gave a negative reaction for oxidase, production of phosphatase, and indole. Using the universal bacterial 16S rDNA primer set, 27f/1541R (4), 1,400-bp fragments were amplified from the 10 strains. The sequences of the 10 fragments (GenBank Accessions KC695819 to KC695828) were identical and had 100% sequence identity with 16S rDNA of Pectobacterium atrosepticum CFBP 1526 (JN600332). Further, the 438-bp and 690-bp fragments were respectively amplified from all 10 strains with the P. atrosepticum-specific primers Y45/Y46 (3) and ECA1f/ECA2r (2). To our knowledge, this is the first report of potato blackleg disease caused by P. atrosepticum (formerly named as Erwinia carotovora subsp. atroseptica) in Guangdong Province, China. References: (1) D. Cupples et al. Phytopathology 64:468, 1974. (2) S. H. De Boer et al. Phytopathology 85:854, 1995. (3) D. Frenchon et al. Potato Research 41:63, 1995. (4) M. Horita et al. J. Gen. Plant Pathol. 70:278, 2004.

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First Report of a Soft Rot of Banana in Mainland China Caused by a Dickeya sp. (Pectobacterium chrysanthemi)

Plant Disease ◽

10.1094/pdis-94-5-0640c ◽

2010 ◽

Vol 94 (5) ◽

pp. 640-640 ◽

Cited By ~ 6

Author(s):

B. R. Lin ◽

H. F. Shen ◽

X. M. Pu ◽

X. S. Tian ◽

W. J. Zhao ◽

...

Keyword(s):

Sequence Similarity ◽

Mainland China ◽

Similarity Index ◽

Soft Rot ◽

Diagnostic Methods ◽

Control Treatment ◽

Sterile Water ◽

Bacterial Isolates ◽

First Report ◽

Pectobacterium Chrysanthemi

Banana is one of the most important fruit crops grown in China (2). A severe outbreak of a soft rot of banana occurred in Guangzhou, China from 2009 to 2010. The disease was characterized by an odorous soft rot of the center of the rhizome. The rot progressed up the pseudostem, destroying the growing point and causing internal decay and often accompanied by vascular discoloration. Yellowing and wilting of the leaves were also characteristic symptoms. A survey of three areas of production of Musa sapientum (cv. ABB) covering 10 ha in Guangzhou revealed that 82% of the fields were affected at an incidence ranging from 20 to 40%. Forty-five bacterial isolates were obtained from lesions on plants sampled from these fields by surface-sterilizing symptomatic tissue in 0.3% NaOCl for 10 min, rinsing the tissue sections three times in sterile water, and plating the sections on nutrient agar. Three representative isolates selected randomly were all gram negative, caused a soft rot of potato disks, utilized malonate, tested positive for phosphatase production, and tested negative for acid production from palatinose, glucopyranoside, and trehalose. A Biolog similarity index of 0.803 indicated that the three isolates had a high similarity to the Biolog reference strain of Pectobacterium chrysanthemi (Version 4.2, Biolog Inc., Hayward, CA). The 16S rDNA sequence (GenBank Accession No. 1321085) of each of the three isolates was determined (1). When compared with sequences in GenBank, the highest degree of sequence similarity was with P. chrysanthemi AF373199. On the basis of a phylogenetic tree of the sequences, the three bacterial isolates are related to Pectobacterium (100% bootstrap values). On the basis of two diagnostic methods, the three isolates were identified as P. chrysanthemi. However, according to Samson et al. (3), they are a Dickeya sp. Additional genetic comparisons with type strains will be needed for the strains to be assigned to a known species of Dickeya. Pathogenicity of each of the three strains on M. sapientum (cv. ABB) was confirmed by injecting 60 40-day-old seedlings each with 5 ml of a suspension of the isolate (108 CFU/ml) into the rhizome. Sixty plants of the same cultivar injected with sterile water served as the control treatment. After 48 h, yellowing and wilting of the leaves, similar to symptoms observed on field plants, were observed on all inoculated seedlings for each of the three bacterial strains. There were no symptoms on the control plants. Koch's postulates were fulfilled by reisolating bacteria from lesions on the leaves of inoculated seedlings. The reisolates were identical to the inoculated strains in biochemical characteristics. Bacteria characteristic of the inoculated strains were not reisolated from the control plants. To our knowledge, this is the first report of a Dickeya sp. causing soft rot of banana in mainland China. References: (1) W. S. Kaneshiro et al. Plant Dis. 92:1444, 2008. (2) Y. P. Ke et al. China Trop. Agric. 1:14, 2008. (3) R. Samson et al. Evol. Microbiol. 55:1415, 2005.

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