Evaluation of a diagnostic microarray for the detection of major bacterial pathogens of potato from tuber samples

Bacterial ring rot of potato caused by Clavibacter sepedonicus: A successful example of defeating the enemy under international regulations

BACKGROUND

Bacterial ring rot of potato (Solanum tuberosum) caused by the gram-positive coryneform bacterium Clavibacter sepedonicus is an important quarantine disease threatening the potato industry around the globe. Since its original description in 1906 in Germany, management of ring rot has been a major problem due to the seedborne nature (via seed tubers not true seeds) of the pathogen allowing the bacterium to be transmitted long distances via infected tubers.

DISEASE SYMPTOMS

On growing potato plants: interveinal chlorosis on leaflets leading to necrotic areas and systemic wilt. On infected tubers: vascular tissues become yellowish brown with a cheesy texture due to bacterial colonization and decay.

HOST RANGE

Potato is the main host of the pathogen, but natural infection also occurs on eggplant, tomato, and sugar beet.

TAXONOMIC STATUS OF THE PATHOGEN

Class: Actinobacteria; Order: Actinomycetales; Family: Microbacteriaceae; Genus: Clavibacter; Species: Clavibacter sepedonicus (Spieckermann and Kotthoff 1914) Li et al. 2018.

SYNONYMS (NONPREFERRED SCIENTIFIC NAMES)

Aplanobacter sepedonicus; Bacterium sepedonicum; Corynebacterium sepedonicum; Corynebacterium michiganense pv. sepedonicum; Clavibacter michiganensis subsp. sepedonicus.

MICROBIOLOGICAL PROPERTIES

Gram-positive, club-shaped cells with creamy to yellowish-cream colonies for which the optimal growth temperature is 20-23°C.

DISTRIBUTION

Asia (China, Japan, Kazakhstan, Nepal, North Korea, Pakistan, South Korea, Uzbekistan, the Asian part of Russia), Europe (Belarus, Bulgaria, Czech Republic, Estonia, Finland, Georgia, Germany, Greece, Hungary, Latvia, Lithuania, Norway, Poland, Romania, European part of Russia, Slovakia, Spain, Sweden, Turkey, Ukraine), and North America (Canada, Mexico, USA).

PHYTOSANITARY CATEGORIZATION

CORBSE: EPPO A2 list no. 51. EU; Annex designation I/A2.

Molecular methods as tools to control plant diseases caused by Dickeya and Pectobacterium spp: A minireview

Dickeya spp. and Pectobacterium spp. are etiological agents of soft rot on crops, vegetables, and ornamentals. They also cause blackleg on potato. These pectinolytic phytopathogens are responsible for significant economic losses, mostly within the potato production sector. Importantly, there are no methods to eradicate these microorganisms once they have infected plant material. Solely preventive measures remain, including early detection and identification of the pathogens, monitoring of their spread in addition to planting certified seed material tested for latent infections. As proper identification of the causative agent allows for efficient limitation of disease spread, numerous detection and differentiation methods have been developed. Most commonly followed procedures involve: isolation of viable bacterial cells (alternatively post-enrichment) on semi-selective media, identification to species level by PCR (single, multiplex, Real time), serology or fatty acids profiling. Differentiation of the isolates is often accomplished by sequencing the housekeeping genes or molecular fingerprinting. In view of lowering total costs of next-generation sequencing (NGS), a huge amount of generated data reveals subtle differences between strains that have proven to be potentially useful for the establishment of specific novel detection pipelines. Successful implementation of molecular diagnostic methods is exemplified by 20-year studies on the populations of pectinolytic bacteria on potatoes in Poland. The presented work aims to gather the characteristics of Dickeya spp. and Pectobacterium spp. important for the identification process in addition to providing an overview of modern and newly developed specific, rapid, high-throughput and cost-effective screening methods for the detection and identification of these phytopathogens.