Pest categorisation of Curtobacterium flaccumfaciens pv. flaccumfaciens

First Report of Curtobacterium flaccumfaciens in Bulgaria

This study aims at the identification and characterization of five actinobacterial strains with presumed belonging to the species Curtobacterium flaccumfaciens isolated from tomato and pepper plants, and establishing the potential role of both plants as natural reservoirs of this phytopathogen. Species identification was performed via MALDI-ToF MS, 16S rDNA sequencing and PCR. The strains were Gram-positive with a coryneform cell shape having yellow/orange-pigmented colonies; positive for catalase and esculin, and starch and casein hydrolysis; oxidase-, urease-, indole- and nitrate-reduction-negative and were strictly aerobic. All isolates produced antimicrobial substances against various phytopathogenic bacteria. Tomato and pepper plants were artificially infected with newly isolated strains in order to establish their role as natural reservoirs of the bacteria. Morphological alterations were observed only in the tomato plants, with defoliation of the first two to four leaves at the 28th day. Then, viable coryneform bacterial isolates (n = 73) were successfully re-isolated only from the stems of the infected plants. The similarity between the re-isolates and the respective initial isolates was confirmed phenotypically and genotypically by RAPD-PCR, confirming that solanaceous vegetables can act as reservoirs of C. flaccumfaciens. This is the first report of C. flaccumfaciens in Bulgaria.

Phytopathogenic Curtobacterium flaccumfaciens Strains Circulating on Leguminous Plants, Alternative Hosts and Weeds in Russia

Many bacterial plant pathogens have a broad host range important for their life cycle. Alternate hosts from plant families other than the main (primary) host support the survival and dissemination of the pathogen population even in absence of main host plants. Metabolic peculiarities of main and alternative host plants can affect genetic diversity within and between the pathogen populations isolated from those plants. Strains of Gram-positive bacterium Curtobacterium flaccumfaciens were identified as being causal agents of bacterial spot and wilt diseases on leguminous plants, and other crop and weed plants, collected in different regions of Russia. Their biochemical properties and susceptibility to copper compounds have been found to be relatively uniform. According to conventional PCR assays, all of the isolates studied were categorised as pathovar Curtobacterim flaccumfaciens pv. flaccumfaciens, a pathogen of legumes. However, the strains demonstrated a substantial diversity in terms of virulence on several tested host plants and different phylogenetic relationships were revealed by BOX-PCR and alanine synthase gene (alaS) sequencing.

Innovative Detection of the Quarantine Plant Pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens, Causal Agent of Bacterial Wilt of Leguminous Plants

Specific, sensitive, and rapid detection of quarantine and regulated plant pathogens is pivotal for the control of the diseases they cause. Here, we describe the PCR-based methods which have been developed for Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), quarantine plant pathogenic bacterium for EU and causal agent of bacterial wilt of Leguminous plants. These methods include an end-point and a real-time PCR test, and a LAMP assay. Their threshold analytical limits range from 100 to 10 fg of DNA template per reaction and are currently used worldwide for routine testing for Cff from laboratory to field scale.

A Powerful LAMP Weapon against the Threat of the Quarantine Plant Pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens

Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) is a Gram-positive phytopathogenic bacterium attacking leguminous crops and causing systemic diseases such as the bacterial wilt of beans and bacterial spot of soybeans. Since the early 20th century, Cff is reported to be present in North America, where it still causes high economic losses. Currently, Cff is an emerging plant pathogen, rapidly spreading worldwide and occurring in many bean-producing countries. Infected seeds are the main dissemination pathway for Cff, both over short and long distances. Cff remains viable in the seeds for long times, even in field conditions. According to the most recent EU legislation, Cff is included among the quarantine pests not known to occur in the Union territory, and for which the phytosanitary inspection consists mainly of the visual examination of imported bean seeds. The seedborne nature of Cff combined with the globalization of trades urgently call for the implementation of a highly specific diagnostic test for Cff, to be routinely and easily used at the official ports of entry and into the fields. This paper reports the development of a LAMP (Loop-Mediated Isothermal Amplification) specific for Cff, that allows the detection of Cff in infected seeds, both by fluorescence and visual monitoring, after 30 min of reaction and with a detection limit at around 4 fg/μL of pure Cff genomic DNA.

Pest categorisation of Curtobacterium flaccumfaciens pv. flaccumfaciens

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of the seed‐borne bacterium Curtobacterium flaccumfaciens pv. flaccumfaciens. The pest is regulated in Council Directive 2000/29/EC (Annex IIB) as a harmful organism whose introduction into, and spread within, the protected zones (PZ) of Greece, Portugal and Spain shall be banned if present on seeds of Phaseolus vulgaris and of Dolichos. The bacterium is widely distributed outside the EU and causes a systemic vascular disease (bacterial wilt of bean) as well as bacterial tan spot disease on soybean. The pest was sporadically recorded in several EU Member States in the past, but is currently not known to occur in the EU. The identity of the bacterium is well established and identification methods are available. The major host is common bean (Phaseolus vulgaris), but other crops and weeds are, or may be, hosts or play a role as reservoirs, with uncertainties. Seed transmission remains uncertain for minor and alternative host species. The main pathway for entry is seed. The role of other pathways (e.g. irrigation water and infected residues) is uncertain. Should the bacterium enter the EU (including the PZ), it may establish, spread and have an impact on its host crops. The use of healthy seeds is the most effective control measure. Curtobacterium flaccumfaciens pv. flaccumfaciens fits all the criteria assessed by EFSA to be regarded as a Union quarantine pest.