Plant Health Laboratories

Virology and Bacteriology Laboratories

The Virology Lab is situated at the Plant Biotechnology Centre in Lija and as with the other laboratories under the Diagnostic Laboratories it forms part of the Diagnostic and Control Unit. At this lab various tests are performed for diagnosing quarantine viruses. These tests are classified into three categories namely the Biological assays, the Serological assays and the Molecular assays.

The Biological assays include mechanical transmission of viruses on specific herbaceous indicators. Biological assay is also used for the confirmation of infection by quarantine pathogens.

Serological assays involves ELISA (Enzyme linked immunosorbent assay), Immunofluorescence, Immunoprinting and Lateral flow immunocromathography. In all tests specific antibodies are used for the detection of particular viruses and bacteria. ELISA is the most frequent used test for diagnosing viral pathogens.

Molecular assays incorporate the Reverse Transcription Polymerase Chain Reaction (RT-PCR) which is used for the confirmation of the presence of various quarantine viruses and bacteria. Double stranded RNA analysis and Molecular hybridisation are also used according the virus or virus like organism being tested for.

An ELISA plate showing positive samples

Surveys

This lab carry annual surveys for quarantine viruses, these include:

- the Citrus Tristeza Virus (CTV) survey on local citrus

- the Pepino Mosaic Virus (PepMV) survey on open field and greenhouse tomatoes

- the Plum Pox Virus Survey

Certification tests

The Virology Lab carries out annual tests for the certification of stone fruit trees at the St Vincent de Paul Government Nursery. In Spring the mother plants at the nursery are inspected for signs of viral infection. All trees are tested individually for the presence of Plum Pox Virus (PPV), a quarantine virus causing severe losses of production in many Mediterranean countries. The trees are also tested for quality viruses affecting stone fruits like Prune Dwarf Virus (PDV) and Prunus Necrotic Ring-spot Virus (PNRV).

Bacteriology Lab

The Bacteriology Section aims to test for and monitor quarantine plant bacteria to prevent the introduction and spread of quarantine diseases in the Maltese Islands. Quarantine plant bacteria tested as yet include:

- The Potato Ring Rot (Clavibacter michiganensis var sepedonicus), as required by Council Directive 93/85/EEC on the Control of Potato Ring Rot and

- The Potato Brown Rot (Ralstonia solanacearum) Council Directive 98/57/EC on the Control of Ralstonia solanacearum (Smith) Yabuuchi et al.

These pathogens pose a serious threat to potato cultivation, which is one of the most economically important crops in the Maltese Islands. As such, annual surveys are carried out involving field visits to potato crops in different areas in the Maltese Islands. Visual inspections for Bacterial Wilt symptoms are made and random samples are taken for laboratory testing. Screening tests include Gram Staining, Immunoflorescence assays and culturing of bacteria on semi-selective media. Additional and confirmatory tests include Polymerase chain reaction inoculation of indicator plants. All tests are performed according to the relevant EU Directive.

Citrus Tristeza Virus (CTV)

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