Always consult local support services for initial advice if possible. If these are unavailable for tree health problems, then it is advisable to consult experts and field workers in related disciplines and sectors such as plant pathology and entomology. The next step may be to collect samples or to invite experts to examine the problem in the field.
If samples are required for laboratory investigation, always try to choose a laboratory or institute as close as possible to the site of the tree health problem. A straightforward diagnostic investigation will involve examination of potential pest-infested material, either in the form of insect samples or perhaps plant tissues with fungal fruiting structures. A more detailed investigation will require isolation and identification of potential pest organisms or rearing of adult insects from larvae.
Always contact the laboratory before sending material to determine its policy for accepting samples or receiving cultures or samples of pest organisms, especially if the laboratory is overseas and quarantine legislation must be respected. Common services available include identification of insects, at least to major orders. Fungi that produce spores on plant material are usually more easy to identify than those that require isolation and culturing. Identifying bacteria is more difficult, while services for identifying viruses and phytoplasma are rare.
Diseased material can be sent through the post, but the ability to isolate pathogens decreases as the time between collection of material and receipt by the diagnostic laboratory increases.
There are several diagnostic and taxonomic institutes worldwide that offer a variety of services. For example, CABI Bioscience offers some limited free services for developing countries with the support of the Department for International Development, UK, as well as paid services for commercial interests. The CABI Bioscience Global Plant Clinic is able to diagnose tree health problems and can identify fungi, bacteria, nematodes, viruses and phytoplasmas. The service does not include insect pests unless they are potential vectors of plant pathogens. Other institutes can be located through Web searches or by recommendation from previous contacts.
Separate guidelines are provided for sending plant material, cultures of fungi or bacteria and insect samples.
The guidelines for sending plant material are as follows.
Collect fresh material that shows the early stages of symptom development or has evidence of pest infestation (e.g. fungus fruiting bodies)
Get it to the investigating laboratory as quickly as possible.
Pack it loosely yet securely to keep humidity low and reduce the chance of mould fungi developing en route. DO NOT PACK IN PLASTIC BAGS!
Provide information on symptoms and other details of the problem.
Give each sample a unique code that will allow the receiving laboratory to keep track of your query.
The type of plant material to send depends greatly on the type of tree health problem. A good preliminary diagnosis based on a visual assessment of the symptoms will assist significantly in deciding what sample to send for investigation.
Do not send wilted leaves, for example, since these indicate a systemic disruption or root disease. Dead leaves have limited value in diagnostic investigations. Examine the roots and stems for internal staining and send small portions showing the symptoms. Leaf materials with lesions can be simply pressed by inserting them between sheets of absorbent paper such as newspaper or kitchen roll and then placing them inside a book or under an object to apply light pressure.
Excise the parts of the stems that show symptoms such as cankers or staining at the junction of healthy and stained or decaying tissue. Materials with suspected virus diseases are best preserved before dispatch. Press leaves between absorbent material (best to use filter paper but improvise if necessary) soaked in 50 percent glycerol to help keep leaf material fresh.
Material with suspected phytoplasma diseases can be sent dried or with leaves and young stems preserved in 1 percent borax. Use rigid bottles (preferably plastic) that have a tight seal and do not leak. Reinforce the seal with plastic tape stretched around the container top.
It is vital that all material be carefully and permanently labelled.
The guidelines for sending specimens or cultures of fungi and/or bacteria are as follows.
Some fungi sporulate on plant structures but others have to be isolated from plant material. Where possible, attempt to do these isolations in situ or at a local laboratory. Simple tap water agar (1.5 percent agar in sterilized tap water) is a useful medium for general purposes.
Only send the most commonly isolated fungi or bacteria for identification. This reduces the potential cost of the investigation and increases the chances of getting a quick reply to your query.
Microfungi should be sent as young, pure cultures. Test tubes, small glass tubes and plastic petri dishes are the simplest containers for sending live fungal material. The safest methods (e.g. freeze-drying) require specialist equipment for preparing cultures.
Always check cultures for mites. These are best kept in
check through sound laboratory
techniques.
Macrofungi (mushrooms, bracket fungi and so on) should be dried and sent in envelopes or paper. DO NOT USE PLASTIC BAGS!
The Plant pathologist's pocketbook (Waller, Lennι and Waller, 2001) provides much useful general information on handling specimens and on growing cultures of fungi. The guidelines for sending insect specimens are as follows.
Larvae are difficult to identify; therefore try to rear the insects to adult stage before sending.
Large insects should be air dried or frozen prior
to dispatch and carefully packed in a small
tube or vial with tissue paper or cotton to avoid damage.
Small insects can be preserved in 75 percent
alcohol. Place identifying labels (written in pencil
or indelible black ink on paper) inside the containers.
All specimens should be carefully labelled with
collector's name, date of collection, site and
any host information (species, size, age).
Keep a carefully labelled reference collection of
all insects sent for identification for future
cross-referencing.
