How to collect and identify plant disease specimens

By collecting and making specimens, we will understand the requirements for collecting plant disease specimens, learn how to collect and record specimens, master the methods of making plant disease specimens, and further consolidate disease knowledge. Each person will draw lots to complete one disease specimen.

Materials and utensils: specimen clips, absorbent paper, plastic bags, paper bags, labels, pencils, markers, knives, pruners, hand saws, specimen jars, copper fermentation, copper sulfate, 95% ethanol, Formaldehyde solution, sulfurous acid, glycerin, distilled water, etc.

Content and methods

(1) Collection of disease specimens

1 Basic requirements for specimen collection

Collect complete specimens, preferably The method is to take pictures first and then press or soak them for preservation. The clearer the pictures, the better. It is required to take pictures of normal plants and diseased parts. For each specimen, the number of samples should be collected at least 2-3.

2 Sampling parts

(1) Samples with fruiting bodies should be collected from old leaves as much as possible

Because it is relatively mature and many fungi have sexual stages The fruiting bodies appear on dead branches and leaves, while the asexual stage fruiting bodies can mostly be found on living bodies.

(2) For soft and juicy fruiting bodies or fruit materials, newly infected young fruits should be collected.

(3) For viral diseases, top tips and new leaves should be collected as much as possible.

(4) Nematode disease specimens should be collected from diseased tissue. For nematode disease specimens that damage the roots, in addition to collecting diseased roots, root soil should also be collected.

(5) Plants that show signs of wilting must be dug out with their roots, and sometimes collected together with the rhizosphere soil.

(6) For thick branches and plants, it is advisable to cut off a piece or cut off a section.

(7) If the disease appears on leaves, fruits and branches, try to collect as comprehensive a collection as possible.

(8) Parasites should be collected together with their hosts. The disease symptoms are very specific and the branches, leaves or flowers of the plant must be collected together in order to identify and name its host.

3 Specimen data records and specimen numbers

The records are required to be accurate, concise and complete. Complete records and labels are also important, including host name, collection date and location, collector's name, ecological conditions and soil conditions, etc.

4 Specimen collection methods

(1) Collection of branch and root disease specimens

Take the diseased parts and use saws, branch shears or high branch shears When taking it, do not break it with your hands, which will affect the beauty of the specimen. You should pay special attention to branches with long and strong fibers.

(2) Collection of leaf disease specimens

Large-leaf plants have large leaves and inflorescences. When collecting specimens, you can collect them in part or in sections, and use them from the same plant. The young leaves plus flowers and fruits form a specimen (also indicate the actual size of the leaves); or segment the leaves and petioles and take part of them;

For parasitic plants such as dodder and redang, they should be accompanied by Collect the hosts together and record the names of the hosts. (3) Collection of disease specimens of succulent or succulent plants (flowers, fruits)

They should be cut lengthwise or crosswise, and sometimes the internal tissues need to be dug out. It is also necessary to consider whether to cut half of the disease specimens. Materials are soaked in preservation solution for preservation. When drying in the field, sprinkle a large amount of salt on the surface of the cut stem. The material wrapped in salt should be placed in a specimen folder with multiple layers of newspapers. The newspapers soaked in salt water should be removed after 24 hours, or use boiling water. The material is scalded to death and then placed in a cardboard-aluminum sandwich to dry.

(2) Preparation of disease specimens

Except for some of the specimens collected from the field used for isolation and identification, it is best to photograph typical disease symptoms first and then press or Preserve by dipping. Pressed or impregnated specimens should maintain their original properties as much as possible. Tiny specimens can be made into slides, such as double-layer slides, pit slides, or stored in other small glass tube bags.

(3) Preservation of disease specimens

1 Drying method is suitable for the preparation of disease specimens such as stems and leaves that generally contain less water. It is the simplest, most economical and most widely used. Clamp the collected specimens in absorbent paper, and put a label with the collection location, date and host name, then press it tightly with the specimen clips and then dry it in the sun or heat to dry it. The faster it dries, the better it will last. The original color and luster, the higher the quality of the specimen. Specimens collected in summer are prone to mold and discoloration when the temperature and humidity are high, so the paper should be changed frequently, usually 1-2 times a day during the first three or four days of pressing (depending on the moisture content of the specimen and the temperature and humidity conditions) , then change it every two or three days until it is completely dry. When changing the paper for the first time, the specimen should be sorted out, because after initial drying, the specimen becomes soft and easy to spread. The stems and leaves of tobacco, broad beans, pears, potatoes, etc. are easy to turn black and discolored, and it is difficult to preserve the color of the specimens. Special attention should be paid to rapid drying during the production process. For dried specimens that need to remain green, the specimens can be soaked in 2-4% copper sulfate solution for 24 hours, or treated with copper acetate solution (for recipes and methods, see the impregnation method of copper acetate in the dipping method) before pressing. You can also apply a layer of liquid paraffin on the leaves and then press them to keep the leaves bright green for 2-3 days.

2 The dipping method is suitable for succulent disease specimens,

such as fruits, roots or fruiting bodies of basidiomycetes, etc., which must be preserved by dipping.

There are many types of immersion liquids, some are purely antiseptic, and some are used to maintain the original color of the specimen. Here we introduce several commonly used and effective methods.

(1) Preservative dipping method: This type of dipping method can only preserve corrosion without color preservation, such as radish, sweet potato, etc. Specimens that do not require color preservation should be directly immersed in the following solution after washing. ①5% formalin immersion solution.

② Sulfurous acid impregnation solution: add 15ml of 5%-6% sulfurous acid to 1000ml of water (generally the content of commercially available sulfurous acid is 5-6%) or use 10.5g of sodium sulfite, 8ml of concentrated sulfuric acid, and 500ml of water Make a mixture.

(2) Impregnating solution and soaking method to maintain green specimens:

① Copper acetate preserving (green) color impregnation method: Gradually add copper acetate crystals to 50% acetic acid to dissolve until saturated as the mother solution (about 1000ml of 50% acetic acid can be saturated by adding 15g of copper acetate), dilute it with water 1-4 times (the dilution factor depends on the color of the specimen, and the dilution factor can be smaller for darker colors). Heat this solution to a boil and put it into the specimen. At first, the green color of the specimen will be washed away. After a few minutes, the specimen will return to green. At this time, take out the specimen immediately, wash it with clean water, and store it in a 5% formalin solution. , this method is called heat treatment. The method of cold treatment is to immerse the specimen in the above diluent for 3 hours. The specimen will fade and return to green after 72 hours. At this time, the specimen will be taken out, rinsed with water, and stored in 5% formalin solution. This method maintains color for a longer time, and the principle of color preservation is roughly the replacement of copper ions with magnesium ions in chlorophyll. Therefore, after the solution is treated with the specimen multiple times, the copper ions will gradually decrease. If you want to continue using it, you should add an appropriate amount of copper acetate. Specimens preserved by this method are often slightly bluish, slightly different from the original color of plant specimens.

② Copper sulfate color preserving (green) color dipping method: Rinse the specimen with clean water and soak it directly in 5% copper sulfate solution for 1-7 days. When the specimen is slightly brown, take it out and rinse with clean water to remove it. The excess copper sulfate solution on the surface of the specimen is then preserved in a sulfurous immersion solution.

③Dipping solution for preserving yellow and orange specimens: Preserve apricot, pear, persimmon, red pepper and other fruit specimens with sulfurous acid dipping solution

The sulfurous acid dipping solution has bleaching effect Therefore, attention should be paid to the concentration when using it. Generally, 1% is enough (the concentration can be diluted when soaking apricots). Because the concentration is too small and the preservative power is not enough, an appropriate amount of alcohol can be added. To prevent the fruit from cracking, add a little glycerin.

④ Dip solution for preserving red specimens: It is difficult to preserve red specimens because red is water-soluble anthocyanin and is difficult to preserve. Hesler dipping solution is commonly used for storage. The ingredients are: 50g zinc chloride, 25ml formalin, 25ml glycerin, and 1000ml water. Dissolve zinc chloride in hot water and add formalin. If there is precipitation, use its clear solution. This solution is suitable for specimens that appear red due to anthocyanins, such as apples, tomatoes, etc.

(4) Preservation of specimens

The prepared specimens are sorted and registered, and then arranged and preserved according to a certain system.

Fungi specimens are generally arranged according to a classification system. There should be two sets of index cards, one for the host index and one for the fungus index, to facilitate searching and sorting.

The specimen room (cabinet) should be kept dry and clean, and pesticides should be applied regularly to prevent insects and mildew.

1 Specimen Box Preservation It is more convenient to store dried disease specimens for teaching and demonstration in glass-topped paper boxes. The suitable size of the glass-topped paper boxes is 20×28×2 cm. First put a layer of cotton in the carton, and add a little camphor powder to the cotton to repel insects. Finally put the specimen and label on the cotton.

2 Specimen bottle preservation: The impregnated specimens are stored in specimen bottles. In order to prevent the specimens from sinking and floating, they can be tied to a glass strip and then placed in the specimen bottle. After the mouth of the specimen bottle is capped, paraffin is added to seal it, and then the label is attached.

3 The paper sleeves are stored in kraft paper folded into 15×33cm paper sleeves. Most of the dried specimens preserved in large quantities are preserved in paper sleeves. The specimens are put into the paper sleeves and affixed to the paper sleeves. Good labels, just put them in the specimen cabinet.