Nematode Paste in Horticultural Crops and their Management

Practical 11

Objective: To collect the nematode infested plant specimens from the field/poly house and preserve them.

Collection: Nematode infested plant specimens/material is collected from the site of infestation. Awareness regarding the specific symptoms caused by nematodes on different crops is essential for collecting such material.
Foliage of the plant showing aerial symptoms is plucked. For underground symptoms like root galls, lesions, rot etc the plants showing symptoms are uprooted after irrigating the soil sufficiently so that the roots remain intact. The specimens are brought to the laboratory and should be preserved when they are fresh.

Precautions

• The plants should be plucked after irrigation in a way that all its parts remain intact.
• The parts showing distinct symptoms of nematode infestation only should be collected.

Preservation: Preservation is a process of fixing the tissue of plants without any further decomposition and for this purpose various preservatives have been tried.

Preservative: Preservative is a chemical which is used to fix the tissue of plants for a very long time without any decomposition by controlling the growth of bacteria and fungi..
The most common solutions recommended for the preservation of plants contain ethyl alcohol, formaldehyde, glycerine or sulfurous acid alone or in combination and frequently salts like copper or zinc are added. However, none of the aqueous preservatives are spoken of very highly as they all tend to render specimens flaccid and do not preserve their natural colours well. Yet some of the commonly used solutions for preserving plant specimens are given below:
i) Ethanol 90%: This is so far the most satisfactory medium for preserving herbaceous structures. However, its availability and cost are both prohibitive for the normal specimen preservation in an under graduate laboratory.
ii) Ethanol formalin combination:
Composition:

One part absolute alcohol
One part formalin
15-20 parts distilled water

iii) Formalin 10%:
Composition

25.0 ml of 37% formaldehyde
75.0 ml distilled water
Formalin can be acidified by adding .02 N H2SO4. The acidified formalin is distinctly superior to those solutions which contain formalin but no acid. Addition of 0.1% Cu SO4 .5 H2O adds to the quality of preservation.
It is one of the most commonly used solution for preserving the plant specimens. However, Formalin does not extract chlorophyll, neither does it preserve the green colour and exposed even to diffused light, the chlorophyll is decomposed and the specimens assume a dull brownish colour and finally is bleached quite white.

iv) Sulfurous acid 1%
Preparation: Dissolve 2.6 g sodium sulfite in 500 ml of water (Stock solution I) and add this solution to 500 ml of aqueous solution containing 18.0 ml of concentrated HCl (stock solution II). These stock solutions are very stable and can be kept in separate containers indefinitely. Mixing of equal quantities of two stock solutions makes 1% sulfurous acid.
It is a superior preserving solution as compared to formalin.
Precautions

• The specimen plants should remain completely submerged in the solution.
• Since most of the preservatives are very volatile, the preservation jars need to be securely sealed.