Taxonomy of nematodes

Taxonomy of nematodes. How to classify PPN's.

1. Taxonomy of nematodes

2. Introduction Nematodes may look or appear to be same i.e thin, long, sausage shape with very few distinguishing features. Once you begin the identification process the similarities or differences allow you to place the nematodes into their different species categories. Taxonomy of plant nematode started in late 1860’s but much of the work was done in the 20 th century.

3. Cont.. Taxonomy (Greek taxis-arrangement; nomos=law) deals with the naming and recognizing taxa. Systematics (Greek system = whole consisting of parts) is a method of arranging taxa into a hierarchical system of classification.

4. Cont.. Taxa are recognized and classified mainly on morphological characters. Recent advances in technology have led new techniques in nematode taxonomy these include: Numerical taxonomy Cytogenetics Physiological Biochemical and molecular Morphological taxonomy

5. Approaches in classification of nematode Numerical taxonomy This is a classification system in biological systematics which deals with the grouping by numerical methods of taxonomic units based on their character states. It aims to create a taxonomy using numeric algorithms like cluster analysis rather than using subjective evaluation of their properties. Proved somewhat unsatisfactory, or inconclusive, but several of its routine procedure e.g. multivariate analysis and clustering, proved useful for specific discrimination within Rotylenchus and several other genera and these methods have been used by a number of researchers. ADD the meaning of numerical taxonomy. Deal with grouping by mathematical methods to evaluate obaservable similarities and differences among different groups

6. Cytogenetic This method allows karyotype, including the number of chromosomes and mode of reproduction to be studied in detail and has proven successful in regard to taxonomy of root-knot and cyst nematodes . Cytological analysis can be utilized in the differentiation of species and pathotypes .

7. Cont.. Chromosomes number has been used in the differentiation between some species of Meloidogyne and between Radopholous similis and R.s.citrophilus , although in the latter case chromosomes number has been shown to be more variable than previously thought and therefore useless as a race marker. Chromosomes number also differs between nematode group, for example Criconematoide a and Haplolamidae have a basic chromosome number of n=5 , Dolichodoridae including Belonolaiminae n=8

8. Physiological They have been developed that use responses in selected host plant species to parasitism as differential character to provide ranking within some nematode groups. This method refers mainly to the different type of syncytia (nurse cell) induced by members of several genera of cyst nematodes.

9. Biochemical These a re the methods which were being used intensively since 1980’s in nematode taxonomy and systematics. Biochemical methods of protein analysis, particularly gel electrophoresis techniques, in spite of some limitations, have been increasingly used for distinguishing species of several economically important genera e.g. Meloidogyne, heterodera and globobera . Gel electrophoresis has been widely used as a technique in the identification of plant-parasitic species. Evans (1971) was able to distinguish between Ditylenchus destuctor and D. myceliophagus population through the study of their esterase patterns as reveled by gel electrophoresis.

10. Cont... Different protein band profile were obtained by using disc electrophoresis separation of soluble protein and enzyme of some species of Ditylenchus , Heterodera and Meloidogyne (Dickson et al., 1971). However these techniques have been used only in a limited manner although the scope is considerable. Immunological techniques involving DNA hybridization and isoenzyme analysis have been applied to certain aspects of plant nematode taxonomy, although specialized biochemical knowledge, skill and instruments are required to use such techniques. The current way forward seems to be via molecular techniques particularly those employing polymerase chain reaction PCR amplification DNA.

11. Rank determination Determining the ranks of the nematodes 3 broadly categories are used. Evolutionary systematics Cladism P henetics

12. Evolutionary systematics The traditional evolutionary approach involves the reconstruction of phylogeny by using past histories of human as revealed by the study of their fossil and comparative morphology.

13. Cladism The cladistics analysis is of interpretation of similarities in and between taxa. The similarities are established by in-group and out-group comparison of two type of character or character states.

14. Phenetics This approach tries to classify organism on over-all similarities in their structure without bothering to know how they come about. The classification of T ylechida has been based almost entirely on structural similarities which have seldom been supplemented with ecological, ethological and physiological data. For this order the phenetic approach will continue to have a major role to play since identification and classification will have to be largely on morphological data.

15. Morphology taxonomy Morphological characters provide more than 90% of the data used in taxonomy and classification of plant and soil nematode. These characters show considerable variation and care must be taken in using them. Morphometric and allometric measurements often vary greatly under influence of geographical and ecological conditions. Techniques type of equipment, methods of observation and personal skills also result in variation.

16. Cont.. Some characters used to differentiate species of Pratylenchus e.g. stylet knob shape, length of outer margin of cephalic framework the shape of the spermathecal and tail, tip, tend to vary through host influence.

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