The genus Aphelenchoides consists of over 140 nominal species, some of which are pathogenic to plants. Nematologists in statutory and other diagnostic laboratories need to be able to distinguish pathogens with confidence if financial losses and unnecessary chemical control are to be avoided, but no complete key to this genus has been available to date. A revised list of species was produced, deleting descriptions considered too poor for subsequent recognition. Key diagnostic characters were identified and promising features for future diagnostic use were investigated. A polytomous key (polykey) was developed and tested on 14 populations. The findings contributed to a further reduction in the number of valid species from a diagnostician's point of view, and also led to revisions of the polykey itself as key characters were tested for their distinguishing power. The primary key characters were identified as the length of the post-vulval sac (pvs) as a percentage of the distance between the vulva and the anus, the shape of the tail terminus and tail, body length, and the ratios `a' (body length divided by greatest body width) and `c' (body length divided by tail length). Promising key characters for the future are c' (tail length divided by body width at the anus or cloaca), the distance from the vulva to the anus, vulval body width, pvs length as a measure of the vulval body width, head width and all measurements associated with the median bulb. The polykey provides the essential foundation for the development of new diagnostic tools, including new keys for diagnostic use; preliminary work with molecular techniques showed promise for inclusion in diagnostic protocols, but further study will be required to develop reliable methodology for each of the economically important species. Nominators of new species should use the recording form to provide details of morphological and morphometric characters and compare resulting polycodes with others in the polykey and associated databases before publication. Likewise, the key should continue to be tested for its validity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:250716 |
| Date | January 2001 |
| Creators | Hockland, Sue |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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