A pragmatic approach to identifying Aphelenchoides species for plant health quarantine and pest management programmes
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
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
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.