Summary
Helicotylenchus microlobus is considered to be a junior synonym of H. pseudorobustus by several authors while others consider it as valid. To clarify the status of both species, 39 samples collected from various countries were subjected to statistical analyses that showed they could be grouped into six groups. Topotypes of H. pseudorobustus and H. microlobus belong to two different groups. However, samples in the other groups were morphologically intermediate between these two groups. Characters used in the past to uphold the validity of H. microlobus were variable and overlapping from group to group. The 28 samples studied are identified as H. pseudorobustus. Helicotylenchus microlobus, H. bradys and H. phalerus are confirmed as junior synonyms of H. pseudorobustus. There was no complete congruence between the morphological groups and molecular groups proposed by other authors. For these, two MOTU (Molecular Operational Taxonomic Unit) are accepted within H. pseudorobustus.
Aphelenchoides besseyi Christie, 1942 is recorded for the first time on rice in Mali and Upper Volta, the morphology is discussed and the description of the species emended. Boehmeria nivea Gaud. (Ramie) is reported as a new host for A. besseyi. A. siddiqii n.sp. is described from Foeniculum vulgare Mill, in Sudan. A key is given to the species of Aphelenchoides with a star tipped tail.
It is proposed to call "Index" the ratios traditionally included in nematode descriptions (ratios a, b, c, V, etc.) when they are used as a numerical expression of an ordered qualitative character (such as the shape or the position of an organ), and to reserve the name of "Ratios" to the entities recently reviewed by Roggen, Revets and Van den Berghe (Nemutofo&z, 1987). It is shown that it is always possible to use an index instead of an ordered qualitative character for describing a shape or a position, as long as the index is biologically related to the characteristic being described. Indexes are more objective than the corresponding qualitative characters. Also, they can be used in parametric statistical analyses, and in particular in discriminant function analyses.
The Nemisys Protect is of interest to marine nematode taxonomists because it is likely to be a valuable teaching aid and may possibly help attract graduate students to study marine nematology.Rowever, at the present time, development of the plant-parasitic part of the protect is more important than inclusion of the marine nematodes.Likewise, the animalparasitic nematodes could be included in the project after it has been developed for the plant and soil nematodes.The most likely schedule for the development of the protect is: 1) incorporation of the plant-parasitic nematodes; 2) free-living soil forms; 3) insect-parasitic forms; 4) freeliving freshwater nematodes; 5) marine; and 6) animal-parasitic forms.Inclusion of the soil and freshwater free-living nematodes into the project requires money for the input of the database and suitable cooperators who are willing to contribute much effort over several years.
291R. Fortuner (ed.), Nematode Identification and Expert System Technology
Toxicity of sulphides to three species of nematodes parasitic on rice from Senegal (Hirsch" n i e h oryzaë, H. spinicandata and Tyleizchorhyizckvs irnashhoodi) was studied in vitro using three different methods.A Sulphide Time Unit (STU) was defined related to the average concentrations of sulphides and their variations during the tests.With hydrogen sulphide dissolved in water, the very low p H increased nematode mortality. When hydrogen sulphide was dissolved in a buffered medium used for bacterial culture, mortality was lower but a shock effect appeared due to sudden contact with high concentrations of sulphides and toxicity of some of the components of the medium. When hydrogen sulphide was produced by sulphate reducing bacteria a similar shock effect was still observed, but only when high concentrations were reached within 1 or 2 days: in such experiments nematodes were killed by low STU, and differences were observed in resistance of the three species. However, when sulphide accumulated more slowly, i.e., when lethal concentrations were reached in 3 or more days, the sensitivity of the three species was similar: 50% mortality was obtained at about 120-130 STU.The possibility of using sulphate reducing bacteria for biological control of parasitic nematodes of rice is discussed.
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