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Volume 10, Part 2 (2002)

Karpouyas, D.G. and Giannakou, I.O.

Biodegradation and enhanced biodegradation: a reason for reduced biological efficacy of nematicides

The phenomenon of enhanced biodegradation of fumigant and non-fumigant nematicides is reviewed. Several cases of reduced nematode control have been linked with rapid microbial degradation of nematicides by a specialized fraction of the soil microflora that has adapted to rapidly metabolize specific nematicides. The mechanisms involved in the development of enhanced degradation are described. High soil pH and optimal moisture and temperature conditions favour the development of enhanced biodegradation in soils. However, the persistence of enhanced biodegradation in the absence of further nematicide applications and the existence of cross-enhancement amongst nematicides are the most important factors controlling the practical significance of the phenomenon. The susceptibility shown to enhanced biodegradation by the majority of the currently available nematicides might intensify the problem in the future compared with the current situation. Sufficient chemical rotation i.e., the use of active ingredients from different chemical groups, in combination with crop rotation and use of resistant cultivars may help to limit the establishment of enhanced biodegradation of nematicides in soils.

Key words: enhanced biodegradation, nematicides, soil microorganisms.

Peña-Santiago, R., Torres, B.  and Liébanas, G.

Nematodes of the order Dorylaimida from Andalucía Oriental, Spain. The genus Discolaimus Cobb, 1913. II. Two previously known species, with comments on their taxonomy

Two close known species of the genus Discolaimus, D. major and D. agricolus, are described and illustrated, including SEM obervations, from material collected in southeastern Spain. The identity and the taxonomy of both species are discussed and new criteria for their separation are proposed. A revision of data from literature reveals that D. major is the most widely distributed Discolaimus species in the world, but also that some of its previous records may be doubtful and/or erroneous. D. paramajor and D. perplexans are considered new junior synonyms of D. major.

Key words: description, Discolaimus, new synonyms, Spain, taxonomy.

Crozzoli, R. and  Lamberti, F.

Species of Criconema Hofmänner & Menzel, 1914 and Ogma Southern, 1914 occurring in Venezuela, with description of Ogma araguaensis sp. n. (Nematoda: Criconematidae)

Five known species of Criconema Hofmänner & Menzel, 1914 and two of Ogma Southern, 1914 and Ogma araguaensis sp. n. are described from Venezuela. Additional morphometric information is provided on C. californicum (Diab & Jenkins, 1966) Siddiqi, 1986, C. calvum (Raski & Golden, 1966) Raski & Luc, 1985, C. demani Micoletzky, 1925, C. mutabile (Taylor, 1936) Raski & Luc, 1985, C. sphagni Micoletzky, 1925, O. civellae (Steiner, 1949) Raski & Luc, 1987, and O. decalineatum (Chitwood, 1957) Andrássy, 1979. C. californicum, C. calvum, C. sphagni and O. decalineatum constitute new records from Venezuela. O. araguaensis sp. n. resembles O. murray Southern, 1914 and Ogma crenulatum Wouts, Yeates & Loof, 1999 from which it differs in its shorter body and more anterior vulva. Dichotomous identification keys to the species of Criconema and Ogma occurring in Venezuela are provided.

Key words: Criconema, dichotomous key, Ogma, Venezuela.

Lamberti, F., Molinari, S., Moens, M. and Brown, D.J.F.

The Xiphinema americanum-group. II. Morphometric relationships

Hierarchical cluster analysis based on morphometrics placed 117 populations, representing 39 putative species, of the Xiphinema americanum group into four clusters. Cluster 1 consisted of three populations identified as X. brevisicum; Cluster 2 consisted of five sub-clusters of populations; and Clusters 3 and 4 each consisted of seven sub-clusters. When several populations ascribed to a putative species were used, they usually clustered with a low range of variability, thus confirming their similarity. A population that had been identified as representing X. diffusum and another as being X. incognitum were placed in clusters different from that which characterized the rest of the populations of each species, respectively. Populations identified as X. americanum sensu stricto, X. thornei, X. santos and X. pachydermum were placed in 2 and 3 different sub-clusters within the same major cluster. Conversely, several populations of X. madeirense, X. duriense, X. simileand X. pachtaicum had a low coefficient of dissimilarity (<2.8), which is considered as being indicative of intra-specific variability. Four populations, each identified as representing X. pachydermum, were placed in three different sub-clusters of Cluster 4, thus indicating wide morphometric variability for this putative species.

Key words: hierarchical cluster analysis, intra-specific variability, morphometrics, nematodes.

Neilson, R. and Boag, B.

Marine nematode associations from an intertidal estuarine biotope

Correlations between the 20 most prevalent marine nematode species from an intertidal estuarine biotope and sedimentary ecological factors yielded few significant relationships. Seven of the 20 nematode species were significantly correlated with distance from a pollution source, although few nematode species were correlated with concentrations of six different heavy metals and organic C. Sediment particle size was significantly correlated with only three species suggesting that as a single factor it had little impact on nematode distributions. The chi-squared test for contingency that tests the joint occurrences between species and indicates the statistical significance of their relationships was applied to the same 20 nematode species. Species abundance data were also analysed to determine whether any correlations existed between species. Many species in this study were significantly associated or correlated with each other. This contrasted with previous studies that reported nematode species from both deep-sea and estuarine biotopes were negatively associated.

Key words: associations, estuarine, intertidal, spatial distribution.

Zheng, J., Pan, C., Furlanetto, C., Nielson, R. and Brown, D.J.F..

The morphology of the odontophore of Longidorus litchii Xu & Cheng, 1992 (Nematoda: Longidoridae)

The morphology of the odontophore of Longidorus litchii Xu & Cheng, 1992, is described and depicted in photomicrographs from specimens collected from the locality of the type habitat i.e. clay soil around roots of litchi trees (Litchi chienesis Sonn) in Zhangzhou, Fujian province, eastern China.The odontophore is swollen and has a tri-radiate base containing well developed flanges.These taxonomically important characteristics were not reported in the original description of the species.

Key words: basal flanges, China, Litchi chienesis, Longidoridae, plant nematode.

Fürst von Lieven, A.

The sister group of the Diplogastrina (Nematoda)

This paper presents arguments for a sister group relationship between diplogastrids and bunonematids. Five synapomorphies were found to substantiate this hypothesis. The pattern of genital papillae in Bunonema pini is homologized with that of diplogastrids. The question whether the stem species of diplogastrids possessed a bursa or not is discussed.

Key words: Bunonema, bursa, genital papillae, haustrulum, pharyngeal sleeve.

Subbotin, S.A., Sturhan, D., Rumpenhorst, H.J. and Moens, M.

Description of the Australian cereal cyst nematode Heterodera australis sp. n. (Tylenchida: Heteroderidae)

Populations of cereal cyst nematode sampled in Australia are described as a new species, Heterodera australis sp. n. This species is morphologically and morphometrically similar to H. avenae. It is distinguished from H. avenae and other species of the H. avenae complex by sequence and RFLP of the ITS region of rDNA and IEF patterns. The phylogenetic relationships among species of the H. avenae complex based on analyses of the ITS-rDNA sequences are presented.

Key words: Australia, cereals, Heterodera avenae, IEF, ITS-rDNA.