Dieter Sturhan

Phylogenetic analysis of Tylenchida Thorne, 1949 as inferred from D2 and D3 expansion fragments of the 28S rRNA gene sequences

The evolutionary relationships of 82 species of tylenchid and aphelenchid nematodes were evaluated by use of sequence data of the D2 and D3 expansion fragments of the 28S ribosomal RNA genes. Nine automatic and one culled sequence alignments were analysed using maximum parsimony and Bayesian inference approaches. The molecular data sets showed that the order Tylenchida comprises lineages that largely correspond to two suborders, Hoplolaimina and Criconematina, and other taxonomic divisions as proposed by Siddiqi (2000). Several significant results also derived from our study include: i) the basal position of groups that include entomoparasitic nematodes within tylenchid trees; ii) paraphyly of the superfamily Dolichodoroidea sensu Siddiqi (2000); iii) evidence for a Pratylenchus, Hirschmanniella and Meloidogyne clade; and iv) lack of support for widely held traditional placement of Radopholus within Pratylenchidae and placement of this genus within Hoplolaimidae or Heteroderidae. Congruence and incongruence of molecular phylogeny and traditional classifications and morphological-based hypotheses of phylogeny of tylenchids are discussed.

Molecular and morphological characterisation of the Heterodera avenae species complex (Tylenchida: Heteroderidae)

Species of the Heterodera avenae complex, including populations of H. arenaria, H. aucklandica, H. australis, H. avenae, H. filipjevi, H. mani, H. pratensis and H. ustinovi, obtained from different regions of the world were analysed with PCR-RFLP and sequencing of the ITS-rDNA, RAPD and light microscopy. Phylogenetic relationships between species and populations of the H. avenae complex as inferred from analyses of 70 sequences of the ITS region and of 237 RAPD markers revealed that the cereal cyst nematode H. avenae is a paraphyletic taxon. The taxonomic status of the Australian cereal cyst nematode H. australis based on sequences of the ITS-rDNA and RAPD data is confirmed. Morphometrical and ITS-rDNA sequence analyses revealed that the Chinese cereal cyst nematode is different from other H. avenae populations infecting cereals and is related to H. pratensis. Bidera riparia Kazachenko, 1993 is transferred to the genus Heterodera as H. riparia (Kazachenko, 1993) comb. n. As a consequence, H. riparia Subbotin, Sturhan, Waeyenberge & Moens, 1997 becomes a junior secondary homonym and is renamed as H. ripae nom. nov. Morphological, morphometrical characters and RFLP profiles for identification of the nine species presently placed in the H. avenae species complex are given.

The genus Hirschmanniella (Tylenchida: Pratylenchidae) in Europe, with description of H. halophila sp. n. from Germany and notes on H. caudacrena.

Four Hirschmanniella species are known to occur in Europe: H. gracilis , H. loofi , H. behningi and H. zostericola ; a fifth species, H. halophila sp. n., is described from Germany, where it was found along the Elbe estuary and on the adjoining coast of the North Sea. Three other species reported for Europe are considered as species inquirendae or appear to be misidentified. Based on sampling material from Germany, detailed morphological descriptions of H. gracilis , H. loofi and H. behningi are given; H. zostericola has not been found since its first description. The variability, even of characters of diagnostic significance, may be enormous, which makes correct identification difficult if little material is available. Hirschmanniella halophila sp. n. is morphologically very close to H. caudacrena , which has been isolated several times from aquarium plants imported from East Asia to Germany and for which morphological details are given. In Germany, H. gracilis is the most common species and is widely distributed; it is also known from many other European countries. Hirschmanniella loofi (also known from The Netherlands, Belgium, Poland and Italy) is less common. Hirschmanniella behningi , previously reported only from Russia and Sweden, was identified from nine places in Germany, including several coastal sites. Most of the Hirschmanniella records refer to moist soils with reed and other grasses or sedges; only H. gracilis was found exceptionally in arable soil. At many sampling sites, two or even three Hirschmanniella species co-occurred. A table for distinguishing the five European species is presented.

Phasmids in Tylenchulidae (Tylenchida: Criconematoidea)

Light-microscope studies revealed the presence of phasmids in the mid-tail region in species of the genera Tylenchulus, Trophotylenchulus (syn. Trophonema), Sphaeronema and Meloidoderita in Tylenchulidae. Scanning electron microscopy studies on Sphaeronema species verified these observations. Absence of phasmids or phasmid-like structures was confirmed for genera placed in Paratylenchinae and Tylenchocriconematinae in the same family, and for other taxa of Criconematoidea. This first record of phasmids in the superfamily Criconematoidea requires reconsideration of the systematic position of Tylenchulidae and of the relationships of the genera currently placed in this family. Presence of phasmids, deirids and other morphological characters place Tylenchulidae in a basal position in Criconematoidea.

Notes on the genus Cactodera Krall & Krall, 1978 and proposal of Betulodera betulae gen. nov., comb. nov. (Nematoda: Heteroderidae)

Based mainly on an analysis of the host ranges of the species presently placed in Cactodera, sensu lato, and of selected morphological characteristics, an attempt is made to improve the definition of the genus which, after exclusion of C. betulae and C. johanseni, is considered to be monophyletic. The host range of Cactodera, sensu stricto, appears to be restricted to the subclass Caryophyllidae with the ten known species showing an adaptive radiation on host genera in five families of the orders Caryophyllales and Polygonales. This may be a result of co-evolution. Cactodera betulae cannot be assigned to any of the presently recognised genera of cyst-forming nematodes and therefore Betulodera gen. nov. is proposed with B. betulae comb. nov. as the type and only species. The relationship of Betulodera gen. nov. to other genera of Heteroderidae and to some undescribed heteroderid species has still to be evaluated. The new genus is characterised by circumfenestrate cysts with only a slightly protruding vulval cone, three incisures in the lateral field of the second-stage juveniles and presence of phasmids in the males. The hosts are in unrelated plant orders and subclasses. Cactodera aquatica, a species inquirenda, is returned to the genus Heterodera and Heterodera johanseni (Sharma et al. , 2001) comb. nov. is proposed for C. johanseni.

An unusual cyst nematode from New Zealand, Paradolichodera tenuissima gen. n., sp. n. (Tylenchida: Heteroderidae).

Summary – A new genus, Paradolichodera gen. n., is proposed for a heteroderid species parasitising the rush Eleocharis gracilis on the banks of a lagoon near Christchurch, New Zealand. The slender body of the second-stage juveniles (a = 61-79) makes the type species, P. tenuissima sp. n., unique among known Heteroderidae species. The females weakly tan after death and retain eggs. The cysts are elongate-ovoid with rounded posterior end, a circumfenestral vulva area in terminal position, an indistinct anus and a cuticle with faint striation anteriorly and punctations posteriorly. The male body is not twisted, a cloacal tube is present and phasmids are lacking. Morphologically, the new genus is closest to Dolichodera in the subfamily Punctoderinae. A phylogenetic analysis of the ITS1-rRNA sequence of P. tenuissima sp. n. shows a close relationship to Punctodera and Globodera.

Morphological and molecular studies on Heterodera sacchari, H. goldeni and H. leuceilyma (Nematoda: Heteroderidae)

Heterodera sacchari, H. leuceilyma and H. goldeni are closely related members of the H. sacchari species complex, which is mainly characterised and distinguished from all other described Heterodera species by the presence of finger-like projections of the strongly developed underbridge in the vulval cone of the cysts. Males are rare in all three species and are described here in H. goldeni for the first time. Reproduction appears to be parthenogenetic. There are only minor morphological distinctions between the three species, particularly after our present studies have emended their original descriptions from various populations. Heterodera sacchari and H. goldeni showed differences in the ITS-rRNA gene sequences. Heterodera sacchari was described and reliably identified from many tropical African countries, H. leuceilyma is known only from Florida, USA, and H. goldeni has been identified in Egypt, Israel and Iran. All three species have grasses and other Poaceae as hosts, H. sacchari commonly attacking rice and sugarcane, and H. goldeni reproducing successfully on sugarcane ratoon seedlings. Morphological data emending the descriptions of H. sacchari, H. goldeni and H. leuceilyma from various populations are presented and discussed along with their host and distribution. Molecular characterisation of H. sacchari and H. goldeni is provided. An analysis of phylogenetic relationships within species of the sacchari-group using ITS-rRNA gene sequences is also presented.

Heterodera circeae sp. n. and H. scutellariae sp. n. (Tylenchida: Heteroderidae) from Germany, with notes on the goettingiana group

Two species of cyst-forming nematodes belonging to the goettingiana group are described from woodland in Germany. Heterodera circeae sp. n., parasitising Circaea lutetiana (Onagraceae), most closely resembles H. carotae and H. cruciferae, from which it differs by larger cysts (430-720 μm) and longer fenestral length (27-54 μm) and rounded stylet knobs of the second-stage juveniles. Heterodera scutellariae sp. n., found on the labiate Scutellaria galericulata (Lamiaceae), is distinguished from the other species of this group by shorter body (358-437 μm) and tail (41-53 μm) of the second-stage juveniles. The ITS-rDNA sequences of the new species are very similar and differ from each other by only a few nucleotides. The phylogenetic position of the new species within the group is presented based on analyses of molecular data. A revised diagnosis of the goettingiana group is proposed. The species of the group have lemon-shaped, ambifenestrate and abullate (small bullae occasionally present) cysts with egg sac, long vulval slit (> 35 μm), thin vulval bridge, low semifenestrae (average fenestral length 30-45 μm), and weak underbridge. Second-stage juveniles are characterised by body length > 400 μm, tail length > 45 μ m, hyaline tail portion > 20 μm, stylet length > 20 μm, lateral field with four incisures and small phasmids. All known species of the goettingiana group exclusively parasitise dicotyledonous plants.

On the presence or absence of phasmids in males of Heteroderidae (Tylenchida)

Published data on the presence or absence of phasmids in males of Heteroderidae species are compiled and critically reviewed. Based mainly on results of previous SEM studies and complemented by light microscopy using DIC optics, the conclusion is drawn that male phasmids appear to be absent in all species of the genera assigned to the subfamilies Heteroderinae and Ataloderinae, but present and often distinct in the Meloidoderinae genera Cryphodera and Meloidodera . The presence of male phasmids is considered as ancestral, and loss of phasmids as a derived character.

Cricodorylaimus gen. n. (Dorylaimida: Qudsianematidae), a unique nematode genus from Benin

The dorylaimid genus Cricodorylaimus gen. n. with the species C. africanus sp. n. is described from arable soil in Benin. The new genus with the only known species is distinctive in having a short obese body with strongly annulated subcuticle, cuticularised pieces around the stoma and a monoprodelphic female genital tract. It differs from all known genera in the family Qudsianematidae in the nature of its subcuticle and in being monoprodelphic.