Abstract
Abstract Two populations of the genus Trophotylenchulus and 10 species of the genus Paratylenchus from Iran were characterized based on morphometric, morphological and molecular characters. Our observations on the two populations of Trophotylenchulus from Iran revealed that T. asoensis and T. okamotoi have been distinguished from T. arenarius, on the basis of the features which cannot be longer considered as stable diagnostic characters. One of the populations shows a mixed combination of the characters of T. arenarius and T. asoensis; it has morphometrics more similar to T. arenarius but shows affinities with T. asoensis in the tail terminus shape of females and second-stage juveniles (J2) and in having a reduced stylet in males. The other population fit well with T. okamotoi; it has females with generally bluntly rounded tails typical for T. okamotoi, but sometimes with finely rounded tail termini, like those of T. arenarius or T. asoensis. The sequences of D2–D3 expansion segments of 28 S rRNA gene for the two populations are identical with each other, but only 4 bp (0.67%) difference with T. arenarius sequence deposited in the GenBank. Considering no stable difference allow separating species, synonymy of T. asoensis and T. okamotoi with T. arenarius, which has already been proposed, is supported and confirmed here. All studied Paratylenchus species with stylets longer than 40 µm, except P. straeleni, formed a basal cluster to Cacopaurus pestis and species of Paratylenchus bearing stylets shorter than 40 µm; thus, validity of Gracilacus cannot be rejected using our data sets. However, the synonymy of Paratylenchoides was supported by the positioning of P. sheri within representatives of Paratylenchus in the inferred phylogenetic tree.
Highlights
Raski (1956) described a nematode species as Sphaeronema arenarium with females being most commonly individual ectoparasites who do not form colonies, as can be seen in the endoparasitic species, S. californicum (Raski and Sher, 1952)
Current taxonomic views on the systematics of the genera included in the family Tylenchulidae have been reviewed recently (Mokaram Hesar et al, 2019); the authors concluded that the genera Cacopaurus (Thorne, 1943), Paratylenchus sensu stricto and Gracilacus (Raski, 1962) in the subfamily Paratylenchinae (Thorne, 1949) are clustered in one clade in the inferred trees of 28 S rRNA and ITS gene sequences
The present study provides morphological and molecular support on the synonymy of T. asoensis (Minagawa, 1983; Siddiqi, 1999) and T. okamotoi (Minagawa, 1983; Siddiqi, 1999) with T. arenarius (Raski, 1956; Siddiqi, 1999) based on the observations made on two populations from Iran
Summary
Raski (1956) described a nematode species as Sphaeronema arenarium with females being most commonly individual ectoparasites who do not form colonies, as can be seen in the endoparasitic species, S. californicum (Raski and Sher, 1952). Gomez-Barcina and Castillo (1990) synonymized Trophonema asoensis and T. okamotoi with Trophonema arenarium because they believed that most diagnostic features used for separating these species are minor quantitative differences, and tail terminus shape of females and juveniles is a variable intraspecific character. These nematodes were considered as separate valid species in the subsequent taxonomic works (Raski, 1991; Inserra et al, 1993; Brzeski, 1998; Siddiqi, 2000; Andrássy, 2007; Ghaderi et al, 2016). Morphological and molecular characterization of 10 species of Paratylenchus (Micoletzky, 1922) was used to obtain a better insight into the intra-generic structure of this genus
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