Abstract
Root-lesion nematode species rank third only to root-knot and cyst nematodes as having the greatest economic impact on crops worldwide. A survey of plant-parasitic nematodes associated with decaying raspberries (Rubus sp.) in northern Italy revealed that root-lesion nematodes were the most frequently occurring species among other phytonematodes. Several Pratylenchus species have been associated with Rubus sp. in Canada (Quebec, British Columbia) and USA (North Carolina, Maryland, New Jersey) including P. penetrans and P. crenatus. In the roots and rhizosphere of symptomatic raspberries, nematodes of two Pratylenchus spp. were detected. Detailed morphometrics of the two root-lesion nematode isolates were consistent with Pratylenchus crenatus and with an undescribed Pratylenchus species. The extracted nematodes were observed and measured as live and fixed materials and subsequently identified by integrative taxonomy (morphometrically and molecularly). The latter species is described herein as Pratylenchus vovlasi sp. nov., resulting morphometrically closest to P. mediterraneus and phylogenetically to P. pratensis. The molecular identification of Pratylenchus vovlasi sp. nov. was carried out by sequencing the ITS region, D2-D3 expansion domains of the 28S rRNA gene and a partial region of the nuclear hsp90 gene. ITS-RFLP and sequence analyses revealed that Pratylenchus vovlasi sp. nov. had species-specific restriction profiles with no corresponding sequences present in the database. The phylogenetic relationships with ITS and D2-D3 sequences placed the Pratylenchus vovlasi sp. nov. in a clade with P. pratensis and P. pseudopratensis. This research confirms the occurrence of cryptic biodiversity within the genus Pratylenchus as well as the need for an integrative approach to the identification of Pratylenchus species.
Highlights
Raspberries (Rubus sp.) have a long history of human consumption and cultivation in Europe, with Russia being the leading producer [1]
The present study reports on the occurrence of two root-lesion nematodes associated with raspberry fields in the Piedmont region, P. crenatus, along with an abundant species identified as P. vovlasi sp. nov
Our results demonstrated that the application of rRNA molecular markers integrated with morphological studies could help in the diagnosis and characterization of root-lesion nematode species
Summary
Raspberries (Rubus sp.) have a long history of human consumption and cultivation in Europe, with Russia being the leading producer [1]. Raspberries are the most productive in areas with mild winters and long, moderate summers. Plant-parasitic nematodes have an important role in the reduction of the raspberry yield [4,5]. The most frequently observed species in soil and the roots of raspberries belong to the root-lesion nematode genus Pratylenchus, mainly P. crenatus Loof, 1960, (71.7% of soil samples, 53.4% of root samples), P. penetrans (Cobb, 1917) Filipjev and Schuurmans Stekhoven, 1941 (51.6%, 54.2%) and P. scribneri Steiner in Sherbakoff and Stanley 1943 (9.2%, 10.2%; [9]). Considering the economic significance of root-lesion nematodes on raspberries and the need to accurately distinguish these damaging species for their practical management in the field, we provide here the morphometrical and molecular characterization of a new root-lesion nematode, Pratylenchus vovlasi sp. The specific objectives of this paper were: (i) to carry out a comprehensive identification with morphological and morphometric approaches of P. vovlasi sp. nov. with a differential diagnosis to closely related species; (ii) to provide a molecular characterization of P. vovlasi sp. nov. and estimate its phylogenetic relationships with other representatives of the Pratylenchus genus using three molecular markers: two ribosomal markers (the D2-D3 expansion segments of the 28S rRNA and the internal transcribed spacer region (ITS rRNA) and the nuclear region of the partial heat shock protein 90 (hsp90) gene
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