A new stem nematode, Ditylenchus oncogenus n. sp. (Nematoda: Tylenchida), parasitizing sowthistle from Adriatic coast dunes in southern Italy

Abstract

Morphological and molecular analyses of a stem nematode causing a severe disease on infected sowthistle (Sonchus bulbosus) plants, involving the formation of gall-like structures on infected leaves and stems, have led to the description of a new species named Ditylenchus oncogenus n. sp. Morphologically, the new species is characterized by a medium to large body size (all adults more than 1 mm in length); a delicate stylet (9.0-11.0 μm long) with minute, rounded knobs; a long post-vulval uterine sac (c. 65% of the vulva-anus distance); six incisures at the lateral fields and characteristic D. destructor-pattern of spicules (with pronounced ventral tumulus and anteriorly pointed, less sclerotized, cuticle parts present within the lamina). The results of molecular analysis of rRNA gene sequences, including the D2-D3 expansion regions of 28S rRNA, internal transcribed spacer (ITS) rRNA, partial 18S rRNA gene, the protein-coding mitochondrial gene, cytochrome oxidase c subunit I (COI), and the heat-shock protein 90 (hsp90) gene, support the new species status. The results of a host-suitability test indicated that the new species does not parasitize potato (Solanum tuberosum) tubers and broad bean (Vicia faba) seedlings. Histopathological observations on naturally infected sowthistle tissues revealed that D. oncogenus n. sp. causes floral stem neoplasia and midrib leaf gall formation on the type, and to date only known, host. The galls were characterized by extensive hyperplasia, where several necrotic cells in the neoplasic area were directly damaged by feeding of the nematode, whereas a number of adjacent cells showed typical cytological changes, such as granulated cytoplasm with hypertrophied nuclei and nucleoli.

Ditylenchus laurae sp. n. (Tylenchida: Anguinidae) from Poland – a new species of the D. dipsaci complex associated with a water plant, Potamogeton perfoliatus L.

“…The newly obtained sequences of the ITS rRNA, COI mtDNA and hsp90 genes were aligned using ClustalX 1.83 with default parameters with their corresponding published gene sequences of species from the D. dipsaci complex and outgroups (Subbotin et al, 2004(Subbotin et al, , 2005Marek et al, 2005Marek et al, , 2010Kerkoud et al, 2007;Chizhov et al, 2010;Vovlas et al, 2011Vovlas et al, , 2016Jeszke et al, 2014, and others). Sequence alignment was manually edited using GenDoc 2.5.0.…”

Anatomical Alterations in Plant Tissues Induced by Plant-Parasitic Nematodes

“…However, most species within this genus are fungal-feeders in the soil. Depending on the species, they could infect a broad number of plants (i.e., Ditylenchus dipsaci ) or be specifically associated with some plants (i.e., D. oncogenus to Sonchus bulbosus or D. gigas to broad beans) (Vovlas et al, 2015b ). Plant responses could also differ depending on the nematode-species or their specific host, for example in the species complex group of D. dipsaci , some hosts (rye and oats) produce an excessive number of tillers and develop puffy sheaths (Hawn, 1969 ); in other hosts, leaves produce small pale-green swellings which contain aggregations of nematodes (Campbell and Griffin, 1973 ), deformed leaves or bulbs as in garlic or onion (Sturhan and Brzeski, 1991 ), or crown-canker in sugar beet (Castillo et al, 2007 ).…”

“…(F) Longitudinal section of parenchyma of a stem portion showing sub-epidermal cavities (ca) surrounded by necrotic cells. (G) Cross-section of flower parenchyma showing a nematode (n), and hypertrophied nuclei (hn) in the attacked cells (Vovlas et al, 2015b ; with permission of Cambridge University Press). Anguina tritici (H–J) : (H) Healthy (left) and infected (right) spike and seed galls of wheat.…”

New record of three species of Ditylenchus Filipjev, 1936 (Nematoda: Anguinidae), with a key to the species reported from Iran

“…Species of the genus are mostly common in temperate zones, including the Mediterranean Basin (Vovlas et al, 2011). Among more than 60 species presently recognized under the genus Ditylenchus (Siddiqi, 2000;Vovlas et al, 2011;Vovlas et al, 2015), only a few are parasites of higher plants, while the majority of species are mycophagous (Sturhan & Brzeski, 1991). The two genera Ditylenchus and Nothotylechus Thorne, 1941 are morphologically closely related (Siddiqi, 2000), but have separated from each other based on the nature of metacorpus (Brzeski, 1981;Fortuner & Maggenti, 1987;Siddiqi, 2000;Andrássy, 2007).…”