Ditylenchus

Abstract: The wide geographic distribution of species of this genus may be interpreted as evidence of an ancient origin of the genus. Stem nematode, stem and bulb nematode 1 A total of 13 nominal species have been synonymized. Most species were generally characterized and distinguished from other nominal stem nematode species by certain host preferences. Stem nematodes in, for example, flower bulbs and seeds of lucerne, field beans, onions, and other Allium species are on the list of quarantine organisms of many countries all over the world. Stem nematodes were found in leaf galls of the false dandelion H.radicata and species of the genus in several European countries and in the western USA, where they are dispersed by seeds of the weed. Leaves are often distorted, discolored and smaller, with reduced and twisted leaf stems or they may obtain a shape morphologically quite different from the normal; in many plant species galls or necrotic spots may develop.

Abstract: Subbotin, S. A., Madani, M., Krall, E., Sturhan, D., and Moens, M. 2005. Molecular diagnostics, taxonomy, and phylogeny of the stem nematode Ditylenchus dipsaci species complex based on the sequences of the internal transcribed spacer-rDNA. Phytopathology 95:1308-1315. The stem nematode Ditylenchus dipsaci is of great economic importance worldwide as a parasite of agricultural crops and horticultural plants. The internal transcribed spacer (ITS) of rDNA from 23 populations of the D. dipsaci complex from various host plants were amplified and sequenced. Seven previously studied populations were also included in the study. The phylogenetic analysis of the full ITS and ITS2 sequence alignments using minimum evolution, maximum parsimony, and Bayesian inference under the complex model of DNA evolution revealed trees with two main clades: (i) D. dipsaci sensu stricto with diploid chromosome numbers and comprising most isolates from agricultural, ornamental, and several wild plants, and (ii) Ditylenchus spp. with polyploid chromosome numbers, reproductively isolated from diploid populations, and subdivided into six subclades (“giant race” from Vicia faba, Ditylenchus species parasitizing various Asteraceae, and a Ditylenchus sp. from Plantago maritima). Using the energy minimization approach and comparative sequence analysis, it has been found that the secondary structure of ditylenchid ITS2 is organized in three main domains. The importance of knowledge on the RNA structure for phylogenetic analysis is discussed. Conventional polymerase chain reaction (PCR) and real-time PCR with SYBR green dye I with a species specific primer have been developed for detection and quantification of D. dipsaci sensu stricto. Validation tests revealed a rather high correlation between real numbers of fourth-stage juveniles of the stem nematodes in a sample and expected numbers detected by real-time PCR. Problems of accuracy of quantification are discussed.

Abstract: During a survey of soil nematodes in Iran, a new species of Ditylenchus Filipjev, 1936 was discovered. Ditylenchus sarvarae sp. n. is characterised by its body length (1.0–1.4 mm), lateral field with seven incisures and without areolation, long postuterine sac (1.8–2.8 times the corresponding body diameter) and conical female tail with pointed tip (68–89 μm long, c = 13.7–18.2, c' = 4.2–5.1). Male specimens have conical tails (64–70 μm long, c = 14.5–16.7, c' = 4.0–4.5), spicules (22–26 μm long) and gubernaculum (8–10 μm long). Measurements and illustrations are provided for this new species. A molecular study of the 28S rDNA region of D. sarvarae sp. n . demonstrates that the Iranian species belongs to a separate group compared with the other molecularly characterized species of genus Ditylenchus .

Abstract: The genus Ditylenchus Filipjev, 1936 is reviewed and 80 valid species are listed. Following species, originally described in Nothotylenchus, are transferred to Ditylenchus : D. dynzocolus (Riihm, 1956) n. comb., D. major(Thorne & Malek, 1968) n. comb., D. montanus (Kiknadze & Eliashvili, 1988) n. comb., D. websten' (Kumar, 1983) n. comb. Following new synonyms are proposed : D. paramonovi (Gagarin, 1974), D. sn'nagarensis (Fotedar & Mahajan, 1974), D. saxemi Fortuner & Maggenti, 1987 and D. alliphilus Fortuner & Maggenti, 1987 are synonymised with D. acutus (Khan, 1965); D. elongatus (Husain & Khan, 1974) with D. cylindn'cus Khan & Siddiqi, 1968) : D. galeopsidis Paramonov, 1970 with D. dipsaci (Kiihn, 1857) : D. sibin'cus German, 1969 with D. equalis Heyns, 1964; D. silvestris (Kazachenko, 1970) and D. protensus Brzeski, 1984 with D. ferepolitor (Kazachenko, 1970). D. maleki Fortuner & Maggenti, 1987 is considered junior objective synonym of D. major (Thorne & Malek, 1968). Eight species previously listed as valid are considered species inquirendue. Tabular characteristic for valid species of the genus is provided. Five new species are described. D. acutatus sp. n. is characterised by six incisures, stylet = 7-8 p, muscular median bulb and offset posterior bulb, V = 77-81, long PUS, spicule = 19 pm and thick tail with more or less pointed terminus. D. apus sp. n. has six incisures, stylet = 8 p, median bulb muscular, oesophageal glands form a long lobe overlapping intestine, V = 75-76, PUS less than half of vulval body width, thick tail with rounded tip. D. filenchulus sp. n. is diagnosed as having s x incisures, stylet = 7-8 Km, muscular median bulb and offset basal bulb, V = 67-72, PUS about a third of vulva-anus distance, spicule = 13-16 pm, tail long and cylindrical in posterior pad, tip rounded, wedge shaped or pointed. D. silvaticus sp. n. is characterised by six incisures, stylet = 7-8 Pm, muscular oesophagus with offset basal bulb, V = 78-81, PUS about a third of vulva-anus distance, body posterior to vulva tapers evenly to thick and variable tail terminus. D. terricolus sp. n. has four incisures, muscular median bulb, posterior bulb overlapping intestine for few pm, V = 71-77, PUS about a third of vulva-anus distance, spicule = 13-14 pm and thick tail mostly with rounded tip with small mucro. Twenty known species of Ditylenchus are redescribed.