Background Sugar beet (Beta vulgaris subsp. vulgaris) is an economically important crop that provides nearly one third of the global sugar production. The beet cyst nematode (BCN), Heterodera schachtii, causes major yield losses in sugar beet and other crops worldwide. The most effective and economic approach to control this nematode is growing tolerant or resistant cultivars. To identify candidate genes involved in susceptibility and resistance, the transcriptome of sugar beet and BCN in compatible and incompatible interactions at two time points was studied using mRNA-seq. Results In the susceptible cultivar, most defense-related genes were induced at 4 dai while suppressed at 10 dai but in the resistant cultivar Nemakill, induction of genes involved in the plant defense response was observed at both time points. In the compatible interaction, alterations in phytohormone-related genes were detected. The effect of exogenous application of Methyl Jasmonate and ET-generator ethephon on susceptible plants was therefore investigated and the results revealed significant reduction in plant susceptibility. Genes putatively involved in the resistance of Nemakill were identified, such as genes involved in phenylpropanoid pathway and genes encoding CYSTM domain-containing proteins, F-box proteins, chitinase, galactono-1,4-lactone dehydrogenase and CASP-like protein. Also, the transcriptome of the BCN was analyzed in infected root samples and several novel potential nematode effector genes were found. Conclusions Our data provides detailed insights into the plant and nematode transcriptional changes occurring during compatible and incompatible interactions between sugar beet and BCN. Many important genes playing potential roles in susceptibility or resistance of sugar beet against BCN, as well as some BCN effectors with a potential role as avr proteins were identified. In addition, our findings indicate the effective role of jasmonate and ethylene in enhancing sugar beet defense response against BCN. This research provides new molecular insights into the plant-nematode interactions that can be used to design novel management strategies against BCN.

Xiphinema granatum n. sp. from pomegranate in Saveh, Markazi province, central Iran, is described and illustrated. The new species belongs to species group 8 of the genus Xiphinema sensu Loof & Luc, 1990. The new species is characterised by a body 3.5-4.1 mm long, 37-49 μm diam., odontostyle and odontophore 118-132 and 65-74 μm long, respectively, presence of sperm in the female genital tracts, uterus devoid of any Z-differentiation or spines, and abundant males with spicules 45-58 μm long. The polytomous identification codes of the new species are: A4, B4, C5a, D5, E56, F4, G23, H2, I3, J4, K2, L2. Beside morphological and morphometric data, molecular analyses of D2-D3 fragments of 28S rRNA gene placed the new species in close relationship with X. vuittenezi and X. italiae and some species belonging to Xiphinema morphospecies group 6, but clearly separated from X. index. In addition, an Iranian population of Longidorus pisi from the same locality is morphologically and molecularly characterised.

The genus Discotylenchus is reported for the first time from Iran. Discotylenchus iranicus n. sp. is described and illustratedbased on morphological and morphometric characters. The new species is characterized by a combination of the followingmorphological features: lip region continuous and smooth, tapering to an offset prominent labial disc, lateral field withfour incisures, stylet length of 14–15μm, vulva position at 70.8–76.5 %, tail length of 81–100μm, conoid with a roundedtip and presence of males. The Iranian population of D. brevicaudatus shows a wider morphometric range compared tothe original description and the male of this species is described for the first time. The morphological characters and range of morphometric data of D. discretus are in full agreement with the original population.

Rotylenchus arasbaranensis n. sp., a new monosexual species is described and illustrated based on morphological, morphometric and molecular studies. The new species is characterised by having an offset and hemispherical lip region with 5-6 annuli, 32-36 μm long stylet, vulva located at 43.9-59.2% with a single epiptygma and rounded tail, rarely bilobed, with 6-8 annuli. The species R. striaticeps and the male of R. buxophilus are reported for the first time from Iran and R. fragaricus is reported and studied for the second time after its original description. The results of the phylogenetic analyses based on the sequences of the D2-D3 expansion region of the 28S, ITS1-rRNA and the partial 18S rRNA genes were provided for the studied species, confirming their differences from each other and determining the position of them and their relationships with closely related taxa. Also, the validity of Plesiorotylenchus is discussed on the basis of molecular data and its synonymisation (with only one sequence) with Rotylenchus is accepted.

Xiphinema zagrosense sp. n. is described based on morphological and molecular characters. The new species belongs to morphospecies group 6 characterised by having two equally developed female genital branches with spines in uterus and a short, rounded tail. The new species is characterised by having spines in the tubular part of the uterus, body length 3.8-5.0 mm, odontostyle length 151-169 μm, odontophore 94-105 μm, conical, dorsally convex tail, four juvenile stages and absence of males. The new species appears closely related to the members of X. pyrenaicum group characterised by a rounded tail with or without an inconspicuous digitate end and a uterus devoid of Z-differentiation but showing spiniform structures. It is compared with X. aceri, X. adenohystherum, X. iranicum, X. mazandaranense, X. nuragicum, X. pyrenaicum, X. robbinsi, X. sphaerocephalum and X. vuittenezi. In addition to morphological and morphometric data, molecular analyses of the near-full-length small subunit rDNA gene (SSU) and large subunit rDNA gene (LSU) D2/D3 placed the new species in close relation with some species belonging to Xiphinema group 6 but differs from other species in the X. pyrenaicum complex.