The root-lesion nematode, Pratylenchus thornei, attacks a wide range of crops and causes significant reductions in global grain production. Breeding programmes are currently restricted to using parents with moderate resistance to P. thornei as cereal cultivars with complete resistance are yet to be identified. This study evaluated 484 of CIMMYT’s spring wheat accessions for resistance to P. thornei of which 56 lines were pre-identified as resistant under controlled growth room conditions. These lines were further evaluated for their resistance and tolerance reactions under field conditions, where 14 accessions maintained their resistance and 16 were moderately resistant against P. thornei. Four lines gave excellent resistant and tolerance reactions to P. thornei. The relationship between the nematode reproduction factor (Pf/Pi) and wheat grain yield in field experiments fits a linear regression model. These findings could be useful for improving P. thornei resistance in wheat.
We analysed the effect of the invasive perennial plant Heracleum sosnowskyi on soil nematode communities and diversity, and plant species composition, by comparing invaded and non-invaded (control) areas in natural conditions. Invasion of H. sosnowskyi caused significant shifts in plant species composition, which subsequently modified nematode assemblages. Stress-sensitive omnivores, fungivores and root-biomass-dependent obligate plant parasites best reflected changes in soil nematode communities under the influence of H. sosnowskyi invasion. The negative effect of H. sosnowskyi was most evident on Aphelenchus, Tylencholaimus, Geocenamus, Helicotylenchus, Pratylenchus, Tylenchorhynchus and Aporcelaimellus. Our results indicate that significant changes in the herbaceous layer after H. sosnowskyi invasion in ecosystems where H. sosnowskyi eventually became dominant impacted soil nematode communities but did not affect nematode diversity. This was in contrast to the habitats where a solitary plant of H. sosnowskyi grew and no significant changes in nematode communities were observed.
This paper presents studies on the life cycle of Heterodera sacchari under in vitro conditions. Pluronic gel was used as a medium for growth of H. sacchari. The life cycle was completed in 7-9 weeks on rice (Oryza sativa, ‘Nipponbare’). After infection, juveniles developed and reached the reproducing adult female stage at 25 days post inoculation (dpi). At 35 dpi, all females produced eggs in various numbers. Some females were translucent and eggs inside could be counted. At 49 dpi females started to tan and developed into dark brown cysts. Hatching of H. sacchari juveniles from cysts could be stimulated by 3 mM ZnCl2 but not by rice root exudates. The in vitro culture of H. sacchari on Pluronic gel can be used efficiently to collect post-infective nematode/host samples at different time points for various studies and to screen different rice cultivars for resistance/susceptibility.
Meloidogyne paranaensis is one of the most destructive root-knot nematode species affecting coffee cultivation. This species presents different esterase phenotypes (Est): P1, P2 and P2a, previous studies showing that Est P2 and P2a populations were more aggressive to susceptible coffee cultivars than populations with Est P1, and local producers have even asked if they may be described as other species. The objective of this study was to characterise M. paranaensis populations of different esterase phenotypes (Est P1, P2 and P2a), regarding morphological, morphometric and phylogenetic relationships in distinct regions of ribosomal DNA (rDNA), mitochondrial gene cytochrome c oxidase II (COII) and nuclear protein coding gene HSP90. All populations were identified by esterase phenotype and SCAR-specific markers. Regarding morphology/morphometrics, the three populations were very similar to the description of the species, differing only in the morphology of the male stylet and second-stage juvenile hyaline tail length. Based on the phylogenetic analysis, a low intraspecific variability was detected among M. paranaensis Est P1 and Est P2 populations from Brazil; the Guatemalan population Est P2a, however, showed a genetic differentiation from the Brazilian populations, confirming the geographic genetic distance of this aggressive population. According to this multi-source approach study, in spite of the intraspecific variation, the phylogenetic position of M. paranaensis is absolute, regardless of the enzymatic phenotype and SCAR markers.
Molecular aspects of the responses of tomato (Solanum lycopersicum) plants to invasion by Meloidogyne incognita, as well as the nematode reproduction capacity, were investigated and the role of jasmonic acid (JA) in these interactions was evaluated. Real-time quantitative PCR analysis showed that resistant and susceptible plants had similar levels of Mi1.2, PR1 and PR6 gene expression in stress-free conditions. During nematode invasion resistant plants showed up-regulation of Mi1.2, PR1 and PR6 genes and no reproduction of M. incognita. By contrast, susceptible plants showed no response in gene expression and the nematode had a high level of reproduction. Treatment of tomato plants with JA modulated Mi1.2 and PR6 gene expression that was accompanied by a suppression of the M. incognita reproduction on the roots of JA-treated susceptible plants.
Litylenchus crenatae n. sp., isolated from leaf galls of Fagus crenata from Japan, is described and figured. The new species is characterised by its dimorphism in adult females, six (or more) lateral lines, a more or less pointed tail tip in both sexes, male bursa arising posteriorly and reaching to near tail tip, presence of a quadricolumella and a post-uterine sac in females. Litylenchus crenatae n. sp. is distinguished from its only congener, L. coprosma, by the number of lateral lines, six or more vs four; the lip morphology, offset with very shallow constriction or dome-shaped without clear constriction vs clearly offset; tail tip morphology, more or less pointed vs blunt; and structure of the median bulb, weakly muscular with a clear valve vs not muscular with an obscure valve. The molecular phylogenetic analysis confirms that the new species is close to, but clearly different from, L. coprosma.
Two populations of Lobocriconema were recovered from the rhizosphere of Parrotia persica in Rango forest, Gorgan, and Nargesi forest, Nokandeh, Golestan province, northern Iran. Both of the recovered populations were characterised using morphological (light and scanning electron microscopy), morphometric and molecular data based upon small, partial large and internal transcribed spacer 1 ribosomal RNA (SSU, LSU D2-D3, ITS1 rDNA) and the mitochondrial cytochrome c subunit oxidase I (COI mtDNA) gene sequences. The first examined population, recovered from Gorgan, was mainly characterised by having 34-39 retrorse body annuli 11-16 μm thick at mid-body with crenate, dentate and lobulate margins, longitudinal cuticular scratches on entire body on both lateral regions, sometimes one or two anastomoses along the body, a single labial annulus with smooth margin and smaller than the first body annulus, four distinct submedian lobes, simple open vulva with no overhang, and a terminal anus. This population was almost identical to Neolobocriconema iranense, a close examination of a topotype population recovered in this study confirming that they were conspecific. The second population, L. nokandense n. sp., was recovered from the Nokandeh and looked similar to the first population but was morphologically separated from it by a slightly crenate labial annulus under SEM (vs smooth), longer tail (13-21 vs 6-10 μm) and smaller ratio c (23.6-32.4 vs 44.7-86.0). In molecular phylogenetic analyses, the two populations formed a clade in both SSU and LSU phylogenies. In ITS1 and COI phylogenies, the Nokandeh population (the new species) formed a separate sister clade to the N. iranense clade. Detailed observations using SEM data revealed a small annulus between the submedian lobes and the single labial annulus, an open vulva and a slightly ornamented cuticle in all three studied populations (the newly recovered populations from Golestan and the topotype population of N. iranense from Mazandaran province and the new species), corroborating their placement under Lobocriconema. As a result, N. iranense was transferred to Lobocriconema as L. iranense n. comb. (= N. iranense). The new species was morphologically compared with its close relatives L. iranense n. comb., L. pauperum, L. incrassatum, and L. nasuense, all of which having the aforementioned small annulus between the submedian lobes and the first labial annulus. The phylogeny of the genus is discussed.
Sivash Bay is the largest hypersaline lagoon in the world. In 1963-1975 the North Crimean Canal was constructed, with water from the River Dnieper and discharge of drainage water collected from agricultural lands into Sivash Bay. Salinity in Sivash Bay began to drop, resulting in a new brackish water ecosystem. The political decision to stop supplying water from the River Dnieper to the Canal was made in 2014, and the discharge of fresh water into the lagoon ended, resulting in an increase in salinity up to 60-75 g l−1. This study showed that the abundance of meiobenthos increased, with Nematoda dominating. The composition of nematode species in the lagoon has not previously been studied. Using samples from 1979, 2013 and 2015, 50 nematode species and forms were identified in 1979, 32 in 2013 and 21 in 2015. The species composition of nematodes at different periods was significantly different. The average abundance of nematodes was 134 198 ind. m−2 in 2013 and 606 660 ind. m−2 in 2015.
Host response of BC2F3 recombinant inbred line (RIL) population derived from a cross between African rice (CG14) and Asian rice (IR64) genotypes was evaluated in the field and quantitative trait loci (QTLs) that confer resistance and tolerance to Meloidogyne graminicola were mapped using SSR markers. Of the 155 BC2F3 progenies evaluated, 23 were resistant and six were partially resistant based on the number of second-stage juveniles (J2) per root system and J2 per g roots. Based on yield reduction, 23 progenies were identified as tolerant and 14 were less sensitive to M. graminicola infection. QTLs related to resistance were detected on chromosomes 6, 7 and 12. QTL for tolerance linked to percentage yield reduction was mapped on chromosome 5. QTLs linked to fresh root weight, dry root weight, dry shoot weight, percentage filled grains per panicle and yields were also mapped. QTLs identified will be useful in a breeding programme to develop M. graminicola-resistant and tolerant rice cultivars.