Soil organisms are a crucial part of the terrestrial biosphere. Despite their importance for ecosystem functioning, no quantitative, spatially-explicit models of the active belowground community currently exist. In particular, nematodes are the most abundant animals on Earth, filling all trophic levels in the soil food web. Here, we use 6,579 georeferenced samples to generate a mechanistic understanding of the patterns of global soil nematode abundance and functional group composition. The resulting maps show that 4.4 ± 0.64  10 20 nematodes (total biomass ~0.3 Gt) inhabit surface soils across the world, with higher abundances in sub-arctic regions (38% of total), than in temperate (24%), or tropical regions (21%). Regional variations in these global trends also provide insights into local patterns of soil fertility and functioning. These high-resolution models provide the first steps towards representing soil ecological processes into global biogeochemical models, to predict elemental cycling under current and future climate scenarios.

From May to June 2011, during a survey of the wheat-growing areas in Meknes in the Saïs Region of Morocco, several cyst nematode populations were detected. Sampling was performed 1 month before wheat (Triticum durum) harvest, in fields showing patches of stunted plants. Plants were growing poorly, had chlorotic lower leaves, and a reduced numbers of ears. Root systems were short and had a bushy appearance because of increased secondary root production. No cysts were visible on the roots, but were found in the soil. Cysts were collected from soil on 200-μm sieves by the modified Cobb decanting and sieving method (1) and identified by morphology and internal transcribed spacer (ITS)-rDNA sequencing. All isolates were identified as Heterodera avenae except the isolate from Aïn Jemâa. From the latter, key morphological features from cysts and second-stage juveniles (J2) were determined. The cysts (n = 10) had the following characteristics: bifenestrate vulval cone, body length without neck 590 μm (551 to 632 μm), body width 393 μm (310 to 490 μm), neck length 75 μm (65 to 90 μm), fenestra length 64 μm (60 to 72 μm) and width 21 μm (18 to 25 μm), underbridge length 96 μm (85 to 115 μm), vulval slit length 8 μm (7 to 9 μm), vulva bridge width 27 μm (24 to 33 μm), and bullae absent. The J2s (n = 10) had the following characteristics: body length 445 μm (412 to 472 μm), body width 19 μm (19 to 21 μm), stylet length 24 μm (23 to 25 μm), four lateral lines, tail length 50 μm (46 to 54 μm), and hyaline terminal tail 28 μm (24 to 31 μm). Values of the morphological characters were within the range of H. latipons reported by Handoo (3). The bifenestrate cysts with a strong underbridge and no bullae and J2 with a tail length greater than 40 μm, a stylet longer than 15 μm, and four incisures in the lateral field were typical for H. latipons. To confirm the identification, molecular observations were made. DNA was extracted from three juveniles from three different cysts separately (4). The ITS-rDNA region was amplified using the primers 5′-CGT AAC AAG GTA GCT GTA G-3′ and 5′-TCC TCC GCT AAA TGA TAT G-3′ as described by Ferris et al. (2). This resulted in a 1,040-bp DNA fragment. The PCR-products were purified and sequenced (Macrogen, Inc., Seoul, Korea). All sequences obtained (GenBank Accession Nos. per cyst: JQ319035, JQ319036, and JQ319037) were compared with sequences available from the GenBank database ( www.ncbi.nlm.nih.gov ), including several species of Heterodera. This comparison revealed a sequence similarity of 97 to 99% with H. latipons and 89% or lower with any other species of Heterodera. Morphological and molecular identification demonstrated that the population of cyst nematodes from a wheat field in Aïn Jemâa, Morocco was H. latipons. In the patches with poor growing plants, 65 cysts per 100 cm3 soil were found. To our knowledge, this detection represents a new record of H. latipons. Since the nematode can cause considerable damage to wheat, one of the main cereals produced in Morocco, care should be taken to prevent the spread to other regions. References: (1) K. R. Barker. Page 19 in: An Advanced Treatise on Meloidogyne. Vol II. Methodology. C. C. Carter and J. N. Sasser, eds. North Carolina State University Graphics, Raleigh, 1985. (2) V. R. Ferris et al. Fundam. Appl. Nematol. 16:177, 1993. (3) Z. A. Handoo. J. Nematol. 34:250, 2002. (4) M. Holterman et al. Mol. Biol. Evol. 23:1792, 2006.

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The RFLP technique was used to establish a reliable diagnostic method for 18 Pratylenchus species: Pratylenchus agilis, P. bolivianus, P. brachyurus, P. coffeae, P. crenatus, P. fallax, P. goodeyi, P. loosi, P. mediterraneus, P. neglectus, P. penetrans, P. pratensis, P. pseudocoffeae, P. scribneri, P. subranjani, P. thornei, P. vulnus and P. zeae. The polymerase chain reaction (PCR) amplified the ITS regions from all species and populations examined and revealed large differences in length, ranging in size from approximately 900 to 1250 bp. The rDNA fragments were digested with five restriction enzymes (CfoI, DdeI, HindIII, HpaII, and PstI). All Pratylenchus species can be differentiated from each other by a combination of at least two enzymes. CfoI differentiated all nematode species with the exception of P. fallax, P. penetrans and P. pseudocoffeae. P. fallax was further separated by a DdeI restriction, and P. pseudocoffeae by a PstI digestion. Intraspecific RFLP were observed. Upon CfoI, DdeI, HindIII, or HpaII digestion, it was possible to separate the three P. coffeae populations studied from each other. La technique RFLP a été utilisée pour créer une méthode fiable de diagnostic pour 18 espèces de Pratylenchus: Pratylenchus agilis, P. bolivianus, P. brachyurus, P. coffeae, P. crenatus, P. fallax, P. goodeyi, P. loosi, P. mediterraneus, P. neglectus, P. penetrans, P. pratensis, P. pseudocoffeae, P. scribneri, P. subranjani, P. thornei, P. vulnus et P. zeae. La réaction de polymérisation en chaîne (PCR) a amplifié les régions de l’ITS pour toutes les espèces et populations étudiées et a mis en évidence de grandes différences dans la taille des gammes de longueur, de 900 à 1250 bp approximativement. Les fragments de rDNA ont été digérés à l’aide de cinq enzymes de restriction (CfoI, DdeI, HindIII, HpaII, and PstI). Toutes les espèces de Pratylenchus ont pu être différenciées les unes des autres par une combinaison d’au moins deux enzymes. CfoI a différencié toutes les espèces à l’exception de P. fallax, P. penetrans et P. pseudocoffeae. P. fallax a été ultérieurement séparé par une restriction DdeI, et P. pseudocoffeae par une digestion PstI. Des RFLP intraspécifiques ont été observés. Par les digestions CfoI, DdeI, HindIII, ou HpaII, il s’est révélé possible de séparer les unes des autres les trois populations étudiées de P. coffeae.

Amplified ITS region products of rDNA from 25 valid species and one unidentified species from the genus Heterodera and from Meloidodera alni were digested by 26 restriction enzymes. A combination of seven enzymes clearly separated the agriculturally most important species from each other and from their sibling species. Species specific digestion profiles of ITS regions and a table with approximate sizes of digested fragments for several identification enzymes are given. Heterogeneity of ITS regions was revealed for some cyst forming nematode species. Des fragments amplifiés de la région de l’ITS du rDNA de 25 espèces valides et d’une espèce non identifiée du genre Heterodera et de Meloidodera alni ont été soumis à une digestion par 26 enzymes de restriction. La combinaison de sept enzymes a permis une séparation nette des espèces les plus importantes en agriculture, tant les unes par rapport aux autres que par rapport aux espèces jumelles. Sont donnés les profils spécifiques de digestion des régions de l’ITS et un tableau regroupant les tailles approximatives des fragments digérés pour plusieurs enzymes d’identification. L’hétérogénéité des régions de l’ITS a été révélée chez quelques espèces de nématodes à kyste.