Robert T. Robbins

Compendium of Longidorus juvenile stages with observations on L. pisi, L. taniwha and L. diadecturus (Nematoda: Longidoridae).

Descriptions and selected redescriptions of the 98 putative species in the genus Longidorus Micoletzky, 1922 were reviewed for information on the occurrence of juvenile stages (=developmental forms). For 43 of the 98 species information on juvenile forms was not available, two species had only the J4 stage described, four species had only the J3 and J4 stages described, for ten species data were provided for three juvenile stages and four juvenile stages were described for 39 species. However, the published morphometrics for numerous species do not allow an unequivocal determination to be made of the developmental stage(s) as described by the authors. In the description of L. jonesi only three groups of juvenile stages were identified and subsequently populations of L. martini and L. taniwha were also reported with only three juvenile stages and not four as is usual for the Nematoda. Populations of L. diadecturus, L. pisi and L. taniwha, each species having a posteriorly located guide ring, were examined. Data are presented which demonstrate that, as with L. martini, L. pisi and L. taniwha, each have only three juvenile stages, whereas L. diadecturus has four such stages. The shift from four to three juvenile stages is considered to be a derived state which may be a result of hormonally mediated heterochrony, possibly expressed as a single gene change. It is proposed that species unequivocally demonstrated to have only three juvenile stages, the terminology should be JI, JII and JIII, whereas for all other species the existing terminology should be used, J1, J2, J3 and J4.

Effect of Chloride and Soybean Cultivar on Yield and the Development of Sudden Death Syndrome, Soybean Cyst Nematode, and Southern Blight

Yields of irrigated soybean in Arkansas are threatened by two problems: chloride toxicity and sudden death syndrome (SDS). Soybeans are sensitive to chloride, which accumulates in the upper soil profile when water with high salt content is used for irrigation. Sudden death syndrome is a soilborne disease often associated with well-irrigated fields. Even though these problems both affect irrigated soybeans, there are no reports on the effect of chloride toxicity on SDS. To determine if there is an effect of chloride toxicity on SDS, a test was established at the Cotton Branch Station, Marianna, AR, in 1995 and 1996. Four cultivars were selected that were either susceptible to SDS (S) or resistant to SDS (R) and either translocated chloride to the leaves (includer, I) or confined chloride in the roots (excluder, E). The cultivars were Hartz 6686 (SE), Terra Vig 6653 (SI), Hartz 6200 (RE), and Asgrow 6297 (RI). Soil chloride concentrations were adjusted by the addition of KCl. Before planting, KCl was applied to achieve the recommended concentration of K over the entire field. At V4, chloride treatments were applied by either adding no additional KCl (low Cl) or adding 1,120 kg of KCl per ha (moderate Cl) or 2,240 kg of KCl per ha (high Cl). Soil samples were taken within the center two rows of each plot at planting, flowering (R2), and harvest and assayed for populations of Fusarium solani and Heterodera glycines. Soil chloride concentrations were determined at R2, and leaf chloride levels were determined at R3. Weekly disease ratings were made on SDS and converted to area under the disease progress curve (AUDPC). Plant lodging and the incidence of southern blight (Sclerotium rolfsii) were determined during mid-reproductive growth. Leaf chloride concentrations were influenced by both chloride treatment and cultivar: elevated concentrations occurred with the includer cultivars in the moderate and the high Cl treatments. Soil concentrations of chloride reflected the chloride treatments in 1995, but not 1996. Soil populations of F. solani did not respond consistently to either chloride treatment or cultivar; however, H. glycines egg densities increased with increased soil chloride treatments in Hartz 6686 (SE) and Terra Vig 6653 (SI) at R2, but not at harvest. Increased soil chloride treatments increased SDS in both years with Hartz 6686 (SE), but did not affect this disease in the other cultivars. Higher soil chloride treatments decreased yield in all cultivars except Hartz 6200 (RE) in 1996. Although Terra Vig 6653 (SI) did not develop severe levels of SDS foliar symptoms, it did have increased lodging and significant increases in southern blight with moderate and high soil chloride treatments. These results indicate that growers with fields that have both elevated concentrations of soil chloride and SDS should select SDS-resistant excluder cultivars to minimize yield losses due to both problems.

Identification of quantitative trait loci underlying resistance to southern root-knot and reniform nematodes in soybean accession PI 567516C

Abstract Soybean cyst nematode (SCN, Heterodera glycine Ichinohe), southern root-knot nematode [SRKN, Meloidogyne incognita (Kofoid and White) Chitwood] and reniform nematode (RN, Rotylenchulus reniformis Linford and Oliveira) are three important plant–parasitic pests in soybean. Previous study showed that plant introduction (PI) 567516C harbored novel quantitative trait loci (QTL) conferring SCN resistance to soybean. However, QTL underlying resistance to SRKN and RN in PI 567516C remain unknown. The objectives of this study were to identify QTL for resistance to SRKN and RN in PI 567516C. Two hundred and forty-seven F6:9 recombinant inbred lines, derived from a cross between cultivar Magellan and PI 567516C, were evaluated for resistance to SRKN and RN. Two hundred and thirty-eight simple sequence repeats and 687 single nucleotide polymorphism markers were used to construct a genetic linkage map. Three significant QTL associated with resistance to SRKN were mapped on chromosomes (Chrs.) 10, 13 and 17. Two significant QTL associated with resistance to RN were detected on Chrs. 11 and 18. Whole-genome resequencing revealed that there might be Peking-type Rhg1 in PI 567516C. Our study provides useful information to employ PI 567516C in soybean breeding in order to develop new cultivars with resistance to multiple nematodes.

{null=Description of Rhyssocolpus vinciguerrae sp. n. (Dorylaimida, Nordiidae) from Iran and the first molecular study of this genus, en=Description of Rhyssocolpus vinciguerrae sp. n. (Dorylaimida, Nordiidae) from Iran and the first molecular study of this genus}

{null=Rhyssocolpus vinciguerrae sp. n., from natural habitats in Iran, is described, illustrated and sequenced. It is characterised by the body length of 1.04-1.37 mm, lip region offset by depression and 11-13 μm broad, odontostyle 8-10 μm or 0.7-0.8 times the lip region diam. long, neck 227-265 μm long, pharyngeal expansion 80-95 μm long or 31-35% of total neck length, a dorsal cell mass present between cardia and the end of the anterior ovary/testis, uterus bipartite, 90-170 μm long, vulva longitudinal (V = 48-55), abundant irregularities in body cuticle around vulva, female tail conical with rounded terminus (35-55 μm, c = 24-34, c′ = 1.4-1.9), spicules 43-51 μm long and 6-8 spaced ventromedian supplements located outside the range of the spicules. It is very similar to R. aquilonius, R. arcticus and R. iuventutis. A molecular characterisation of the new species was done on ribosomal DNA nearfull-length small subunit 18S gene, internal transcribed spacer and partial 5.8S gene. The results obtained support a close relationship between Rhyssocolpus and Heterodorus, and a more distant relationship with Enchodelus., en= Rhyssocolpus vinciguerrae sp. n., from natural habitats in Iran, is described, illustrated and sequenced. It is characterised by the body length of 1.04-1.37 mm, lip region offset by depression and 11-13 μm broad, odontostyle 8-10 μm or 0.7-0.8 times the lip region diam. long, neck 227-265 μm long, pharyngeal expansion 80-95 μm long or 31-35% of total neck length, a dorsal cell mass present between cardia and the end of the anterior ovary/testis, uterus bipartite, 90-170 μm long, vulva longitudinal (V=48-55), abundant irregularities in body cuticle around vulva, female tail conical with rounded terminus (35-55 μm, c=24-34, c′=1.4-1.9), spicules 43-51 μm long and 6-8 spaced ventromedian supplements located outside the range of the spicules. It is very similar to R. aquilonius, R. arcticus and R. iuventutis. A molecular characterisation of the new species was done on ribosomal DNA near-full-length small subunit 18S gene, internal transcribed spacer and partial 5.8S gene. The results obtained support a close relationship between Rhyssocolpus and Heterodorus, and a more distant relationship with Enchodelus. }

Molecular identification of some Hoplolaimus species from the USA based on duplex PCR, multiplex PCR and PCR-RFLP analysis

Two different molecular approaches, a multiplex PCR and PCR-RFLP of ITS-rDNA, were developed for the identification of Hoplolaimus species. DNA sequences of H. columbus, H. galeatus, H. concaudajuvencus, H. magnistylus, H. seinhorsti and three undescribed Hoplolaimus species were used to design species-specific primers. Three reverse species-specific PCR primers for H. columbus, H. galeatus and H. magnistylus were developed using the ITS1 region exhibiting interspecific variation. Three species-specific PCR primers in combination with the forward primer, Hoc-1f, produced distinct amplicons of 580 bp for H. columbus, 120 bp for H. galeatus and 340 bp for H. magnistylus. We successfully identified each of three species by multiplex PCR when all three were mixed in a single PCR reaction. Restriction enzyme digests of the PCR amplicon using HaeIII and RsaI permitted discrimination of H. columbus, H. galeatus, H. magnistylus, H. concaudajuvencus, H. sp. 1, H. sp. 2 and H. sp. 3 from each other. These results suggest that these molecular techniques allow for rapid, easy and reliable identification of Hoplolaimus species.

Description of Xiphinema castilloi sp. n. (Dorylaimida: Longidoridae) from Iran and its phylogenetic relationships.

Xiphinema castilloi sp. n., a new species of morphogroup 5 sensu Loof & Luc, 1990, is described and illustrated based on morphological, morphometric and molecular data. The new species is characterised by a 4.2-5.0 mm body assuming an open C to J shape after heat fixation, lip region separated from the body by a shallow depression, a 101-126 mu m odontostyle, two equally developed genital tracts with pseudo-Z-organ in uterus (8-11 globular structures) and devoid of spines, tail dorsally convex conoid with a mucro, presence of functional males, and four juvenile developmental stages. By having two equally developed genital tracts, presence of pseudo-Z-organ, and similarities in tail shape of females and juveniles, the new species comes more close to X. artemisiae, X. diversicaudatum, X. erriae, X. jomercium, X. lapidosum, X. lusitanicum and X. ripogranum. The Bayesian inference (BI) and Maximum Likelihood (ML) analyses using 707 bp partial sequences of D2-D3 segment of 28S rDNA placed the new species in a monophyletic group with X. dentatum, another member of morphospecies group 5 with 1.00 Bayesian posterior probability (BPP).

Description of Longidorus hangzhouensis sp. n. (Nemata: Longidoridae) from Zhejiang province, new geographical records of L. henanus Xu & Cheng, 1992, and an identification key for Longidorus species occurring in China.

Specimens of a Longidorus species, here described as L. hangzhouensis sp. n., were recovered from the rhizosphere of sweet-scented Osmanthus growing in Hangzhou, Zhejiang province, China, and a second population was collected from Camellia japonica, Fuyang, Zhejiang province. The species is characterised by medium-sized body length (3.1-4.9 mm), head region narrow (8-12 μm), anteriorly rounded, with continuous, funnel-shaped amphidial pouches, a relatively long odontostyle (97-126 μm) and a short, almost hemispherical tail. Three juvenile development stages were identified, J2, J3 and J4. A second Longidorus species, identified as L. henanus Xu & Cheng, 1990, previously known only from the type locality in Henan province, was recovered from the rhizosphere of bamboo from Beijing and of poplar from Yuanqu county, Shanxi province. A dichotomous key is provided for the Longidorus species reported from China.

Advancements in breeding, genetics, and genomics for resistance to three nematode species in soybean

Key messageIntegration of genetic analysis, molecular biology, and genomic approaches drastically enhanced our understanding of genetic control of nematode resistance and provided effective breeding strategies in soybeans.AbstractThree nematode species, including soybean cyst (SCN, Heterodera glycine), root-knot (RKN, Meloidogyne incognita), and reniform (RN, Rotylenchulus reniformis), are the most destructive pests and have spread to soybean growing areas worldwide. Host plant resistance has played an important role in their control. This review focuses on genetic, genomic studies, and breeding efforts over the past two decades to identify and improve host resistance to these three nematode species. Advancements in genetics, genomics, and bioinformatics have improved our understanding of the molecular and genetic mechanisms of nematode resistance and enabled researchers to generate large-scale genomic resources and marker-trait associations. Whole-genome resequencing, genotyping-by-sequencing, genome-wide association studies, and haplotype analyses have been employed to map and dissect genomic locations for nematode resistance. Recently, two major SCN-resistant loci, Rhg1 and Rhg4, were cloned and other novel resistance quantitative trait loci (QTL) have been discovered. Based on these discoveries, gene-specific DNA markers have been developed for both Rhg1 and Rhg4 loci, which were useful for marker-assisted selection. With RKN resistance QTL being mapped, candidate genes responsible for RKN resistance were identified, leading to the development of functional single nucleotide polymorphism markers. So far, three resistances QTL have been genetically mapped for RN resistance. With nematode species overcoming the host plant resistance, continuous efforts in the identification and deployment of new resistance genes are required to support the development of soybean cultivars with multiple and durable resistance to these pests.

Description of one new, and new data on two known, species of Enchodelus Thorne, 1939 (Dorylaimida: Nordiidae) from Iran

This contribution provides a study of one new and two known species of Enchodelus. Enchodelus sardashtensis sp. n. is characterised by its 1.3-1.5 mm long body, lip region 13-15 μm broad and offset by marked depression, odontostyle 22-27 μm or 1.5-1.8 lip region diam. long, neck 290-310 μm long, pharyngeal expansion 100-110 μm long or 35-38% of total neck length, a dorsal cellular mass (pseudocoelomocyte) present between cardia and proximal end of anterior ovary, uterus tripartite and 95-145 μm long, V = 44-48, female tail rounded conoid (19-23 μm, c = 61-76, c′ = 0.7-0.8) and bearing saccate bodies, and male unknown. This species is close to E. altherri and E. arcticus. Enchodelus groenlandicus and E. longispiculus are recorded for the first time in Iran and in Asia, respectively and compared to other known populations of these species. A molecular characterisation of E. longispiculus is also performed based on ribosomal DNA near-full-length small subunit 18S gene, internal transcribed spacer and partial 5.8S gene. Phylogenetic analysis revealed E. sardahtensis sp. n. and E. longispiculus to be in a monophyletic clade with all other Enchodelus with rounded tail.

Morphological and molecular characterisation of Enchodelus babakicus n. sp. and E. macrodorus Thorne, 1939 (Nematoda: Nordiidae) from Iran

A new species with a rounded tail belonging to the Enchodelus macrodorus-group is described from a natural habitat in the vicinity of Kaleibar City, north-west Iran. Enchodelus babakicus n. sp. is characterised by its medium sized body (1.21-1.56 mm), lip region offset by a marked constriction, odontostyle 40-45 μm long, tripartite uterus and presence of abundant males with 49-61 μm long spicules and 10-14 spaced ventromedian supplements. The new species is close to E. distinctus, E. groenlandicus, E. macrodorus, E. microdoroides and E. saxifragae. A population of E. macrodorus was also found in the same sample as the new species. Molecular analysis was inferred from sequencing of 18S rDNA and ITS1 regions of three species of the genus from Iran, including E. babakicus n. sp., E. macrodorus and E. veletensis, together with other available sequences in GenBank. The sequences showed that E. babakicus n. sp. belongs to a clade formed by Enchodelus species characterised by a rounded tail.