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.
Root-knot nematodes, Meloidogyne spp., cause great losses to coffee crops in Brazil and worldwide. However, little is known about the physiological changes that these pathogens induce in coffee plants. The present work aimed to compare the physiological variables of coffee seedlings (Coffea arabica ‘Catuaí Vermelho IAC 144’) infected with Meloidogyne paranaensis or M. exigua with healthy coffee plants. Nematode-infected plants showed reductions in height and starch content in roots compared to healthy plants. In addition, the infected plants had a reduction in transpiration, stomatal conductance and CO2 concentration. However, only the coffee seedlings infected with M. paranaensis showed reduction in the rate of photosynthesis. Nematode-infected plants had lower leaf contents of P, K, Mn and Fe when compared to healthy plants. However, only coffee seedlings parasitised by M. paranaensis exhibited lower levels of Ca in the leaves. Therefore, M. paranaensis and M. exigua, with emphasis on M. paranaensis, alter the normal coffee seedling physiology.
Root-lesion nematodes, Pratylenchus spp., are one of the most important nematode groups in economic terms. The combination of morphological analyses and molecular analyses based on D2-D3 of 28S rDNA, ITS rDNA, and COI mtDNA regions supported the establishment of a new Pratylenchus species, making a total of 103 valid Pratylenchus species. The females of P. horti n. sp. are characterised by the following traits: low labial region with two annuli continuous to the body, en face form belonging to group II sensu Corbett & Clark (1983) with submedian triangular-shaped segments fused with the oral disc and separated from the lateral segments, lateral field with four incisures at vulval level and lacking areolation, robust stylet 15-17 μm long with rounded knobs, and subcylindrical tail with smooth tail tip. The males are largely similar to the females but differ from the females by the partially areolated lateral field, slightly ventrally arcuate and weakly cephalated spicules (15-19 μm), and ventrally curved elongate conical tail with a poorly protruding, crenate bursa. The new species was recovered from soil and root samples from the rhizosphere of Hedychium greenii growing in the Botanical Garden, Ghent University, Belgium.
Cryptaphelenchus baujardi n. sp. is described and illustrated based on two populations from Golestan province, northern Iran. The new species is characterised by female and male body length of 224 (190-261) and 215 (195-229) μm, respectively, offset cephalic region with a shallow constriction, delicate stylet 6.6 (6.0-7.0) μm long, four incisures in the lateral field, presence of a rudimentary post-uterine sac in the female gonoduct, elongate-conoid female tail ending in an acute to finely rounded terminus, male tail conical, male with seven caudal papillae and delicate spicules. The new species shows a strong resemblance to C. varicaudatus and C. iranicus, but has a sclerotised mass near the tip of the spicule and an indistinct spermatheca. Phylogenetic analyses based on both partial SSU and LSU rDNA sequences confirm its status as a new taxon.
Dokdo Island has a unique biodiversity that has been preserved as a natural monument. Although the biodiversity of Dokdo has been investigated, little information is available regarding the nematodes. The diversity of plant-parasitic nematodes was investigated using both ITS and D2-D3 sequences. Nematodes extracted from 59 rhizosphere soil samples were morphologically identified as belonging to eight genera: Geocenamus, Helicotylenchus, Rotylenchulus, Heterodera, Paratylenchus, Pratylenchus, Pratylenchoides and Xiphinema. Further, nucleotide sequences were determined from 85 individuals of different genera for species diagnosis. We identified 13 species, including three species of the genus Pratylenchus (P. crenatus, P. kumamotoensis and P. neglectus), Helicotylenchus sp. 1, Rotylenchulus sp. 1, Paratylenchus nanus, Heterodera trifolii, Heterodera spp., Pratylenchoides ritteri, Geocenamus sp. 1, Geocenamus sp. 2, Xiphinema brevicollum and Xiphinema sp. 1. The dominant plant-parasitic nematode on Dokdo was P. crenatus, which was found in 25.4% of the samples. Our study provides important information about the biodiversity of plant-parasitic nematodes on Dokdo Island.
Root-knot nematodes (Meloidogyne spp.) are one of the most economically important groups of plant-parasitic nematodes on potato (Solanum tuberosum), but there has been little study regarding their occurrence on potato in China. In this study, the nematodes in two nematode-infected potato samples collected from Yunnan Province were identified as Meloidogyne spp. Amplicon sizes with species-specific PCR primers indicated that one sample was M. javanica and the other was M. incognita. Cultures established from these two isolates were used to screen 28 potato genotypes in China. All genotypes were susceptible to both M. javanica and M. incognita. However, the mean root galling index and number of egg masses were generally higher for M. javanica than M. incognita. Variable susceptibility was demonstrated among the tested potato genotypes. No available resistant potato cultivars plus a rapid spread of Meloidogyne spp. will result in a potential threat to potato production in China.
Bealius pinus n. sp. is described and illustrated based on its morphological, morphometric, and molecular characters. The new species is characterised by a body length of 1040 (920-1124) μm (females) and 985 (990-1043) μm (males), lip region continuous, 7.2 (7.0-8.0) μm broad, 3.3 (3.0-4.0) μm high, stylet length 8.4 (7.0-9.0) μm or ca 1.0-1.3 times the lip region diam., lateral fields with five or six incisures, the outer incisures crenate and inner incisures weakly crenate, and excretory pore situated 156 (141-170) μm from the anterior end. The basal pharyngeal bulb has a short posterior extension projecting dorsally into the intestine. Post-uterine sac absent. Functional males common in the population, spicules 29 (28-30) μm long. Tail cylindrical with broadly rounded terminus in the female and conical, arcuate, completely enveloped by a well-developed bursa in the male. The new species is compared with two known species of the genus, B. bisulcus and B. pissodi. Molecular phylogenetic studies of the new species using partial sequences of small subunit (SSU) rDNA revealed that it forms a clade with several nematode species belonging to genera in the Sphaerularioidea, namely: Sphaerularia, Paurodontella, Nothotylenchus, and Deladenus.
A new species of Aporcelinus, collected in a natural habitat of central Mexico, is described and illustrated, including molecular (D2-D3 28S-rRNA) data. Aporcelinus zapotitlanensis sp. n. is characterised by its 1.19-1.43 mm long body, lip region offset by a deep constriction and 16.5-18.5 μm broad, odontostyle 19.5-22 long, neck 325-368 μm long, pharyngeal expansion 150-201 μm long or 46-55% of the total neck length, uterus 130-167 μm long and tripartite, V = 54-56, tail conical with finely rounded tip (30-37 μm, c = 34-43, c′ = 1.2-1.4) lacking a distinct dorsal concavity, spicules 48-51 μm long, and 11-12 spaced ventromedian supplements with one or two of them located within the range of the spicules. Molecular analyses confirm the monophyly of Aporcelinus and places the new species within a clade shared with A. infundibulicaudatus and A. amazonicus.
Chitwoodius coffeae sp. n. is described, including SEM observations and molecular (D2-D3 expansion segment of the rDNA 28S) analysis, from a coffee plantation in the Central Highlands of Vietnam. The new species is characterised by its 1.69-2.01 mm long body in females and 1.29-1.51 mm in males, lip region offset by deep constriction and 15-17 μm broad, odontostyle 27-30 μm long, neck 340-473 μm long, pharyngeal expansion occupying 52-54% of total neck length, uterus a simple tube-like structure 68-106 μm long, vulva longitudinal (V = 54-59), tail short and rounded conoid (20-28 μm, c = 54-88, c′ = 0.6-0.8) with a nearly terminal projection of inner cuticle layer, spicules 60-64 μm long, and 7-10 spaced ventromedian supplements without hiatus. SEM pictures, available for the first time for a representative of the genus, show a hexagonal (nearly hexastellate) oral field divided into six sectors by the existence of six deep incisures. Molecular analyses, also presented for the first time for a representative of the genus, results in a narrow evolutionary relationship among Chitwoodius and Tylencholaimus, and supports the monophyly of the Tylencholaimidae. This is the first record of Chitwoodius in Asian Far East territories. Chitwoodius ahmadi sp. n. is proposed for a misattributed population of C. seshadrii.