Pristionchus bucculentus n. sp. was isolated from a shining mushroom beetle, Episcapha gorhami, associated with white rot on a decaying log in Hokkaido, Japan. The new species is distinguished by its stomatal morphology, which includes three regularly shaped, conical left subventral denticles and a vacuolated cheilostom with weak internal sclerotization. Also distinguishing P. bucculentus n. sp. are male sexual characters, including arrangement of genital papillae, a rounded and ventrally skewed manubrium, and a gubernaculum with a large, deep posterior curvature and a short, shallow anterior curvature. Morphological and molecular evidence support the new species as being close to P. elegans, which was previously the most basal known species of the genus. Comparative morphology of basal Pristionchus species is supported by a molecular phylogeny inferred from a partial small subunit ribosomal rRNA gene and 25 ribosomal protein-coding genes. Description of P. bucculentus n. sp. provides a new point of comparison for reconstructing the evolution of stomatal characters in the comparative model system of Pristionchus.
Evolution; morphology; morphometrics; ribosomal protein genes; new species; phylogeny; stoma; taxonomy
Belonolaimus longicaudatus and Helicotylenchus pseudorobustus are among the most common nematode parasites of turfgrasses in Florida. Bermudagrass (Cynodon dactylon × C. transvaalensis) and seashore paspalum (Paspalum vaginatum) are the two turf species most commonly used on Florida golf courses. This paper explores the interactions between B. longicaudatus and H. pseudorobustus on bermudagrass and seashore paspalum hosts. Data collected from thousands of nematode samples submitted to the Florida Nematode Assay Lab over a 8-yr period revealed a negative relationship between B. longicaudatus and H. pseudorobustus on bermudagrass, but not seashore paspalum. In a multi-year field plot experiment using multiple cultivars of bermudagrass, and seashore paspalum B. longicaudatus and H. pseudorobustus were negatively related on both turf species. Greenhouse trials where multiple cultivars of both turf species were inoculated with different combinations of B. longicaudatus and H. pseudorobustus found that each nematode species was inhibitory to the other on both host species. Belonolaimus longicaudatus and H. pseudorobustus clearly impact each other on turfgrass hosts, although the mechanism of the nematode-nematode interactions is unknown.
Belonolaimus longicaudatus; bermudagrass; Cynodon dactylon; Helicotylenchus pseudorobustus; interaction; Paspalum vaginatum; seashore paspalum; spiral nematode; sting nematode; turfgrass
The soybean cyst nematode (SCN), Heterodera glycines, is a major factor limiting soybean yield. Experiments were conducted in 2009 and 2010 to determine the effects of liquid swine manure and chemical fertilizer PK on soybean and corn yields, and on SCN population in an SCN-suppressive field (S-Site) and an SCN-conducive field (C-Site) in Minnesota. The experiment was a split-plot design with crop sequences as main plots and fertilizer treatments as subplots. The 2-yr crop sequences were Sus-Sus, Res-Sus, and Corn-Sus, where Sus was SCN-susceptible soybean, and Res was SCN-resistant soybean. The fertilizer treatments were manure, PK, and a nonfertilizer as control. Manure did not reduce SCN egg population density but resulted in 31% lower SCN second-stage juvenile (J2) population density at the S-Site at 45 d after planting (DAP) in 2009. Manure also reduced spiral nematode (Helicotylenchus spp.) population density by 52% compared with PK and nonfertilizer treatments at S-Site at 45 DAP in 2009. The crop sequence of Corn-Sus and Res-Sus reduced the SCN egg and J2 but increased spiral nematode population density at both sites. An increase of 1.4 Mg/ha and 0.5 Mg/ha in yield of susceptible soybean was observed in manure and PK treatments, respectively, at the C-Site in 2009. Corn yield was 2.8 Mg/ha and 5.0 Mg/ha greater when treated with manure than nonfertilizer at the S-Site and C-Site, respectively. This study suggests that soil fertility management may be a useful strategy to alleviate the SCN damage to soybean.
Helicotylenchus; Heterodera glycines; management; nematode suppressive soil; swine manure; soybean; soybean cyst nematode
The seed gall nematode, Anguina agrostis, feeds and reproduces within the developing ovaries of bentgrass seeds and overwinters in seed galls as anhydrobiotic juveniles. These dormant juveniles can survive within the seed gall for many years. In this dehydrated state, they are more tolerant to extreme environmental conditions than are their hydrated counterparts. Nematodes in seed galls were exposed to various high temperatures (80 to 160°C) for time intervals of 5 to 30 min. Survival decreased as time and temperature increased. Remarkably, these nematodes survived exposure to 155°C for 5 min, higher than that recorded for any other metazoan. In contrast, seed galls that had been stored at room temperature and humidity for 5 yr also survived exposure to extreme temperatures; however, their survival rates were not as high as those for freshly collected galls. Juveniles within the seed gall were coiled and grouped together conforming to the shape of the seed gall. The gross morphology of the cuticle of the juveniles was very smooth and relatively undistorted by the shrinkage from the loss water from their body tissues. Wherever the nematodes were cut with a razor blade, a small amount of their contents oozed out of the opening and coalesced with that of other nearby specimens and appeared gel-like. Elucidation of the mechanisms that enable these nematodes to remain viable after exposure to extreme heat remains a mystery. Understanding the changes that occur in these nematodes as they rehydrate and return to life from an ametabolic state may have major impacts on the life sciences, including insights into the answer of the age-old question: “What is life?”
Agrostis stolonifera; ametabolic; Anguina agrostis; anhydrobiosis; desiccation; extremist; feeding site; host-parasitic relationship; longevity; survival; thermal death point; morphology; thermophilic
Resistance to Meloidogyne spp. in commonly used resistant grape rootstocks is slightly compromised at soil temperatures above 27°C. Newly released UCD-GRN series rootstocks, which have broad nematode resistance, exhibit trace infections by Meloidogyne spp. at elevated temperature. Pathotypes of M. incognita and M. arenaria that are virulent on ‘Harmony’ rootstock, as well as M. incognita Race 3, which is avirulent on ‘Harmony’, failed to produce egg masses on the UCD-GRN series rootstocks and other resistant selections at 24°C. At 27°C and above, there was increased nematode galling and egg mass production; at 30°C, egg mass production levels of M. incognita Race 3 on ‘Harmony’ were up to 12% of that on susceptible ‘Colombard’ while reproduction of the virulent pathotypes on the UCD-GRN series was less than 5% of that on ‘Colombard’. Resistance of several of the parental genotypes of the UCD-GRN rootstock series was slightly compromised at soil temperatures of 30°C and above; however, others maintained their resistance to even the virulent M. arenaria pathotype A at high temperatures. Effects of high temperature on resistance to Xiphinema index could not be assessed because of temperature sensitivity of the nematodes while resistance to Mesocriconema xenoplax was not compromised at high soil temperature. Resistance to Meloidogyne spp. in the UCD-GRN series rootstocks was not compromised when plants and nematodes were subjected to cyclical high and low temperature conditions, indicating that once initiated, the resistance mechanism is not reversed.
Broad resistance; durable resistance; host status; temperature effects
Two new species, Neotobrilus nicsmolae n. sp. and Chronogaster carolinensis n. sp. are described from a small, acidic, temperate, natural lake in North Carolina. N. nicsmolae n. sp. comes close to three members of the genus reported from North America, N. filipjevi, N. longus, and N. hopei. However, N. nicsmolae is unique with in the genus in having a combination of characters: size smaller than 1,700 μm, shorter outer labial and cephalic setae, tail shorter than 250 μm, last ventromedian supplement close (about 5 μm) to cloacal opening, spicule length of 61 to 85 μm, flagelloid sperm, and possession of subterminal setae. Assessment of relationships among clades within the Triplonchida using DNA sequences of the D2D3 expansion segment of the LSU rDNA showed that the family Trichodoridae and the genus Tripyla were recovered as monophyletic. The genus Tobrilus was recovered as monophyletic in the neighbor-joining and maximum likelihood trees, but that was not so in the maximum-parsimony tree. The separation among genera of the Trichodoridae, i.e., Trichodorus and Paratrichodorus, was not clear-cut in all phylograms. Chronogaster carolinensis n. sp. in having one ventral mucro with no spine and vacuolated lateral glandular bodies comes close to C. typica and C. ethiopica but differs from all hitherto known species in a combination of characteristics: in having long cephalic setae, long stoma, crystalloid bodies, vacuolated lateral glandular bodies, and a tail terminus with blunt ventral mucro, and its lack of lateral line.
Free-living nematode; freshwater nematode; new species; taxonomy
Nematicide/irrigation rate trials were conducted in Texas (TX) in 2009 and 2010 in cotton grown at three irrigation rates, where irrigation rate (base (B), B - 33%, B + 33%) was the main plot and treatment (untreated check, aldicarb, and nematicide seed treatment (NST) and NST + aldicarb) were the subplots. Aldicarb improved cotton lint yield with the base (medium) irrigation rate over the untreated check, but not at the B - 33% and B + 33% irrigation rates. In a second evaluation, 20 tests conducted over 7 yr at the same field in TX and 12 tests conducted over 6 yr at the same field in Alabama (AL) were examined for impact of environmental variables (EV) on the response to NST (containing thiodicarb or abamectin), aldicarb, a nontreated check (CK), insecticide seed treatment (TX only), and a combination of NST + aldicarb + oxamyl (NST/A/O, AL only) on root galls (TX only), early season nematode eggs (AL only), and yield (both sites). Galls/root system were lower with aldicarb-treated plots, than for the CK- or NST-treated plots. As water (irrigation plus rain) in May increased, galls/root system increased for CK or insecticide-only-treated plots, and decreased for NST- and aldicarb-treated plots, suggesting efficacy of nematicides was strongly improved by adequate soil moisture. Nematode reproduction was not affected by EV in either location, though yield was negatively affected by root-knot nematode eggs in AL at 60 d. Yield in both AL and TX was negatively related to temperature parameters and positively related to water parameters. With the addition of EV in TX, chemical treatments went from not significantly different in the absence of EV to aldicarb-treated plots having higher yields than nonnematicide-treated plots in the presence of EV. In AL, NST/A/O-treated plots yielded similar to aldicarb and better than CK or NST in the absence of EV and had significantly higher yields than all other treatments in the presence of most EV.
abamectin; aldicarb; Gossypium hirsutum; Meloidogyne incognita; oxamyl; thiodicarb
In the Pacific Northwest, alfalfa (Medicago sativa) is host to two species of root-knot nematodes, including race 2 of the Columbia root-knot nematode (Meloidogyne chitwoodi) and the northern root-knot nematode (Meloidogyne hapla). In addition to the damage caused to alfalfa itself by M. hapla, alfalfa’s host status to both species leaves large numbers of nematodes available to damage rotation crops, of which potato is the most important. A nematode-resistant alfalfa germplasm release, W12SR2W1, was challenged with both nematode species, to determine the correlation, if any, of resistance to nematode reproduction. Thirty genotypes were screened in replicated tests with M. chitwoodi race 2 or M. hapla, and the reproductive factor (RF) was calculated. The distribution of natural log-transformed RF values was skewed for both nematode species, but more particularly for M. chitwoodi race 2, where more than half the genotypes screened were non-hosts. Approximately 30 percent of genotypes were non-hosts or very poor hosts of M. hapla, but RF values for M. hapla on susceptible genotypes were generally much higher than RF values for genotypes susceptible to M. chitwoodi race 2. The Spearman rank correlation was positive (0.52) and significant (p-value = 0.003), indicating there is some relationship between resistance to these two species of root-knot nematode in alfalfa. However the relationship is not strong enough to suggest genetic loci for resistance are identical, or closely linked. Breeding for resistance or immunity will require screening with each species separately, or with different DNA markers if marker-assisted breeding is pursued. A number of genotypes were identified which are non-hosts to both species. These plants will be intercrossed to develop a non-host germplasm.
alfalfa; host status; Meloidogyne chitwoodi; Meloidogyne hapla; pest resistance
Desiccation tolerance plays an important role in the overwinter survival of the foliar nematode Aphelenchoides fragariae. Survival rates of A. fragariae were compared with those of the anhydrobiotic soil-dwelling nematode Aphelenchus avenae after desiccation (90% RH), cold (4°C) and osmotic (500 mM sucrose) stress treatments. A. fragariae formed aggregates during desiccation and showed higher survival rates than A. avenae under desiccation and osmotic stress. Analysis of transcripts with Illumina RNA-seq indicated that glutaredoxin and other antioxidant-related genes were up-regulated under desiccation stress. Quantitative RT-PCR demonstrated 2.8 fold and 1.3 fold up-regulation of a glutaredoxin gene under desiccated and osmotic stress, respectively, suggesting the participation of antioxidant mechanisms in desiccation tolerance of A. fragariae.
Aphelenchoides fragariae; desiccation; cold stress; osmotic stress; glutaredoxin; survival rate
One hundred and eleven golf courses from 39 counties in the Carolinas were surveyed for plant-parasitic nematodes. Species diversity within habitats was analyzed with five diversity indices including Diversity index (H’), Evenness (J’), Richness (SR), Dominance (λ) and Diversity (H2). The results revealed a remarkably high diversity of 24 nematode species belonging to 19 genera and 11 families. Of those, 23 species were found in SC, 19 species in NC, and 18 species were detected in both states. Helicotylenchus dihystera, Mesocriconema xenoplax, Hoplolaimus galeatus, Tylenchorhynchus claytoni, Belonolaimus longicaudatus, Meloidogyne graminis and Paratrichodorus minor were the most prevalent and abundant species in golf course turfgrasses in both states. Twelve species were new records of plant parasitic nematodes in turfgrasses in both NC and SC. The results also revealed effects of different habitats on diversity of nematode species in turfgrass ecosystem. H’ and SR values were higher in SC than in NC. H’, J’ and H2 values were significantly higher in sandy than in clay soil in NC, but no significant differences between sand and clay soil were detected in SC or in pooled data from both states. There were no significant differences for all indices among the management zones (putting green, fairway and tee) in NC. However, in SC and pooled data, H’, SR and H2 were significantly higher in putting greens than in fairways and tees. Significant differences from different grass species (bermudagrass, creeping bentgrass and zoysiagrass) were detected only in H’, which was significantly higher in zoysiagrass than in bentgrass or bermudagrass in NC. In pooled data, H’ was significantly higher in zoysiagrass samples than in creeping bentgrass samples but was not significantly different from bermudagrass samples.
North Carolina; South Carolina; detection; distribution; diversity; ecology; golf course; identification; plant-parasitic nematode; turfgrass
Previously we showed in laboratory studies that the fungivorus nematode, Aphelenchoides hylurgi, was attracted to and fed upon the chestnut blight fungus, Cryphonectria parasitica, from American chestnut bark cankers and was a carrier of biocontrol, white hypovirulent C. parasitica strains. In the present field study, we recovered Aphelenchoides spp. in almost all (97.0 %) of 133 blight canker tissue assays (three 5-g samples each) from four eastern states. High mean population densities (227 to 474 nematodes per 5 g tissue) of Aphelenchoides spp. were recovered from cankers in Virginia, West Virginia, and Tennessee but not from New Hampshire (mean = 75 nematodes per 5 g tissue). Overall, most canker assays yielded population densities less than 200 nematodes per 5 g tissue. All of 12 very small or young cankers yielded a few to many Aphelenchoides spp. Regression analysis indicated greatest recovery of Aphelenchoides spp. occurred in the month of May (r = 0.94). The results indicate that Aphelenchoides spp. appear to be widespread in blight cankers on American chestnut trees and could play a role in biocontrol of chestnut blight.
biocontrol; chestnut blight; fungivorus nematodes; hypovirulence
In an outside pot experiment, dry pig manure processed on pine sawdust litter and fermented for seven days by house fly larvae (fermented manure), and pine sawdust applied alone, and in combination with a spring application of inorganic nitrogen fertilizer were used to determine their effects on plant parasitic and free-living soil nematodes on sugar beets (cv. Antek). Non amended soil was used as a control. All treatments with fermented pig manure and sawdust with nitrogen fertilizer decreased number of plant parasitic nematodes and also root-fungal feeding nematodes compared to the untreated control. Sawdust applied alone had no effect on plant parasitic and root-fungal feeding nematode suppression. Free-living nematodes which were mainly bacteriovores and fungivores were significantly more abundant in soil amended with fermented pig manure, while the sawdust had no effect on these nematodes. The effect of all tested treatments on omnivores-predators was rather random, and in general, the number of these nematodes decreased after soil amendment applications compared to the untreated control.
fermented animal manure; nematode trophic groups; nitrogen amendments; phytoparasitic nematodes; sawdust
A survey was conducted to determine the assemblage and abundance of plant-parasitic nematodes and their associations with soil factors in organically farmed fields in Minnesota. A total of 31 soil samples were collected from southeast (SE), 26 samples from southwest (SW), 28 from west-central (WC), and 23 from northwest (NW) Minnesota. The assemblage and abundance of plant-parasitic nematodes varied among the four regions. The soybean cyst nematode, Heterodera glycines, the most destructive pathogen of soybean, was detected in 45.2, 88.5, 10.7, and 0% of organically farmed fields with relative prominence (RP) values of 10.3, 26.5, 0.6, and 0 in the SE, SW, WC, and NW regions, respectively. Across the four regions, other common genera of plant-parasitic nematodes were Helicotylenchus (42.6, RP value, same below), Pratylenchus (26.9), Tylenchorhynchus and related genera (9.4), Xiphinema (5.6), and Paratylenchus (5.3). Aphelenchoides, Meloidogyne, Hoplolaimus, Mesocriconema, and Trichodorus were also detected at low frequencies and/or low population densities. The similarity index of plant-parasitic nematodes between two regions ranged from 0.44 to 0.71 and the similarity increased with decreasing distance between regions. The densities of most plant-parasitic nematodes did not correlate with measured soil factors (organic matter, pH, texture). However, the densities of Pratylenchus correlated negatively with % sand, and Xiphinema was correlated negatively with soil pH.
Aphelenchoides; Helicotylenchus; Heterodera glycines; Hoplolaimus; Meloidogyne; Mesocriconema; nematode community; organic-farming; Paratylenchus; Pratylenchus; soybean cyst nematode; Trichodorus; Tylenchorhynchus; Xiphinema
Populations of Bakernema inaequale, C. petasum, C. sphagni, C. mutabile, Ogma octangulare, Xenocriconemella macrodora and Hemicriconemoides chitwoodi were identified and re-described from different geographical areas in the continental United States and molecularly characterized. Two new species of spine nematodes Criconema arkaense n. sp. from Washington County and Lee County, Arkansas and Criconema warrenense n. sp from Warren, Bradley County, Arkansas are also described and named. Criconema arkaense is characterize by having a conspicuous lip region offset from the body with two annuli, short rounded tail with a thin cuticular sheath and subterminal anus. Criconema warrenense n. sp. has two lip region annuli about the same width, first annulus directed posteriorly, separated by a narrow neck annulus and a short conoid tail, unilobed non-folded annulus. The molecular characterization of Criconema arkaense and Criconema warrenense using ITS1 rDNA gene sequence and the molecular phylogenetic relationships of these new species along with the known spines nematodes are provided.
Bakernema inaequale; Criconematidae; Criconema,Criconema arkaense n.sp.; Criconema mutabile; Criconema petasum; Criconema sphagni; Criconema warrenense n.sp.; Hemicriconemoides; Hemicriconemoides chitwoodi; internal transcribed spacer 1; morphology; molecular biology; Ogma; Ogma octangulare; phylogenesis; taxon; Xenocriconemella; Xenocriconemella macrodora
Microorganisms produce volatile organic compounds (VOCs) which mediate interactions with other organisms and may be the basis for the development of new methods to control plant-parasitic nematodes that damage coffee plants. In the present work, 35 fungal isolates were isolated from coffee plant rhizosphere, Meloidogyne exigua eggs and egg masses. Most of the fungal isolates belonged to the genus Fusarium and presented in vitro antagonism classified as mutual exclusion and parasitism against the nematode-predator fungus Arthrobotrys conoides (isolated from coffee roots). These results and the stronger activity of VOCs against this fungus by 12 endophytic bacteria may account for the failure of A. conoides to reduce plant-parasitic nematodes in coffee fields. VOCs from 13 fungal isolates caused more than 40% immobility to Meloidogyne incognita second stage juveniles (J2), and those of three isolates (two Fusarium oxysporum isolates and an F. solani isolate) also led to 88-96% J2 mortality. M. incognita J2 infectivity decreased as a function of increased exposure time to F. oxysporum isolate 21 VOCs. Gas chromatography-mass spectrometry (GC-MS) analysis lead to the detection of 38 VOCs produced by F. oxysporum is. 21 culture. Only five were present in amounts above 1% of the total: dioctyl disulfide (it may also be 2-propyldecan-1-ol or 1-(2-hydroxyethoxy) tridecane); caryophyllene; 4-methyl-2,6-di-tert-butylphenol; and acoradiene. One of them was not identified. Volatiles toxic to nematodes make a difference among interacting microorganisms in coffee rhizosphere defining an additional attribute of a biocontrol agent against plant-parasitic nematodes.
biological control; Meloidogyne exigua; Fusarium; antagonism
A novel entomopathogenic nematode species, Heterorhabditidoides rugaoensis n. sp. RG081015, collected from Rugao, China, is described. The new species is morphologically very similar to H. chongmingensis but can be distinguished from it on the basis of some morphological characteristics, combined with molecular data and a cross-hybridization test. Males of the new species can be recognized on the basis of body length averaging 1396.2 μm; lateral field with one ridge; metastome isoglottoid with one hemispherical swellings comprised of two to three well-developed warts; asymmetric spicules; peloderan bursa. In IJs, EP = 134.5 μm; ES = 149.3 μm; tail length = 82.5 μm; and a = 20.5. Hermaphroditic females have four to five lateral ridges. The 18S rDNA and ITS sequences of the two nematodes share 99% and 98% identity, respectively. Phylogenetic trees of 18S rDNA and ITS indicate that the new species is most closely related to H. chongmingensis; thus, the two nematodes belong to the same genus. Failure of cross-hybridization between them indicates that nematode strain RG081015 is a novel species and is described herein as H. rugaoensis n. sp. The LC50 of the novel species against Galleria mellonella were 24.35 IJs / ml within 48 hours of infection. Morphological characteristics, genetic similarity analyses, and phylogenetic relationships provide strong evidence that some species of Oscheius/Insectivora-group should be reassigned to the genus Heterorhabditidoides.
Entomopathogenic nematode; Heterorhabditidoides rugaoensis n. sp.; Insectivora-group; new nematode species; pathogenicity; phylogeny; Oscheius; taxonomy
Populations of Mesocriconema curvatum, M. kirjanovae, M. onoense, M. ornatum, M. sphaerocephala, M. surinamense, M. vadense, M. xenoplax, and Criconemoides informis from different geographical areas in the continental United States were characterized morphologically and molecularly. A new ring nematode from Washington County, Arkansas, is also described and named Mesocriconema ozarkiense n. sp., This new species is characterized by females with small flattened submedian lobes, lower than or at the same level as the labial disc, vagina straight, very well developed spermatheca without sperm, no more than one anastomoses, L=379-512 μm, V=89-93, stylet length = 49-61 μm, R=107-119, annuli with slightly crenate margins on tail portion and a simple anterior vulval lip. The molecular characterization of M. ozarkiense n. sp. using the ITS rRNA gene sequence and the phylogenesis relationship of this new species with the ring nematodes included in this study are provided.
Criconematidae; Criconemoides; Criconemoides informis; internal transcribed spacer 1; Mesocriconema; Mesocriconema ozarkiense n. sp. M. crenatum; M. curvatum; M. kirjanovae; M. onoense; M. ornatum; M. sphaerocephala; M. surinamense; M. vadense; M. xenoplax; molecular biology; morphology; phylogenesis; taxon
The foliar nematode Aphelenchoides besseyi causes white tip disease in rice (Oryza sativa L.) and floral malady in tuberose (Polianthes tuberosa L.). This nematode is widely distributed in the rice fields of many states of India, including West Bengal (WB), Andhra Pradesh (AP), Madhya Pradesh (MP) and Gujarat (GT). In order to generate information on intraspecific variations of A. besseyi as well as to confirm the identity of the nematode species infecting these important crops, morphological observation was undertaken of A. besseyi isolated from tuberose and rice from WB and rice from AP, MP and GT. The molecular study was only done for rice and tuberose populations from AP and WB. The variations were observed among the populations in the tail, esophageal and anterior regions, including the occurrence of four as well as six lateral lines in the lateral fields. The morphometrics of observed populations showed variations and those could be regarded as a consequence of host-induced or geographical variations. PCR amplification of the rDNA ITS 1 and 2 region of rice (AP) and tuberose (WB) populations of A. besseyi generated one fragment of approximately 830 bp, and the size of the ITS region was 788 bp and 791 bp for tuberose and rice population, respectively. Alignment of the two sequences showed almost 100% similarity. Blast analysis revealed a very high level of similarity of both the Indian strains to a Russian population. The Indian and Russian strains could be differentiated using restriction enzyme Bccl. Host tests revealed that rice (cv. IET 4094), oat (cv. OS-6) and teosinte (cv. TL-1) showed a typical distortion due to the infection of A. besseyi. Five germplasm lines of oat showed no infection of the nematode under field conditions. Local cultivars of onion, maize, chrysanthemum, gladiolus, and Sorghum halepense were also not infected by A. besseyi.
Aphelenchoides besseyi; diagnosis; distribution; host; India; morphology; rice; tuberose
Candidate grape rootstocks were selected through a rigorous screening program initiated with important sources of resistance to Meloidogyne pathotypes and to Xiphinema index in Muscadinia rotundifolia and Vitis species native to North America. Based on their rooting capability and horticultural characteristics, 200 candidates were selected from 5,000 progeny of multiple crosses between commercial grape rootstocks and wild grape species that exhibited resistance to nematodes. After a 15-year screening process, 13 selections emerged with either almost complete or complete combined resistance to M. incognita Race 3, M. incognita pathotype Harmony C, M. arenaria pathotype Harmony A, and X. index, important nematode pests of grapevines. Durability of this broad resistance was tested by challenging the selections with the target nematodes in combination and with the target nematodes in combinations with species not included in the screening process. Durability of resistance of the candidate rootstocks was also tested by exposure to the nematode communities of infested field soils from different locations. Breadth of resistance was determined on the basis of their host status to non-target nematodes, including Mesocriconema xenoplax, Pratylenchus vulnus, Tylenchulus semipenetrans and Paratylenchus hamatus. After a total of 204 separate trials, the rootstocks were released to the grape industry as UCD GRN1, UCD GRN2, UCD GRN3, UCD GRN4, and UCD GRN5. We provide a compilation of current knowledge of the host status of these five newly released rootstocks and of 27 other rootstock cultivars to plant-parasitic nematodes.
Screening; selection; host status; broad resistance; durable resistance
Multiple images of a whole nematode specimen were taken with a high power oil-immersion objective lens and joined together to form one high-resolution megapixel, mosaic photomicrograph of the entire specimen, with the use of a relatively new mounting technique made with a 4% water agar pad. The agar pad kept the specimen nearly level and lateral, and when amended with 10 mM sodium azide, this mounting technique gradually paralyzed the nematode in a natural pose to enable production of sharp, clear images. The individual photographs were joined together and merged into one very large, seamless image. These montaged images will be useful for teaching because the student has access to a virtual specimen that is mounted in the correct orientation, imaged with a research grade microscope, and preserved in a narcotized, living condition. Such specimen images can also serve as representatives of type and voucher specimens without the deterioration typical of real types. The files can be copied and viewed with a computer almost anywhere and at any time, rather than using a more cumbersome, limiting, and expensive microscope.
agar pad technique; digital micrographs; mounting nematodes; type specimens; voucher specimens
Root-knot nematode (Meloidogyne graminicola), an important and widespread pathogen, causes high yield losses in rice with limited information on wheat and on efficient management. Absence of uniform screening protocols is contributing to slow progress of host resistance development. To develop an efficient screening protocol, several greenhouse studies were conducted, and effects of incubation period, inoculum level, inoculation method, seedling age, and their interactions on root-galling severity (RGS) ratings and reproductive factor (RF) values of M. graminicola were determined. At 2 eggs/cm3 soil, significantly lower RGS but higher RF values were observed at 60 days than at 45 days of incubation. Meloidogyne graminicola reproduced six times more on rice than on wheat where the RGS index in both crops increased steadily with increasing inoculum levels, but RF increased at lower levels and decreased beyond a maximum at medium inoculum levels. Inoculum level, container size, seedling age, inoculation method, and their interactions impacted nematode infection and reproduction. The protocol was verified on eleven rice germplasm lines and seven wheat cultivars using the resistance index (RI) calculated from RGS and RF, to screen rice and wheat germplasm.
Meloidogyne graminicola; screening protocol; rice and wheat
A new genus, one new and two known species belonging to family Rhabdolaimidae are described and illustrated. Mediolaimus n. gen. is characterized by small-sized body; papilliform outer labial and cephalic sensilla; long, tubular stoma with stegostom having relatively larger dorsal and smaller sub ventral denticles at same level; cylindrical pharynx with expanded basal bulb having thickened lumen; didelphic gonad having outstretched ovaries; elongate-conoid tail with hemispherical terminus without mucro or spinneret and caudal glands obscure. Mediolaimus obtusicaudatus n. gen. n. sp. is characterized by stoma with a relatively larger dorsal denticle and two fine subventral denticles at same level; amphidelphic reproductive system with outstretched ovaries; tail elongate conoid with smooth hemispherical terminus and absence of male. Rhabdolaimus terrestris
de Man, 1880 and Udonchus tenuicaudatus
Cobb, 1913 are described with additional details. The inter population variations are discussed in the latter species along with a detailed note on the status of Rhabdolaimidae and its proposed placement under superfamily Rhabdolaimoidea of suborder Campydorina.
India; Mediolaimus obtusicaudatus; Udonchus tenuicaudatus; new genus; new species; Rhabdolaimidae; taxonomy
Soil nematode community response to treatments of three, four-year crop rotations (spring wheat-pea-spring wheat-flax, spring wheat-green manure-spring wheat-flax, and spring wheat-alfalfa-alfalfa-flax) under conventional and organic management, and native tall grass restoration (restored prairie) were assessed in June 2003, and July and August 2004. The research site was the Glenlea Long-term Rotation and Crop Management Study, in the Red River Valley, Manitoba, established in 1992. The nematode community varied more with sample occasion than management and rotation. The restored prairie favored high colonizer-persister (c-p) value omnivores and carnivores, and fungivores but less bacterivores. The restored prairie soil food web was highly structured, mature and low-to-moderately enriched as indicated by structure (SI), maturity (MI) and enrichment (EI) index values, respectively. Higher abundance of fungivores and channel index (CI) values suggested fungal-dominated decomposition. Nematode diversity was low even after more than a decade of restoration. A longer time may be required to attain higher diversity for this restored fragmented prairie site distant from native prairies. No consistent differences were found between organic and conventional management for nematode trophic abundance, with the exception of enrichment opportunists of the c-p 1 group which were favored by conventional management. Although EI was lower and SI was higher for organic than conventional their absolute values suggested decomposition channels to be primarily bacterial, and fewer trophic links with both management scenarios. A high abundance of fungivores in the rotation including the green manure indicates greater fungal decomposition.
nematode diversity; organic management; prairie restoration; soil food web