Juvenile Nematodes Research Articles

A rice root-knot nematode Meloidogyne graminicola-resistant mutant rice line shows early expression of plant-defence genes

Resistance to rice root-knot nematode Meloidogyne graminicola in a mutant rice line is suggested to be conferred by higher expression of several genes putatively involved in damage-associated molecular pattern recognition, secondary metabolite biosynthesis including phytoalexins, and defence-related genes. Meloidogyne graminicola has emerged as the most destructive plant-parasitic nematode disease of rice (Oryza sativa L.). Genetic resistance to M. graminicola is one of the most effective methods for its management. A M. graminicola-resistant O. sativa ssp. indica mutant line-9 was previously identified through a forward genetic screen (Hatzade et al. Biologia 74:1197-1217, 2019). In the present study, we used RNA-Sequencing to investigate the molecular mechanisms conferring nematode resistance to the mutant line-9 compared to the susceptible parent JBT 36/14 at 24h post-infection. A total of 674 transcripts were differentially expressed in line-9. Early regulation of genes putatively related to nematode damage-associated molecular pattern recognition (e.g., wall-associated receptor kinases), signalling [Nucleotide-binding, Leucine-Rich Repeat (NLRs)], pathogenesis-related (PR) genes (PR1, PR10a), defence-related genes (NB-ARC domain-containing genes), as well as a large number of genes involved in secondary metabolites including diterpenoid biosynthesis (CPS2, OsKSL4, OsKSL10, Oscyp71Z2, oryzalexin synthase, and momilactone A synthase) was observed in M. graminicola-resistant mutant line-9. It may be suggested that after the nematode juveniles penetrate the roots of line-9, early recognition of invading nematodes triggers plant immune responses mediated by phytoalexins, and other defence proteins such as PR proteins inhibit nematode growth and reproduction. Our study provides the first transcriptomic comparison of nematode-resistant and susceptible rice plants in the same genetic background and adds to the understanding of mechanisms underlying plant-nematode resistance in rice.

Root Endophytism by Pochonia chlamydosporia Affects Defense-Gene Expression in Leaves of Monocot and Dicot Hosts under Multiple Biotic Interactions.

A study was carried out on the effect of the root endophytic fungus Pochonia chlamydosporia on plant systemic signal of defense related genes during fungal or nematode parasitism. Different biotic stress factors were examined, inoculating roots of dicot and monocot hosts with the endophyte, and measuring the expression of defense genes in leaves. A first greenhouse assay was carried out on expression of PAL, PIN II, PR1 and LOX D in leaves of tomato cv Tondino inoculated with Phytophthora infestans (CBS 120920), inoculating or not the roots of infected plants with P. chlamydosporia DSM 26985. In a second assay, plants of banana (Musa acuminata cv Grand Naine) were artificially infected with Fusarium oxysporum f. sp. cubense Tropical race 4 (TR4) and inoculated or not with DSM 26985. In a further experiment, banana plants were inoculated or not with P. chlamydosporia plus juveniles of the root knot nematode (RKN) Meloidogyne incognita. A similar assay was also carried out in vitro with adults and juveniles of the lesion nematode Pratylenchus goodeyi. Differential expression of the defense genes examined was observed for all plant-stress associations, indicative of early, upward systemic signals induced by the endophyte. Changes in expression profiles included a 5-fold down-regulation of PIN II at 2 dai in leaves of tomato plants treated with P. infestans and/or P. chlamydosporia, and the up-regulation of PAL by the endophyte alone, at 2 and 7 dai. In the TR4 assay, PR1 was significantly up-regulated at 7 dai in banana leaves, but only in the P. chlamydosporia treated plants. At 10 dai, PIN II expression was significantly higher in leaves of plants inoculated only with TR4. The banana-RKN assay showed a PR1 expression significantly higher than controls at 4 and 7 dai in plants inoculated with P. chlamydosporia alone, and a down-regulation at 4 dai in leaves of plants also inoculated with RKN, with a PR1 differential up-regulation at 10 dai. Pratylenchus goodeyi down-regulated PIN at 21 dai, with or without the endophyte, as well as PAL but only in presence of P. chlamydosporia. When inoculated alone, the endophyte up-regulated PR1 and LOX. The gene expression patterns observed in leaves suggest specific and time-dependent relationships linking host plants and P. chlamydosporia in presence of biotic stress factors, functional to a systemic, although complex, activation of defense genes.

Efficacy of aqueous extracts of some solanaceous plants on juveniles mortality and egg hatching on the root knot nematode, Meloidogyne javanica under laboratory conditions

Aqueous extracts of black nightshade, Solanum nigrum; deadly nightshade, Atropa belladonna; Egyptian henbane, Hyoscyamus muticus; thorn apple, Datura innoxia; ashwagndha, Withania somnifera leaves and fruits of chili pepper, Capsicum frutescens were assessed on juvenile mortality and egg hatching of the root knot nematode, Meloidogyne javanica in vitro. The nematode mortalities were in the range of (54.33 to 100.0 %) in concentrations S/16, S/8 and S/4 compared to distilled water (1.33 %) and increased with the increase of the exposure time from 24 to 72 hrs. Deadly nightshade and chili pepper extracts were the most effective against second stage juveniles of nematode at concentration of S/4, followed by aqueous extracts of ashwagndha, thorn apple, black nightshade. Result showed that, the highest reduction in hatching inhibition percentage was recorded with concentration (S/4) of ashwagndha (97.63 %) followed by Egyptian henbane, deadly nightshade, black nightshade, thorn apple and chili pepper with inhibition percentages as (95.42, 94.60, 92.87, 79.61 and 67.97%) respectively.

Assessing the predatory activity of Arthrobotrys oligosporus strain C-2197 as biocontrol of the root-knot nematode Meloidogyne spp.

The root-knot nematode, Meloidogyne spp., is an endoparasite that infects plants' root system and causes yield losses in several important crops. Meloidogyne is one of the most devastating pests, so searching for effective biological agents is needed to mitigate its damage. In this study, the predatory activity of Arthrobotrys oligosporus Fresen strain C-2197, obtained from a tropical dry forest of Ecuador, was evaluated as a biocontrol alternative for root-knot caused by Meloidogyne spp. Our results showed that A. oligosporus C-2197 has predatory activity against juvenile nematodes, 72.31%, and 79% efficacy, for in vitro and greenhouse conditions. Besides, the studied strain showed growth-promoting activity, increasing leaf and root area of inoculated plants. Growth promoting activity was also observed in field tests. The present study validates the potential use of A. oligosporus as a biocontrol of Meloidogyne spp. in tomato production systems under greenhouse. It also presents useful information on the use of different cultivation media and substrates for massive A. oligosporus spore concentrates.

Screening of peach rootstock hybrids for resistance to root-knot nematode

Two peach genotypes ‘Sharbati’ and ‘Flordaguard’ were crossed to develop F1 hybrid rootstocks and subsequently tested for resistance against root-knot nematode. Minimum reduction in plant height after 120 days of nematode inoculation was recorded in Flordaguard (11.07%), it was followed by Sharbati × Flordaguard (16.73%). Sharbati × Flordaguard seedlings inoculated with nematode juveniles had high plant height, root length, leaf chroma, ‘b’ values, hue angle, leaf size and leaf area. Flordaguard seedlings had higher shoot dry weight, ‘a’ value, spad values, petiole length and leaf number but, lower plant height, leaf area, leaf size, chroma values, hue angle. Hybrid seedlings from both the cross combinations had dark red coloured young leaves, a trait from Flordaguard. Number of juveniles penetrated the root system was negatively correlated with shoot dry weight, internodal length, leaf number, petiole length, spad values, ‘a’ value shoot dry weight and positively correlated with ‘L’value, ‘b’ value, chroma and hue angle. The highest number of juvenile penetration per root system was recorded in Sharbati with (38 juvenile per roots system) followed by seedlings of Sharbati × Flordaguard (15 juvenile per root system) and Flordaguard × Sharbati (11 juveniles per root system). Shoot dry weight, internodal length, petiole length, spad values, ‘a’ value, and hue angle vary among the hybrid seedlings with lower nematode population and root penetration whereas higher nematode population and root penetration were abserved among the seedling population. These characters can be used to assess nematode tolerance/resistance in peach hybrid seedlings.

First report of Seville root-knot nematode, Meloidogyne hispanica (Nematoda: Meloidogynidae) in the USA and North America.

A high number of second stage juveniles of the root-knot nematode were recovered from soil samples collected from a corn field, located in Pickens County, South Carolina, USA in 2019. Extracted nematodes were examined morphologically and molecularly for species identification which indicated that the specimens of root knot juveniles were Meloidogyne hispanica. The morphological examination and morphometric details from second-stage juveniles were consistent with the original description and redescriptions of this species. The ITS rRNA, D2-D3 expansion segments of 28S rRNA, intergenic COII-16S region, nad5 and COI gene sequences were obtained from the South Carolina population of M. hispanica. Phylogenetic analysis of the intergenic COII-16S region of mtDNA gene sequence alignment using statistical parsimony showed that the South Carolina population clustered with Meloidogyne hispanica from Portugal and Australia. To our best knowledge, this finding represents the first report of Meloidogyne hispanica in the USA and North America.

Behavioral and molecular response of the insect parasitic nematode Steinernema carpocapsae to cues emitted by a host, the red palm weevil, Rhynchophorus ferrugineus

As the larvae of the date palm pest, the red palm weevil, Rhynchophorus ferrugineus, feeds on the host tissue, they emit a distinctive sound which can be recorded outside of the infected tree. We evaluated the response of infective juveniles (IJs) of the entomopathogenic nematodes Steinernema carpocapsae to the R. ferrugineus larvae and it’s sound source, separately. In the presence of the insect larvae, 50.2 % of total IJs moved toward those larvae. Recorded insect larvae sound emitted by the speaker resulted in 7% of total IJs near the sound source. RNA-Seq data indicated that more genes were downregulated in S. carpocapsae IJs exposed to insect and speaker compared to non-stimulated IJs. IJs exposed to insect exhibited more up-regulated genes than IJs exposed to speaker. Enriched pathways and biological processes in IJs were similar for both stimuli. The inhibition of locomotion, regulation of neurotransmitter secretion, response to biotic stimulus, and cellular response to chemical stimuli were enriched with unique GO terms for speaker treatment. The regulation of localization, sodium ion transmembrane transport, regulation of response to stress and response to organic substances were the GO categories enriched unique to insect. The host-parasitic interaction was regulated by the differential expression of Ras/MAP kinase, TGF-beta signaling, insulin signaling, AMPK signaling, PPAR signaling pathways and many developmental pathways. More prominent R. ferrugineus host localization by S. carpocapsae was primarily due to the differential transcriptional regulation of olfactory signal transduction, FOXO-family proteins, calcium signaling, WNT and mTOR signaling pathway. The neural basis for the nematode attraction to insect host is based on the chemosensation and the mechanosensation. Many neuropeptides and neuromodulators are involved in regulating the foraging behavior of S. carpocapsae. The results of this study provide new insights into the molecular mechanisms that allow these nematodes to seek insect hosts. Our finding, especially the molecular ones suggest that chemical cues emitted by the active insect host are stimulants of nematodes attraction. Whereas the sound emitted by the insect has minor effects on the nematode behavior.

Fluopyram Controls Shoot-galling Caused by Pacific Shoot-gall Nematode and Improves Turf Quality in Annual Bluegrass Putting Greens

Golf courses in coastal regions of northern California are often faced with severe injury caused by pacific shoot-gall nematodes (Anguina pacificae) on their annual bluegrass (Poa annua) host in putting greens. For years, fenamiphos was used for mitigating disease outbreaks until its registration was withdrawn in 2008. An alternative product containing azadirachtin was intended for nematode suppression. Still, it required repeated applications throughout the year with questionable efficacy, making attempts to lessen the impact of the pathogen costly. This study evaluated fluopyram as a novel nematicide for control of pacific shoot-gall disease. Various application frequencies and rates were tested at several golf courses affected by the nematode. Results revealed that fluopyram applied once at 0.22 lb/acre reduced the number of new shoot-galls and improved annual bluegrass appearance for several months. Increased rates and application frequency occasionally improved the efficacy further. Although the visual quality of turf treated with this plant protection compound was tremendously enhanced, and the number of new shoot-galls was reduced, rarely a significant effect was observed on the population density of several soil-dwelling plant-parasitic nematodes, including pacific shoot-gall nematode. It is hypothesized that fluopyram did not move significantly past the thatch layer and into the soil. However, it effectively reduced the ability of pacific shoot-gall nematode juveniles to induce new shoot galls. Due to its long half-life, it likely protected against both new nematode infections and dissemination of pacific shoot-gall nematode when the shoot-galls decomposed.

UDP-Glycosyltransferases and Albendazole Metabolism in the Juvenile Stages of Haemonchus contortus.

The nematode Haemonchus contortus, a gastrointestinal parasite of ruminants, can severely burden livestock production. Although anthelmintics are the mainstay in the treatment of haemonchosis, their efficacy diminishes due to drug-resistance development in H. contortus. An increased anthelmintics inactivation via biotransformation belongs to a significant drug-resistance mechanism in H. contortus. UDP-glycosyltransferases (UGTs) participate in the metabolic inactivation of anthelmintics and other xenobiotic substrates through their conjugation with activated sugar, which drives the elimination of the xenobiotics due to enhanced solubility. The UGTs family, in terms of the biotransformation of commonly used anthelmintics, has been well described in adults as a target stage. In contrast, the free-living juvenile stages of H. contortus have attracted less attention. The expression of UGTs considerably varies throughout the life cycle of the juvenile nematodes, suggesting their different roles. Furthermore, the constitutive expression in a susceptible strain with two resistant strains shows several resistance-related changes in UGTs expression, and the exposure of juvenile stages of H. contortus to albendazole (ABZ) and ABZ-sulfoxide (ABZSO; in sublethal concentrations) leads to the increased expression of several UGTs. The anthelmintic drug ABZ and its primary metabolite ABZSO biotransformation, tested in the juvenile stages, shows significant differences between susceptible and resistant strain. Moreover, higher amounts of glycosidated metabolites of ABZ are formed in the resistant strain. Our results show similarly, as in adults, the UGTs and glycosidations significant for resistance-related differences in ABZ biotransformation and warrant further investigation in their individual functions.

Surrounding the swollen roots of sweetpotato with a decomposing band of an organic amendment enhances nematode-suppressive services and reduces damage caused by root-knot nematode

A previous field trial showed that marketable yield increased and root-knot nematode populations declined when the swollen roots of sweetpotato were surrounded by a sawdust-based amendment. Further evidence that such amendments provide worthwhile levels of nematode control was obtained in this study. Customised pots filled with an organic amendment or amended soil were kept in a greenhouse or buried in the field for various times and then the nematode-control potential of various treatments was assessed by surrounding the pots with soil infested with Meloidogyne incognita. Swollen root production generally increased, and root-knot nematode populations consistently declined, when sawdust was used as an amendment. The addition of an organic nitrogen source generally improved the level of control. Laboratory and greenhouse assays confirmed that amended soils were biologically suppressive, as root-knot nematode numbers were lower and fewer galls were produced in soil containing decomposing amendments than in soil or sand that had been heated to kill the soil biota. A predatory nematode morphologically similar to Clarkus papillatus was one of the suppressive agents as numbers were very high in some experiments. Mesostigmatid mites in the family Laelapidae and genera Sejus, Protogamasellus, Holaspulus and Gamasiphis were also contributing, while an acarid mite (Rhizoglyphus robini) occurred in high numbers and was observed devouring root-knot nematode juveniles on agar plates. Nematophagous fungi were also involved as three species of nematode-trapping fungi (Arthrobotrys musiformis, A. thaumasia and A. oligospora) and an unidentified fungus that captures nematodes on bulbous hyphal extensions were consistently isolated from amended soils. These results suggest that sawdust-based amendments enhance the nematode-suppressive services provided by a wide range of predators.

Xenorhabdus nematophila bacteria shift from mutualistic to virulent Lrp-dependent phenotypes within the receptacles of Steinernema carpocapsae insect-infective stage nematodes.

Xenorhabdus nematophila bacteria are mutualists of Steinernema carpocapsae nematodes and pathogens of insects. Xenorhabdus nematophila exhibits phenotypic variation between insect virulence (V) and the mutualistic (M) support of nematode reproduction and colonization initiation in the infective juvenile (IJ) stage nematode that carries X. nematophila between insect hosts. The V and M phenotypes occur reciprocally depending on levels of the transcription factor Lrp: high-Lrp expressors are M+V- while low-Lrp expressors are V+M-. We report here that variable (wild type) or fixed high-Lrp expressors also are optimized, relative to low- or no-Lrp expressors, for colonization of additional nematode stages: juvenile, adult and pre-transmission infective juvenile (IJ). In contrast, we found that after the bacterial population had undergone outgrowth in mature IJs, the advantage for colonization shifted to low-Lrp expressors: fixed low-Lrp expressors (M-V+) and wild type (M+V+) exhibited higher average bacterial CFU per IJ than did high-Lrp (M+V-) or no-Lrp (M-V-) strains. Further, the bacterial population becomes increasingly low-Lrp expressing, based on expression of an Lrp-dependent fluorescent reporter, as IJs age. These data support a model that virulent X. nematophila have a selective advantage and accumulate in aging IJs in advance of exposure to insect hosts in which this phenotype is necessary.

콩씨스트선충(Heterodera glycines)과 반짝이콩씨스트선충(H. sojae)의 온도별 부화와 살선충 물질에 대한 알과 유충의 약제 반응 비교

콩씨스트선충(Heterodera glycines)과 반짝이콩씨스트선충(H. sojae)의 온도별 부화와 살선충 물질에 대한 알과 유충의 약제 반응 비교

Occurrence of two species of Bursaphelenchus (Nematoda: Aphelenchoididae) in the reproductive organs of Monochamus saltuarius (Coleoptera: Cerambycidae)

Summary To clarify the species composition and residency of Bursaphelenchus nematodes in the bodies of Monochamus saltuarius adults, we dissected 70 adults that had emerged from cut pine bolts set at two locations at the frontline of pine wilt disease spread in Nagano Prefecture, Japan. Fourth-stage dispersal juveniles of Bursaphelenchus nematodes were detected in 39 insects; PCR-based identification showed that the insects mainly harboured B. mucronatus, but could sometimes harbour B. xylophilus or both. Detailed dissection of 17 insects revealed that hundreds of Bursaphelenchus nematodes were often found in the reproductive organs of both sexes, including the inner parts such as the internal sac and the ejaculatory ducts in males. Thus, the residence of Bursaphelenchus nematodes in the reproductive organs of their vectors is not an accidental invasion but indicative of the phoretic nature of the nematodes.

Monochamus Saltuarius Endangers Pinus tabuliformis Carr. and Carries Bursaphelenchus xylophilus (Steiner and Buhrer) in China

The pinewood nematode (Bursaphelenchus xylophilus) can cause fatal damage to trees and is transmitted by the vector species of the Monochamus genus. In December 2017, pinewood nematodes were found to be harming a large plot of pine trees, Pinus tabuliformis, in a new region with an average annual temperature of 6.7 °C in China. However, the vector insects were unknown and urgently needed to be identified. Hence, in April 2018, we collected wood sections of P. tabuliformis trees that had died from pine wilt disease. All 127 longhorn beetles that emerged from the P. tabuliformis samples were identified as Monochamus saltuarius, and the nematodes they carried were fourth-stage dispersal juveniles of the pinewood nematode. The carrier rate of pinewood nematodes in the M. saltuarius population was 58.3%, and the average carrying capacity was 642.4 ± 89.3. In the same P. tabuliformis plot, 742 M. saltuarius beetles were collected from hormone traps. Our results revealed that M. saltuarius can damage P. tabuliformis and is a new vector species of the pinewood nematode in China. These findings can inform the prevention and control of pinewood nematode damage to pine forests.

Investigation of Pinewood Nematodes in Pinus tabuliformis Carr. under Low-Temperature Conditions in Fushun, China

In recent years, the pinewood nematode has continuously adapted to low-temperature environments and expanded from the South to the North of China. In December 2018, a large area of pinewood nematode was suspected to be harmful to Pinus tabuliformis under natural conditions in Fushun City, Liaoning Province. In order to clarify the low-temperature environment and population characteristics of pinewood nematodes in this new epidemic area, we analyzed the difference in temperature between the inside and outside of P. tabuliformis in low-temperature environments, conducted the morphological and molecular identification of pinewood nematodes in P. tabuliformis, summarized the distribution characteristics of the wintering of pinewood nematodes and explored the population structure of pinewood nematodes under different low-temperature conditions. The results indicated that the diurnal variation of temperature in dead P. tabuliformis was significantly less than the environment temperature. The lowest temperature in P. tabuliformis was 3.2 °C higher than the lowest temperature in the environment in one day; the pathogen of a large area of dead P. tabuliformis in Fushun was pinewood nematode (Bursaphelenchus xylophilus); 84.9% of the average populations of pinewood nematodes were third-stage dispersal juveniles, which mainly gathered in 5 cm within the pupal chamber of Monochamus saltuarius Gebler. At −40 ℃, most of the third-stage dispersal juveniles of pinewood nematode in dead pine can still survive. Our study laid a foundation for the understanding of the low-temperature adaptation mechanism of pinewood nematode and contributed to the monitoring of pine wilt disease in the mid-temperate zone.

Aqueous extracts of Crambe abyssinica seed cake: Chemical composition and potential for nematode control

Plants of the family Brassicaceae are known to produce compounds with nematicidal activity, such as glucosinolates. Although these compounds may find application in the control of plant-parasitic nematodes, they are generally obtained as hydroalcoholic extracts, which can be toxic to plants and the environment. This study investigated the chemical composition of aqueous extracts of crambe (Crambe abyssinica Hochst ex Re Fries) seed cake and their efficiency in controlling the root-knot nematode Meloidogyne javanica (Treub) Chitwood in soybean (Glycine max (L.) Merrill). Four extraction methods were used: water extraction at 25 °C, water extraction at 100 °C, autoclave treatment of a crambe cake/water mixture, autoclave treatment of crambe cake followed by water extraction at room temperature. Compounds were determined by high-performance liquid chromatography and nuclear magnetic resonance spectroscopy. Extracts were diluted to 5, 10, 15, 20, and 25% (v/v) in distilled water for determination of their effects on M. javanica egg hatching and juvenile mortality (in vitro) and nematode reproduction on soybean (in vivo). Chromatographic analysis identified the following nematicidal compounds (100 g−1): gallic acid (250.15 mg), syringic acid (201.46 mg), hydroxybenzoic acid (175.05 mg), chlorogenic acid (129.81 mg), ferulic acid (41.82 mg), trans-cinnamic acid (28.40 mg), and coumaric acid (16.75 mg). Sucrose and epiprogoitrin were detected in a proportion of 56.73 to 43.27%. All extracts reduced egg hatching and increased juvenile mortality, reaching a plateau at a concentration of about 5%. Extract concentrations of 5% and higher decreased nematode reproduction, with the maximum effect estimated to occur at 13%. Crambe cake extracts also increased plant height, shoot fresh weight, and root fresh weight. The compounds from aqueous extracts of crambe seed cake, acting together or separately, may be responsible for the suppressive effects of nematodes and plant growth promoters.

In-vitro and In-vivo management of Meloidogyne incognita (Kofoid and White) Chitwood and Rhizoctonia bataticola (Taub.) Butler in cotton using organic's.

Root-knot nematodes Meloidogyne incognita (Kofoid and White) Chitwood and Rhizoctonia bataticola (Taub.) Butler, fungus, are very dangerous root damaging pathogens. Present study was planned to establish a chemical control of these root deteriorating pathogens under lab conditions as well as in field. Maximum death rate of nematode juveniles and minimum numbers of nematode eggs hatched were recorded in plates treated with Cadusafos (Rugby® 100G) @12 g/100 ml and Cartap® (4% G) @9g/100 ml. Chemical treatment of Rhizoctonia bataticola with Trifloxystrobin + Tebuconazole (Nativo®) @0.2 g/100 ml and Mancozeb + Matalaxyl (Axiom) @0.25 g/100 ml significantly controlled the mycelial growth in plates. The best treatments tested in laboratory were applied in field as protective and curative treatments. Results proved that chemical control of root-knot nematode and root rot fungi by tested chemicals at recommended time and dose is a significant management technique under field conditions.

The Screening of Resistance against Meloidogyne graminicola in Oats

Including pest resistance elements against the major local concern is naturally important in the breeding process. Oat (Avena sativa L.) has been recently reintroduced into Taiwan as a winter alternative forage crop, and its agronomic performance has been evaluated at different locations in the country. This study examined the resistance to root-knot nematode, Meloidogyne graminicola, in four oat (Avena sativa L.) breeding lines of mass planting potential for winter in Taiwan. The host attraction level to the nematode, and the penetration and reproduction ability of nematode towards host roots were evaluated by chemotaxis assay, root staining assay, root galling, and nematode extraction. Based on the gall index (GI) and multiplication factor (R), the resistance of each oat line was evaluated. At 24 h postinoculation, second-stage juvenile (J2) nematodes appeared most attracted by oat breeding lines UFRGS136104-3 and UFRGS136119-2. The number of J2s successfully penetrated into the two breeding lines were also high. However, at 40 days postinoculation, observation of the oats in the newly developed culture bag nematode-inoculation system revealed that the amount of root galls and 2nd generation nematodes were significantly higher in line LA08085BS-T2 than in other lines. In sum, oat breeding line UFRGS136104-3 was highly resistant to M. graminicola by inhibiting the gall formation and nematode reproduction, while UFRGS136106-3 and UFRGS136119-2 showed relatively weak resistance and oat line LA08085BS-T2 would be a moderately susceptible host to M. graminicola, with high numbers of root gall formation. The outcome of this study provides ground information for nematode-resistant oat cultivar breeding.

Constituents Leached by Tomato Seeds Regulate the Behavior of Root-Knot Nematodes and Their Antifungal Effects against Seed-Borne Fungi.

Germinating seeds can release diverse phytochemicals that repel, inhibit, or kill pathogens such as root-knot nematodes and seed-borne fungi. However, little is known about the composition of these phytochemicals and their effects on pathogens. In this study, we demonstrated that tomato seed exudates can attract the nematode Meloidogyne incognita using a dual-choice assay. Eighteen compounds were then isolated and identified from the exudates. Of these, esters (1-3), fatty acids (4-6), and phenolic acids (10-12) were proven to be the signaling molecules that facilitated the host-seeking process of second-stage juveniles (J2s) of nematodes, while alkaloids (17 and 18) disrupted J2s in locating their host. Furthermore, some phenolic acids and alkaloids showed antifungal effects against seed-borne fungi. In particular, ferulic acid (12) showed obvious activity against Aspergillus flavus (minimum inhibitory concentration (MIC), 32 μg/mL), while dihydrocapsaicin (17) showed noticeable activity against Fusarium oxysporum (MIC, 16 μg/mL). Overall, this study presents the first evidence that M. incognita can be attracted to or deterred by various compounds in seed exudates through identification of the structures of the compounds in the exudates and analysis of their effects on nematodes. Furthermore, some antifungal compounds were also found. The findings of this work suggest that seed exudates are new source for finding insights into the development of plant protective substances with nematocidal and antifungal effects.

Nematicidal effects of piperine on the pinewood nematode Bursaphelenchus xylophilus

The plant-parasitic nematode Bursaphelenchus xylophilus is a notorious forest pest and the cause of pine-wilt disease which is becoming a serious issue in Asia and Europe. Few available pesticides or nematicides effectively kill B. xylophilus and the topic is the subject of on-going research. This study describes the killing effects of three constituents (piperine, piperlongumine, and piperonal) of the long pepper on the pinewood nematode juveniles. Piperine at 50 µg/mL achieved killing of B. xylophilus juveniles in 6 h, and uniquely, the pattern of killing involved rapid curling (1 h), aggregation (2 h), and death (6 h). Also, piperine adversely affected the fecundity and locomotor traits in B. xylophilus while piperine had marginal effect on the growth of plant seed germination. Computational studies showed piperine interacts with the Gln219 residue of glutamate gated chloride ion channel (GluCl) receptor, a residue associated with receptor activation. Furthermore, the mode of action of piperine resembled that of ivermectin in in silico studies. These results suggest that piperine (the major component of peppers) be regarded a potential nematicide for pinewood nematodes and warrant further field investigations.