Overexpression of NtEXPA7 promotes seedling growth and resistance to root-knot nematode in tobacco.

Root-knot nematode (RKN) is one of the most damaging plant pathogen in the world. They exhibit a wide host range and cause serious crop losses. The cell wall, encasing every plant cell, plays a crucial role in defending of RKN invasion. Expansins are a group of cell wall proteins inducing cell wall loosening and extensibility. They are widely involved in the regulation of plant growth and the response to biotic and abiotic stresses. In this study, we have characterized the biological function of tobacco (Nicotiana tabacum) NtEXPA7, the homologue of Solyc08g080060.2 (SlEXPA18), of which the transcription level was significantly reduced in susceptible tomato upon RKN infection. The expression of NtEXPA7 was up-regulated after inoculation of RKNs. The NtEXPA7 protein resided in the cell wall. Overexpression of NtEXPA7 promoted the seedling growth of transgenic tobacco. Meanwhile the increased expression of NtEXPA7 was beneficial to enhance the resistance against RKNs. This study expands the understanding of biological role of expansin in coordinate plant growth and disease resistance.

Exogenous ABA promotes resistance to Sitobion avenae (Fabricius) in rice seedlings.

BACKGROUND: Over the course of evolution, plants have developed various sophisticated defense mechanisms to resist pests and diseases. The phytohormone abscisic acid (ABA) has an important role in the growth and development of plants and confers tolerance to selected abiotic stressors, such as drought. Previous studies have shown that ABA promotes the deposit of callose in response to piercing/sucking insect pests. The English grain aphid, Sitobion avenae Fabricius, causes huge losses in rice and is especially harmful to rice seedlings. RESULTS: Exogenous ABA promoted growth and reduced the feeding behavior of S. avenae nymphs in rice. Our results suggested that enhanced trichome density and increased expression of related genes may be associated with rice resistance to aphids. An analysis of volatiles revealed the production of seven compounds associated with pest resistance. CONCLUSION: These results indicate that ABA reduces aphid feeding in rice. Our findings provide a basis for understanding ABA-mediated defense responses in rice and provide insights on more environmentally-friendly approaches to control. © 2024 Society of Chemical Industry.

Effects of elevated CO2 treatment of Populus davidiana × P. bolleana on growth and detoxifying enzymes in gypsy moth, Lymantria dispar.

To date, elevated CO2 concentrations in the environment caused by various human activities influence diverse areas of life, including the interactions between insects and plants. The Lymantria dispar is one of the most severely destructive pests, which further could inflict ecological and economical damage. In this experiment, one-year-old Populus davidiana × P. bolleana plants were grown in CO2-enhanced environments for one month at three different CO2 concentrations: 397 ppm (atmospheric CO2 concentration), 550 ppm and 750 ppm (two predicted elevated CO2 concentrations). The 3rd instar L. dispar larvae then fed on the treated poplar seedlings covered in a nylon bag. The L. dispar larvae fed on poplar seedling treated for 96 h showed the highest growth rate at all CO2 concentrations. Enzymatic activity of treated larvae showed the highest GST and P450 activity at 750 ppm CO2. The relative expressions of seven CYP and ten GST genes in L. dispar larvae were analyzed quantitatively using real-time RT-PCR, which the results were expressed variably. Compared to 397 ppm CO2, the expression of CYP4L23 was down-regulated, while the expressions of other CYP genes were up-regulated. Meanwhile, only GSTo1 gene showed down-regulated at 48 h and 96 h in 750 ppm CO2 treatment, while GST expression level for the other nine GST genes showed up-regulated at 48 h and 72 h. These results offer the insight into plant-insect interactions under global climate change and furthermore will provide essential information for strategic pest control based on biochemical and molecular levels changes in gypsy moths.

A temperature-sensitive FERONIA mutant allele that alters root hair growth.

In plants, root hairs undergo a highly polarized form of cell expansion called tip-growth, in which cell wall deposition is restricted to the root hair apex. In order to identify essential cellular components that might have been missed in earlier genetic screens, we identified conditional temperature-sensitive (ts) root hair mutants by ethyl methanesulfonate mutagenesis in Arabidopsis thaliana. Here, we describe one of these mutants, feronia-temperature sensitive (fer-ts). Mutant fer-ts seedlings were unaffected at normal temperatures (20°C), but failed to form root hairs at elevated temperatures (30°C). Map based-cloning and whole-genome sequencing revealed that fer-ts resulted from a G41S substitution in the extracellular domain of FERONIA (FER). A functional fluorescent fusion of FER containing the fer-ts mutation localized to plasma membranes, but was subject to enhanced protein turnover at elevated temperatures. While tip-growth was rapidly inhibited by addition of rapid alkalinization factor 1 (RALF1) peptides in both wild-type and fer-ts mutants at normal temperatures, root elongation of fer-ts seedlings was resistant to added RALF1 peptide at elevated temperatures. Additionally, at elevated temperatures fer-ts seedlings displayed altered reactive oxygen species (ROS) accumulation upon auxin treatment and phenocopied constitutive fer mutant responses to a variety of plant hormone treatments. Molecular modeling and sequence comparison with other Catharanthus roseus receptor-like kinase 1L (CrRLK1L) receptor family members revealed that the mutated glycine in fer-ts is highly conserved, but is not located within the recently characterized RALF23 and LORELI-LIKE-GLYCOPROTEIN 2 binding domains, perhaps suggesting that fer-ts phenotypes may not be directly due to loss of binding to RALF1 peptides.

Root discoloration and shoot symptoms in silver birch after Phytophthora infection in vitro.

There are no records of established plant pathogenic Phytophthora species in Finnish forests, but they are likely in the future. Therefore, the effects of Phytophthora inoculations on young, ca. 2-month-old silver birch (Betula pendula) seedling roots and shoots were investigated. Visual inspection of dark discoloration, direct PCR and re-isolation, and detailed root morphology analyses were used to evaluate the effects of Phytophthora inoculation on roots. Symptoms in leaves and stems were also recorded. Phytophthora was successfully re-isolated from 67% of the surface-sterilized roots of inoculated seedlings, but not from the non-inoculated control seedlings. Dark discolorations were found more often in the root segments of inoculated seedlings than in control seedlings. In the Phytophthora-treated seedlings, discoloured root segments were usually linked and found primarily in the main root or lateral roots attached to it, whereas in the control seedlings a few single discoloured root segments were scattered throughout the root systems. The number of root segments was lower in the inoculated than in the control seedlings, indicating root loss after Phytophthora inoculation. In the shoots of inoculated birches, leaf and shoot wilting was observed. The appearance of wilting in shoots without visible dark discoloration in the base of stems indicated that symptoms originated from roots inoculated with Phytophthora.

Expression of Thioredoxin/Thioredoxin Reductase System Genes in Aphid-Challenged Maize Seedlings.

Thioredoxins (Trxs) and thioredoxin reductases (TrxRs) encompass a highly complex network involved in sustaining thiol-based redox homeostasis in plant tissues. The purpose of the study was to gain a new insight into transcriptional reprogramming of the several genes involved in functioning of Trx/TrxR system in maize (Zea mays L.) seedlings, exposed to the bird cherry-oat aphid (Rhopalosiphum padi L.) or the rose-grass aphid (Metopolophium dirhodum Walk.) infestation. The biotests were performed on two maize genotypes (susceptible Zlota Karlowa and relatively resistant Waza). The application of real-time qRT-PCR technique allowed to identify a molecular mechanism triggered in more resistant maize plants, linked to upregulation of thioredoxins-encoding genes (Trx-f, Trx-h, Trx-m, Trx-x) and thioredoxin reductase genes (Ftr1, Trxr2). Significant enhancement of TrxR activity in aphid-infested Waza seedlings was also demonstrated. Furthermore, we used an electrical penetration graph (EPG) recordings of M. dirhodum stylet activities in seedlings of the two studied maize varieties. Duration of phloem phase (E1 and E2 models) of rose-grass aphids was about three times longer while feeding in Waza plants, compared to Zlota Karlowa cv. The role of activation of Trx/TrxR system in maintaining redox balance and counteracting oxidative-induced damages of macromolecules in aphid-stressed maize plants is discussed.

Arbuscular mycorrhizal fungi decrease Meloidogyne enterolobii infection of Guava seedlings.

Guava (Psidium guajava L.) production is prominent in the irrigated fruit growing area of Brazil. However, the parasite Meloidogyne enterolobii (a phytonematode) has caused a decrease in guava production. Arbuscular mycorrhizal fungi (AMF) are known to be beneficial to plants; however, their ability to protect plants against nematodes such as M. enterolobii remains poorly known. This study aimed to monitor M. enterolobii infection in guava seedlings inoculated with three AMF species. After AMF inoculation, the seedlings were grown in sterile soil for 60 days before inoculation with 2000 M. enterolobii eggs. Plant growth parameters, mycorrhizal colonization and the number of Meloidogyne in the roots were determined over time (30 and 60 days after Meloidogyne inoculation). The AMF enhanced guava seedling growth, and reduced the amount of Meloidogyne in the roots at 30 and 60 days after nematode inoculation, indicating that these AMF species could serve as biocontrol agents of M. enterolobii in guava cultivation.

Changes in reflectance of rice seedlings during planthopper feeding as detected by digital camera: Potential applications for high-throughput phenotyping.

Damage to grasses and cereals by phloem-feeding herbivores is manifest as nutrient and chlorophyll loss, desiccation, and a gradual decline in host vigour. Chlorophyll loss in particular leads to a succession of colour changes before eventual host death. Depending on the attacking herbivore species, colour changes can be difficult to detect with the human eye. This study used digital images to examine colour changes of rice seedlings during feeding by the brown planthopper, Nilaparvata lugens (Stål) and whitebacked planthopper, Sogatella furcifera (Horváth). Values for red (580 nm), green (540 nm) and blue (550 nm) reflectance for 39 rice varieties during seedling seed-box tests were derived from images captured with a digital camera. Red and blue reflectance gradually increased as herbivore damage progressed until final plant death. Red reflectance was greater from plants attacked by the brown planthopper than plants attacked by the whitebacked planthopper, which had proportionately more green and blue reflectance, indicating distinct impacts by the two planthoppers on their hosts. Analysis of digital images was used to discriminate variety responses to the two planthoppers. Ordination methods based on red-green-blue reflectance and vegetation indices such as the Green Leaf Index (GLI) that included blue reflectance were more successful than two-colour indices or indices based on hue, saturation and brightness in discriminating between damage responses among varieties. We make recommendations to advance seed-box screening methods for cereal resistance to phloem feeders and demonstrate how images from digital cameras can be used to improve the quality of data captured during high-throughput phenotyping.

Identification of Naturally Occurring Polyamines as Root-Knot Nematode Attractants.

Root-knot nematodes (RKNs; genus Meloidogyne) are a class of plant parasites that infect the roots of many plant species. It is believed that RKNs target certain signaling molecules derived from plants to locate their hosts; however, currently, no plant compound has been unambiguously identified as a universal RKN attractant. To address this question, we screened a chemical library of synthetic compounds for Meloidogyne incognita attractants. The breakdown product of aminopropylamino-anthraquinone, 1,3-diaminopropane, as well as its related compounds, putrescine and cadaverine, were found to attract M. incognita. After examining various polyamines, M. incognita were found to be attracted specifically by natural compounds that possess three to five methylene groups between two terminal amino groups. Using cryo-TOF-SIMS/SEM, cadaverine was indeed detected in soybean root cortex cells and the surrounding rhizosphere, establishing a chemical gradient. In addition to cadaverine, putrescine and 1,3-diaminopropane were also detected in root exudate by HPLC-MS/MS. Furthermore, exogenously applied cadaverine is sufficient to enhance M. incognita infection of Arabidopsis seedlings. These results suggest that M. incognita is likely attracted by polyamines to locate the appropriate host plants, and the naturally occurring polyamines have potential applications in agriculture in developing protection strategies for crops from RKN infection.

Changes in the content of thiol compounds and the activity of glutathione s-transferase in maize seedlings in response to a rose-grass aphid infestation.

The rose-grass aphid (Methopolophium dirhodum Walk.) is a major pest of maize (Zea mays L.), but little is known about the biochemical interactions between M. dirhodum and its host plant. Thiol compounds and glutathione S-transferase (GST) play a crucial role in the defense responses of maize to biotic stress factors, including aphids. The purpose of this research was to evaluate the impact of M. dirhodum herbivory on the total thiol (TT), protein bound thiol (PT), reduced glutathione (GSH) and oxidized glutathione (GSSG) contents as well as the activity of GST in three varieties of Z. mays (Zlota Karlowa, Ambrozja and Plomyk), that were classified as aphid-susceptible, aphid-relatively resistant and aphid-resistant, respectively. The earliest and strongest aphid-triggered alterations in the levels of TT, PT and GSH, and the greatest induction of GST activity, were recorded in the resistant Plomyk seedlings in relation to the relatively resistant Ambrozja and the susceptible Zlota Karlowa.

Aphid-Triggered Changes in Oxidative Damage Markers of Nucleic Acids, Proteins, and Lipids in Maize (Zea mays L.) Seedlings.

Prior experiments illustrated reactive oxygen species (ROS) overproduction in maize plants infested with bird-cherry-oat (Rhopalosiphum padi L.) aphids. However, there is no available data unveiling the impact of aphids feeding on oxidative damages of crucial macromolecules in maize tissues. Therefore, the purpose of the current study was to evaluate the scale of oxidative damages of genomic DNA, total RNA and mRNA, proteins, and lipids in seedling leaves of two maize genotypes (Zlota Karlowa and Waza cvs-susceptible and relatively resistant to the aphids, respectively). The content of oxidized guanosine residues (8-hydroxy-2'-deoxyguanosine; 8-OHdG) in genomic DNA, 8-hydroxyguanosine (8-OHG) in RNA molecules, protein carbonyl groups, total thiols (T-SH), protein-bound thiols (PB-SH), non-protein thiols (NP-SH), malondialdehyde (MDA) and electrolyte leakage (EL) levels in maze plants were determined. In addition, the electrical penetration graphs (EPG) technique was used to monitor and the aphid stylet positioning and feeding modes in the hosts. Maize seedlings were infested with 0 (control), 30 or 60 R. padi adult apterae per plant. Substantial increases in the levels of RNA, protein and lipid oxidation markers in response to aphid herbivory, but no significant oxidative damages of genomic DNA, were found. Alterations in the studied parameters were dependent on maize genotype, insect abundance and infestation time.

Body position of the stink bug Dichelops melacanthus (Dallas) during feeding from stems of maize seedlings / Posição do corpo do percevejo Dichelops melacanthus (Dallas) durante a alimentação em hastes de plântulas de milho

Abstract The Neotropical green-belly stink bug, Dichelops melacanthus (Dallas) is a major pest of maize, Zea mays L. in the main production areas of Brazil. It usually feeds on the stems of young plants (seedlings) causing heavy damage by affecting the plant growth and mitigating seed yield. Laboratory studies were conducted to determine body position (upward or downward) of the bug on plant (seedling) stem during feeding and not feeding activities. Ten visual records were taken per day, each spaced one hour during 30 days of 10 adult bugs of similar age exposed to maize seedlings inside cages (plastic tubes). At each observation, it was recorded if the bug was feeding on the stem (i.e., stylets inserted into the plant tissue) or not, and its body position. During feeding, waveforms were recorded using the EPG (electropenetrography) technique, which were correlated with histological studies to reveal the feeding sites. Results indicated that when they were feeding, the majority of the bugs were in the downward position. In contrast, when the bugs were on the plants, and not feeding, they were mostly in the upward position. Waveforms generated using the EPG coupled with histological studies demonstrated that during ingestion bugs fed from the xylem vessels and from the parenchyma tissue using cell rupture strategy in the latter. No clear explanation was found to explain the preferred downward body position during ingestion, but some hypothesis are speculated.

Resumo O percevejo barriga-verde, Dichelops melacanthus (Dallas) é uma praga importante do milho, Zea mays L. nas principais áreas produtoras do Brasil. Usualmente alimenta-se nas hastes de plantas jovens (plântulas) causando danos severos no seu crescimento e reduzindo o rendimento de grãos. Estudos foram conduzidos em laboratório para determinar a posição do corpo (voltado para cima ou para baixo) dos percevejos nas hastes das plântulas de milho durante as atividades de alimentação e não-alimentação. Foram feitas dez observações por dia, espaçadas por uma hora, durante 30 dias em 10 percevejos adultos com idade semelhante sobre plântulas de milho colocadas em gaiolas (tubos de plástico). Em cada observação, anotou-se se o percevejo estava se alimentando (i.e., estiletes bucais inseridos no tecido vegetal) ou não, e a posição do corpo. Durante a alimentação, ondas eletromagnéticas foram registradas utilizando-se o EPG (técnica da eletropenetrografia), as quais foram correlacionadas com estudos histológicos para revelar os locais de alimentação. Os resultados indicaram que quando os percevejos estavam se alimentando, a maioria estava voltado para baixo. Em contraste, os percevejos sem se alimentar nas plântulas estavam a maioria voltados para cima. As ondas geradas pelo EPG junto com os estudos histológicos revelaram que os percevejos se alimentaram dos vasos do xilema e do tecido parenquimatoso usando a estratégia de ruptura celular no último. Não foi encontrada uma explicação clara para a preferência dos percevejos em se alimentarem na posição voltados para baixo, mas algumas hipóteses são especuladas.

Body position of the stink bug Dichelops melacanthus (Dallas) during feeding from stems of maize seedlings.

The Neotropical green-belly stink bug, Dichelops melacanthus (Dallas) is a major pest of maize, Zea mays L. in the main production areas of Brazil. It usually feeds on the stems of young plants (seedlings) causing heavy damage by affecting the plant growth and mitigating seed yield. Laboratory studies were conducted to determine body position (upward or downward) of the bug on plant (seedling) stem during feeding and not feeding activities. Ten visual records were taken per day, each spaced one hour during 30 days of 10 adult bugs of similar age exposed to maize seedlings inside cages (plastic tubes). At each observation, it was recorded if the bug was feeding on the stem (i.e., stylets inserted into the plant tissue) or not, and its body position. During feeding, waveforms were recorded using the EPG (electropenetrography) technique, which were correlated with histological studies to reveal the feeding sites. Results indicated that when they were feeding, the majority of the bugs were in the downward position. In contrast, when the bugs were on the plants, and not feeding, they were mostly in the upward position. Waveforms generated using the EPG coupled with histological studies demonstrated that during ingestion bugs fed from the xylem vessels and from the parenchyma tissue using cell rupture strategy in the latter. No clear explanation was found to explain the preferred downward body position during ingestion, but some hypothesis are speculated.

Volatile unsaturated hydrocarbons emitted by seedlings of Brassica species provide host location cues to Bagrada hilaris.

Bagrada hilaris Burmeister, is a stink bug native to Asia and Africa and invasive in the United States, Mexico, and more recently, South America. This species can cause serious damage to various vegetable crops in the genus Brassica, with seedlings being particularly susceptible to B. hilaris feeding activity. In this study, the role of volatile organic compounds (VOCs) emitted by seedlings of three Brassica species on the host preference of B. hilaris was evaluated. In dual choice arena and olfactometer bioassays, adult painted bugs preferred B. oleracea var. botrytis and B. napus over B. carinata. Volatiles from B. oleracea seedlings were collected and bioassayed with B. hilaris adults and late stage nymphs, using electroantennographic (EAG) and behavioral (olfactometer) techniques. When crude extracts of the VOCs from B. oleracea var. botrytis seedlings and liquid chromatography fractions thereof were bioassayed, B. hilaris adults and nymphs were attracted to the crude extract, and to a non-polar fraction containing hydrocarbons, whereas there were no responses to the more polar fractions. GC-MS analysis indicated that the main constituents of the non-polar fraction was an as yet unidentified diterpene hydrocarbon, with trace amounts of several other diterpene hydrocarbons. The major diterpene occurred in VOCs from both of the preferred host plants B. oleracea and B. napus, but not in VOCs of B. carinata. Our results suggest that this diterpene, alone or in combination with one or more of the minor compounds, is a key mediator in this insect-plant interaction, and could be a good candidate for use in lures for monitoring B. hilaris in the field.

Aphid parasitism and parasitoid diversity in cotton fields in Xinjiang, China.

Aphids are major pests of cotton crops in the Xinjiang Uygur Autonomous Region in China, and parasitoids are considered as important natural enemies in regulating aphid populations. However, information on aphid parasitoids in the Xinjiang cotton fields is limited, which hinders the study of aphid-parasitoid interactions and the application of conservation biological control against cotton aphids. In this study, a 3-year survey was conducted in a large geographical range that included three primary cotton planting areas in southern and northern Xinjiang. The population dynamics and the parasitism levels of an assemblage of aphids in the cotton fields were investigated along with the composition of the parasitoid community associated with these aphids. Aphid parasitization varied significantly within both years and seasons, with parasitism levels ranging from 0 to 26%, indicating that there is less effective biological control of parasitoids on aphids under field conditions. Among the primary parasitoids described, Binodoxys communis (Gahan) constituted 95.19% of the parasitoid species, followed by Praon barbatum Mackauer (3.15%), Trioxys asiaticus Telenga (1.01%) and Lysiphlebus fabarum Marshall (0.65%). Significant differences were found in the composition of the primary parasitoid species between the cotton seedling period (June) and the flowering period (July-August), and two more primary aphid parasitoids were found in the seedling period. Twelve hyperparasitoid species belonging to six genera were found in our study, of which Pachyneuron aphidis (Bouché), Syrphophagus species and Dendrocerus laticeps (Hedicke) were the dominant species. The composition of the hyperparasitoid community also differed significantly between the seedling and the flowering periods. The description of this parasitoid community-associated assemblage of aphids in cotton fields will facilitate the study of aphid-parasitoid interactions and promote the development of effective cotton aphid management strategies in Xinjiang.

Detection of Two Peronospora spp., Responsible for Downy Mildew, in Opium Poppy Seed.

Downy mildew is a serious threat to opium poppy production globally. In recent years, two pathogen species, Peronospora somniferi and Peronospora meconopsidis, which induce distinct symptoms, have been confirmed in Australia. In order to manage the spread of these pathogens, identifying the sources of inoculum is essential. In this study, we assessed pathogen presence associated with poppy seed. We developed PCR and qPCR assays targeting the coxI and coxII gene regions, for the detection, differentiation, and quantification of P. somniferi and P. meconopsidis in poppy seed. These results were complemented and compared with direct seed histological examination and a seed washing combined with viability staining for oospore detection. The majority of seed lots from all harvest years contained detectable P. meconopsidis, the earliest (1987) predating the first official record of the disease in Tasmania (1996). In contrast, only seed lots harvested in 2012 or later contained P. somniferi, evidence of its more recent introduction. P. meconopsidis contamination was estimated to be as high as 33.04 pg DNA/g of seed and P. somniferi as high as 35.17 pg DNA/g of seed. Incidence of pathogen contamination of seeds, estimated via a group testing protocol, ranged from 0 to 9% (P. meconopsidis) or 0 to 11% (P. somniferi). Mycelia were predominately found external to the seed coat. Seed washing and viability staining demonstrated that putatively viable oospores were present in the majority of seed lots. Transmission testing confirmed both pathogens can be successfully transmitted from infested seed to infected seedling. PCR and qPCR pathogen assays were found to be reliable and offer a routine test for determining pathogen inoculum in poppy seeds.

The Effect of Cold Stress on Damping-Off of Soybean Caused by Pythium sylvaticum.

To improve our understanding of the timing of cold stress and its effect on Pythium damping-off, we performed a factorial experiment with two cold stress temperatures (4 and 10°C); exposure to 96 h of cold stress at 0, 1, 2, 4, 6, and 8 days after planting; and inoculation with Pythium sylvaticum-infested millet or control. Increased susceptibility to damping-off resulting in reduced emergence was found in inoculated plants when the cold stress period began 2 or 4 days after planting. In the noninoculated controls, no effect of cold stress on emergence was observed. Slower seedling growth was observed during the cold stress period and in inoculated plants after exposure to cold stress. Seed exudation, mycelial growth, and sporangia germination of P. sylvaticum was evaluated at 4, 10, and 18°C. The greatest seed exudation was observed at 4°C. Low temperatures delayed mycelial growth of P. sylvaticum, although the pathogen was still able to grow at 4°C. Sporangia incubated for 3 h at 18°C in the presence of seed exudates had higher germination in comparison with sporangia incubated at 10 or 4°C. Moreover, more sporangia germinated in response to seed exudates that were previously collected from seed imbibed for 24 h at low temperatures (4°C). These results suggest that cold stress 2 to 4 days after planting increases soybean susceptibility to damping-off, presumably because of increased seed exudation and delayed seedling growth.

Responses of Heterodera glycines and Meloidogyne incognita Infective Juveniles to Root Tissues, Root Exudates, and Root Extracts from Three Plant Species.

The infective juvenile (J2) stage of endoparasitic plant nematodes uses plant chemical signals, released from roots, to localize and infect hosts. We examined the behaviors of soybean cyst nematode (Heterodera glycines) and root-knot nematode (Meloidogyne incognita) J2 in the presence of root signals from marigold (Tagetes patula), soybean (Glycine max), and pepper (Capsicum annuum). Signals were obtained from sources commonly used in phytoparasitic nematode chemotaxis studies: root tips, root exudates, and root extracts. Root tips from each plant species attracted M. incognita but H. glycines was attracted only to soybean. In contrast, root exudates prepared from marigold, pepper, or soybean seedlings were attractive to H. glycines but were repellent to M. incognita. Root extracts had the same effect as exudates. Fractionation of exudates by reversed-phase high-performance liquid chromatography (HPLC) (acetonitrile [CH3CN] and 0.1% trifluoroacetic acid) revealed highly polar and less polar components affecting behaviors. Fractions eluting at 12% CH3CN from all three plants attracted H. glycines and repelled M. incognita. None of the less polar HPLC fractions (>15% CH3CN) affected H. glycines but those from G. max and T. patula repelled M. incognita. Differences among exudates and effects of fractionation on behavior are discussed.

Potent Attractant for Root-Knot Nematodes in Exudates from Seedling Root Tips of Two Host Species.

Root-knot nematodes (RKN; Meloidogyne spp.) can parasitize over 2,000 plant species and are generally considered to be the most agriculturally damaging group of plant-parasitic nematodes worldwide. Infective juveniles (J2) are non-feeding and must locate and invade a host before their reserves are depleted. However, what attracts J2 to appropriate root entry sites is not known. An aim of this research is to identify semiochemicals that attract RKN to roots. J2 of the three RKN species tested are highly attracted to root tips of both tomato and Medicago truncatula. For both hosts, mutants defective in ethylene signaling were found to be more attractive than those of wild type. We determined that cell-free exudates collected from tomato and M. truncatula seedling root tips were highly attractive to M. javanica J2. Using a pluronic gel-based microassay to monitor chemical fractionation, we determined that for both plant species the active component fractionated similarly and had a mass of ~400 based on size-exclusion chromatography. This characterization is a first step toward identification of a potent and specific attractant from host roots that attracts RKN. Such a compound is potentially a valuable tool for developing novel and safe control strategies.

Single-generation effects on terpenoid defenses in lodgepole pine populations following mountain pine beetle infestation.

The recent mountain pine beetle outbreak in western Canada provides an opportunity to study the selection and heritability of tree defenses. We examined terpenoid-based defenses of seedling lodgepole pines which were offspring of mature trees subjected to high levels of mountain pine beetle selective pressure. Seedlings were grown from one of three types of cones: old cones on live trees; young cones on live trees; and cones on trees killed by beetles. Offspring thus represented crosses of non-surviving (NS) x surviving (S), S x S, and NS x NS parents, respectively. Methyl jasmonate was used to induce a defensive reaction in the seedlings. Seed source had a significant effect on levels of ten different terpenes, but not on total terpene concentrations. When the seedlings were grouped by location and treatment type, the seedlings of different cone types could be almost entirely distinguished by terpene profiles.