Nematicidal activity of anion transport blockers against Meloidogyne incognita, Caenorhabditis elegans and Heterorhabditis bacteriophora

BACKGROUND: Because methyl bromide has been phased out as a soil sterilant, new nematicides are urgently needed. Four different chemical classes of organic acids acting as anion transport (AT) blockers were tested against a free-living nematode, Caenorhabditis elegans Maupas, a plant-parasitic nematode, Meloidogyne incognita (Kofoid and White) Chitwood, and an entomopathogenic nematode, Heterorhabditis bacteriophora Poinar, in toxicity bioassays. The materials tested were DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid), 9-AC (anthracene-9-carboxylic acid), NPPB [5-nitro-2-(3-phenylpropylamino)benzoic acid] and IAA-94 (indanyloxyacetic acid). RESULTS: All the compounds showed slowly developing nematicidal activity against second-stage juveniles of M. incognita and adults of C. elegans, but not against H. bacteriophora infective-stage juveniles. The LC(50) values of these compounds were < 50 mg L(-1) after 48 and 72 h incubation, while at 168 h incubation the LC(50) values were < 10 mg L(-1) for both sensitive species. Across both species and time, the LC(50) values generally differed no more than twofold among the four compounds tested in this study. In contrast, none of the compounds (200 mg L(-1)) caused more than control mortality to H. bacteriophora, even after 168 h of incubation. CONCLUSION: These compounds are potential leads for commercial nematicides. The insensitivity to H. bacteriophora is consistent with the natural exposure of this nematode to DST (3,5-dihydroxy-4-isopropylstilbene), a stilbene produced by its symbiotic bacterium. Based on the known activity of the compounds used in this study, it is suggested that anion transporters form the probable target sites for DIDS, 9-AC, NPPB and IAA-94 in nematodes.     

Short soaking in water inhibits germination of Datura ferox L. and D. stramonium L. seeds

Summary. Seed coat structures may play a major role in determining the germination of seeds. The involvement of seed coat characteristics in the inhibition of germination observed when dry seeds of Datura ferox L. and D. stramonium L., were rinsed or soaked in water for 1–5 min ('soaking effect') was investigated. Germination was inhibited by soaking D. ferox seeds even at late stages of the germination process up to one day before root protrusion. Simulation of the 'soaking effect' was achieved by blocking the hilum with lanolin, enamel lacquer or agar during imbibition. Blocking the hilum did not prevent water uptake by the seeds. Seed coat integrity was necessary for the 'soaking effect' since germination inhibition was eliminated by removing or cracking the seed coat. Drying the seeds up to 12 h after soaking reversed the inhibitory effect. SEM observations of both species revealed a loose outer parenchymatous tissue covering the hilum, an inner spongy tissue between the nucellus and the hilum and a space between the seed coat and the nucellus. We concluded that during soaking, water is trapped in the space between the seed coat and the nucellus, and in the intracellular spaces of the spongy tissue within the hilum. This water 'plug' may limit the diffusion of gas(es) to and from the embryo through the hilum, thus inhibiting germination.     

Weed hosts of Meloidogyne spp. and the effect of aqueous weed extracts on egg hatching

Weeds have a great economic impact on agricultural production because they compete with crops for resources and are alternative hosts for pests, microbial pathogens and plant-parasitic nematodes. This study aimed to investigate the susceptibility of weeds to the root-knot nematodes Meloidogyne javanica and Meloidogyne incognita and assess the effect of aqueous weed extracts on M. javanica egg hatching. Four experiments were conducted, two for each nematode species. Weeds were inoculated with 2000 nematode eggs and grown for 60 days under greenhouse conditions. Soyabean cv. Monsoy 7110 was used as control. The weeds Ipomoea grandifolia, Solanum americanum, Digitaria horizontalis, Amaranthus deflexus, Sorghum halepense and Commelina benghalensis were susceptible to M. javanica and M. incognita in at least one experiment (reproduction factor, RF >1). Crotalaria juncea and Eleusine indica were susceptible to M. incognita in one experiment, and Digitaria insularis, Sida rhombifolia, Bidens pilosa, Urochloa decumbens, Crotalaria breviflora, Cenchrus echinatus, Crotalaria ochroleuca and Crotalaria spectabilis were immune or resistant (RF <1 or RF = 0). Alternanthera tenella, C. juncea, S. rhombifolia, C. ochroleuca, C. spectabilis, C. breviflora, B. pilosa, E. indica, U. decumbens and C. echinatus were resistant or immune to M. javanica (RF <1 or RF = 0). Compared with the control (water), all weed extracts reduced M. javanica egg hatch. Our results highlight the importance of weed control in agricultural systems, as nematodes can survive and multiply in weed roots during the off-season. Weed leaves and shoots, however, may be an interesting source of compounds with nematicidal activity.     

不同植物秸秆对番茄及南方根结线虫的影响

为有效防治南方根结线虫,本试验研究了添加不同剂量的玉米秸秆(8.32、4.16、2.08g/kg)、辣椒秸秆(4.16、2.08、1.04g/kg)和茵陈蒿秸秆(4.16、2.08、1.04g/kg)对温室大棚番茄及根结线虫的影响。结果显示,在根结线虫侵染的土壤中添加植物秸秆后30d,玉米秸秆(4.16、2.08g/kg)对番茄株高有显著影响,辣椒(4.16、1.04g/kg)和茵陈蒿(4.16、2.08g/kg)秸秆对番茄茎粗影响显著;60d时经茵陈蒿处理的番茄植株比对照生长发育良好,对形态指标的影响程度依次为茎粗开花分枝;120d时番茄的茎粗、分枝和果实重量均显著高于对照。末次接种后20d调查,每种作物秸秆处理以高剂量对根结线虫的防治效果最好,防治效果依次为:茵陈蒿秸秆辣椒秸秆玉米秸秆,分别为79.60%、71.32%、68.89%,表明茵陈蒿秸秆处理既可降低根结线虫危害程度,又可提高番茄产量。本研究为温室大棚有效防治根结线虫提供了依据。     

Diversity of Meloidogyne incognita populations from cotton and aggressiveness to Gossypium spp. accessions

The root-knot nematode (RKN) Meloidogyne incognita is the main nematode causing losses to the cotton crop in Brazil. In order to implement control strategies within integrated management, an accurate identification of the nematode populations prevailing in the cotton production areas is necessary. This study aimed to assess the genetic variability and aggressiveness of RKN populations from cotton production areas in Bahia state, Brazil. All populations were characterized biochemically and molecularly and identified as M. incognita. RAPD and AFLP markers detected 44% of polymorphic fragments among the 13 populations of this species. The 10 M. incognita populations collected in Bahia presented 33.7% of diversity when compared to each other, and 25% when the population from Barreiras (the most polymorphic) was excluded. This polymorphism increased when populations from other Brazilian states were included. The aggressiveness and virulence among populations from Bahia towards different cotton accessions (susceptible/resistant) was also studied. None of the populations showed virulence against the moderately resistant (Clevewilt 6, Wild Mexican Jack Jones and LA 887) and highly resistant (CIR1348 and M-315 RNR) cultivars. Two M. incognita populations from Barreiras were the most aggressive, reaching reproduction factors of 539 and 218, respectively, in the susceptible cultivar FiberMax 966. The most aggressive population (8) was also the most genetically divergent in phylogenetic analyses. These results demonstrate that diversity of M. incognita populations from cotton farms in Bahia is not related to virulence against resistant accessions, which suggests that cultivars containing one or two resistance genes with good agronomic characteristics could be used in infested commercial areas in Bahia state, Brazil.     

南方、花生和爪哇根结线虫PCR检测方法

为快速、准确、稳定的鉴定南方、花生和爪哇根结线虫,利用已报道的南方和爪哇根结线虫的两对特异性引物,结合本研究设计的花生根结线虫特异性引物,通过优化PCR反应体系,建立了3种根结线虫的PCR检测方法。结果表明,该方法能够特异性扩增以上3种根结线虫,特征片段长度分别为399、335和670 bp,灵敏度达到单条2龄幼虫的水平。研究结果将为以上3种根结线虫的快速鉴定提供技术支持。     

Nematicidal fluorescent pseudomonads for the in vitro and in vivo suppression of root knot (Meloidogyne incognita) of Capsicum annuum L

BACKGROUND: Considerable attention has been paid to plant‐growth‐promoting rhizobacteria (PGPR), especially the fluorescent group of Pseudomonas species, as the best alternatives to chemicals for facilitating ecofriendly biological control of soil‐ and seedborne microorganisms. On the basis of their novel plant‐growth‐promoting attributes, two rhizobacteria Pseudomonas aeruginosa VP1 and VP2 selected out of over 63 isolates from the rhizosphere of chilli (Capsicum annuum) were identified as potential candidates for biocontrol of the root‐knot nematode Meloidogyne incognita on chilli. RESULTS: The nematicidal activity of both strains was evaluated in vitro and in vivo for their efficacy against M. incognita. P. aeruginosa VP2 exhibited strong nematicidal activity in comparison with VP1, based on the in vitro killing of the second‐stage juveniles (J2) of M. incognita. Seed bacterisation with both strains VP1 and VP2 was able to manage root‐knot M. incognita on chilli (C. annuum) in a pot trial study. Increase in root and shoot length and in fresh and dry weight of root and shoot and reduction in the root‐knot index over the control were attained. In overall performance, VP2 was 29.5% more effective than VP1, and about 30% more effective than the control (non‐bacterised). CONCLUSION: The application of P. aeruginosa VP1 and P. aeruginosa VP2 controls the development of M. incognita in C. annuum, and hence they are recommended as efficient plant growth promotors and biocontrolling agents for raising healthy crop of C. annuum that can promote the growth of plants and reduce the nematode (M. incognita) population. Copyright © 2012 Society of Chemical Industry     

Control of Datura stramonium L. with oxadiazon under simulated spray and furrow irrigation

Cotton, soybeans and the weed species Datura stramonium L. were grown in the glasshouse under simulated spray and furrow irrigation. Oxadiazon at different rates was applied as a pre-emergence treatment. The number of Datura, was decreased by higher rates of oxadiazon under spray irrigation but not with sub-irrigation. Control at 4 kg/ha with spray irrigation was 75% but less than 15% with sub-irrigation. Soybeans were less tolerant to oxadiazon than cotton but phytotoxicity was evident in both crops at 4 kg/ha. La lutte contre le Datura stramonium L. avec l'oxadiazon sous irrigation simulée par aspersion ou par submersion. Du coton, des sojas et une espèce de mauvaise herbe: Datura stramonium L., ont été cultivés en serre, sous irrigation simulée par aspersion ou par submersion. L'oxadiazon a été appliqué h différents taux en traitement de prévlevée. Le nombre de Datura a été diminué parles doses les plus élevées d'oxadiazon sous irrigation par aspersion mais pas par submersion. L'efBcacité herbicide à,4 kg/ha a été de 57% avec l'irrigation par aspersion mais moins de 15% avec l'irrigation par submersion. Les sojas se sont montrés moins résistants à l'oxadiazon que le coton, mais la phytotoxicitéétait évidente dans ces deux cultures à 4 kg/ha. Die Bekämpfung von Datura stramonium L. mit Oxadiazon unter simulierter Beregnung und Furchenbewässerung Baumwolle, Sojabohnen und das Unkraut Datura stramonium L. wurden unter simulierter Beregnung und Furchenbewasserung im Gewachshaus gezogen. Oxadiazon wurde mit verschiedenen Aufwandmengen im Vorauflauf angewendet. Bei hoheren Aufwandmengen ging die Anzahl von Datura bei Beregnung zuruck, nicht aber bei UntergrundbewSsser-ung. Bei 4 kg/ha und Beregnung betrug die Bekampfung 75 %, bei UntergrundbewSsserung aber weniger als 15%. Die Sojabohnen waren gegenuber Oxadiazon weniger tolerant als Baumwolle, aber bei beiden Kulturpflanzen trat bei 4 kg/ha Phytotoxizitat auf.     

Virulence of Meloidogyne incognita populations and Meloidogyne enterolobii on resistant cucurbitaceous and solanaceous plant genotypes

Journal of Plant Diseases and Protection - Root-knot nematodes (Meloidogyne spp.) cause extensive damage to tomato and cucurbit crops in protected cultivation systems. An environmentally benign...     

阿维菌素和硫线磷对南方根结线虫的毒力

利用阿维菌素和硫线磷处理南方根结线虫离体卵与幼虫,测试其对线虫卵和卵块孵化以及对2龄幼虫的致死作用、活动能力、侵入能力的影响。结果表明阿维菌素和硫线磷均对线虫卵和卵块的孵化表现很强的抑制作用,阿维菌素5 μg/mL处理24 h对卵孵化抑制率高达82.57%,而硫线磷40 μg/mL处理24 h对卵孵化抑制率为73.05%;阿维菌素和硫线磷处理48 h对2龄幼虫的LD50分别为7.346 1、13.345 6 μg/mL;在阿维菌素2 μg/mL和硫线磷3 μg/mL处理中,2龄幼虫在沙柱中的平均移动距离仅为0.04 cm和0.05 cm,而对照处理的线虫平均移动距离为1.04 cm;在阿维菌素2 μg/mL和硫线磷50 μg/mL处理2龄幼虫48 h后,对番茄根部的侵入率为0.12%和0.45%,而空白对照处理线虫的侵入率达21.85%。     

温度和湿度对南方根结线虫存活的影响

在实验室条件下,测试了不同温度处理对离体南方根结线虫存活的影响,结果表明,在25、30、35℃和40℃下,杀死90%以上离体南方根结线虫分别需要30d(100%)、26d(96.6%)、24d(94.1%)和9d(99.6%),而45、50℃下则需要15min和2.3min。同时测试了不同温湿度处理对土壤中南方根结线虫存活的影响,结果表明,25、30℃是土壤中根结线虫的适宜温度,当土壤含水量为14%时,40d死亡率分别为91.1%、90.4%;35℃线虫处于抑制状态,40d死亡率为85.3%;而线虫对40℃以上的高温敏感,随着处理温度升高,杀死线虫所需时间缩短。根结线虫在不同温湿度下的死亡情况不同,土壤温度为25～35℃,土壤含水量为6%是线虫的适宜湿度;土壤温度达到40℃且含水量为6%和14%时,杀死100%根结线虫仅需4d,不利于其存活;而50℃的高温和含水量达18%的高湿更不利于其存活。     

Nematicidal activity of the leaf powder and extracts of Myrtus communis against the root‐knot nematode Meloidogyne javanica

Nematicidal activity of the leaf powder, leaf extracts and formulated leaf extracts of Myrtus communis, an evergreen shrub that is widely distributed in Israel and other Mediterranean countries, was evaluated using the root‐knot nematode Meloidogyne javanica in in vitro and pot experiments. Leaf powder added to sand at 0·1% (w/w) reduced the number of juveniles recovered from the sand by more than 50%. Reduction in galling index and number of nematode eggs on tomato roots was also observed by incorporating the leaf powder at 0·1–0·4% (w/w) in the soil in pot experiments. Leaf powder extracts with methanol or ethanol showed the highest nematicidal activity among all extracts tested. Emulsifiable concentrates of leaf‐paste extract at a concentration as low as 0·005% (a.i., w/w) reduced the number of juveniles recovered from treated sand and the gall index of cucumber seedlings. The extract paste at 26 g m^?2 was also effective in reducing the gall index of tomato plants in field‐plot experiments. The leaf powder at 0·2% and the formulated leaf‐paste extract at 0·02% were also nematicidal to Tylenchulus semipenetrans and Ditylenchus dipsaci, but not to Pratylenchus penetrans or Steinernema feltiae. At least three nematicidal compounds were found in the leaf extract upon fractionation by thin‐layer chromatography. The results suggest that the leaf powder and paste extract of M. communis are potential nematicides against root‐knot nematodes.     

Velvetbean (Mucuna pruriens) extracts: impact on Meloidogyne incognita survival and on Lycopersicon esculentum and Lactuca sativa germination and growth

Velvetbean (Mucuna spp.) is a summer annual that has been used as a cover crop to reduce erosion, fix nitrogen and suppress weeds and plant-parasitic nematodes. Crude aqueous extracts (1:15 dry weight plant/volume water) were made from velvetbean plant parts, and various concentrations of the extracts were evaluated in vitro for toxicities to different stages of Meloidogyne incognita (Kofoid and White) Chitwood and for suppression of hypocotyl and root growth and inhibition of germination of tomato (Lycopersicon esculentum L.) and lettuce (Lactuca sativa L.). Germination was only affected by the full-strength extract from leaf blades. Lettuce root growth was the most sensitive indicator of allelopathic activity of the plant part extracts. Lettuce and tomato root growth was more sensitive to the extract from main roots than to extracts of other plant parts, with lethal concentration (LC50) values of 1.2 and 1.1% respectively. Meloidogyne incognita egg hatch was less sensitive to extracts from velvetbean than the juvenile (J2) stage. There was no difference among LC50 values of the extracts from different plant parts against the egg stage. Based on LC50 values, the extract from fine roots was the least toxic to J2 (LC50 39.9%), and the extract from vines the most toxic (LC50 7.8%). The effects of the extracts were nematicidal because LC50 values did not change when the extracts were removed and replaced with water.     

Dose-response effects of clove oil from Syzygium aromaticum on the root-knot nematode Meloidogyne incognita

BACKGROUND: Clove oil, derived from the plant Syzygium aromaticum (L.) Merr. & Perry, is active against various organisms, and was prepared in a soy lecithin/detergent formulation to determine concentrations active against the root-knot nematode Meloidogyne incognita (Kofoid and White) Chitwood. RESULTS: In microwell assays, the mean effective clove oil concentration that reduced egg hatch by 50% (EC(50)) was 0.097% (v/v) clove oil; the EC(50) for second-stage juvenile (J2) viability was 0.145% clove oil (compared with carrier control treatments). Volatiles from 5.0% clove oil reduced nematode egg hatch in water by 30%, and decreased viability of hatched J2 by as much as 100%. Reductions were not as large with nematodes in carrier. In soil trials with J2 recovered from Baermann funnels, the EC(50) = 0.192% clove oil (compared with water controls). CONCLUSION: The results demonstrated that the tested formulation is active against M. incognita eggs and J2, that the EC(50) values for J2 in the microwell studies and the soil recovery tests were similar to each other and that direct contact with the clove oil is needed for optimal management results with this natural product.     

Effects of shade on reproduction and some morphological characteristics oi Abutilon theophrasti Medicos, Datura stramonium L. and Sorghum halepense L. Pers.

Relations between availability of light and reproductive activity in several of the most damaging summer weeds (Abutilon theophrasti Medicus, Datura stramonium L., Sorghum halepense L. Pers.) were studied, in order to investigate seed production capacity of these weed species in the unfavourable conditions occurring under a crop canopy simulated by shade cloths. Decrease in seed production under shading appeared to be due to a decrease in the number of fruits per plant, while the quantity of seed per fruit proved to be fairly stable. Biomass partitioning within the plant reduced the percentage of dry matter accumulated in reproductive organs, leading to a marked decrease in the harvest index. Further-more, shading caused a species-dependent delay in onset of the flowering and ripening stages. In Datura stramonium shading led to a greater de-crease in seed production and, consequently, in the harvest index than in the other species examined. Finally, laboratory tests demonstrated that the percentage of dormant seeds remained unmodified in all species examined. Effet de l'ombragesur la reproduction et quelques caracteristiques morphologiques de Abutilon theophrasti Medicus, Datura stramonium E. et Sorghum halepense L. Pers. Les relations entre la fourniture de lumière et l'activité reproductrice de quelques unes des mauvaises herbes les plus importantes (Abutilon tiieophrasti Medicus, Datura stramonium L., Sorghum halepense L. Pers.) ont étéétudiées en vue de déterminer leur capacitéà produire des graines dans les conditions défavorables qui prévalent sous les couverts végétaux. La diminution de la production de graines était due à une diminution du nombre de fruit par plante, alors que la quantité de graines par fruits restait à peu près stable. La distribution de la biomasse dans la plante conduisait à une diminution du pour-centage de matière seche accumulée dans les organes reproducteurs, ce qui se traduisait par une diminution de l'indice de récolte. De plus, l'ombrage causait un retard (variable selon l'espece) du début de la floraison et de la maturation. Chez Datura stramonium, l'ombrage conduisait à la réduction la plus importante de la production de graines (et par conséquent de l'indice de récolte). Enfin, des tests en laboratoire ont montré que le pourcentage de graines dormantes n'était modifie chez aucune des espèces testées. Einfluß von Beschattung auf Vermehrung und morphologische Eigenschaften von Abutilon theophrasti Medicus, Datura stramonium E. und Sorghum halepense (E.) Pers. An einigen sommerannuellen Unkräutem (Abutilon theophrasti Medicus, Datura stramonium L. und Sorghum halepense (L.) Pers.) wurde die Beziehung zwischen der Lichtverfügbarkeit und der Samenproduktion dieser Arten unter den ungünstigen Bedingungen der Beschattung in einem Kulturpflanzenbestand, die durch Beschattungsgewebe simuliert wurde, untersucht. Die Abnahme der Samenproduktion bei Beschattung ist durch die geringere Fruchtzahl pro Pflanze bedingt; die Samenzahl pro Frucht erwies sich als ziemlich stabil. Die Biomasseverteilung in den Pflanzen führte zu einer Abnahme der Trockenmasse der Reproduktionsorgane und damit zu einem deutlich kleineren Ertragsindex. Außerdem wurden durch die Beschattung der Blühbeginn und das Reifestadium verzögert. Bei Datura stramonitim war die Abnahme der Samenbildung und somit des Ertragsindex stärker als bei den anderen Arten. Der Anteil dormanter Samen blieb bei alien Arten durch die Beschattung einbeeinflußt.     

南方根结线虫对生姜生长及内源激素的影响

 试验结果表明,南方根结线虫侵染生姜后,首先损伤根系,进而显著降低生姜植株的株高、地上鲜重、根系鲜重和根茎重,减产47.96%。南方根结线虫侵染可使生姜叶片中赤霉素(GA)、吲哚乙酸(IAA)、玉米素核苷(ZR)含量显著降低,感病生姜的脱落酸(ABA)则表现为前期降低,后期增加的趋势,并促使叶片中GA/ABA的迅速下降,严重影响了生姜的生长,使感病植株矮小、叶片黄化,提前衰老。感病生姜根茎GA、IAA、ZR、ABA的变化规律与叶片相似,但9月份ZR、IAA含量的迅速上升,与根结线虫建立侵染据点、形成巨型细胞,从而造成根茎的局部疣裂有关。南方根结线虫侵染可引起病株根系GA/ABA升高以及GA含量在生长后期上升,促进营养物质向根部运输,从而造成根系的补偿性生长;但IAA和ZR含量的下降不利于根结线虫建立侵染据点,不能在根系中形成过多的根结。     

Biometrical, biological, biochemical and molecular characteristics of Meloidogyne incognita isolates and related species

Meloidogyne incognita is one of the most polyphagous species of root-knot nematodes occurring in Brazil and worldwide. Eight M. incognita isolates were studied, representing two enzymatic phenotypes (esterase and malate desydrogenase: I1/N1, I2/N1) and four cryptic Meloidogyne sp.1 (S2/N1) isolates, representing one cytological type (3n?=?40–46). Three M. hispanica isolates (Hi3/N1, 2n?=?32–36) and two of an atypical Meloidogyne sp.2 (S2a/N3, 3n?=?40–44) were included in this study for comparison. All isolates were tested with three M. incognita-specific molecular markers. The primer pairs B06F/R, miF/R and incK14F/R amplified three species-specific fragments of 1,200?bp, 955?bp and 399?bp, respectively for M. incognita and Meloidogyne sp.1 isolates. No amplification occurred in the M. hispanica and Meloidogyne sp.2 isolates, except with primers miF/R (1,650?bp). The genetic variability of the Meloidogyne spp. isolates was evaluated, using RAPD and ISSR markers. The phylogenetic analyses revealed two strongly supported monophyletic clades: clade I, consisting of M. hispanica and the atypical Meloidogyne sp.2 isolates, and clade II, clustering together all M. incognita and the Meloidogyne sp.1 isolates. Considering the biometrical, cytological and molecular approaches, it was possible to conclude that the isolates with three enzymatic phenotypes (I1/N1, I2/N1 and S2/N1) presented the characteristics described for M. incognita. Some correlations were detected between the isozymatic phenotypes and the tree topology (S2a/N3, Hi3/N1, I1/N1, S2/N1), but no strict correlation could be observed for the phenotype I2/N1 and one isolate of S2/N1. Morphologically, the Msp.2 isolates differ from M. incognita and M. hispanica by the female stylet features presenting straight cone tip and round pear shaped knobs, posteriorly sloping. The results of this study suggested that the Msp.2 isolates with phenotypes S2aN3 belong to a new or an unidentified species closely related to M. hispanica.