Chemical signals coordinate the dispersal of a plant-parasitic nematode with the metamorphosis of its vector beetle

With the support by the National Natural Science Foundation of China and the Chinese Academy of Sciences,Prof.Sun Jianghua(孙江华),Zou Zhen and Zhao Lilin et al.at the State Key Laboratory of Integrated Management of Pest Insects and Rodents,Institute of Zoology,Chinese Academy of Sciences,uncovered that ascarosides coordinate the dispersal of a plant-parasitic nematode with the metamorphosis

Large-scale interplant exchange of macromolecules between soybean and dodder under nutrient stresses

Parasitic plants and their hosts communicate through haustorial connections.Nutrient deficiency is a common stress for plants,yet little is known about whether and how host plants and parasites communicate during adaptation to such nutrient stresses.In this study,we used transcriptomics and proteomics to analyze how soybean(Glycine max)and its parasitizing dodder(Cuscuta australis)respond to nitrate and phosphate deficiency(-N and-P).After-N and-P treatment,the soybean and dodder plants exhibited substantial changes of transcriptome and proteome,although soybean plants showed very few transcriptional responses to-P and dodder did not show any transcriptional changes to either-N or-P.Importantly,large-scale interplant transport of mRNAs and proteins was detected.Although the mobile mRNAs only comprised at most 0.2%of the transcriptomes,the foreign mobile proteins could reach 6.8%of the total proteins,suggesting that proteins may be the major forms of interplant communications.Furthermore,the interplant mobility of macromolecules was specifically affected by the nutrient regimes and the transport of these macromolecules was very likely independently regulated.This study provides new insight into the communication between host plants and parasites under stress conditions.

Natural nematicidal active compounds:Recent research progress and outlook

Plant-parasitic nematodes cause substantial economic losses to global agriculture yearly.The use of nematicides is an effective way of controlling plant-parasitic nematodes.However,the long-term use of traditional organophosphorus and carbamate chemical nematicides can lead to increased nematode resistance.With the increasing awareness of the necessity for the protection of the environment and human health,highly toxic nematicides no longer meet the developmental requirements of modern agriculture.Recently,many studies have been undertaken on the isolation and nematicidal activity of natural products against plant-parasitic nematodes and Caenorhabditis elegans.As an important model nematode,C.elegans plays a vital reference role in studying plant-parasitic nematodes regarding nematicidal activity,metabolic mechanism,and modes of action and target.We reviewed the latest research progress of natural nematicidal active compounds against plantparasitic nematodes and C.elegans over the past ten years,discussed the structure-activity relationship and mechanism of action,and examined the development and application of natural nematicidal active compounds.

Biofumigation: An alternative strategy for the control of plant parasitic nematodes

Plant-parasitic nematodes wreak havoc on the yield and quality of crops worldwide.Damage from these pests is estimated to exceed US$100 bllion annually but is likely higher due to misdiagnosis.Nematode damage may be catastrophic,but historically the solution has been damaging as well.Use of the synthetic nematicide methyl bromide(MBr)poses risks to the environment and to human health.Biofumigation,the use of plant material and naturally produced compounds to control pests,is an increasingly feasible method of pest management.The process acts through the growth or incorporation of plant material into the soil,that,over the course of its degradation,releases glucosinolates that break down into nematotoxic isothiocyanates.These secondary plant metabolites exist naturally in commonly grown plants,most of which belong to the Brassicaceae family.Research endeavors have increasingly explored the potential of biofumigation.The reaction of target pests,the selection of biofumigant,and ideal environments for efficacy continue to be evaluated.This review seeks to provide a cost and benefit assessment of the status of biofumigation for the control of plant-parasitic nematodes as an alternative to conventional methyl bromide usage.

Molecular and morphological characterization of stunt nematodes of wheat, maize, and rice in the savannahs of northern Nigeria

Stunt nematodes(Tylenchorhynchus spp.)are obligate migratory root ecto-parasitic nematodes found in the fields of many cultivated crops.These nematodes,with phyto-sanitary potential,are frequently ignored or misdiagnosed as pests,and this may pose a threat to food security.The accuracy of its identification based on a morphological approach has been challenged recently,due to the overlapping of the morphological and morphometric characters of the species.Consequently,the objective of this study is to identify and characterize stunt nematodes present in 54 fields cultivated with cereal crops(wheat,maize and rice)in the savannahs of northern Nigeria,using integrative taxonomy and molecular approaches.The molecular and morphological studies identified and confirmed the presence of T.annulatus as the occurring specie in the savannahs of northern Nigeria.The phylogenetic analysis was carried out using the internal transcribed spacer(ITS)and 28S genes of ribosomal DNA further confirmed the presence of T.annulatus.The first molecular characterization and sequences of the ITS and 28S rDNA gene for T.annulatus from Nigeria were provided by this research.Also,according to our literature search,this is the first report on T.annulatus in wheat,maize and rice in the savannahs of northern Nigeria.Further study to test the pathogenicity of the parasitic nematode species found in this survey is recommended for the prioritization and development of efficient management strategies.

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 aminopropylam ino-anthraquinone,1,3-diam inopropane,as well as its related compounds,putrescine and cadaverine,were found to attract M.incognita.After exam ining various polyamines,M.incognita were found to be attracted specifically by natural com pounds that possess three to five methylene groups between two terminal amino groups.Using cryo-TO F-SIM S/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-diam inopropane were also detected in root exudate by HPLC-MS/MS.Furtherm ore,exogenously applied cadaverine is sufficient to enhance M.incognita infection of Arabidopsis seedlings.These results suggest that M.incognita is likely attracted by polyam ines 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.

Biofumigation effects of brassicaceous cover crops on soil health in cucurbit agroecosystems in Hawaii, USA

Brassicaceous cover crops, such as brown mustard (Brassica juncea) and oil radish (Raphanus sativus), are commonly used for biofumigation, a process that utilizes isothiocyanates (ITCs) generated from the hydrolysis of glucosinolates in Brassica plants to suppress soil-borne pathogens, including plant-parasitic nematodes. Given the biocidal nature of ITCs, limited information is available on the non-target effects of biofumigation on free-living nematodes, which are reliable soil health indicators. The objectives of this study were to determine if biofumigation methods effective against plant-parasitic nematodes would have non-target effects on free-living nematodes, and to examine the relationships between biofumigation indicators and nematode communities. Three field trials were conducted to examine whether different biofumigation methods would affect free-living nematodes. Tissue maceration of biofumigant crops, soil tillage, and black plastic mulching were adopted singly or in combination to generate different regimes of biofumigation efficacy. Termination of biofumigant crops by tissue maceration and soil tillage followed by black plastic mulching for one week was most effective in suppressing plant-parasitic nematodes and enhancing bacterial decomposition. However, these effects did not last through the subsequent zucchini (Cucurbita pepo) crop cycle. When comparing changes in soil glucose and sulfate concentrations as indicators of biofumigation efficacy, we found that soil sulfate was a better indicator of biofumigation efficacy than soil glucose, owing to the more stable state of sulfate in soil. Canonical correspondence analysis between soil sulfate as a biofumigation indicator and nematode soil health indicators revealed strong positive correlations of sulfate level with the abundances of bacterivorous and carnivorous nematodes, enrichment index, brown mustard biomass, and soil temperature. However, biofumigation did not affect the nematode community structure. This study demonstrated that biofumigation can suppress plant-parasitic nematodes without compromising soil health.

Carbon nanomaterial addition changes soil nematode community in a tall fescue mesocosm

Carbon nanomaterials have been widely used in industry and inevitably enter the environment.However,there is little information about their influence on the abundance and diversity of soil nematode community.We evaluated the impact of three kinds of carbon nanomaterials(graphene,graphene oxide,and carbon nanotubes)on the abundance and diversity of soil nematodes after growing tall fescue for 130 d using a laboratory pot experiment.A total of 29 genera of nematodes were identified in all the treatments.Carbon nanomaterials significantly increased the abundance of total nematodes and plant parasites.The presence of graphene and graphene oxide increased the numbers of bacterivores,and graphene benefited fungivores.The total nematode abundance was1.9-2.9 times greater in the carbon nanomaterial treatments than in the control with no carbon nanomaterial addition.However,graphene oxide and carbon nanotubes decreased the values of nematode community parameters,e.g.,diversity,species richness,and structure index.Compared with the control,the addition of graphene resulted in a community with a higher plant-parasitic index(i.e.,the maturity index of the plant-parasitic nematodes).Overall,our findings highlight that the addition of carbon nanomaterials has a negative influence on the composition and diversity of the nematode community,simplifying the community structure.

New insights on the utilization of ultrasonicated mustard seed cake:chemical composition and antagonistic potential for root-knot nematode,Meloidogyne javanica

This study focused,for the first time,on the effect of ultrasonic features on the extraction efficiency of secondary metabolites in mustard seed cake(MSC).The nematostatic potential of sonicated seed cake was examined against the second-stage juveniles(J2s)of root-knot nematode,Meloidogyne javanica.The results show that a 35 ppm(parts per million)concentration of a sonicated extract(SE)sample of MSC caused 65%J2s mortality at 18 h exposure period in vitro.It also significantly suppressed the root-knot index(RKI=0.94)in tomato roots.The lethal concentration values for SE were 51.76,29.79,and 13.34 ppm,respectively,at 6,12,and 18 h of the exposure period,and the lethal concentration values for the non-sonicated extract(NSE)sample were 116.95,76.38,and 55.59 ppm,respectively,at similar exposure time.Sinapine and gluconapin were identified as the major compounds in ultrasonic-assisted MSC.Because of the high extraction efficiency of metabolites in the SE,all treat‐ments of SE were shown to be antagonistic to J2s.Thus,this study of ultrasonication activity-based profiling of MSC may help generate target-based compounds at a scale relevant to the control of disease caused by nematodes in economic crops.