Host Roots Research Articles

The metabolic profiles of phenolic acids and aromatic amino acids in the Orobanche crenata parasite and its host faba bean at different infestation stages

Orobanche crenata is a root holoparasite that depends on its host for nutritional requirements. The shikimate pathway that metabolizes about 30% of the assimilated carbon in photosynthetic plants plays a role in host-parasite relationships. Aromatic amino acids (AAAs) and phenolic acids are derived from the shikimate pathway and serve as precursors of a wide number of primary and secondary metabolites. The effects of the O. crenata parasite on the phenolic acid and AAA profiles of two faba bean varieties and the differences of these compounds between the host organs and attached parasite at infestation stages were studied. Hosts and attached parasites were collected and divided, depending on the stage of parasite development, into four stages. The results revealed that phenolic acids and free AAAs tended to increase in parasitized roots compared to those of healthy roots, and the greatest increase in phenolic contents occurred at the first infestation stage. Syringic acid was observed to be unique to the parasite. Profiles of phenolic acids and AAAs were changed during the developmental stages of the parasite and differed from those of its host. Caffeic in the parasite reached more than 100 times that in Nubaria 4 host roots at the fourth infestation stage. Free phenylalanine in the parasite ranged between 2.2 and 5.5 times its level in host roots at all infestation stages. This study provides much evidence that indicates O. crenata is able to self-regulate its phenolic and AAA metabolites during its developmental stages, which differ from those of its host.

Parasitic plants show striking convergence in host preference across angiosperm lineages.

The host specificity of a parasite underpins its ecology, distribution, invasive potential and adaptability, yet for most parasitic plants host ranges are poorly understood. We examine host-parasite relationships across lineages to infer how host specificity may have influenced the evolution of parasitism in plants. Host preference data for all plant holoparasite species were manually collected from literature and herbarium specimens, then analysed to investigate and visualise host diversity and specificity. We reveal a disproportionality in host preference across host lineages: the Asteraceae contains 10% of angiosperm diversity but is infected by 31% of parasite species; meanwhile Monocots comprise 23% but are infected by just 3.2%. Furthermore, we observe striking convergence in host preference: Asteraceae, Euphorbiaceae and Fabaceae are infected by six, five and four independent parasite lineages, respectively. We also demonstrate considerable variation in the degree of host specificity among closely related parasite species; a result that does not reflect the expectation of holoparasites - especially endoparasites - as host specialists. The marked pattern of convergence in preference across disparate lineages points to a common pathway in the evolution of parasitism of eudicots in preference to monocots, which may have in turn have been driven by a divergence in host root and vascular architecture. The unexpected variation in host specificity among closely related species suggests that even apparent generalists may comprise cryptic host-specific taxa. This highlights the value of host preference as an additional consideration in parasitic plant taxonomy. Together, our data point to a complex interplay between ecological and physiological factors driving the evolution of host-parasite interactions. Moreover, they emphasize how little is known about the ecology of most holoparasitic plants, a group of organisms that are especially vulnerable at a time of unprecedented biodiversity loss and extinction.

Functional traits of Epifagus virginiana (Orobanchaceae) tubers as adaptations to the Mexican beech microenvironment

Epifagus virginiana (Orobanchaceae), known as beechdrops, is a holoparasitic plant that acquires all its resources from a narrow range of host plants, restricted to North American Fagus species. To do so, beechdrops develop a vascular connection with the host via a terminal haustoria that develops as a tuber attached to the host root. We hypothesized that microenvironmental conditions can influence functional traits of the E. virginiana tuber despite this parasite's complete reliance on the host plant for its nutrition. Therefore, the aims of this study were i) to analyze the structure of the tubers of E. virginiana; ii) to assess the variation in tuber functional traits between two E. virginiana populations; and iii) to analyze how microenvironmental factors influence functional traits in the tuber. We detected that functional trait of beechdrops tuber along Mexican beech microenvironmental covaried with traits important for below-ground processes. Boosted regression trees provided a powerful analysis tool, giving substantially superior predictive performance to generalized additive models, despite the fitting of interaction terms in the latter.

The poplar SWEET1c glucose transporter plays a key role in the ectomycorrhizal symbiosis.

The mutualistic interaction between ectomycorrhizal fungi and trees is characterized by the coordinated exchange of soil nutrients with soluble sugars. Despite the importance of this process, the precise mechanism by which sugars are transported from host roots to colonizing hyphae remains unclear. This study aimed to identify the specific membrane transporters responsible for the unloading of sugars at the symbiotic interface, with a focus on the role of the root Sugars Will Eventually Be Exported Transporter (SWEET) uniporters. Our study used RNA sequencing and quantitative PCR to identify PtaSWEET gene expression in Populus tremula × alba-Laccaria bicolor ectomycorrhizal root tips. Our results suggest that symbiosis-induced PtaSWEET1c is primarily responsible for transporting glucose and sucrose, as demonstrated by the yeast assays. Moreover, we used a promoter-YFP reporter to confirm the localization of the PtaSWEET1c expression in cortical cells of ectomycorrhizal rootlets, supporting its major role in supplying glucose at the symbiotic interface. Furthermore, our observations confirmed the localization of PtaSWEET1c-GFP in the plasma membrane. The inactivation of PtaSWEET1c reduced ectomycorrhizal root formation and 13C translocation to ectomycorrhizal roots. Our findings highlight the crucial role of PtaSWEET1c in facilitating glucose and sucrose transport at the symbiotic interface of Populus-L. bicolor symbiosis.

Anthoxanthum odoratum (Poaceae) as a bioindicator of arbuscular mycorrhizal fungi abundance prior to native revegetation on agricultural soils

ABSTRACT Mycorrhizal fungi, which form symbiotic associations with plant roots, can be critical to the successful establishment of plants. Up to 90% of land plant species form associations with arbuscular mycorrhizal fungi (AMF), which develop fungal structures inside host roots. Common site preparation practices prior to ecological restoration, such as soil disturbance and herbicide application, may lessen the availability of AMF, potentially jeopardising plant establishment. However, the state of the soil microbiome can be difficult to assess directly. This study examines the potential of the widespread pasture grass Anthoxanthum odoratum (Sweet Vernal, Poaceae) as a bioassay of AMF abundance in soils. We present a rapid clearing and staining protocol for visualising AMF structures in the roots of A. odoratum. We then compare % colonisation on roots of naturally established A. odoratum plants collected from undisturbed pastures vs. sprayed and tilled pastures. Roots of A. odoratum collected from sprayed and tilled pastures showed a significantly lower average AMF colonisation at 43.8% compared with 57.6% on roots from undisturbed pastures. However, all plants sourced from the sprayed and tilled pastures still showed some AMF structures. Our results strongly suggest that A. odoratum can be a useful bioindicator of AMF presence and abundance in soils, offering a promising tool for seed-based restoration on retired agricultural land.

Conserved perception of host and non-host signals via the a-pheromone receptor Ste3 in Colletotrichum graminicola.

Understanding the interactions between fungal plant pathogens and host roots is crucial for developing effective disease management strategies. This study investigates the molecular mechanisms underpinning the chemotropic responses of the maize anthracnose fungus Colletotrichum graminicola to maize root exudates. Combining the generation of a deletion mutant with monitoring of disease symptom development and detailed analysis of chemotropic growth using a 3D-printed device, we identify the 7-transmembrane G-protein coupled receptor (GPCR) CgSte3 as a key player in sensing both plant-derived class III peroxidases and diterpenoids. Activation of CgSte3 initiates signaling through CgSo, a homolog to the Cell Wall Integrity Mitogen-Activated Protein Kinase (CWI MAPK) pathway scaffold protein identified in other filamentous fungi, facilitating the pathogen's growth towards plant defense molecules. The NADPH oxidase CgNox2 is crucial for peroxidase sensing but not for diterpenoid detection. These findings reveal that CgSte3 and CWI MAPK pathways are central to C. graminicola's ability to hijack plant defense signals, highlighting potential targets for controlling maize anthracnose.

Involvement of G-protein alpha subunit in soybean cyst nematode chemotaxis

The soybean cyst nematode (SCN; Heterodera glycines Ichinohe) is a significant agricultural pest that causes extensive damage to soybean production worldwide. Second-stage juveniles (J2s) of the SCN migrate through the soil and infest the roots of host plants in response to certain chemical substances secreted from the host roots. Therefore, controlling SCN chemotaxis could be an effective strategy for its management.In the present study, we identified the Hg-gpa-3d gene, which encodes the G protein alpha subunit, as a key regulator of SCN chemotaxis. Gene silencing of Hg-gpa-3d reduced the attraction of SCN J2s to host roots, as well as to nitrate ions, a chemoattractant recognized through a mechanism different from that of host recognition. However, silencing of Hg-gpa-3d did not affect avoidance behavior towards unpleasant temperatures or stylet protrusion. These results suggest that Hg-gpa-3d is a crucial gene in the regulation of SCN chemotaxis and provide new insights into the chemotactic mechanisms of the SCN.

Auxin-Mediated Lateral Root Development in Root Galls of Cucumber under Meloidogyne incognita Stress.

Root-knot nematodes induce the formation of feeding sites within the host roots and the relocation of auxin into galls results in abnormal lateral root growth. Here, we analyzed the changes in cucumber root architecture under Meloidogyne incognita stress and the distribution of auxin in these morphological and molecular root changes. The number of root tips significantly decreased, and regression analysis showed a positive relationship between the size of root galls and the numbers of nematodes in galls compared with the lateral roots on galls, emphasizing the effect of nematode parasitism on root development. Data generated via a promoter-reporter system using the transgenic hairy root system first characterized the auxin distribution during nematode parasitism in cucumber. Using DR5:GUS staining of root galls, we further detected the expression of CsPIN1 and CsAUX1, which regulate polar auxin transport. The results showed that both CsPIN1 and CsAUX1 were induced in galls, and the relative expression of the two genes significantly increased at 21 DAI. The TIBA treatment, which can disrupt polar auxin transport inhibited the numbers of cucumber root tips and total length following increasing concentration gradients. Moreover, the numbers of galls were significantly affected by TIBA treatment, which showed the vital role of auxin during nematode parasitism. Our findings suggest that the transportation of auxin plays an important role during gall formation and induces cucumber lateral root development within nematode feeding sites.

WOX11-mediated cell size control in Arabidopsis attenuates growth and fecundity of endoparasitic cyst nematodes.

Cyst nematodes establish permanent feeding structures called syncytia inside the host root vasculature, disrupting the flow of water and minerals. In response, plants form WOX11-mediated adventitious lateral roots at nematode infection sites. WOX11 adventitious lateral rooting modulates tolerance to nematode infections; however, whether this also benefits nematode parasitism remains unknown. Here, we report on bioassays using a 35S::WOX11-SRDX transcriptional repressor mutant to investigate whether WOX11 adventitious lateral rooting promotes syncytium development and thereby female growth and fecundity. Moreover, we chemically inhibited cellulose biosynthesis to verify if WOX11 directly modulates cell wall plasticity in syncytia. Finally, we performed histochemical analyses to test if WOX11 mediates syncytial cell wall plasticity via reactive oxygen species (ROS). Repression of WOX11-mediated transcription specifically enhanced the radial expansion of syncytial elements, increasing both syncytium size and female offspring. The enhanced syncytial hypertrophy observed in the 35S::WOX11-SRDX mutant could be phenocopied by chemical inhibition of cellulose biosynthesis and was associated with elevated levels of ROS at nematode infection sites. We, therefore, conclude that WOX11 restricts radial expansion of nematode-feeding structures and female growth and fecundity, likely by modulating ROS-mediated cell wall plasticity mechanisms. Remarkably, this novel role of WOX11 in plant cell size control is distinct from WOX11 adventitious lateral rooting underlying disease tolerance.

Pisolithus microcarpus isolates with contrasting abilities to colonise Eucalyptus grandis exhibit significant differences in metabolic signalling

Biotic factors in fungal exudates impact plant-fungal symbioses establishment. Mutualistic ectomycorrhizal fungi play various ecological roles in forest soils by interacting with trees. Despite progress in understanding secreted fungal signals, dynamics of signal production in situ before or during direct host root contact remain unclear. We need to better understand how variability in intra-species fungal signaling at these stages impacts symbiosis with host tissues. Using the ECM model Pisolithus microcarpus, we selected two isolates (Si9 and Si14) with different abilities to colonize Eucalyptus grandis roots. Hypothesizing that distinct early signalling and metabolite profiles between these isolates would influence colonization and symbiosis, we used microdialysis to non-destructively collect secreted metabolites from either the fungus, host, or both, capturing the dynamic interplay of pre-symbiotic signalling over 48 hours. Our findings revealed significant differences in metabolite profiles between Si9 and Si14, grown alone or with a host root. Si9, with lower colonization efficiency than Si14, secreted a more diverse range of compounds, including lipids, oligopeptides, and carboxylic acids. In contrast, Si14's secretions, similar to the host's, included more aminoglycosides. This study emphasizes the importance of intra-specific metabolomic diversity in ectomycorrhizal fungi, suggesting that early metabolite secretion is crucial for establishing successful mutualistic relationships.

Duality of H2O2 detoxification and immune activation of Ralstonia solanacearum alkyl hydroperoxide reductase C (AhpC) in tobacco

Although microbial pathogens utilize various strategies to evade plant immunity, host plants have evolved powerful defense mechanisms that can be activated in preparation for threat by infective organisms. Here, we identified one 24 kDa alkyl hydroperoxide reductase C (AhpC) from the culture supernatant of Ralstonia solanacearum strain FQY-4 (denoted RsAhpC) in the presence of host roots. RsAhpC contributes to H2O2 detoxification and the pathogenicity of R. solanacearum. However, the introduction of RsAhpC into the apoplast could activate immune defense, leading to suppression of pathogen colonization in both Nicotiana benthamiana and the Honghua Dajinyuan (HD) cultivar of N. tabacum. Consequently, overexpression of RsAhpC in the HD cultivar enhanced the resistance of tobacco to bacterial wilt disease caused by FQY-4. Overall, this study provides insight into the arms race between pathogens and their plant hosts. Specifically, it is firstly reported that plants can sense pathogen-derived AhpC to activate defenses, in addition to the role of AhpC in pathogen ROS detoxification. Therefore, the macromolecule AhpC produced by Ralstonia solanacearum has the ability to enhance plant defense as an elicitor, which provides a practical strategy for disease resistance breeding.

Native root hemiparasites form haustorial attachments with multiple invasive and expansive species

Parasitic plants are known for shaping plant communities, mainly by suppressing dominant species. This suppression, in some cases, fosters species coexistence and boosts overall diversity. Recent studies reveal that certain parasitic plants can curb invasive alien plants or expansive native species. In this study, we followed previous case studies, investigating the ability of three common Central European hemiparasitic species to attach to roots and form functional haustoria across a broad range of invasive and expansive hosts. For each host-hemiparasite pair, we posed two questions: (i) Do the hemiparasites produce haustoria on the host's roots or rhizomes? (ii) Does the anatomical structure of the haustoria include all features necessary for their functionality? We cultivated three hemiparasitic species, Melampyrum arvense L., Rhinanthus alectorolophus (Scop.) Pollich, and Odontites vernus subsp. serotinus (Dumort.) Corb., in pots with 18 candidate hosts. After cultivation, we dissected the root systems to determine haustoria abundance and to collect them for anatomical study to assess their functionality. Hemiparasite individuals in each pot were also counted. The hemiparasitic species produced haustoria on the majority of tested hosts (37 out of 44 combinations), with little difference between native expansive and alien invasive plant species. In 13 host-hemiparasite combinations (including eight combinations with invasive species), we identified abundant functional haustoria and good establishment of the hemiparasites. Remarkably, all three hemiparasitic species formed functional haustoria on invasive Asteraceae hosts. By contrast, Melampyrum arvense performed poorly when cultivated with grasses. We identified a series of hemiparasite-host combinations, which should be further tested for the potential hemiparasite effect on host fitness in the field. The abundance and anatomical structure of the haustoria indicates that the recognised low specificity of the hemiparasitic interactions applies also to associations with alien invasive species, with which they do not share a common evolutionary history.

Monitoring of parasite Orobanche cumana using Vis-NIR hyperspectral imaging combining with physio-biochemical parameterson host crop Helianthus annuus.

This study provided a non-destructive detection method with Vis-NIR hyperspectral imaging combining with physio-biochemical parameters in Helianthus annuus in response to Orobanche cumana infection that took insights into the monitoring of sunflower weed. Sunflower broomrape (Orobanche cumana Wallr.) is an obligate weed that attaches to the host roots of sunflower (Helianthus annuus L.) leading to a significant reduction in yield worldwide. The emergence of O. cumana shoots after its underground life-cycle causes irreversible damage to the crop. In this study, a fast visual, non-invasive and precise method for monitoring changes in spectral characteristics using visible and near-infrared (Vis-NIR) hyperspectral imaging (HSI) was developed. By combining the bands sensitive to antioxidant enzymes (SOD, GR), non-antioxidant enzymes (GSH, GSH + GSSG), MDA, ROS (O2-, OH-), PAL, and PPO activities obtained from the host leaves, we sought to establish an accurate means of assessing these changes and conducted imaging acquisition using hyperspectral cameras from both infested and non-infested sunflower cultivars, followed by physio-biochemical parameters measurement as well as analyzed the expression of defense related genes. Extreme learning machine (ELM) and convolutional neural network (CNN) models using 3-band images were built to classify infected or non-infected plants in three sunflower cultivars, achieving accuracies of 95.83% and 95.83% for the discrimination of infestation as well as 97.92% and 95.83% of varieties, respectively, indicating the potential of multi-spectral imaging systems for early detection of O. cumana in weed management.

Enhancing arbuscular mycorrhiza symbiosis effectiveness through the involvement of the tomato GRAS transcription factor SCL3/SlGRAS18

Arbuscular mycorrhizal (AM) fungi improve plant growth, nutrition, fitness and stress tolerance while AM fungi obtain carbohydrates and lipids from the host. This whole process of mutual benefit requires substantial alterations in the structural and functional aspects of the host root cells. These modifications ultimately culminate in the formation of arbuscules, which are specialized intraradical and highly branched fungal structures. Arbuscule-containing cells undergo massive reprogramming to hosting arbuscule and members of the GRAS transcription factor family have been characterized as AM inducible genes which play a pivotal role in these process. Here, we show a functional analysis for the GRAS transcription factor SCL3/SlGRAS18 in tomato. SlGRAS18 interacts with SlDELLA, a central regulator of AM formation. Silencing of SlGRAS18 positively impacts arbuscule development and the improvement in symbiotic status, favouring flowering and therefore progress in the formation and development of fruits in SlGRAS18 silenced plants which parallel to a discernible pattern of mineral nutrient redistribution in leaves. Our results advance the knowledge of GRAS transcription factors involved in the formation and establishment of AM symbiosis and provide experimental evidence for how specific genetic alterations can lead to more effective AM symbiosis.

The dual role of a novel Sinorhizobium meliloti chemotaxis protein CheT in signal termination and adaptation.

Sinorhizobium meliloti senses nutrients and compounds exuded from alfalfa host roots and coordinates an excitation, termination, and adaptation pathway during chemotaxis. We investigated the role of the novel S. meliloti chemotaxis protein CheT. While CheT and the Escherichia coli phosphatase CheZ share little sequence homology, CheT is predicted to possess an α-helix with a DXXXQ phosphatase motif. Phosphorylation assays demonstrated that CheT dephosphorylates the phosphate-sink response regulator, CheY1~P by enhancing its decay two-fold but does not affect the motor response regulator CheY2~P. Isothermal Titration Calorimetry (ITC) experiments revealed that CheT binds to a phosphomimic of CheY1~P with a KD of 2.9 μM, which is 25-fold stronger than its binding to CheY1. Dissimilar chemotaxis phenotypes of the ΔcheT mutant and cheT DXXXQ phosphatase mutants led to the hypothesis that CheT exerts additional function(s). A screen for potential binding partners of CheT revealed that it forms a complex with the methyltransferase CheR. ITC experiments confirmed CheT/CheR binding with a KD of 19 μM, and a SEC-MALS analysis determined a 1:1 and 2:1 CheT/CheR complex formation. Although they did not affect each other's enzymatic activity, CheT binding to CheY1~P and CheR may serve as a link between signal termination and sensory adaptation.

A single viral amino acid shapes the root system architecture of a plant host upon virus infection

BackgroundGrapevine fanleaf virus (GFLV) is one of the most detrimental viral pathogens of grapevines worldwide but no information is available on its effect on the root system architecture (RSA) of plant hosts. We used two wildtype GFLV strains and their single amino acid mutants to assess RSA traits in infected Nicotiana benthamiana and evaluate transcriptomic changes in host root gene expression in replicated time course 3’RNA-Seq experiments. Mutations targeted the multi-functional GFLV-encoded protein 1EPol*/Sd, a putative RNA-dependent RNA polymerase and determinant of foliar symptoms in N. benthamiana plants.ResultsPlant infection with wildtype GFLV strain GHu and mutant GFLV strain F13 1EPolG802K, both carrying a lysine in position 802 of protein 1EPol*/Sd, resulted in a significantly lower number of root tips (-30%), and a significantly increased average root diameter (+ 20%) at 17 days post inoculation (dpi) in comparison with roots of mock inoculated plants. In contrast, the RSA of plants infected with wildtype GFLV strain F13 and mutant GFLV strain GHu 1EPolK802G, both carrying a glycine in position 802 of protein 1EPol*/Sd, resembled that of mock inoculated plants. Modifications of RSA traits were not associated with GFLV titer. Root tissue transcriptome analysis at 17 dpi indicated dysregulation of pattern recognition receptors, plant hormones, RNA silencing, and genes related to the production of reactive oxygen species (ROS). For wildtype GFLV strain GHu, RSA modifications were correlated with an abundant accumulation of ROS in the pericycle of primary roots at 7 dpi and the duration of vein clearing symptom expression in apical leaves. Dysegulation of a hypersensitive response was an overarching gene ontology found through enrichment analyses of 3’RNA-Seq data.ConclusionsOur findings revealed the causative role of lysine in position 802 of protein 1EPol*/Sd in a novel RSA phenotype during viral infection and documented GFLV-N. benthamiana interactions at the root level based on (i) antiviral response, (ii) receptor mediated production of ROS, and (iii) hormone regulation. A correlation between above and below ground symptoms was reported for the first time in plants infected with wildtype GFLV strain GHu. Further work is warranted to test whether the modified RSA of a plant host might impact GFLV acquisition and transmission by the ectoparasitic dagger nematode Xiphinema index.

Radicle Growth Regulation of Root Parasitic Plants by Auxin-related Compounds.

Root parasitic plants in the Orobanchaceae, such as Striga and Orobanche, cause significant damage to crop production. The germination step of these root parasitic plants is induced by host-root-derived strigolactones. After germination, the radicles elongate toward the host and invade the host root. We have previously discovered that a simple amino acid, tryptophan (Trp), as well as its metabolite, the plant hormone indole-3-acetic acid (IAA), can inhibit radicle elongation of Orobanche minor. These results suggest that auxin plays a crucial role in the radicle elongation step in root parasitic plants. In this report, we used various auxin chemical probes to dissect the auxin function in the radicle growth of O. minor and Striga hermonthica. We found that synthetic auxins inhibited radicle elongation. In addition, auxin receptor antagonist, auxinole, rescued the inhibition of radicle growth by exogenous IAA. Moreover, a polar transport inhibitor of auxin, N-1-naphthylphthalamic acid, affected radicle bending. We also proved that exogenously applied Trp is converted into IAA in O. minor seeds, and auxinole partly rescued this radicle elongation. Taken together, our data demonstrate a pivotal role for auxin in radicle growth. Thus, manipulation of auxin function in root parasitic plants should offer a useful approach to combat these parasites.

Biocontrol of Bacterial Wilt Biotic Stress in Tomato Plants by Successful Host Root Colonization and Inducing Host Resistance

Biocontrol of Bacterial Wilt Biotic Stress in Tomato Plants by Successful Host Root Colonization and Inducing Host Resistance

Lure and starve: Host root exudates to suppress field populations of cyst nematodes

Plant parasitic nematodes are a burden to global food security, accounting for substantial yield losses in agricultural production worldwide. Increasing concerns over the environment and health issues have led to diminishing control options at the disposal of agricultural producers. Lure and starve, a strategy that is based on stimulating hatching of second stage juveniles (J2) of some cyst forming plant parasitic nematodes in the absence of their host plant seems a promising approach to maintain sustainability in crop production. Here we examined in-situ hatching of encysted eggs of the potato cyst nematode Globodera pallida and the carrot cyst nematode Heterodera carotae following exogenous applications of host root exudates in repeated field experiments during autumn and spring seasons. Population densities (viable J2 g−1 of soil) were assessed prior and post-application of root exudates. Results showed hatching induction of up to 83 % for G. pallida and 54 % for H. carotae in field plots drenched with their respective host root exudates. Spring season experiments were characterised by limited soil moisture and did not reduce nematode population densities for G. pallida. The potential for host root exudates in suppressing field population of cyst nematode in lure and starve strategies looks promising for both cyst nematode species investigated.

Inter-species interaction of bradyrhizobia affects their colonization and plant growth promotion in Arachis hypogaea.

Bradyrhizobia are the principal symbiotic partner of the leguminous plant and take active part in biological nitrogen-fixation. The present investigation explores the underlying competition among different strains during colonization in host roots. Six distinct GFP and RFP-tagged Bradyrhizobium strains were engineered to track them inside the peanut roots either independently or in combination. The Bradyrhizobium strains require different time-spans ranging from 4 to 21days post-infection (dpi) for successful colonization which further varies in presence of another strain. While most of the individual strains enhanced the shoot and root dry weight, number of nodules, and nitrogen fixation capabilities of the host plants, no significant enhancement of plant growth and nodulation efficiency was observed when they were allowed to colonize in combinations. However, if among the combinations one strains is SEMIA 6144, the co-infection results in higher growth and nodulation efficiency of the hosts. From the competition experiments it has been found that Bradyrhizobium japonicum SEMIA 6144 was found to be the most dominant strain for effective nodulation in peanut. The extent of biofilm and exopolysaccharide (EPS) production by these isolates, individually or in combinations, were envisaged to correlate whether these parameters have any impact on the symbiotic association. But the extent of colonization, growth-promotion and nitrogen-fixation ability drastically lowered when a strain present together with other Bradyrhizobium strain. Therefore, it is imperative to understand the interaction between two co-inoculating Bradyrhizobium species for nodulation followed by plant growth promotion to develop suitable consortia for enhancing BNF in peanut and possibly for other legumes.