Roots Of Host Plants Research Articles

Soil, climate, and management practices associated with the prevalence of clubroot in Colombia

Clubroot disease caused by Plasmodiophora brassicae is a major constraint for cruciferous crops in Colombia; however, information regarding its spread and the relationship between environmental and crop management practices with its occurrence in the country is scarce. This research established clubroot prevalence in the main cruciferous productive areas in Colombia and the relation of its occurrence with crop management practices, soil, and climatic characteristics. In total, 127 fields were visited along eight departments. Clubroot infestation was determined either by direct inspection of roots of host plants for clubroot symptoms or by report of previous observation of the disease symptoms by the farmers. Soil samples were collected for physical and chemical analysis, climatic information was obtained, and farmers were surveyed on the management practices of the production systems. The survey confirmed the presence of the disease in 53.6% of the visited fields. The only department where the disease symptoms were not observed nor reported was Nariño. A negative correlation was found between the disease occurrence and the content of aluminum in the soil, the number of days with rain per year, and the cultivation of clubroot-resistant hybrids. Moreover, a positive correlation was observed with the inclusion of cruciferous crops in the rotation scheme, the effective cation exchange capacity of the soil, soil pH, and the content of phosphorus, calcium, boron, and copper in the soil.

Strigol induces germination of the facultative parasitic plant Phtheirospermum japonicum in the absence of nitrate ions

ABSTRACT Root parasitic plants in the family Orobanchaceae, such as Striga and Orobanche spp., infest major crops worldwide, leading to a multibillion-dollar loss annually. Host-derived strigolactones (SLs), recognized by a group of α/β hydrolase receptors (KAI2d) in these parasites, are important determinants for germinating root parasitic plants near the roots of host plants. Phtheirospermum japonicum, a facultative hemiparasitic Orobanchaceae plant, can germinate and grow in the presence or absence of the host and can also exhibit root chemotropism to host-derived SLs that are perceived via KAI2d. However, the importance of SLs in P. japonicum germination remains unclear. In this study, we found that germination of P. japonicum was suppressed in the absence of nitrate ions and that germination of P. japonicum was promoted by exogenous strigol, an SL, under such conditions. We propose a model in which P. japonicum may select either independent living or parasitism in response to ambient nitrogen conditions and host presence.

Exploring fine-scale assembly of ectomycorrhizal fungal communities through phylogenetic and spatial distribution analyses.

Ectomycorrhizal fungi (EMF) form symbiotic relationship with the roots of host plants. EMF communities are composed of highly diverse species; however, how they are assembled has been a long-standing question. In this study, we investigated from a phylogenetic perspective how EMF communities assemble on Pinus densiflora seedlings at different spatial scales (i.e., seedling scale and root tip scale). P. densiflora seedlings were collected from different habitats (i.e., disturbed areas and mature forests), and their EMF communities were investigated by morphotype sequencing and next-generation sequencing (NGS). To infer assembly mechanisms, phylogenetic relatedness within the community (i.e., phylogenetic structure) was estimated and spatial distribution of EMF root tips was analyzed. The EMF communities on pine seedlings were largely different between the two habitats. Phylogenetically restricted lineages (Amphinema, /suillus-rhizopogon) were abundant in the disturbed areas, whereas species from diverse lineages were abundant in the mature forests (Russula, Sebacina, /tomentella-thelephora, etc.). In the disturbed areas, phylogenetically similar EMF species were aggregated at the seedling scale, suggesting that disturbance acts as a powerful abiotic filter. However, phylogenetically similar species were spatially segregated from each other at the root tip scale, indicating limiting similarity. In the mature forest seedlings, no distinct phylogenetic signals were detected at both seedling and root tip scale. Collectively, our results suggest that limiting similarity may be an important assembly mechanism at the root tip scale and that assembly mechanisms can vary across habitats and spatial scales.

Domates (Solanum lycopersicium L.) Bitkisinde, Verticillium Solgunluğu (Verticillium Dahliae Kleb.) ve Erken Yanıklığı [Alternaria solani (Ell. Ve G. Martin) Sor.] Hastalıklarına Karşı Clonostachys rosea (Sch.) Schroers ve Samuels’nin Etkisinin Belirlenmesi

The effectiveness of Clonostachys rosea against Verticillium wilt (Verticillium dahliae) and early blight (Alternaria solani) diseases, as the two most important problems in tomato cultivation with significant economic losses, was determined. It was determined that C. rosea was effective on A. solani and V. dahliae and suppressed mycelial growth. Also, the C. rosea on wheat grains inoculated to plants at 20 g, 30 g, and 40 g concentrations before and after pathogens inoculation. Then, fungal discs (2 mm in diameter) from V. dahliae growing colonies were inoculated on the host plant root zone. A. solani was also inoculated (1x106 conidia ml-1) by spraying the foliar parts of the plants. Results showed that V. dahliae caused 76.0% disease severity in control plants, while the disease severity indices were 58.3%, 55.3%, and 25.3% at 20 g, 30 g, and 40 g C. rosea application, respectively. In A. solani x C. rosea treatments, the disease severities were determined as 96.6%, 63.3%, 43.6% and 46.6% in control, 20 g, 30 g, and 40 g application of C. rosea, respectively. The pathogen suppression rates by C. rosea at 30g application dose was 54.8% against A. solani and at 40 g application dose was 66.6% against V. dahliae. The effects of C. rosea on plant growth parameters were also determined. Results showed that C. rosea had a positive effect on the morphological parameters in tomato plants.

The Minichromosome Maintenance Complex Component 2 (MjMCM2) of Meloidogyne javanica is a potential effector regulating the cell cycle in nematode-induced galls

Root-knot nematodes Meloidogyne spp. induce enlarged multinucleate feeding cells—galls—in host plant roots. Although core cell-cycle components in galls follow a conserved track, they can also be usurped and manipulated by nematodes. We identified a candidate effector in Meloidogyne javanica that is directly involved in cell-cycle manipulation—Minichromosome Maintenance Complex Component 2 (MCM2), part of MCM complex licensing factor involved in DNA replication. MjMCM2, which is induced by plant oxilipin 9-HOT, was expressed in nematode esophageal glands, upregulated during parasitic stages, and was localized to plant cell nucleus and plasma membrane. Infected tomato hairy roots overexpressing MjMCM2 showed significantly more galls and egg-mass-producing females than wild-type roots, and feeding cells showed more nuclei. Phylogenetic analysis suggested seven homologues of MjMCM2 with unknown association to parasitism. Sequence mining revealed two RxLR-like motifs followed by SEED domains in all Meloidogyne spp. MCM2 protein sequences. The unique second RxLR-like motif was absent in other Tylenchida species. Molecular homology modeling of MjMCM2 suggested that second RxLR2-like domain is positioned on a surface loop structure, supporting its function in polar interactions. Our findings reveal a first candidate cell-cycle gene effector in M. javanica—MjMCM2—that is likely secreted into plant host to mimic function of endogenous MCM2.

Good News for Cabbageheads: Controlling Phelipanche aegyptiaca Infestation under Hydroponic and Field Conditions.

Phelipanche aegyptiaca (Orobanchaceae) is a parasitic weed that causes severe yield losses in field crops around the world. After establishing vascular connections to the host plant roots, P. aegyptiaca becomes a major sink that draws nutrients, minerals, and water from the host, resulting in extensive crop damage. One of the most effective ways to manage P. aegyptiaca infestations is through the use of herbicides. Our main objective was to optimize the dose and application protocol of herbicides that effectively control P. aegyptiaca but do not damage the cabbage crop. The interactions between the cabbage roots and the parasite were first examined in a hydroponic system to investigate the effect of herbicides on initial parasitism stages, e.g., germination, attachment, and tubercles production. Thereafter, the efficacy of glyphosate and ethametsulfuron-methyl in controlling P. aegyptiaca was examined in five cabbage fields naturally infested with P. aegyptiaca. The herbicides glyphosate and ethametsulfuron-methyl were applied on cabbage foliage and in the soil solution, both before and after the parasite had attached to the host roots. A hormesis effect was observed when glyphosate was applied at a dose of 36 g ae ha−1 in a non-infested P. aegyptiaca field. Three sequential herbicide applications (21, 35, and 49 days after planting) effectively controlled P. aegyptiaca without damaging the cabbages at a dose of 72 g ae ha−1 for glyphosate and at all the examined doses for ethametsulfuron-methyl. Parasite control with ethametsulfuron-methyl was also effective when overhead irrigation was applied after the herbicide application.

Cultivation, identification, and application of arbuscular mycorrhizal fungi associated with date palm plants in Drâa-Tafilalet oasis

Arbuscular mycorrhizal fungi (AMF) have been frequently reported as effective tools for alleviating environmental stresses and promoting plant growth and yield. In this study, we aimed to isolate, culture, and identify molecular and morphological AMF species associated with date palms and spontaneous plants present at eight sites in the arid agroecosystem of the Drâa-Tafilalet oasis of Morocco. We tested the capacity of AMF to colonize micropropagated date palm seedlings at their first acclimatization stage. Soil and root samples were collected to propagate indigenous AMF strains using trap culture techniques under greenhouse conditions and, at the same time, their root colonization potential was evaluated. We used freshly propagated spores to establish a collection of single spore-derived cultures. Morphological, microscopic, and molecular approaches were adopted to quantify AMF communities in the roots and rhizosphere and identify the recovered AMF species present at the eight sites. In an inoculation experiment, a micropropagated date palm was inoculated with a consortium of four cultured AMF strains, alone or in combination with synthetic fertilizer or compost. Our results showed that after two cycles of trap culturing, the frequency and intensity of AMF colonizing host plant roots significantly increased, exceeding 91% and 50%, respectively. Using three trap plant species and favorable growing conditions helped increase root colonization rates and AMF proliferation. AMF propagation resulted in the cultivation of 13 AMF strains. Molecular and morphological analyses revealed six different AMF species within our cultures: Pervetustus simplex, Claroideoglomus etunicatum, Albahypha drummondii, Septoglomus xanthium, Funneliformis mosseae, and Rhizoglomus irregulare. Results of the inoculation experiment revealed that root colonization was higher in treatments augmented with synthetic fertilizers than those supplemented with compost with 84.4% as against 46.7% and 26.1% as against 12.3%, respectively, for colonization frequency and intensity. In contrast, shoot length and stem diameter of date palms were significantly higher in treatments augmented with compost and AMF than that with synthetic fertilizers. Synthetic fertilizers might have been partially immobilized directly after application, limiting availability and resulting in lower growth performance of date palms. These findings indicated that date palm groves are a niche for efficient indigenous AMF strains that can colonize and enhance date palm growth at the early stages.

Microbiome as a Key Player in Sustainable Agriculture and Human Health

The aggregate of microorganisms in the soil environment is a microbiome that emerged as a vital component of sustainable agriculture in the recent past. These beneficial microorganisms perform multiple plant growth-promoting activities including fixation, mineralization, solubilization, and mobilization of nutrients, production of siderophores, antagonistic substances, antibiotics, and release of plant growth-promoting substances, such as auxin and gibberellin hormones, mediated by interactions between host plant roots and microbes in the rhizosphere. Numerous plant species forms symbiotic association with microbes and draw the benefit of mineral nutrient supply with the expense of minimal energy, and their distribution is governed by nature and the number of root exudates, crop species, and cultivars. On the other hand, microorganisms with critical roles in the microbiome can be isolated, formulated, and developed as a new biological product called biofertilizers. Agriculturally, important microbes with Fe- and Zn-solubilizing attributes can be used for the biofortification of micronutrients in different cereal crops. Regardless of the approach to be used, innovations with the use of microbiomes represent the future of sustainable agriculture. Probiotic microbes, such as Lactobacillus, etc., are increasingly being used as dietary supplements in functional food products. Effective utilization of microbiome aids in promoting sustainable agriculture that accomplishes a safe environment, which in turn manifests positively on human health.

Host plant rhizo-microbiome interactions: Seasonal variation and microbial community structure analysis associated with Barleria prionitis

The host plant root ecosystem, microorganisms and the soil forms below the ground rhizo-microbiome environment in the rhizosphere soil of the associated host plant species. Microorganisms comprising the associated biomes deliberately modulate the mutual relationships with distinct genomic attributes improving the overall fitness in specific ecological and environmental habitats including the pathogenic behavior and symbiosis. Identification of the natural host microbial diversity is key features of the understanding the host plant rhizomicrobiome interaction dynamics. These interactions play pivotal role in plant adaption and ecological behavior of the most widely distributed plant species across the world. In this research study, microbial diversity assessment of the Barleria prionitis . has been investigated under the different environmental conditions. The dominant microbial communities at phylum level were represented by Proteobacteria , Actinobacteria , Firmicutes , and Actinobacteria . Similarly, at the family level Bacillaceae, Pseudonocardiaceae, Streptosporangiaceae, Pseudomonadaceae , and Solibacteraceae . Apart from the bacterial domains, actinomycetes were also found to be dominant in rhizosphere samples along with the taxonomically unclassified sequences. Further, functional genomics approach can reveal the role of the harboring microbial communities identified in the rhizosphere metagenomics approach using 16S ribosomal RNA (rRNA) gene amplicon sequencing approach. Furthermore, investigating the season variations of rhizomicrobiome interactions could infer the microbial community structure dynamics and its potential role in nutrient uptake, climate resilience, phytopathology and disease resistance in various ecosystems. • Microbial community structure analysis of the Barleria prionitis in natural ecosystem. • Core microbiome analysis and microbial co-occurrence network analysis revealed the dominant taxa. • Host dynamics and rhizomicrobiome interactions and seasonal variations in microbial diversity.

Isolation of rhizosheath and analysis of microbial community structure around roots of Stipa grandis

Root zone microbial structure is particularly complex in plants with rhizosheaths, and greater understanding of the rhizosheath may play an important role in the future development of sustainable agricultural practices. However, one important reason to focus study on rhizosheath microbial structure is that there is no definite method for rhizosheath separation. The aim of this study was to explore rhizosheath isolation methods and the diversity characteristics of microorganisms around the rhizosphere. In this study, we isolated the rhizosheath of Stipa grandis, a dominant species in desert steppe, and the microorganisms in the roots, root epidermis, rhizosheath and rhizosphere soil were extracted and sequenced by 16S rRNA and ITS. The alpha diversity index of bacteria in Stipa grandis rhizosphere soil was the greatest, followed by rhizosheath, and the alpha diversity index of endophytic bacteria in root system was the smallest. The alpha diversity index of fungi in the rhizosheath and rhizosphere soil were significantly higher than that in the root epidermis and root system. There were significant differences in bacterial community structure between the root epidermis, endophytic bacteria, rhizosheath and rhizosphere soil. Unlike bacterial community structure, the community structure of fungi in the root epidermis was similar that of endophytic fungi, but significantly different from those in rhizosheath and rhizosphere soil. This study demonstrated a feasible method for separating plant rhizosheath and root epidermis. We suggest that the root epidermis can act as the interface between the host plant root and the external soil environment. We will have to re-examine the biological and ecological significance of rhizosheath and microorganisms in rhizosheath, as well as the mechanism explaining the close relationship of the rhizosheath and the plant root epidermis. This study provides theoretical and technical guidance for the isolation of the plant rhizosheath and the study of microorganisms in plant rhizosheath.

Impact of Witch Weeds (<i>striga hermonthica</i>) on Sorghum Production and Its Managements in Ethiopia

<i>Striga hermonthica</i> (Del.) Benth is a major constraint to sorghum productivity. Striga can cause a small percentage loss in yield and, in some situations, complete crop collapse. Striga resistant sorghums can be a valuable component if resistance is built into well-adapted and productive cultivars. Sorghum's potential output has been diminished due to a variety of abiotic and biotic stresses. Abiotic stressors like as drought and low soil fertility (nutrient deficit) are two of the most common. Parasitic animals are expected to cost the world £1.5 trillion every year. Heterotrophic flowering plants that may cling to their host crop are known as parasitic weeds. Haustorium acts as a physiological link between the parasite and the plant it parasitizes. Striga is a genus of Orobanchaceae hemiroot parasites that includes roughly thirty species. Striga is a photosynthesizing obligate hemi-parasite. Striga can be found in Africa, the Middle East, Asia, and Australia in tropical and semi-arid climates. Striga are root-parasitic, annual, chlorophyll-bearing plants that require a host plant to complete their life cycle. Striga seeds can produce 100,000 to 200,000 seeds per plant, but they must be pretreated and stored in a moist, warm environment (300C in germination). Over the course of its 20-year existence, Striga has the ability to produce thousands of seeds. If a chemical cue is released by the host plant's roots, they germinate. Therefore the purpose of this review paper is to assess influence of witch weeds (<i>striga hermonthica</i>) on sorghum production and its management’s methods.

Biological Observations on the Salsola tragus L. Weed Feeder Conorhynchus kindermanni Faust, 1904 (Coleoptera: Curculionidae) in Ağrı Mountain Lowland Area

The weevil Conorhynchus kindermanni Faust, 1904 (Curculionidae: Lixinae: Cleonini) was detected in close association with Salsola tragus L. (Amaranthaceae) in Ağrı Mountain soutwestern lowland area where sandy desert. The aim of this study is to determine the life cycle of C. kindermanni feeding on S. tragus. The field research was conducted between Iğdır and Doğubayazıt district of Ağrı Province Turkey in the summer of 2020. According to the results, adults of C. kindermanni feed on S. tragus starting on the rosette stage of this weed. Mating occurs on the ground among young plants, and eggs were laid on roots attached with a glue-like secretion. The legless larvae are freely able to move in sandy soil to reach lateral branches of roots for feeding. The mature larva prepares a solitary soil-case for pupal development in the soil near the host plant root. New generation adults hibernate inside the chamber until emergence from soil in early spring. This species produces one generation in a year in the Ağrı Mountain lowland desert habitat. Key words: Conorhynchus kindermanni, Salsola tragus, weed, biological observation, Ağrı Mountain

Hormonomic Changes Driving the Negative Impact of Broomrape on Plant Host Interactions with Arbuscular Mycorrhizal Fungi.

Belowground interactions of plants with other organisms in the rhizosphere rely on extensive small-molecule communication. Chemical signals released from host plant roots ensure the development of beneficial arbuscular mycorrhizal (AM) fungi which in turn modulate host plant growth and stress tolerance. However, parasitic plants have adopted the capacity to sense the same signaling molecules and to trigger their own seed germination in the immediate vicinity of host roots. The contribution of AM fungi and parasitic plants to the regulation of phytohormone levels in host plant roots and root exudates remains largely obscure. Here, we studied the hormonome in the model system comprising tobacco as a host plant, Phelipanche spp. as a holoparasitic plant, and the AM fungus Rhizophagus irregularis. Co-cultivation of tobacco with broomrape and AM fungi alone or in combination led to characteristic changes in the levels of endogenous and exuded abscisic acid, indole-3-acetic acid, cytokinins, salicylic acid, and orobanchol-type strigolactones. The hormonal content in exudates of broomrape-infested mycorrhizal roots resembled that in exudates of infested non-mycorrhizal roots and differed from that observed in exudates of non-infested mycorrhizal roots. Moreover, we observed a significant reduction in AM colonization of infested tobacco plants, pointing to a dominant role of the holoparasite within the tripartite system.

Agrobacterium tumefaciens fitness genes involved in the colonization of plant tumors and roots.

Agrobacterium tumefaciens colonizes the galls (plant tumors) it causes, and the roots of host and nonhost plants. Transposon-sequencing (Tn-Seq) was used to discover A.tumefaciens genes involved in reproductive success (fitness genes) on Solanum lycopersicum and Populus trichocarpa tumors and S.lycopersicum and Zea mays roots. The identified fitness genes represent 3-8% of A. tumefaciens genes and contribute to carbon and nitrogen metabolism, synthesis and repair of DNA, RNA and proteins and envelope-associated functions. Competition assays between 12 knockout mutants and wild-type confirmed the involvement of 10 genes (trpB, hisH, metH, cobN, ntrB, trxA, nrdJ, kamA, exoQ, wbbL) in A.tumefaciens fitness under both tumor and root conditions. The remaining two genes (fecA, noxA) were important in tumors only. None of these mutants was nonpathogenic, but four (hisH, trpB, exoQ, ntrB) exhibited impaired virulence. Finally, we used this knowledge to search for chemical and biocontrol treatments that target some of the identified fitness pathways and report reduced tumorigenesis and impaired establishment of A.tumefaciens on tomato roots using tannic acid or Pseudomonas protegens, which affect iron assimilation. This work revealed A.tumefaciens pathways that contribute to its competitive survival in plants and highlights a strategy to identify plant protection approaches against this pathogen.

Adaptive defence and sensing responses of host plant roots to fungal pathogen attack revealed by transcriptome and metabolome analyses

Plant root-produced constitutive and inducible defences inhibit pathogenic microorganisms within roots and in the rhizosphere. However, regulatory mechanisms underlying host responses during root-pathogen interactions are largely unexplored. Using the model species Brachypodium distachyon (Bd), we studied transcriptional and metabolic responses altered in Bd roots following challenge with Fusarium graminearum (Fg), a fungal pathogen that causes diseases in diverse organs of cereal crops. Shared gene expression patterns were found between Bd roots and spikes during Fg infection associated with the mycotoxin deoxynivalenol (DON). Overexpression of BdMYB78, an up-regulated transcription factor, significantly increased root resistance during Fg infection. We show that Bd roots recognize encroaching Fg prior to physical contact by altering transcription of genes associated with multiple cellular processes such as reactive oxygen species and cell development. These changes coincide with altered levels of secreted host metabolites detected by an untargeted metabolomic approach. The secretion of Bd metabolites was suppressed by Fg as enhanced levels of defence-associated metabolites were found in roots during pre-contact with a Fg mutant defective in host perception and the ability to cause disease. Our results help to understand root defence strategies employed by plants, with potential implications for improving the resistance of cereal crops to soil pathogens.

Mechanism of Action of Endophytic Fungi Hypocrea lixii and Beauveria bassiana in Phaseolus vulgaris as Biopesticides against Pea Leafminer and Fall Armyworm.

Endophytic fungal isolates Hypocrea lixii F3ST1 and Beauveria bassiana G1LU3 were evaluated for their potential to endophytically colonize and induce active compounds in Phaseolus vulgaris, as a defense mechanism against pea leafminer (Liriomyza huidobrensis) and fall armyworm (Spodoptera frugiperda). Endophytic colonization was achieved through seed inoculation with the volatile emissions from P. vulgaris plants being analyzed using GC-MS. The crude extracts of P. vulgaris obtained using methanol and dichloromethane were assayed against leafminer and fall armyworm larvae using leaf dipping and topical application, respectively. The two isolates successfully colonized the entire host plant (roots, stems, and leaves) with significant variation (p < 0.001) between fungal isolates and the controls. The results showed qualitative differences in the volatile profiles between the control plants, endophytically colonized and insect-damaged plants attributed to fungal inoculation and leafminer damage. The crude methanol extracts significantly reduced the percentage pupation of 2nd instar leafminer larvae (p < 0.001) and adult-flies emergence (p < 0.05). The survival of the 1st instar fall armyworm larvae was also significantly reduced (p < 0.001) compared to the controls. This study demonstrated the high potential of endophytic fungi H. lixii and B. bassiana in inducing mainly specific defense compounds in the common bean P. vulgaris that can be used against pea leafminer and fall armyworm.

The GpIA7 effector from the potato cyst nematode Globodera pallida targets potato EBP1 and interferes with the plant cell cycle programme.

The potato cyst nematode Globodera pallida acquires all of its nutrients from an elaborate feeding site that it establishes in a host plant root. Normal development of the root cells is re-programmed in a process coordinated by secreted nematode effector proteins. The biological function of the G. pallida GpIA7 effector was investigated in this study. GpIA7 is specifically expressed in the subventral pharyngeal glands of pre-parasitic stage nematodes. Ectopic expression of GpIA7 in potato plants affected plant growth and development, suggesting a potential role for this effector in feeding site establishment. Potato plants overexpressing GpIA7 were shorter, with reduced tuber weight and delayed flowering. We provide evidence that GpIA7 associates with the plant growth regulator StEBP1 (ErbB-3 epidermal growth factor receptor-binding protein 1). GpIA7 modulates the regulatory function of StEBP1, altering the expression level of downstream target genes, including ribonucleotide reductase 2, cyclin D3;1, and retinoblastoma related 1, which are down-regulated in plants overexpressing GpIA7. We provide an insight into the molecular mechanism used by the nematode to manipulate the host cell cycle and demonstrate that this may rely, at least in part, on hindering the function of host EBP1.

Imazapic Herbigation for Egyptian Broomrape (Phelipanche aegyptiaca) Control in Processing Tomatoes-Laboratory and Greenhouse Studies.

Parasitic plants belonging to the Orobanchaceae family include species that cause heavy damage to crops in Mediterranean climate regions. Phelipanche aegyptiaca is the most common of the Orobanchaceae species in Israel inflicting heavy damage to a wide range of broadleaf crops, including processing tomatoes. P. aegyptiaca is extremely difficult to control due to its minute and vast number of seeds and its underground association with host plant roots. The highly efficient attachment of the parasite haustoria into the host phloem and xylem enables the diversion of water, assimilates and minerals from the host into the parasite. Drip irrigation is the most common method of irrigation in processing tomatoes in Israel, but the delivery of herbicides via drip irrigation systems (herbigation) has not been thoroughly studied. The aim of these studies was to test, under laboratory and greenhouse conditions, the factors involved in the behavior of soil-herbigated imazapic, and the consequential influence of imazapic on P. aegyptiaca and tomato plants. Dose-response Petri dish studies showed that imazapic does not impede P. aegyptiaca seed germination and non-attached seedlings, even at the high rate of 5000 ppb. Imazapic applied to tomato roots inoculated with P. aegyptiaca seeds in a PE bag system revealed that the parasite is killed only after its attachment to the tomato roots, at concentrations as low as 2.5 ppb. Imazapic sorption curves and calculated Kd and Koc values indicated that the herbicide Kd is similar in all soils excluding a two-fold higher coefficient in the Gadash farm soil, while the Koc was similar in all soils except the Eden farm soil, in which it was more than twofold lower. In greenhouse studies, control of P. aegyptiaca was achieved at >2.5 ppb imazapic, but adequate control requires repeated applications due to the 7-day half-life (t1/2) of the herbicide in the soil. Tracking of imazapic in soil and tomato roots revealed that the herbicide accumulates in the tomato host plant roots, but its movement to newly formed roots is limited. The data obtained in the laboratory and greenhouse studies provide invaluable knowledge for devising field imazapic application strategies via drip irrigation systems for efficient and selective broomrape control.

Analysis of Genetic Diversity and Population Structure of Orobanche foetida Populations From Tunisia Using RADseq.

Orobanche foetida Poiret is a holoparasitic plant that lacks chlorophyll and totally depending on its host for its growth. Orobanche foetida parasitizes host plant roots and extract nutrient and water via a haustorium. Although O. foetida distributes in the Mediterranean region as a wild plant parasite, it parasitizes faba bean causing serious damages which may reach 90% yield losses in Tunisia. Analysis of genetic diversity of the parasite is important to better understand its evolution and spread, remained largely unknown. In this work, we present the first study on genetic diversity and population structure using the robust technique Restriction-site-Associated DNA sequencing (RADseq) for Orobanche spp. We collected 244 samples of O. foetida from 18 faba bean fields in the north of Tunisia including 17 populations from the north-west and one population form the north-east. To overcome the difficulty of SNP discovery in O. foetida genome as a non-model and tetraploid plant, we utilized three different informatics pipelines, namely UNEAK, pyRAD and Stacks. This study showed that genetic differentiation occurred in the Tunisian O. foetida emphasizing the isolation by distance effect. However, no strong population clustering was detected in this work basing on the three data sets and clustering methods used. The present study shed the light on the current distribution and the genetic variation situation of the fetid broomrape in Tunisia, highlighting the importance of understanding the evolution of this parasite and its genetic background. This will aid in developing efficient strategies to control this parasite and its expansion in Tunisia and worldwide.

Targeted mutagenesis of two homologous ATP-binding cassette subfamily G (ABCG) genes in tomato confers resistance to parasitic weed Phelipanche aegyptiaca.

Phelipanche aegyptiaca and Orobanche spp. are obligate plant root-parasitic weeds that cause extensive damage in agricultural crop plants. Their germination requires exposure to strigolactones (SLs) exuded by the host plant roots. Here we studied genes in the host plant tomato involved in SL exudation and their impact on parasitic weeds. We provide evidence that CRISPR/Cas9-mediated targeted mutagenesis of two homologous ATP-binding cassette subfamily G (ABCG) genes, ABCG44 (Solyc08g067610) and ABCG45 (Solyc08g067620), in tomato significantly reduces SLs in the root exudate and abolishes germination of the root-parasitic weed P. aegyptiaca. Based on genome sequence similarity between ABCG44 and ABCG45, a 20-bp target sequence in their exon region was selected to design single guide RNA targeting both genes using CRISPR/Cas9. The plant binary vector constructs harboring the specific Cas9 and single guide RNA were transformed into tomato. Selected T0 mutated tomato plants showed different types of deletions at both gene loci. Genotype analysis of T1 plants suggested stable inheritance of the introduced mutations without any potential off-target effects. The phenotype of Cas9-mutated plants included increased shoot branching and growth of axillary buds, and reduced length of primary stems. Interestingly, reduced germination of P. aegyptiaca resulted from a decrease in the SL orobanchol in the root exudate of Cas9-mutated plants; however, orobanchol content in the root extract was unchanged compared to control plants. Moreover, in single and double ABCG mutants, expression of the SL-biosynthesis genes CCD8 and MAX1 decreased. The current study offers insights into CRISPR-mediated mutagenesis of ABCG genes, which could serve as an efficient control method to prevent root-parasitic weed germination.