Striga Germination Research Articles

A powerful molecular marker to detect mutations at sorghum LOW GERMINATION STIMULANT 1.

The parasitic weed Striga (Striga hermonthica) limits productivity of sorghum (Sorghum bicolor) and other cereals in sub-Saharan Africa and elsewhere. Improved host plant genetics is an effective control method but verified loci contributing to Striga resistance are limited. LOW GERMINATION STIMULANT 1 remains the only known sorghum locus affecting resistance to Striga. Functional loss (lgs1) alleles at this locus result in low Striga germination stimulant activity. We developed a robust polymerase chain reaction (PCR)-based LGS1 marker that detects all known natural lgs1 alleles. We have successfully used this marker to improve Striga resistance in our sorghum breeding program. To check its utility among diverse sets of germplasm, we genotyped 406 lines of the sorghum association panel (SAP) with the marker and phenotyped them for Striga germination stimulant activity. The SAP contains 23 lines (6%) with lgs1 mutations that involve a complete loss of this gene. Three previously described deletion alleles (lgs1-1, lgs1-2, and lgs1-3) ranging from 28.5 to 34kbp are present among SAP members with a new one, lgs1-6, missing nearly 50kbp relative to the reference genome. All 23 members of the SAP carrying lgs1 alleles had low Striga germination stimulant activity. The smaller previously described intragenic deletion mutations lgs1-4 and lgs1-5 are not present in the SAP. The LGS1 marker is useful for both detecting sources of lgs1 and introgressing Striga resistance into new genetic backgrounds.

Strigolactone biosynthesis lgs1 mutant alleles mined from the sorghum accession panel are a promising resource of resistance to witchweed (Striga) parasitism

Societal Impact StatementStriga is a parasitic plant that greatly limits the production of Africa's most staple cereals, including sorghum. Infection occurs when the parasite germinates in response to biomolecules emitted into the soil from the host's roots. Some sorghum genotypes harbor a mutation that makes them ineffective in stimulating Striga seed germination. This resistance is of great importance because of its possible application in Striga management. Here, additional resistant sorghum genotypes with varying levels of Striga resistance are discussed in the context of their candidacy for integration in breeding programs and their possible role in alleviating food insecurity in sub‐Saharan Africa by reducing crop losses because of Striga infestation.Summary Sorghum is a food staple for millions of people in sub‐Saharan Africa, but its production is greatly diminished by Striga, a parasitic weed. An efficient and cost‐effective way of managing Striga in smallholder farms in Africa is to deploy resistant varieties of sorghum. Here, we leverage genomics and the vast genetic diversity of sorghum—evolutionarily adapted to cope with Striga parasitism in Africa—to identify new Striga‐resistant sorghum genotypes by exploiting a resistance mechanism hinged on communication molecules called strigolactones (SLs), exuded by hosts to trigger parasite seed germination. We achieved this by mining for mutant alleles of the LOW GERMINATION STIMULANT 1 (LGS1) that are ineffective in stimulating Striga germination from the sorghum accession panel (SAP). Our analysis identified lgs1 sorghum genotypes, which we named SAP‐lgs1. SAP‐lgs1 had the SL exudation profile of known lgs1 sorghum, whose hallmark is the production of the low inducer of germination, orobanchol. Laboratory and field resistance screens showed that the SAP‐lgs1 genotypes also exhibited remarkable resistance against Striga. Our findings have the potential to reduce crop losses because of Striga parasitism and therefore have far‐reaching implications for improving food security in Africa.

Essential plant nutrients impair post‐germination development of Striga in sorghum

Societal Impact StatementInfestation by the parasitic weed Striga is a major cause of cereal crop production losses on smallholder farms in Africa. Essential plant nutrients play an important indirect role in parasite seed germination, the first prerequisite for successful parasitism. Here, we demonstrate that increasing the nutrient availability for the host plant can also impede Striga development beyond its germination, independent of the resistance levels of the sorghum host. This insight provides additional support for crop protection recommendations to Striga‐affected farmers. Growing a resistant crop variety combined with adequate levels of fertilisers should be the backbone of defence against this parasitic weed.Summary Striga hermonthica is a widespread parasitic weed in sub‐Saharan Africa and an important biotic constraint to sorghum production. Resistant varieties and fertilisers are crucial components of integrated Striga management. N and P fertilisers reduce the production of host‐plant strigolactones, known as Striga germination stimulants, and thereby reduce infection. Whether essential plant nutrients affect the parasite–host interaction beyond Striga germination is unknown. We conducted mini‐rhizotron assays to investigate the effects of macronutrient and micronutrient availability on post‐germination Striga development. Four sorghum genotypes (Framida, IS10978, N13, IS9830) covering the complete array of known mechanisms of post‐attachment resistance were compared with susceptible genotype Ochuti. Plants were infected with pre‐germinated Striga seeds and subjected to four nutrient treatment levels: (1) 25% of the optimal concentration of Long Ashton solution for cereals; (2) 25% macronutrient and optimal micronutrient concentration; (3) optimal macronutrient and 25% micronutrient concentration; and (4) optimal macronutrient and micronutrient concentrations. Compared with the 25% base nutrient level, treatments supplemented with macronutrients reduced the number of viable vascular connections established by pre‐germinated Striga seedlings as well as the total parasite biomass on the sorghum root system. Macronutrient treatment effects were observed across sorghum genotypes, independent of the presence and type of post‐attachment resistance, but appeared to specifically improve mechanical resistance, hypersensitive and incompatibility responses before Striga reaches the host‐root xylem. This study demonstrates, for the first time, that nutrient availability drives Striga parasitism beyond the germination stages. Increased availability of nutrients, in particular macronutrients, enhances host‐plant resistance in post‐attachment stages, reinforcing the importance of current fertiliser recommendations.

CRISPR/Cas9-Mediated Mutagenesis of Carotenoid Cleavage Dioxygenase (CCD) Genes in Sorghum Alters Strigolactone Biosynthesis and Plant Biotic Interactions

Strigolactones are a group of small molecules that play critical roles in plant developmental processes and root biotic interactions. Strigolactones are agronomically important due to their role as a signal for the germination of a parasitic weed ( Striga spp.) that reduces yields of cereal crops worldwide. To identify the genes encoding strigolactones in sorghum and their function, we characterized two CRISPR/Cas9-mediated gene knockouts of carotenoid cleavage dioxygenase 8 ( CCD8) genes ( SbCCD8a and SbCCD8b), which have been shown in other plant species to be involved in strigolactone biosynthesis. Although strigolactones are important for the parasitization of sorghum in Africa, the functions of members of the CCD8 family have not been characterized. The impact of the knockouts on strigolactone production, plant growth and development, resistance to the parasitic weed Striga, and the root-associated microbiomes were investigated in this study. The results revealed that knockout of SbCCD8 genes in sorghum significantly reduced orobanchol production and Striga germination. Strigolactone deficiency altered the shoot and root architecture and reduced grain yield of sorghum. The knockout of the SbCCD8b gene significantly affected the rhizosphere bacterial diversity and community composition at sorghum plant grain-fill stage due to the abolition of orobanchol exudation from roots. Reduced amounts of orobanchol in root exudates also influenced root-associated fungal taxa abundance. Our findings provide new insights into potentially sustainable approaches for the recruitment of beneficial microbes and for parasitic weed control through manipulation of strigolactone production in sorghum.

Cytokinins as an alternative suicidal Striga germination compound

AbstractThe witchweed Striga hermonthica, an obligate and noxious root–parasitic plant, remains a persistent threat to cereal production and poses a great challenge to smallholder farmers in Sub‐Saharan Africa. Inducing suicidal germination of Striga seeds by applying strigolactone analogs is a promising strategy to deplete the Striga seed bank of infested soils. Nevertheless, there is a need to increase the efficiency and improve the applicability of this strategy, which may be achieved by testing further Striga germination stimulants. Herein, we explored the potential of cytokinins in inducing Striga seed germination. We investigated their activity as a suicidal germination agent along with fluridone that inhibits carotenoid biosynthesis and hence reduces abscisic acid formation and facilitates breaking of seed dormancy. Under lab conditions, application of fluridone (at 100 μM) or cytokinins (at 100 μM) showed 19% and 63% Striga germination, respectively, while combining different cytokinins with fluridone led to above 93% germination of treated seeds, with thidiazuron as the most active cytokinin. Using rice (cv IAC‐165), we also show that co‐application of fluoridone and thidiazuron to Striga infested pots before planting the host led to up to 86%–100% reduction in Striga emergence. In summary, cytokinins, particularly thidiazuron, could be useful suicidal agents to induce Striga seed germination and ultimately deplete the seedbank in Striga‐infested regions.

Gibberellins promote seed conditioning by up-regulating strigolactone receptors in the parasitic plant Striga hermonthica.

Dormant seeds of a root parasitic plant Striga hermonthica sense strigolactones from host plants as environmental cues for germination. This process is mediated by diversified member of strigolactone receptors encoded by HYPOSENSITIVE TO LIGHT/KARRIKIN INSENSITIVE2 genes. It is known that warm and moist treatment of seed conditioning gradually turns dormant Striga seeds competent to respond strigolactones, while the mechanism behind it has been poorly understood. In this report, we show that plant hormone gibberellins increase the strigolactone-competence by up-regulating mRNA expressions of the major strigolactone receptors during the conditioning period. This idea was supported by poor germination phenotype when gibberellin biosynthesis is depleted by paclobutrazol during conditioning. Moreover, live-imaging with fluorogenic strigolactone-mimic, yoshimulactone green W, revealed that paclobutrazol treatment during conditioning caused aberrant dynamics of strigolactone perception after germination. These observations revealed an indirect role of gibberellins to the seed germination in Striga, which is contrastive to their roles as dominant germination stimulating hormone in non-parasitic plants. We propose a model of how the role of gibberellins become indirect during the evolution of parasitism in plants. Our work also highlight the potential role for gibberellins in field application, for instance, elevating the sensitivity of the seeds towards strigolactones in the current suicidal germination approach to alleviate the agricultural threats caused by this parasite in Africa.

Transcriptome atlas of Striga germination: Implications for managing an intractable parasitic plant

Societal Impact StatementWitchweeds, parasitic plants of the genus Striga, are nicknamed “cereal killers” because of their devastating destruction of Africa's most staple cereals, including maize, sorghum, millets, and upland rice. The parasite relies on biomolecules emitted from the host roots to germinate and therefore initiate its infectious lifecycle. Some sorghum varieties have evolved to not produce effective germination stimulants, making them resistant to the parasite. Here, the genetic factors that underpin Striga germination were assessed, followed by a discussion of how such knowledge can be used to develop new Striga management strategies through the disruption of host–parasite communication exchange.Summary Seeds of the parasitic plant Striga are dormant. They only germinate in response to biomolecules emitted from the host's root exudate, strigolactones (SL). But it is now emerging that Striga germination is a much more complex process regulated by crosstalk of hormone signaling pathways. To further understand the genetic basis of the communication exchange between Striga and its host sorghum, we performed a comparative transcriptomic analysis. We sought to identify major transcriptomic changes that define the germination process in Striga and a set of genes that may contribute to the differences in germination rates. Results showed that germination proceeds immediately after SL perception and is marked by a wave of transcriptional reprogramming to allow for metabolic processes of energy mobilization. Cluster analysis using self‐organizing maps revealed a time‐phased and genotype‐differentiated response to germination stimulation. The variation in germination was also a function of hormonal crosstalk. The early germination stage was associated with significant repression of genes in the abscisic acid (ABA) biosynthesis pathway. Other hormones influenced germination as follows: (i) ABA and auxin repressed germination; (ii) brassinosteroid, ethylene, and jasmonic acid promoted germination; and (iii) cytokinin had a more prominent role post‐germination rather than during germination. Perception of SL sets the germination program leading to different rates of germination in sorghum, followed by a complex hormonal regulation network that acts to either repress or enhance germination. We discuss the implications of these findings and present new plausible Striga management strategies.

Conferring resistance to parasitic witchweed by shifting strigolactone biosynthesis

Strigolactones from the exudates of maize root induce germination of the parasitic witchweed Striga. Recently, Li et al. characterized the biosynthesis pathway of two strigolactones, zealactol and zealactonoic acid, which induce less Striga germination than the major maize strigolactone, zealactone. This study provides a promising strategy for plant protection against parasitic witchweed.

Germination, Attachment and Development of Striga hermonthica (Del.) Benth Induced by Host and Non-host Crops

Striga hermonthica (Del) Benth is a semi-parasitic weed thatreduces yields of sorghum, maize, pearl millet, sugarcane and rice in thesemi-arid tropics. Germination of striga seed is induced by stimulantsexuded by roots of host and non-host plants. The objectives of this studywere to compare the ability of some host and non-host crops to inducestriga seed germination and haustoria formation as well as to confirm thesusceptibility of wheat and barley to infestation. S. hermonthica seedswere collected from Abu Haraz, Gezira State, Sudan, in 2004/2005, andtheir germination on some host and non-host crops was investigated usingroot chambers that allow observation of striga underground stages. Strigaseeds germinated with all tested crops. Besides sorghum varieties andmaize, S. hermonthica germinated, attached and developed to completestriga plants with barley and two cultivars of wheat from Sudan. This isthe first report of S. hermonthica parasitizing wheat and barley in Sudan.Use of root chambers proved that some leguminous crops weresusceptible to S. hermonthica. Chick pea (Cicer arietinum L.),phillipesera (Vigna trilobata L.), brown seed cowpea [Vigna unguiculata(L.) Walp.], hyacinth bean (Lablab purpureus L.), peas (Pisum sativumL.) pigeon pea (Cajanus cajan L.), faba bean and mung bean inducedseed germination, attachment and development of complete green strigaplants. Soybean, roselle, safflower and sunflower supported germinationand attachment of S. hermonthica, but there was no further developmentof the semi-parasitic weed. A natural brownish colouration around the

Canonical strigolactones are not the major determinant of tillering but important rhizospheric signals in rice.

Strigolactones (SLs) are a plant hormone inhibiting shoot branching/tillering and a rhizospheric, chemical signal that triggers seed germination of the noxious root parasitic plant Striga and mediates symbiosis with beneficial arbuscular mycorrhizal fungi. Identifying specific roles of canonical and noncanonical SLs, the two SL subfamilies, is important for developing Striga-resistant cereals and for engineering plant architecture. Here, we report that rice mutants lacking canonical SLs do not show the shoot phenotypes known for SL-deficient plants, exhibiting only a delay in establishing arbuscular mycorrhizal symbiosis, but release exudates with a significantly decreased Striga seed-germinating activity. Blocking the biosynthesis of canonical SLs by TIS108, a specific enzyme inhibitor, significantly lowered Striga infestation without affecting rice growth. These results indicate that canonical SLs are not the determinant of shoot architecture and pave the way for increasing crop resistance by gene editing or chemical treatment.

Aqueous extracts from indigenous plant in Burkina Faso with bio-herbicide properties to reduce Striga hermonthica (Del.) Benth propagation

BackgroundThe genus Striga includes 11 parasitic plants species of food crops in at least 50 African countries. Striga hermonthica (Del.) Benth. is a major biotic constraint to the cereal crops production in Africa. It is the most widespread species in fields in Burkina Faso and grows on all types of soil inducing losses estimated at 35–40% on sorghum and millet. The substantial reductions in yield caused by S. hermonthica contribute significantly to an insufficient food supply for the populations in the area.MethodsThis study aims to identify local plants with bio-herbicidal properties for the management of S. hermonthica. The inhibiting and stimulating effect of aqueous extracts from 13 local plant species on the germination of S. hermonthica seeds was assessed in vitro.ResultsThe aqueous extracts from the leaves of Azadirachta indica A. Juss, Jatropha curcas L., Jatropha gossypiifolia L., Lawsonia inermis L. and those from the leafy stems of Cassia obtusifolia L., Crotalaria retusa L., Phyllanthus amarus L. completely inhibited germination of Striga. Five other plant extracts significantly stimulated germination, of which the highest germination rate (60%) was recorded with the extract from Euphorbia hirta L. leafy stems.ConclusionsThe plant extracts thus constitute an ecological avenue for S. hermonthica control. Further experiments could lead to the formulation of bio-herbicides against the parasitic plant to improve cereal production while limiting environmental pollution.

Nutritional management and maize variety combination effectively control Striga asiatica in southern Africa

Maize (Zea mays L.) is an important staple food crop in sub-Saharan Africa (SSA) and contributes significantly to food security. Due to Striga, maize yield loss is estimated between 20 and 80% forcing some farmers to abandon their land therefore threatening food security. Many strategies have been applied to combat Striga infested fields to improve maize yields but alternative feasible approaches are still required. This study aimed at determining effects of phosphorus (P) and maize variety on Striga asiatica germination and attachment. A factorial experiment of eight P levels (0, 10, 20, 30, 40, 50, 60 and 70 kg ha−1), six maize varieties and Striga (inoculated and non-inoculated) in a 4 × 24 α-lattice design with three replications was set in a glasshouse at the University of Zimbabwe. A similar experiment was set under laboratory conditions using agar gel plates to determine S. asiatica germination using a complete randomized design with three replications. Adding P (at 40 kg ha−1) to soil infected with Striga, significantly (p < 0.05) reduced Striga counts and haustorial root attachments in all varieties with CV4 and R201 supporting lowest numbers. P also significantly (p < 0.05) improved plant height, chlorophyll content, leaf, cob, total biomasses and grain yield across all maize genotypes. Cultivar CV4 produced the highest grain yield under Striga attack. Furthermore, cultivars CV4 and CV1 had significantly (p < 0.05) lowest Striga seed maximum germination distance and percentages at zero P. Application of P reduced Striga germination, attachments and emergence in all varieties and increased tolerance of maize varieties.

In vitro evaluation of marker assisted conversion of adapted sorghum varieties into Striga hermonthica resistant versions

Striga has long been recognized to infest staple food crops like sorghum in Ethiopia. This study was designed to introgress Striga-resistance genes into popular and farmer-preferred varieties through marker-assisted backcrossing and to assess resistance based on Striga germination stimulant activity inagar-gel assay (aga). The experiment was arranged in completely randomized design with four replications. Genotypes performance, heritability and genetic advance were analyzed and Germination rate was measured. The progeny showed significant genetic variation for maximum germination distance (mgd), germination rate (gr), and germination index (gi). The mean mgd ranged from 0.0 mm to 29.45 mm and gr ranged from 0.0% to 72.38%.Of the 118 backcrossed lines, 22.9% showed less than 10 mm of mgd and gr of &lt;30%, revealing provision of low germination stimulant/strigolactones production (lgs). There were significant positive (r = 0.4-0.81) correlations showing the roles of these parameters as selection criteria in breeding for resistance. The existence of higher heritability (h2b = 77-83%) and genetic advance (ga = 62-93%) for the germination parameters indicated possibilities for improving resistance against Striga through selection. Genotypes that carry different qtls showed different capacity of producing Striga germination stimulants in the aga. The combined effect of two qtls (lgs2_SBI-05_60404021 and lgs_3_60629027) at a time showed lower Striga germination stimulant activity and better field resistance indicating existence of possible cumulative effects. Thus, the study showed that marker-assisted backcrossing for transfer of lgs qtls from donor into popular and farmers preferred cultivars has the potential to enhance tolerance/resistance to Striga in sorghum.

Striga hermonthica Suicidal Germination Activity of Potent Strigolactone Analogs: Evaluation from Laboratory Bioassays to Field Trials.

The obligate hemiparasite Striga hermonthica is one of the major global biotic threats to agriculture in sub-Saharan Africa, causing severe yield losses of cereals. The germination of Striga seeds relies on host-released signaling molecules, mainly strigolactones (SLs). This dependency opens up the possibility of deploying SL analogs as “suicidal germination agents” to reduce the accumulated seed bank of Striga in infested soils. Although several synthetic SL analogs have been developed for this purpose, the utility of these compounds in realizing the suicidal germination strategy for combating Striga is still largely unknown. Here, we evaluated the efficacy of three potent SL analogs (MP3, MP16, and Nijmegen-1) under laboratory, greenhouse, and farmer’s field conditions. All investigated analogs showed around a 50% Striga germination rate, equivalent to a 50% reduction in infestation, which was comparable to the standard SL analog GR24. Importantly, MP16 had the maximum reduction of Striga emergence (97%) in the greenhouse experiment, while Nijmegen-1 appeared to be a promising candidate under field conditions, with a 43% and 60% reduction of Striga emergence in pearl millet and sorghum fields, respectively. These findings confirm that the selected SL analogs appear to make promising candidates as simple suicidal agents both under laboratory and real African field conditions, which may support us to improve suicidal germination technology to deplete the Striga seed bank in African agriculture.

Mechanisms of pre-attachment Striga resistance in sorghum through genome-wide association studies.

Witchweeds (Striga spp.) greatly limit production of Africa's most staple crops. These parasitic plants use strigolactones (SLs)-chemical germination stimulants, emitted from host's roots to germinate, and locate their hosts for invasion. This information exchange provides opportunities for controlling the parasite by either stimulating parasite seed germination without a host (suicidal germination) or by inhibiting parasite seed germination (pre-attachment resistance). We sought to determine genetic factors that underpin Striga pre-attachment resistance in sorghum using the genome wide association study (GWAS) approach. Results revealed that Striga germination was associated with genes encoding hormone signaling functions, e.g., the Novel interactor of jaz (NINJA) and, Abscisic acid-insensitive 5 (ABI5). This pointed toward abscisic acid (ABA) and gibberellic acid (GA) as probable determinants of Striga germination. To test this hypothesis, we conditioned Striga using: ABA, ABA + its inhibitor fluridone (FLU), GA or water. Unexpectedly, Striga conditioned with FLU germinated after 4days without SL. Upon germination stimulation using sorghum root exudate or the synthetic SL GR24, we found that ABA conditioned seeds had above 20-fold reduction in germination. Conversely, FLU conditioned seeds recorded above 20-fold increase in germination. Conditioning with GA reduced Striga seed germination 1.5-fold only in the GR24 treatment. Germination assays using seeds of a related parasitic plant (Alectra vogelii) showed similar degrees of stimulation and reduction of germination by the hormones further affirming the hormonal crosstalk. Our findings have far-reaching implications in the control of some of the most noxious pathogens of crops in Africa.

A New Formulation for Strigolactone Suicidal Germination Agents, towards Successful Striga Management.

Striga hermonthica, a member of the Orobanchaceae family, is an obligate root parasite of staple cereal crops, which poses a tremendous threat to food security, contributing to malnutrition and poverty in many African countries. Depleting Striga seed reservoirs from infested soils is one of the crucial approaches to minimize subterranean damage to crops. The dependency of Striga germination on the host-released strigolactones (SLs) has prompted the development of the “Suicidal Germination” strategy to reduce the accumulated seed bank of Striga. The success of aforementioned strategy depends not only on the activity of the applied SL analogs, but also requires suitable application protocol with simple, efficient, and handy formulation for rain-fed African agriculture. Here, we developed a new formulation “Emulsifiable Concentration (EC)” for the two previously field-assessed SL analogs Methyl phenlactonoate 3 (MP3) and Nijmegen-1. The new EC formulation was evaluated for biological activities under lab, greenhouse, mini-field, and field conditions in comparison to the previously used Atlas G-1086 formulation. The EC formulation of SL analogs showed better activities on Striga germination with lower EC50 and high stability under Lab conditions. Moreover, EC formulated SL analogs at 1.0 µM concentrations reduced 89–99% Striga emergence in greenhouse. The two EC formulated SL analogs showed also a considerable reduction in Striga emergence in mini-field and field experiments. In conclusion, we have successfully developed a desired formulation for applying SL analogs as suicidal agents for large-scale field application. The encouraging results presented in this study pave the way for integrating the suicidal germination approach in sustainable Striga management strategies for African agriculture.

A novel strigolactone receptor antagonist provides insights into the structural inhibition, conditioning, and germination of the crop parasite Striga

Crop parasites of the Striga genera are a major biological deterrent to food security in Africa and are one of the largest obstacles to poverty alleviation on the continent. Striga seeds germinate by sensing small-molecule hormones, strigolactones (SLs), that emanate from host roots. Although SL receptors (Striga hermonthica HYPOSENSITIVE TO LIGHT [ShHTL]) have been identified, discerning their function has been difficult because these parasites cannot be easily grown under laboratory conditions. Moreover, many Striga species are obligate outcrossers that are not transformable, hence not amenable to genetic analysis. By combining phenotypic screening with ShHTL structural information and hybrid drug discovery methods, we discovered a potent SL perception inhibitor for Striga, dormirazine (DOZ). Structural analysis of this piperazine-based antagonist reveals a novel binding mechanism, distinct from that of known SLs, blocking access of the hormone to its receptor. Furthermore, DOZ reduces the flexibility of protein–protein interaction domains important for receptor signaling to downstream partners. In planta, we show, via temporal additions of DOZ, that SL receptors are required at a specific time during seed conditioning. This conditioning is essential to prime seed germination at the right time; thus, this SL-sensitive stage appears to be critical for adequate receptor signaling. Aside from uncovering a function for ShHTL during seed conditioning, these results suggest that future Ag-Biotech Solutions to Striga infestations will need to carefully time the application of antagonists to exploit receptor availability and outcompete natural SLs, critical elements for successful parasitic plant invasions.

STRIGA HERMONTHICA SUICIDAL GERMINATION ACTIVITY OF TEN SOYABEAN, COWPEA AND GROUNDNUT VARIETIES IN NIGER STATE, NIGERIA

The obligate hemiparasite Striga hermonthica is one of the major global biotic threats to agriculture in sub-Saharan Africa, causing severe yield losses of cereals. The germination of Striga seeds relies on host-released signaling molecules, mainly Strigolactones (SLs). Strigolactones (SLs) are plant hormones that regulate the branching of plants and seed germination stimulants of root parasitic plants. Striga hermonthica’s non-hosts stimulate parasite seed to germinate without getting infected because the non-hosts produce unique germination stimulants Strigolactones). This phenomenon called suicidal seed germination is greatly used in S. hermonthica control. For improved efficiency of the suicidal seed germination method in S. hermonthica control, detailed analysis of comparative ability of potential trap crops to stimulate germination is critical. This study was undertaken with the aim to screen 10 genotypes each of soybean, cowpea and groundnut as trap crops for Striga: the potential ability of their root exudates to stimulate germination of Striga seed was evaluated. The results indicate that soyabean varieties TGX 1019-2EB and TGX 1448-2E delayed Striga emergence in 2013 and 2014 respectively compared to other varieties. In the results of the Striga count, plant height and grain yield, Soyabean variety TGX 1448-2E generally performed better than other varieties. 2.5 g Striga level gave better results in all the parameters measured compared to 5 g Striga level. Cowpea varieties IT04K-339-1 and IT07K-25-3-3 delayed Striga emergence in 2013 and 2014 respectively, while in Striga count and plant height, cowpea variety IT04K-217-5 performed better than other varieties but higher grain yield was recorded in cowpea variety IT04K-339-1 compared to other varieties. Groundnut varieties TES, QH 243C, RMP-12 and RMP-91 delayed Striga emergence compared to other varieties in 2014. Groundnut variety RMP-91 performed better in Striga count, plant height and grain yield in both planting years 2013 and 2014 compared to other varieties.

Discovery of a Broad-Spectrum Fluorogenic Agonist for Strigolactone Receptors through a Computational Approach.

Strigolactones (SLs) are plant hormones that play various roles in plant physiology, including provoking the germination of parasitic weeds Orobanche and Striga. A family of α/β-hydrolases have been proposed to be the SL receptor proteins. Effective assays for measuring the activity of SL receptors could promote the development of SL-related biology and chemistry. In this study, we developed a new approach called pharmacophore-linked probe virtual screening (PPVS). Its application yielded an effective "off-on" probe named Xilatone Red (XLR). This probe showed a broad spectrum and excellent sensitivity toward SL receptors, including ShD14 (Striga D14), for which the detection limit was determined to be in the micromolar range, outperforming that of the commercial fluorogenic agonist Yoshimulactone Green (YLG). Upon hydrolysis by SL receptors, XLR provided fluorogenic and colorimetric signaling responses. Furthermore, XLR could induce germination of Phelipanche aegyptiaca seeds and prevent Arabidopsis max4-1 branching defects at micromolar concentrations. Our molecular simulations revealed the essential factors in the molecular perception of XLR. We anticipate that this study can prompt the discovery of high-performance SL agonists/antagonists to combat parasitic weeds.

Characterization of growth and development of sorghum genotypes with differential susceptibility to Striga hermonthica.

Two sorghum varieties, Shanqui Red (SQR) and SRN39, have distinct levels of susceptibility to the parasitic weed Striga hermonthica, which have been attributed to different strigolactone composition within their root exudates. Root exudates of the Striga-susceptible variety Shanqui Red (SQR) contain primarily 5-deoxystrigol, which has a high efficiency for inducing Striga germination. SRN39 roots primarily exude orobanchol, leading to reduced Striga germination and making this variety resistant to Striga. The structural diversity in exuded strigolactones is determined by a polymorphism in the LOW GERMINATION STIMULANT 1 (LGS1) locus. Yet, the genetic diversity between SQR and SRN39 is broad and has not been addressed in terms of growth and development. Here, we demonstrate additional differences between SQR and SRN39 by phenotypic and molecular characterization. A suite of genes related to metabolism was differentially expressed between SQR and SRN39. Increased levels of gibberellin precursors in SRN39 were accompanied by slower growth rate and developmental delay and we observed an overall increased SRN39 biomass. The slow-down in growth and differences in transcriptome profiles of SRN39 were strongly associated with plant age. Additionally, enhanced lateral root growth was observed in SRN39 and three additional genotypes exuding primarily orobanchol. In summary, we demonstrate that the differences between SQR and SRN39 reach further than the changes in strigolactone profile in the root exudate and translate into alterations in growth and development.