Striga Germination Stimulants 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.

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.

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.

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 <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.

Crystal structure and biochemical characterization of Striga hermonthica HYPO-SENSITIVE TO LIGHT 8 (ShHTL8) in strigolactone signaling pathway

Striga is a parasitic weed that disperses easily, and its seeds can persist in the soil for many years, presenting long-term threats to food security. If SLs stimulate the seed germination of root parasitic weeds before planting, weeds will wither due to no host. Therefore, it is necessary to determine the mechanism of strigolactone (SL) signaling in Striga to reduce the impacts of this parasitic weed. Striga has eleven different kinds of HYPO-SENSITIVE to LIGHT (ShHTL) hydrolases. Different ShHTL hydrolases exhibit distinct responses to SLs, despite these ShHTLs exhibiting more than 60% sequence identity. Currently, structural information is available for only five ShHTL proteins, and more structural information is needed to design Striga germination stimulants or inhibitors. In this paper, we report the crystal structure of ShHTL8, which is determined at a resolution of 1.4 Å. Scanning fluorimetry and HPLC assays indicate that L125, M147, M154 and I194 are important binding sites, and of which L125 may act as a key holder involved in the catalytic reaction. Additionally, the corresponding residue, Y124 of ShHTL1 and F135 of ShHTL2 also play a significant role in the substrate recognition.

Genetic variation in Sorghum bicolor strigolactones and their role in resistance against Striga hermonthica.

Sorghum is an important food, feed, and industrial crop worldwide. Parasitic weeds of the genus Striga constitute a major constraint to sorghum production, particularly in the drier parts of the world. In this study we analysed the Striga germination stimulants, strigolactones, in the root exudates of 36 sorghum genotypes and assessed Striga germination and infection. Low germination-stimulating activity and low Striga infection correlated with the exudation of low amounts of 5-deoxystrigol and high amounts of orobanchol, whereas susceptibility to Striga and high germination-stimulating activity correlated with high concentrations of 5-deoxystrigol and low concentrations of orobanchol. Marker analysis suggested that similar genetics to those previously described for the resistant sorghum variety SRN39 and the susceptible variety Shanqui Red underlie these differences. This study shows that the strigolactone profile in the root exudate of sorghum has a large impact on the level of Striga infection. High concentrations of 5-deoxystrigol result in high infection, while high concentrations of orobanchol result in low infection. This knowledge should help to optimize the use of low germination stimulant-based resistance to Striga by the selection of sorghum genotypes with strigolactone profiles that favour normal growth and development, but reduce the risk of Striga infection.

Mutation in sorghum LOW GERMINATION STIMULANT 1 alters strigolactones and causes Striga resistance

Striga is a major biotic constraint to sorghum production in semiarid tropical Africa and Asia. Genetic resistance to this parasitic weed is the most economically feasible control measure. Mutant alleles at the LGS1 (LOW GERMINATION STIMULANT 1) locus drastically reduce Striga germination stimulant activity. We provide evidence that the responsible gene at LGS1 codes for an enzyme annotated as a sulfotransferase and show that functional loss of this gene results in a change of the dominant strigolactone (SL) in root exudates from 5-deoxystrigol, a highly active Striga germination stimulant, to orobanchol, an SL with opposite stereochemistry. Orobanchol, although not previously reported in sorghum, functions in the multiple SL roles required for normal growth and environmental responsiveness but does not stimulate germination of Striga This work describes the identification of a gene regulating Striga resistance and the underlying protective chemistry resulting from mutation.

Genotypic Variation for Low Striga Germination Stimulation in Sorghum “<i>Sorghum bicolor</i> (L.) Moench” Landraces from Eritrea

Sorghum (Sorghum bicolour (L.) Moench), the second most important staple crop in Sub-Saharan Africa (SSA) after maize, is well adapted to marginal environments of drought stress and high temperatures. But besides drought stress, the obligate root-parasitic flowering plant Striga hermonthica is an equally economically important biotic stress in agro-ecological zones where soils are marginal. Notwithstanding widespread and intense Striga infestation, genetic variations in defence mechanisms against the parasite have been reported. Sorghum variants, producing low levels of chemical stimulants such as sorgolactones that deter the advance of Striga seed germination and are therefore deemed resistant to the parasite, have been also reported in a few studies. But the existence of sorghum genetic variation for this resistance especially among farmers’ landraces is yet to be demonstrated. The objective of this study was therefore to determine the levels of Striga germination stimulants in response to each of the 111 collected sorghum landraces and their progenies from Eritrea. The ability of a sorghum genotype to cause germination of a Striga seed as a measure of the amount of the germination stimulant produced was used to assess the resistance of these accessions. The data were recorded as Striga germination percentage by counting the number of germinated Striga seeds. Landraces EG47, EG1261, EG830, EG1076, EG54 and EG746 with 14.68%, 15.32%, 11.85%, 13.05%, 15.74% and 16.5% germination percentages respectively were found to stimulate low levels of Striga germination percentage compared to commercial checks, IS9830, SRN39, Framida, with 22.46%, 22.67%, 23.27% germination respectively. While these variants did not show complete resistance against Striga seed germination, the low level production of stimulant indicated their high level of resistance to Striga . These results implied that these accessions are likely potential sources of resistance against Striga infestation in SSA sorghum breeding programs.

Determination of levels of Striga germination Stimulants for maize gene bank accessions and elite inbred lines

Parasitism by Striga hermonthica (Del) Benth is a severe constraint in maize production in sub-Saharan Africa. Varying levels of tolerance to Striga attack have been identified and exploited in breeding programs of several crops. However, the level and stability of the tolerance is generally unacceptable in field-practice. Only limited exploration has been undertaken among the farmers’ landraces to find the presence of viable sources of resistance to Striga. The objective of this study was to examine and document the presence of the Striga germination stimulants from a collection of some 420 maize landraces, populations and elite inbred lines. The genotypes were variously sourced from International Maize and Wheat Improvement Center (CIMMYT), International Institute for Tropical Agriculture (IITA) and Kenya Agricultural Research Institute (KARI). The ability to effect germination as a measure of the amount of germination stimulant produced was used to assess the materials, using the standard procedures. Data were recorded on Striga germination by counting Striga seeds with protruding radicle. Highly significant (P=0.001) differences were observed among the germplasm screened. Several landraces were found to stimulate low levels of Striga germination compared to the commercial checks. Landraces CRIC 51, CUBA T-31, BRAZ 1758, BRAZ 1279 and VERA 217 exhibited the lowest Striga germination, an indication of high level of resistance to Striga. The inbred lines were found to have a higher Striga germination percent compared to the landraces, a likelihood of a higher concentration of strigol, the stimulant causing chemical. CIMMYT lines CML 202 IR, CML 445 IR and CML 204 IR induced the least amount of Striga seeds to germinate. Higher levels of germination of Striga seeds were found in the IITA lines which are known to be

Striga hermonthica parasitism in maize in response to N and P fertilisers

Parasitism by the parasitic weed, Striga hermonthica (Striga), constitutes a major biological constraint to maize production in sub-Sahara Africa. Nutrient deficiency is known to aggravate Striga infestation and in a number of plant species it was recently shown that this may be due to increased secretion of Striga germination stimulants into the soil. The present study was designed to observe the connection between soil fertility, secretion of germination stimulants and Striga infection in maize under greenhouse and field conditions. The experiments were conducted during two successive cropping seasons (2008 and 2009). The greenhouse study showed that maize secretes a number of so far unidentified strigolactones that induce Striga seed germination and the amount of these strigolactones increases upon N and P deficiency. The increased secretion of germination stimulants under N and P deficiency resulted in increased Striga infection in pot experiments. The on-station and on-farm field trials in Western Kenya also showed reduction in Striga infestation with the application of mineral nutrients but the results were less consistent than in the greenhouse. Increasing levels of N showed a fair reduction of Striga in the field especially during the first year, whereas P application did not have much effect in contrast to the greenhouse study where both N and P clearly reduced Striga infection. The likely explanation for this discrepancy is that availability of mineral nutrients under field conditions is less predictable than under greenhouse conditions, due to a number of factors such as soil texture and structure, pH, salinity, drought, leaching and runoff. Hence, further studies are needed on the importance of these factors before a fertiliser application strategy can be formulated to improve control of Striga in maize in the field.

Molecular tagging and validation of microsatellite markers linked to the low germination stimulant gene (lgs) for Striga resistance in sorghum [Sorghum bicolor (L.) Moench

Striga is a devastating parasitic weed in Africa and parts of Asia. Low Striga germination stimulant activity, a well-known resistance mechanism in sorghum, is controlled by a single recessive gene (lgs). Molecular markers linked to the lgs gene can accelerate development of Striga-resistant cultivars. Using a high density linkage map constructed with 367 markers (DArT and SSRs) and an in vitro assay for germination stimulant activity towards Striga asiatica in 354 recombinant inbred lines derived from SRN39 (low stimulant)×Shanqui Red (high stimulant), we precisely tagged and mapped the lgs gene on SBI-05 between two tightly linked microsatellite markers SB3344 and SB3352 at a distance of 0.5 and 1.5cM, respectively. The fine-mapped lgs region was delimited to a 5.8cM interval with the closest three markers SB3344, SB3346 and SB3343 positioned at 0.5, 0.7 and 0.9cM, respectively. We validated tightly linked markers in a set of 23 diverse sorghum accessions, most of which were known to be Striga resistant, by genotyping and phenotyping for germination stimulant activity towards both S. asiatica and S. hermonthica. The markers co-segregated with Striga germination stimulant activity in 21 of the 23 tested lines. The lgs locus similarly affected germination stimulant activity for both Striga species. The identified markers would be useful in marker-assisted selection for introgressing this trait into susceptible sorghum cultivars. Examination of the sorghum genome sequence and comparative analysis with the rice genome suggests some candidate genes in the fine-mapped region (400kb) that may affect strigolactone biosynthesis or exudation. This work should form a foundation for map-based cloning of the lgs gene and aid in elucidation of an exact mechanism for resistance based on low Striga germination stimulant activity.

Striga hermonthica (Del.) Benth Germination Stimulant(s) from Menispermum dauricum (DC.) Root Culture

Germination of Striga hermonthica, an important root parasitic weed on cereals, is induced by stimulants exuded by roots of host and some nonhost plants. Efforts to isolate active compounds have focused on root exudates from intact plants. In this paper, a much easier and less laborious novel approach, based on root cultures, is described. Menispermum dauricum roots cultured in a modified B5 medium produced and exuded into the medium compounds with activity comparable to that of the synthetic strigol analogue GR24. The active components stimulate germination by induction of ethylene biosynthesis. Their accumulation in roots and culture medium, as indicated by activity, was at a maximum 6−8 weeks after subculturing and was positively correlated with root growth (r = 0.76−0.92). HPLC and TLC of the culture filtrate revealed at least two or three compounds, none of which had chromatographic properties consistent with those of strigol. The results indicate the potentials of root cultures as a possible source of novel Striga germination stimulants. Keywords: Germination stimulant; root culture; Striga hermonthica

Influence of conditions and genotype on the amount of Striga germination stimulants exuded by roots of several host crops

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfluence of conditions and genotype on the amount of Striga germination stimulants exuded by roots of several host cropsYohan. Weerasuriya, Bupe A. Siame, Dale. Hess, Gebisa. Ejeta, and Larry G. ButlerCite this: J. Agric. Food Chem. 1993, 41, 9, 1492–1496Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https://doi.org/10.1021/jf00033a026RIGHTS & PERMISSIONSArticle Views188Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (616 KB) Get e-Alerts Get e-Alerts

Selecting sorghum genotypes expressing a quantitative biosynthetic trait that confers resistance to Striga

One of the best characterized mechanisms of host resistance to witchweeds ( Striga spp.) is exudation by host plant roots of relatively low amounts of compounds that Striga seeds require as stimulants for germination. We find that all sorghums tested, regardless of whether they are susceptible or resistant to Striga, produce equivalent amounts of sorgoleone, the alkylated hydroquinone we previously identified from sorghum root exudate as the first host-derived Striga germination stimulant to be characterized. In contrast, some highly resistant sorghums produce relatively tiny amounts of another germination stimulant, as yet unidentified but with properties quite different from sorgoleone, whereas all susceptible sorghums produce relatively large amounts. A simple, rapid and nondestructive agar gel assay which detects this second stimulant, but not sorgoleone, reliably distinguishes low ( Striga resistant) and high ( Striga susceptible) stimulating parental genotypes and progenies from crosses among them. Because the lack of a reliable and rapid method for screening germplasm and breeding progenies has hampered the development of crop varieties resistant to Striga, this gel assay is expected to greatly enhance the efficiency of sorghum breeding for Striga resistance.

Persistence of GR7 and Striga germination stimulant(s) from Euphorbia aegyptiaca Boiss. in soils and in solutions

SummaryThe activity of GR7 and Striga germination stimulant(s) from Euphorbia aegyptiaca Boiss. showed adequate persistence (6–8 days) in acidic soils (pH 5·0–6·3), but residual activity was short (1–3 days) in alkaline soils. The compounds tended to lose activity at a faster rate in the alkaline clay Gezira soil (pH 7·8), than in its sandy equivalent (pH 8·1). In solution, pH had no influence on initial activity, but residual action was reduced more rapidly by alkalinity and high temperature. However, the rate of loss of activity in solution was slower than in soils.

A novel approach to Striga and Orobanche control using synthetic germination stimulants

Summary:A series of synthetic germination stimulants for the plant parasites Striga and Orobanche has been prepared. These compounds, analogues of the natural Striga germination stimulant, strigol (I), (Cook et al., 1966, 1972) cause signiticant germination of Striga hermonthica (Del.) Benth. seed at concentrations as low as 10−9 M, and an even greater activity against species of Orobanche has been demonstrated. Initial outdoor box trials of the compounds against Striga asiatica (L.) O. Ktze. in Hyderabad, India, have shown a reduction of up to 65% of the seed after a single treatment of the soil 6 weeks before the planting of the sorghum host.

Promotion of Germination of Striga asiatica Seed by Coumarin Derivatives and Effects on Seedling Development

OUR efforts to isolate and characterize the Striga germination stimulant in root exudates of maize were accompanied by testing more than 270 compounds for their capacity to stimulate germination. A previous paper1 reported the stimulation of Striga asiatica (witchweed) seed germination and described morphogenic effects on the seedlings induced by kinetin and certain other 6-(substituted) purines. This communication reports the results obtained with 41 coumarin derivatives, two of which stimulated germination of witchweed seeds.

The Production of theStrigaandOrobancheGermination Stimulants by Maize Roots

Six serial segments, each 3·0 mm. in length, have been excised from the tip backwards along the maize root and groups of each fragment have been aerated in water and in solutions of sugars for varying times. The amounts of the complex of Orobanche and Striga germination stimulants which accumulate in the culture fluids have been assessed and compared with the amounts initially present in the tissue at the time of excision from the root. It is shown that with each fragment more of the complex appears externally when sugar is supplied. 10−2 M. solutions of glucose, fructose, or sucrose promote an optimal effect. The amounts in the external solutions are inversely proportional to the initial contents of the segments. The first segment (0–3 mm.) contains the highest proportion of the complex initially, but when immersed in water or the sugar solution very little of it appears externally. The second segment (3–6 mm.) contains the least initial quantity of the complex but in water or sugar produces considerably more than any other segment and more than is originally present. As the series is traversed from segments 2 to 6, the segments have progressively larger initial contents than has segment 2, but after aeration in the sugar solutions the amounts accumulating externally are less than with segment 2 and decrease with their increasing distance from the root tip. The significance of these observations is discussed.

The Production of theStrigaandOrobancheGermination Stimulants by Maize Roots

By means of paper partition chromatography and a suitable biological test, the number and variety of the Orobanche and Striga germination stimulants produced by maize roots have been assessed. It is shown that extracts of maize roots and aqueous solutions in which roots have been suspended (diffusate solutions) contain a complex of stimulating substances consisting of, at least, one water-soluble and a number of ether-soluble stimulants. Germination of O. minor is promoted by the water-soluble stimulant and one of the ether-soluble stimulants (Mo). Germination of S. hermonthica is promoted by another ether-soluble stimulant (Ms). Aqueous extracts are rich in Ms and the water-soluble material, whereas the diffusate contains a higher proportion of Mo and only a trace of the water-soluble stimulant. The complex of ether-soluble stimulants, but not the water-soluble stimulant, accumulates in a solution of glucose when it is exposed to fragments of maize roots. These solutions contain a high proportion of Mo which is synthesized by the fragments and passes out into the sugar solution. It is suggested that the water-soluble stimulant is a precursor of Mo. The effects of the water-soluble stimulant and of Ms and Mo are greatly enhanced if a trace of the diffusate solution from linseed roots is mixed with them. The significance of the enhancement is discussed.

Effect of the Striga Germination Stimulant on the Respiration of Striga Seeds

THE demonstration by Vallance1 of the effect of the stimulant solution on the respiration of Striga seeds is a matter of some importance. Vallance, however, suggests that this effect is independent of that described by Brown, Robinson and Johnson2, who showed that the Striga stimulant may promote extension growth.