SEARCH · PubMed Health

Results for “Striga”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed2003

In vitro germination of Striga hermonthica and Striga aspera seeds by 1-aminocyclopropane-1-carboxylic acid.

Treatment of conditioned seeds of four isolates of Striga hermonthica and one isolate of Striga aspera with various concentrations of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), caused complex stimulation of germination patterns. GR 24, the strigol analogue served as a positive control and its stimulatory activity was comparable to that of ACC. When conditioned Striga seeds were treated with negative control that did not contain ACC, the stimulatory effect was lost. Overall, the germination data suggested a hormonal mode of action by ACC, which involves indirect stimulation of biosynthesis of ethylene that then triggers seed germination. The various mechanisms that have been proposed for the chemical and biological oxidation of ACC to generate ethylene are discussed.

Amino Acids, Cyclic↗

PubMed2003

Arbuscular mycorrhizal fungi-parasite-host interaction for the control of Striga hermonthica (Del.) Benth. in sorghum [Sorghum bicolor (L.) Moench].

Five Glomus species (G. intraradices, G. albidum, G. mosseae, G. fasciculatum, and G. etunicatum) were compared against a check [without arbuscular mycorrhizal (AM) fungi, plus Striga] and control (without AM fungi or Striga) treatments for the control of Striga in a tolerant sorghum variety (War-wara bashi) in an experiment carried out in 12-cm-diameter clay pots. The experiment was carried out in a controlled growth chamber. G. mosseae significantly reduced the number of Striga emerging per plant, increased plant growth, shoot and total dry matter yield of sorghum, did not affect the root dry matter compared with the other AM fungi species, but had a comparable effect to the control treatment. All the AM fungi except G. mosseae, and also the Striga-infested treatment, increased the root:shoot ratio compared to the control treatment. The percent reduction (62%) of Striga emergence after G. mosseae inoculation resulted in about a 30% increase in total dry matter yield of sorghum over the control, while the total loss in dry matter yield of sorghum due to Striga infestation was 36%. Root colonization of sorghum by AM fungi was highest for G. mosseae (44%) followed by G. intraradices (24%) and G. albidum (23%) then G. fasciculatum (18%), with the lowest recorded for G. etunicatum (14%). No colonization of Striga roots was observed. The potential of AM fungi to reduce or to compensate for Striga infestation could be important for soil management, especially in the tropics, and for the reduction of Striga-resistant varieties of sorghum which are mycorrhiza-responsive.

Fungi↗

PubMed1987

Gas exchange characteristics of the sorghum-striga host-parasite association.

Gas exchange characteristics are reported for both members of the sorghum-Striga host-parasite association. Both Striga hermonthica (Del.) Benth and Striga asiatica (L.) Kuntze had transpiration rates considerably in excess of those of sorghum (Sorghum bicolor (L.) Moench, cv CSH1). Stomatal conductance in both Striga spp. showed little response to periods of darkness and moderate water stress. Low rates of net CO(2) fixation and high rates of dark respiration led to no net daily (24 hours) C gain, and Striga would appear to be reliant on its host for photosynthate. Infection of sorghum plants with either S. hermonthica or S. asiatica reduced host photosynthetic capacity. Infected sorghum plants were also more prone to water stress, but reduced rates of CO(2) fixation could not be accounted for in terms of lower stomatal conductance. Lower stomatal conductances were associated with an increase in water use efficiency (WUE) in uninfected sorghum; however, Striga-infected sorghum plants had lower WUE than those of uninfected plants. We suggest that Striga exerts a specific effect on processes affecting C acquisition in sorghum leaves. The water relations of S. hermonthica and S. asiatica are not characteristic of plants growing in semiarid environments and are more likely to reflect the nature of the parasitic life-style. Despite transfer of water and solutes from host to parasite, the reduction in C fixation observed in infected sorghum plants appears to be the major determinant of growth reductions observed in sorghum supporting Striga.

Journal Article↗

PubMed2005

Molecular marker-based genetic diversity assessment of Striga-resistant maize inbred lines.

Striga-resistant maize inbred lines are of interest to maize breeding programs in the savannas of Africa where the parasitic weed is endemic and causes severe yield losses in tropical maize. Assessment of the genetic diversity of such inbred lines is useful for their systematic and efficient use in a breeding program. Diversity analysis of 41 Striga-resistant maize inbred lines was conducted using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers to examine the genetic relationships among these lines and to determine the level of genetic diversity that exists within and between their source populations. The two marker systems generated 262 and 101 polymorphic fragments, respectively. Genetic similarity (GS) values among all possible pairs of inbred lines varied from 0.45 to 0.95, with a mean of 0.61+/-0.002 for AFLPs, and from 0.21 to 0.92, with a mean of 0.48+/-0.003, for SSRs. The inbred lines from each source population exhibited a broad range of GS values with the two types of markers. Both AFLPs and SSRs revealed similar levels of within population genetic variation for all source populations. Cluster and principal component analysis of GS estimates with the two markers revealed clear differentiation of the Striga-resistant inbred lines into groups according to their source populations. There was clear separation between early- and late-maturing Striga-resistant inbred lines. Considering the paucity of germplasm with good levels of resistance to Striga in maize, the broad genetic diversity detected within and among source populations demonstrates the genetic potential that exists to improve maize for resistance to Striga.

Breeding↗

PubMed2002

The use of legume trap crops for control of Striga hermonthica (Del.) Benth. in sorghum (Sorghum bicolor L. Moench) in northern Nigeria.

Two different field trials (one trial on sorghum intercropped with groundnut [Arachis hypogaea L.], and another trial on sorghum intercropped with bambara groundnut [Vigna subterranea L. Verdc.]) were conducted during the 1995 and 1996 rainy seasons at the Teaching and Research Farm of the Department of Crop Science, Faculty of Agriculture, University of Maiduguri, Maiduguri (11 degrees 51' N; 13 degrees 15' E) to evaluate the effect of intercropping resistant and susceptible sorghum varieties with the two legume crops for the control of Striga hermonthica (Del.) Benth, in sorghum. The sorghum varieties used for both trials were ICSV 1002, ICSV 1007 (resistant varieties) and War-warabashi (susceptible). Ex-Dakar variety of groundnut was used for the sorghum-groundnut trial, while a creamed brown eyed local bambara groundnut was used for the sorghum-bambara groundnut trial. There were six treatments with the groundnut trial and nine treatments with the bambara trial and all were laid out in a randomised complete block design (RCBD) replicated four times. In the sorghum-groundnut trial, the results show that the intercropping of sorghum with groundnut significantly reduced Striga infestation up to 50% in sorghum in both years. Both resistant varieties supported significantly fewer number of Striga on sorghum when intercropped with groundnut compared with the sole sown susceptible variety. In both years and the combined analyses of 1995 and 1996 data, however, there was no significant difference in grain yield of sorghum due to the treatments. In the sorghum-bambara groundnut trial, the results show that Striga shoot count at harvest in sole sown ICSV 1007 was significantly lower than the ICSV 1002 variety, while the susceptible variety supported significantly higher Striga shoot count than the resistant varieties in both years and the combined analyses. Alternating stands of sorghum and bambara groundnut within the same row, in general, reduced Striga shoot count in all the varieties with a range of 56%-91% reduction than intercropping with sorghum varieties in alternate rows with bambara groundnut with a range of 45%-96% reduction, or sole sorghum of each variety. This resulted in significantly higher grain yield of ICSV 1002 (1175.0 kg ha-1 in 1995, 814.8 kg ha-1 in 1996, and 994.9 kg ha-1 in the combined data) than ICSV 1007 (892.6 kg ha-1 in 1995, 666.7 kg ha-1 in 1996, and 779.6 kg ha-1 in the combined data) when both were planted in alternate stands in the same row with bambara groundnut. This studies have confirmed the potentials of groundnut and bambara groundnut as trap crops in the management of S. hermonthica in sorghum under a dried environment.

Agriculture↗

PubMed2004

Genomic regions influencing resistance to the parasitic weed Striga hermonthica in two recombinant inbred populations of sorghum.

Molecular markers for resistance of sorghum to the hemi-parasitic weed Striga hermonthica were mapped in two recombinant inbred populations (RIP-1, and -2) of F(3:5) lines developed from the crosses IS9830 x E36-1 (1) and N13 x E36-1 (2). The resistant parental lines were IS9830 and N13; the former is characterized by a low stimulation of striga seed germination, the latter by "mechanical" resistance. The genetic maps of RIP-1 and RIP-2 spanned 1,498 cM and 1,599 cM, respectively, with 137 and 157 markers distributed over 11 linkage groups. To evaluate striga resistance, we divided each RIP into set 1 (116 lines tested in 1997) and set 2 (110 lines evaluated in 1998). Field trials were conducted in five environments per year in Mali and Kenya. Heritability estimates for area under the striga number progress curve (ASNPC) in sets 1 and 2 were respectively 0.66 and 0.74 in RIP-1 0.81 and 0.82 in RIP-2. Across sites, composite interval mapping detected 11 QTL (quantitative trait loci) and nine QTL in sets 1 and 2 of RIP-1, explaining 77% and 80% of the genetic variance for ASNPC, respectively. The most significant RIP-1 QTL corresponded to the major-gene locus lgs (low stimulation of striga seed germination) in linkage group I. In RIP-2, 11 QTL and nine QTL explained 79% and 82% of the genetic variance for ASNPC in sets 1 and 2, respectively. Five QTL were common to both sets of each RIP, wtih the resistance alleles deriving from IS9830 or N13. Since their effects were validated across environments, years and independent RIP samples, these QTL are excellent candidates for marker-assisted selection.

Area Under Curve↗

PubMed1999

NRSA-1: a resistance gene homolog expressed in roots of non-host plants following parasitism by Striga asiatica (witchweed).

Studies of the initial interactions of Striga asiatica with the non-host plant species Tagetes erecta (marigold) established that parasite penetration through the root is arrested most frequently in the cortex. The arrest of parasite ingress is associated with browning and necrosis of root cortical cells flanking the invading endophyte and with increased intracellular wall appositions on the root cell walls directly adjacent to the plant-parasite interface. Using a polymerase chain reaction-based differential cDNA amplification strategy followed by 5'-RACE, we have identified several gene products whose expression is induced in marigold roots during attempted parasitism by Striga. Among these was a 917 bp cDNA encoding a 221 amino acid protein with significant homology to proteins encoded by disease resistance genes from other plant species, including N, RPP5, L6 and M. This cDNA was subsequently used to isolate a nuclear gene, designated NRSA-1, for non-host resistance to Striga asiatica. NRSA-1 is a member of a small gene family in marigold consisting of two to four members. RNA gel blot analysis showed that NRSA-1 transcripts accumulate to high levels in roots near the site of Striga invasion within 120 h after parasite attachment, and appear at lower levels throughout the rest of the plant under Striga parasitism. NRSA-1 expression is rapidly induced by treatment with jasmonic acid (JA), but not by mechanical wounding, treatment with salicylic acid, paraquat or ABA. A possible role for NRSA-1 in the non-host resistance mechanism is discussed.

Amino Acid Sequence↗

PubMed1990

Control of Germination in Striga asiatica: Chemistry of Spatial Definition.

Striga asiatica (Scrophulariaceae), a member of a heterogeneous group known as the parasitic plants, is totally dependent on host root attachment for survival. In agar, Striga seeds germinated in high percentages within 5 millimeters of a sorghum (Sorghum bicolor (L.) Moench) host root surface, and no germination was observed at distances greater than 1 centimeter. This spatially restricted germination may be explained by the chemistry of a single compound, 2-hydroxy-5-methoxy-3-[8'Z, 11'Z)-8', 11', 14' -pentadecatriene]-p-hydroquinone, structure 1, which is exuded by sorghum roots. The presence of the compound was chemically imaged with pigments such as methylene blue. The use of methylene blue suggested that structure 1 was exuded along the entire surface of the root for long periods. This exudation and the inherent instability of structure 1 together establish an apparent steady state concentration gradient of the germination stimulant around the sorghum root. The Striga seed must be exposed to micromolar concentrations of 1 for >/=5 hours before high germination percentages were observed. Such a requirement for a long term exposure to a steady state concentration of an inherently labile, exuded compound would provide an extra degree of resolution to signal detection and host commitment in Striga parasitism.

Journal Article↗

PubMed2005

The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway.

The seeds of parasitic plants of the genera Striga and Orobanche will only germinate after induction by a chemical signal exuded from the roots of their host. Up to now, several of these germination stimulants have been isolated and identified in the root exudates of a series of host plants of both Orobanche and Striga spp. In most cases, the compounds were shown to be isoprenoid and belong to one chemical class, collectively called the strigolactones, and suggested by many authors to be sesquiterpene lactones. However, this classification was never proven; hence, the biosynthetic pathways of the germination stimulants are unknown. We have used carotenoid mutants of maize (Zea mays) and inhibitors of isoprenoid pathways on maize, cowpea (Vigna unguiculata), and sorghum (Sorghum bicolor) and assessed the effects on the root exudate-induced germination of Striga hermonthica and Orobanche crenata. Here, we show that for these three host and two parasitic plant species, the strigolactone germination stimulants are derived from the carotenoid pathway. Furthermore, we hypothesize how the germination stimulants are formed. We also discuss this finding as an explanation for some phenomena that have been observed for the host-parasitic plant interaction, such as the effect of mycorrhiza on S. hermonthica infestation.

Abscisic Acid↗

PubMed1997

Actin genes with unusual organization in the parasitic angiosperm Striga asiatica L. (Kuntze).

In order to better understand the regulation of cellular differentiation during haustorial development in parasitic angiosperms, we have begun to examine the structure and expression characteristics of genes encoding various components of the plant cytoskeleton in Striga asiatica L. (Kuntze). We describe here the cloning and characterization of three actin genes from Striga with significant similarity at the nucleotide level and encoding proteins having greater than 98% identity. However, the three genes (designated SAAc-1, SAAc-2 and SAAc-3) differ from each other in their organization and SAAc-3 contains an unusual exon-intron arrangement relative to genes encoding actins described in other higher plants. The significance of these observations concerning the evolutionary origins and potential roles of Striga actin genes is discussed.

Actins↗

PubMed2001

GC-MS analysis of hydrophobic root exudates of sorghum and implications on the parasitic plant Striga asiatica.

Striga asiatica is a parasitic angiosperm that responds to germination stimulants produced by host plants, including many grasses. GC-MS analyses of hydrophobic root exudates of sorghum revealed the root exudates to be composed of fatty acids, resorcinol, and a series of structurally related hydroquinones, three of which were previously unknown. High yields of resorcinol and the hydroquinone series were detected in sorghum. At least one of the hydroquinones induces germination in Striga, and the resorcinol is thought to stabilize the hydroquinones in the soil. The previously unknown series of hydroquinones offers insight into the possible biosynthesis of the components of the exudate and their possible importance in initiating Striga germination.

Gas Chromatography-Mass Spectrometry↗

PubMed1999

A critical account on the inception of Striga seed germination.

The seeds of the parasitic weed Striga germinate in response to stimulants exuded by the roots of host plants and some nonhost plants. Literature data are summarized that support the view that strigolactones induce germination of parasitic weed seeds via a receptor-mediated mechanism. The suggestion by Lynn et al. that the strigol D-ring is solely responsible for germinating Striga seeds via a redox reaction was based on hypothesized structural similarities between the natural compound dihydrosorgoleone (SXSg) and the strigol D-ring. Experiments have shown that the mechanistic connection between SXSg and the strigol D-ring is not valid, and therefore the proposed redox mechanism for the induction of Striga seed germination by strigolactones does not hold.

Lactones↗

PubMed1991

Role of Ethylene in the Germination of the Hemiparasite Striga hermonthica.

Seed germination of the hemiparasitic angiosperm Striga hermonthica (Del.) Benth is elicited by compounds present in the root exudates of the host plant. Although a variety of compounds can substitute for the host-derived signal, the mechanism through which these act is unknown. In the present study, an inhibitor of ethylene biosynthesis, aminoethoxyvinyl glycine, was found to inhibit germination. Addition of an intermediate in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid, was found to override this inhibition and to act as a substitute for the host-derived signal. 2,5-Norbornadiene, an inhibitor of ethylene action, was also found to inhibit germination. Ethylene is rapidly produced by Striga seeds after treatment with host root exudates. These results are consistent with a model for Striga seed germination in which host-derived signals and other compounds act by eliciting the synthesis of ethylene and in which ethylene itself initiates the biochemical changes leading to germination.

Journal Article↗

PubMed2006

A novel form of resistance in rice to the angiosperm parasite Striga hermonthica.

The root hemiparasitic weed Striga hermonthica is a serious constraint to grain production of economically important cereals in sub-Saharan Africa. Breeding for parasite resistance in cereals is widely recognized as the most sustainable form of long-term control; however, advances have been limited owing to a lack of cereal germplasm demonstrating postattachment resistance to Striga. Here, we identify a cultivar of rice (Nipponbare) that exhibits strong postattachment resistance to S. hermonthica; the parasite penetrates the host root cortex but does not form parasite-host xylem-xylem connections. In order to identify the genomic regions contributing to this resistance, a mapping population of backcross inbred lines between the resistant (Nipponbare) and susceptible (Kasalath) parents were evaluated for resistance to S. hermonthica. Composite interval mapping located seven putative quantitative trait loci (QTL) explaining 31% of the overall phenotypic variance; a second, independent, screen confirmed four of these QTL. Relative to the parental lines, allelic substitutions at these QTL altered the phenotype by at least 0.5 of a phenotypic standard deviation. Thus, they should be regarded as major genes and are likely to be useful in breeding programmes to enhance host resistance.

Chromosome Mapping↗

PubMed2002

AFLP markers linked to resistance against Striga gesnerioides race 1 in cowpea (Vigna unguiculata).

Amplified fragment length polymorphism (AFLP) analysis was used in combination with bulked segregant analysis (BSA) to identify molecular markers linked to two cowpea (Vigna unguiculata (L.) Walp.) genes conferring resistance to Striga gesnerioides race 1. After AFLP analysis of an F2 population derived from a cross between the resistant cultivar Gorom and the susceptible cultivar Tvx 3236, seven AFLP markers were identified that are linked to Rsg3, the gene conferring race I resistance in 'Gorom'. The distances between these markers and Rsg3 ranged from 9.9 to 2.5 cM, with two markers, E-AGA/M-CTA460 and E-AGA/M-CAG300, flanking Rsg3 at 2.5 and 2.6 cM, respectively. Analysis of a second F2 population derived from the cross between 'Tvx 3236' and the resistant cultivar IT81D-994 identified five AFLP markers linked to the race 1 resistance gene 994-Rsg present in 'IT81D-994'. The two markers showing the tightest linkage to the 994-Rsg locus were E-AAG/M-AAC450 and E-AAG/M-AAC150 at 2.1 and 2.0 cM, respectively. Two of the markers linked to 994-Rsg, E-AGA/M-CAG300 and E-AGA/M-CAG450, were also linked to Rsg3. The identification of molecular markers in common between the two sources of race 1 resistance suggests that either Striga resistance genes are clustered in these plants or that these loci are allelic. Mapping of the resistance loci within the cowpea genome revealed that three markers linked to Rsg3 and (or) 994-Rsg are located on linkage group 6.

Chromosome Mapping↗

PubMed1994

Characterization of actin-gene family members and their expression during development in witchweed (Striga asiatica L).

Partial cDNAs and genomic fragments representing three different actin genes of witchweed (Striga asiatica L. Kuntze) have been isolated using the polymerase chain reaction. The three genes differ in nucleotide sequence within their coding and 3' non-coding regions but encode proteins identical over the regions where sequence is available. Southern blot hybridization analysis of total genomic DNA showed that the three actin genes belong to a multigene family. Expression studies using gene-specific probes showed that transcripts of each of the three Striga actin genes were present at comparable levels in roots, shoots, and 24-h-induced haustoria. The relative abundance of the three transcripts within roots or shoots, however, differed appreciably. Such differences in transcript accumulation within organs indicate that differences might exist in their cell- or tissue-specific mode of regulation.

Actins↗

PubMed2001

Limonoids from Nigerian Harrisonia abyssinica and their stimulatory activity against Striga hermonthica seeds.

Deoxyobacunone (1), a new limonoid with a double bond in ring D, has been isolated from the root bark of Harrisonia abyssinica collected in Nigeria. Also, the known limonoids obacunone (2), harrisonin (3), 12beta-acetoxyharrisonin (4), and pedonin (5) have been isolated. The structure of 1 was assigned unambiguously by spectral data analysis. Under laboratory conditions, 10(-3)-10(-5) M concentrations of compounds 1-5 exhibited significant stimulatory activity (12-98%) against conditioned Striga hermonthica seeds. This study provided useful insight regarding the functionalities required for activity of limonoids against Striga seeds. The variation in activity was rationalized through quantitative structure-activity relationship (QSAR) models based on several molecular descriptors including van der Waals volume (VDW(v)), molecular polarizability (alpha), dipole moment (mu), log P, and the differences between the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO-LUMO gap).

Benzopyrans↗

PubMed1990

Effect of Potassium Levels on the Stomatal Behavior of the Hemi-Parasite Striga hermonthica.

The hemi-parasite Striga hermonthica, exhibits an anomalous pattern of stomatal response, stomata remaining open in darkness and when subjected to water stress. This suggests irregularity in stomatal response due to malfunction of the stomatal mechanism. To test this suggestion guard cells were isolated from the effects of surrounding cells, by incubating epidermal strips at low pH. These stomata responded rapidly to low CO(2) concentrations, darkness, and ABA. Thus, a paradox exists between stomatal behavior observed in whole leaves and that in isolated guard cells. However, when incubated in the presence of high potassium concentrations (>200 millimolar KCl) stomatal responses in epidermal strips resembled those found in whole leaves, with enhanced opening and reduced closing responses. It is suggested that the anomalous behavior of stomata in Striga and other leafy hemiparasites can be explained by the modulatory effects of high potassium concentrations which accumulate in the leaves as a consequence of high transpiration rates and the lack of a retranslocation system.

Journal Article↗