Effects of N, P and K on Striga asiatica (L.) Kuntze seed germination and infestation of sorghum

Sorghum (Sorghum bicolor (L.) Moench) plants were grown in pots with 12.5 and 50 mg applied N kg^?1 soil. With an increase of soil N, the Striga asiatica (L.) Kuntze infestation, as well as the sorghum shoot dry matter losses due to infestation, decreased. The relative differences in stimulant capacity to induce Striga seed germination among the four sorghum genotypes were not consistent over the 0 to 150 mg N 1^?1 range. The sorghum root exudate was considerably more active at 0 mg N 1^?1, than at 30 mg N 1^?1, and the stimulant produced at 150 mg N 1^?1 failed to induce Striga seed germination. Presence of N in the growth medium considerably reduced the effectiveness of the stimulating substance produced by sorghum roots, whereas K promoted stimulant activity only in the absence of N. The presence or absence of P in the growth medium did not affect Striga seed germinability, probably due to the inability of this element to interfere with the production or activity of the stimulating substance from the host plants. It can be concluded, therefore, that sorghum plants seem to produce active root exudate only in conditions of N deficiency.     

The role of infection time in the differential response of sorghum cultivars to Striga hermonthica infection

Striga hermonthica is an important parasitic weed that severely reduces yields of sorghum in sub‐Saharan Africa. Pot experiments with the sensitive sorghum cultivar CK60‐B and the tolerant Tiémarifing were conducted in 1999 and 2000 to investigate the role of infection time on the interaction between sorghum and Striga hermonthica. Timing of Striga inoculation was used to establish delays of one and two weeks in first attachment of the parasite. In 1999, early Striga inoculation resulted in a relatively early first Striga attachment on CK60‐B. Although first infection of Tiémarifing occurred one week later, an identical final number of emerged Striga plants was observed. Plants of CK60‐B were more severely affected and supported a higher total Striga biomass. Only with this cultivar the interaction between host and parasite was significantly affected by delayed infection. Parasite biomass was most sensitive and already significantly reduced following a 1‐week delay in infection time. With a further 1‐week delay, an additional reduction in parasite biomass was accompanied by a strong and significant increase in total and panicle dry weight of the host plant. In 2000, first infection of CK60‐B was relatively late and occurred simultaneously with first infection of Tiémarifing and no significant effect of delayed infection on Striga biomass or host‐plant performance was observed. The results indicate that the influence of delayed infection strongly depends on actual infection time and confirm that earlier observed differences in time of first infection between the two cultivars do contribute to the more tolerant response of Tiémarifing to Striga infection.     

Striga seed avoidance by deep planting and no-tillage in sorghum and maize

The possibility of reducing Striga hermonthica (Del.) Benth. parasitism in severely infested fields, by means of deep planting - thereby reducing the root length in the upper layers of the soil where Striga seeds are predominantly found - was tested in field trials with maize and sorghum in western Kenya. Sorghum seeds were planted in Striga-infested fields approximately 2.5 cm deep in the soil or at the bottom of conically-shaped plant holes (15-20 cm deep). Depth of plant holes for maize varied from 0 to 30 cm, in un-tilled soil. Deep planting in un-tilled soil gave higher (up to double) grain yields, compared with standard planting in tilled soil. Parasite emergence was related negatively to planting depth of maize (p< 0.05). Deep planting in tilled soil gave 74% more sorghumgrain yield relative to standard planting. In this treatment Striga seed production was not reduced but in un-tilled fields with deeply planted sorghum Striga seed production was completely suppressed. Therefore, a combination of zero-tillage and deep planting seems to be the most effective treatment. The probable mechanism causing these results is avoidance of Striga seed by the host root system, resulting in a delay in the onset of Striga attachment and the formation of smaller numbers of attachments.     

A new experimental approach to the chemical control of Striga using simplified models in vitro

Two species of the parasitic genus Striga, S. hermonthica (Del.) Benth. and S. gesnerioides Willd., cause severe damage to graminaceous and leguminous crops, respectively, in tropical and semi tropical areas. Striga seed germination requires the presence of germination stimulants exuded by the roots of host plants. After attachment to the host root, the young parasite exhibits a subterranean stage of development during which it already induces considerable damage in the crop. Then, the parasite emerges from the soil, develops chlorophyllous shoots and, after flowering, produces a large number of minute seeds. Many field experiments performed in the USA to control another species (S. asiatica) have shown that application of chlorthaldimethyl, di camba or dinitroanilines prevented Striga emergence. Nevertheless the phenological stages of the parasite which are sensitive to the herbicides, as well as the mode of action of these products, are still unknown. Our experiments, performed in vitro, clearly show that chlorthal-dimethyl, dicamba or pendimethalin inhibit germination of S. hermonthica and S. gesnerioides seeds in the presence of natural germination stimulants. Moreover dicamba, clopyralid and linuron are able to induce the germination of S. gesnerioides seeds in the absence of stimulants (suicidal germination). Even if the mode of action of these herbicides in inhibition or induction of Striga seed germination has yet to be studied, such products can be useful to control Striga before attachment, thus preventing the crop from suffering the early damaging effect of the parasite. Moreover bromoxynil, ioxynil, bentazone and pyridate are potent inhibitors of photosynthesis in S. hermonthica, while they do not affect the hosts (maize and sorghum). Linuron also inhibits photosynthesis in the parasite, but it may affect these crops according to the rate applied. All these inhibitors of photosystem II could be used to control S. hermonthica after emergence, thus preventing seed production. Nouvelle approche expérimentale pour la recherche de méthodes de lutte chimique contre les Striga: utilisation de modelès simplifiés in vitro Les Striga sont des Scrophulariacées hémi-parasites de racine. Deux espèces, S. hermonth-ica (Del.) Benth. et S. gesnerioides Willd. provoquent des pertes de rendement très importantes respectivement dans les céréales et les légumineuses, notamment dans la zone inter tropicale de l'Afrique. La germination des graines de Striga nécessite la présence de stimulants de germination exsudés par les racines de l'hôte. Après fixation sur les racines de son hôte, le jeune parasite présente une phase de vie souterraine hétérotrophe au cours de laquelle il inflige déjà de sévères dommages à la culture. Après émergence le parasite développe un ap-pareil aérien chlorophyllien fleurit et fructifie, produisant des milliers de graines minuscules. De nombreux essais, réalisés en plein champ aux USA pour lutter contre une autre espèce (S. asiatica) ont montré que l'application de chlorthal-diméthyle, de dicamba ou de diverses dinitroanilines inhibe partiellement l'émergence du parasite. Le stade phénologique du parasite sur lequel ces produits agissent, de même que leur mode d'action sont inconnus. Nos expériences, réalisées in vitro, montrent chlorthal-diméthyle, le dicamba et la pendiméthaline inhibent la germination des graines de S. hermonthica et S. gesnerioides en présence des stimulants de germination. En outre, le dicamba, le clopyralid, et surtout le linuron, sont capables d'induire la germination des graines de S. gesnerioides en l'absence des stimulants (germination suicide). Tous ces produits, dont le mode d'action dans l'inhibition ou l'induction de la germination reste èétudier, ouvrent des perspectives prometteuses pour la lutte préventive—la plus efficace—contre les Striga. En outre le bromoxynil, l'ioxynil, la bentazone et le pyridate, sélectifs du Maïs et du Sorgho, sont d'excellents inhibiteurs de la photosynthèse de S. hermonthica. Le linuron inhibe également la photosynthèse du parasite, mais il est moins sélectif des céréales. Ces herbicides inhibiteurs du photosystème II pourraient être utilisés dans le cadre d'un programme de lutte pour détruire S. hermonthica après émergence, empêchant ainsi la production des graines.     

Vegetative Growth of Sorghum and Striga hermonthica in Response to Nitrogen and the Degree of Host Root Infection

The effects of nitrogen and the extent of sorghum root infection by Striga hermonthica on host-parasite association during vegetative growth were studied using a split root system in a 3 × 3 factorial combination of N (37mg on one, 18.5 or 37mg on both root-halves) and Striga (no, one or both root-half infection). High N increased sorghum shoot weight by 22% more than low N, but did not significantly affect Striga growth 64 days after transplanting sorghum (DAP). Striga reduced sorghum stem height and weight by 22% and 25% at 38 DAP, and by 34% and 36% at 64 DAP, respectively. Leaf weight was not affected. Striga stimulated root growth 38 DAP, but not 64 DAP. In partially infected sorghum, 64 DAP, the parasite shoot number, shoot height and shoot dry weight were 36%, 46% and 35%, respectively and host shoot dry matter was 142% of those in fully infected plants, indicating an inverse relationship between the degree of host root infection and the level of resistance. The results suggest that sorghum released resistance-confering substances to the infection points after sensing infection. When infection points are widely distributed as in fully infected sorghum, less of such substances appear to render the host more vulnerable.     

Fenugreek root exudates show species-specific stimulation of Orobanche seed germination

Various Orobanche species are weedy and cause severe reduction in the yields of many important crops. The seeds of these parasitic weeds may remain dormant in the soil for many years until germination is stimulated by the release of a chemical signal from a host plant. In order to determine the effects of fenugreek root exudate on the induction of Orobanche crenata, Orobanche ramosa and Orobanche foetida seed germination, root exudate was collected from hydroponically grown fenugreek seedlings. Fractionation patterns obtained from column and thin layer chromatography of the fenugreek root exudate showed a set of metabolites differing in their polarity with stimulatory activity on Orobanche seed germination. The crude root exudate stimulated both O. ramosa and O. crenata seed germination to the same level caused by the synthetic germination stimulant GR24 at 10 mg L^?1. It also stimulated O. foetida seed germination which did not respond to GR24. Active fractions of root exudate stimulated the germination of Orobanche species differentially.     

Effect of growth medium, Striga seed burial distance and depth on efficacy of Fusarium isolates to control Striga hermonthica in Burkina Faso

Striga hermonthica is a destructive parasite of cereal crops in the semi‐arid tropical zone. Two greenhouse experiments were conducted at Kamboinsé, Burkina Faso, to investigate the effect of inoculum substrate and location of Striga seeds on the ability of 14 indigenous Fusarium isolates to control the parasite. In Expt 1, Fusarium isolates reduced emerged Striga number, Striga vigour and dry biomass. As a result, sorghum dry biomass and grain yield were enhanced. Inoculum substrate did not influence the ability of Fusarium isolates to control Striga. In Expt 2, Fusarium isolates, substrate and their interaction significantly influenced germination of Striga seeds at both 35 and 50 days after sowing. Isolates grown on compost were more effective at reducing germination of Striga seeds than those grown on chopped sorghum straw. The per cent germination of seeds 50 days after sowing, buried at 5 cm depth, was significantly lower than that of seeds buried at 10 cm. At 10 cm depth, Fusarium isolates still reduced Striga seed germination with respect to the control; horizontal planting distance, 5 or 10 cm from sorghum hills, had no effect.     

An in-vitro growth system for studying the parasitism of cowpea (Vigna unguiculata) by Striga gesnerioides

An in-vitro growth system for investigating the behaviour of S. gesnerioides on cowpea has been developed. The roots of young cowpea plants were spread over glass fibre filter paper in a shallow plastic tray, and a known number of germinated Striga seeds were placed on the cowpea root surface. This allowed the infection process of the parasite to be quantified. Good access to the host-parasite association enabled the entire infection process to be easily monitored and tissue removed for cytological studies. Observations revealed for the first time that contact of S. gesnerioides radicles with host roots stimulated the development of radicular hairs and swelling of the tip of these radicles. Furthermore, penetration of cowpea roots by Striga was shown to be localized and to cause very little damage to the host roots. Swollen parasite tubercles developed on the surface of the roots only after the host stele had been penetrated by invading Striga cells. This growth system is suitable for in-vestigating the mechanisms of host resistance. and also for rapidly screening cowpea germplasm for new sources of resistance to the Parasite. Resistant cowpea cultivars offer the best potential solution for control of this Parasite.     

根寄生杂草种子萌发剂概述

独脚金属（Striga spp.）及列当属（Orobanche spp.和Phelipanchce spp.）杂草是世界范围内对农业生产危害严重的根寄生杂草,主要依靠寄生茄科、豆科、谷类等作物获得水分和营养。根寄生杂草种子只有在合适的萌发诱导物（如独脚金内酯）刺激下才能萌发。文章从根寄生杂草的分类、分布及危害,种子萌发剂类型及适用范围,种子萌发剂独脚金内酯的生物合成及分离鉴定,根寄生杂草种子萌发诱导剂的作用机制以及种子萌发过程中激素间协同调控作用等方面进行了综述,并展望了种子萌发剂设计筛选及其在根寄生杂草化学防控中的潜在应用前景。     

Influence of Root Exudates on Orobanche Seed Germination*

Broomrape (Orobanche ramosa L.) is a common root parasite of solanaceous, leguminous and other crops grown in the semi-arid regions of the world. The seeds germinate when root exudates from host plants are released in their immediate vicinity (Lindley, 1853; Koch, 1887; Chabrolin, 1934). Brown et al. (1951a) reported that non-host plants, such as flax (Linum usitatissimum L.) may stimulate Orobanche seed germination without being parasitized. The stimulating properties of flax exudate were studied by Brown et al. (1951b). They reported that the stimulant was unstable in alkaline solutions, but moderately stable in weakly acidic media, which may indicate the presence of an acidic (lactone) grouping. Nash & Wilhelm (1960) reported that gibberellic acid in agar media stimulated O. ramosa seed germination. Abu- Shakra, Miah & Saghir (1970) found that pre-treatment of 0. ramosa seeds with 100 ppm of gibberellic acid followed by incubation on a flax-root diffusate agar medium gave a high (81·7%) germination. The purpose of this study was to collect root exudates from three species of plants cultured under three experimental systems, namely (a) germ-free, (b) glasshouse (non-sterile), and (c) growth chamber (hydroponic, initially aseptic), and to evaluate their biological activity as germination stimulants for O. ramosa seeds. The plants used were tomato (Lycopersicon esculentum Mill.), sorghum (Sorghum vulgare Pers.) and flax. Exudate from marigold (Tagetes erecta L.) also was collected from germ-free culture.     

Genetic diversity of East and West African Striga hermonthica populations and virulence effects on a contrasting set of sorghum cultivars

The root hemiparasite Striga hermonthica causes very significant yield loss in its dryland staple cereal host, Sorghum bicolor. Striga‐resistant sorghum cultivars could be an important part of integrated S. hermonthica control. For effective resistance breeding, knowledge about the diversity of the parasite is essential. This study aimed (i) to determine the genetic diversity within and between seven S. hermonthica populations from East and West Africa using 15 microsatellite markers and (ii) to assess the virulence and host–parasite interactions of these Striga populations grown on 16 diverse sorghum genotypes in a glasshouse trial. Most of the genetic variance (91%) assessed with microsatellite markers occurred within S. hermonthica populations. Only a small portion (8%) occurred between regions of origin of the populations. A positive correlation (R² = 0.14) between pairwise geographic and genetic distances reflected the slightly increasing differentiation of S. hermonthica populations with increasing geographic distance. East African S. hermonthica populations, especially those from Sudan, had significantly greater average infestation success across all sorghum genotypes than West African populations. Some specific host–parasite interaction effects were observed. The high genetic variation among individuals of each S. hermonthica population underlines the high potential adaptability to different hosts and changing environments. This points to the need to manage sorghum resistance alleles in space and time and to employ resistant varieties as part of integrated S. hermonthica control, so as to hinder the parasite overcoming resistance.     

Nature of resistance to Striga hermonthica (Del.) Benth. parasitism in some Sorghum vulgare (Pers.) cultivars

Ten Sorghum vulgare (Pers.) cultivars varying in tolerance to Striga hermonthica (Del.) Benth. parasitism were grown with or without Striga infection. Endodermal thickening, pericycle lignification and silica crystal deposition were studied microscopically and measured for infected and non-infected sorghum cultivars. Although differences in the root character measurements were statistically significant they were not closely related to the response of the plant to infection. Low stimulant producing cultivars showed low or medium root cell thickening. The cv. Framida had both low stimulant production and high root cell thickening and was the best of the tolerant cultivars. High stimulant producing, tolerant cultivars generally showed heavy or intermediate cell thickening. The high stimulant producing, susceptible cultivar Debaikri also showed intermediate root cell thickening.‘Antibiosis', measured by the content of phenolic compounds in the plant, was then studied. Varietal differences in quality and quantity of phenolic substances in the roots and shoots of sorghum cultivars infected or non-infected with Striga were observed. Infection increased total phenolic contents in both shoot and root extracts. Differences in the total phenolic content in the shoot of non-infected cultivars did not reflect tolerance to Striga infection. The total phenolic acid content of the root extracts was closely related to the response of the host plant to Striga infection, tolerant cultivars having greater total phenolic acid content than susceptible ones.     

Cytotoxic constituents of Alectra and Striga species

Decimation of cereal growth and yields by hemiparasitic Striga species cannot be accounted for entirely by the removal of host‐plant resources. The production of toxic compounds by the parasite has been suggested. An investigation of three species of the economically important Striga and the related Alectra vogelii has now resulted in the isolation of eight iridoid glucosides (mussaenosidic acid, mussaenoside, gardoside methyl ester, bartsioside, isoaucubin, melittoside, aucubin and eurostoside), two caffeoyl phenylethyl glycosides (calceolarioside  A and verbascoside) as well as shikimic acid and trigonelline, all identified by NMR spectroscopy. The iridoids are potent cytotoxins and probably represent an anti‐herbivore defence system common to Scrophulariaceae (sensu lato). This has the potential to explain differences in tolerance apparent for contrasting host taxa and cultivars. The nature of the iridoids present also provides additional validation of the recent transferral of parasitic Scrophulariaceae (s.l.) to Orobanchaceae.     

Suicidal germination for parasitic weed control

Parasitic weeds of the genera Striga and Orobanche spp. cause severe yield losses in agriculture, especially in developing countries and the Mediterranean. Seeds of these weeds germinate by a chemical signal exuded by the roots of host plants. The radicle thus produced attaches to the root of the host plant, which can then supply nutrients to the parasite. There is an urgent need to control these weeds to ensure better agricultural production. The naturally occurring chemical signals are strigolactones (SLs), e.g. strigol and orobanchol. One option to control these weeds involves the use of SLs as suicidal germination agents, where germination takes place in the absence of a host. Owing to the lack of nutrients, the germinated seeds will die. The structure of natural SLs is too complex to allow multigram synthesis. Therefore, SL analogues are developed for this purpose. Examples are GR24 and Nijmegen‐1. In this paper, the SL analogues Nijmegen‐1 and Nijmegen‐1 Me were applied in the field as suicidal germination agents. Both SL analogues were formulated using an appropriate EC‐approved emulsifier (polyoxyethylene sorbitol hexaoleate) and applied to tobacco (Nicotiana tabacum L.) fields infested by Orobanche ramosa L. (hemp broomrape), following a strict protocol. Four out of 12 trials showed a reduction in broomrape of ≥95%, two trials were negative, two showed a moderate result, one was unclear and in three cases there was no Orobanche problem in the year of the trials. The trial plots were ca 2000 m²; half of that area was treated with stimulant emulsion, the other half was not treated. The optimal amount of stimulant was 6.25 g ha^?1. A preconditioning prior to the treatment was a prerequisite for a successful trial. In conclusion, the suicidal germination approach to reducing O. ramosa in tobacco fields using formulated SL analogues was successful. Two other options for weed control are discussed: deactivation of stimulants prior to action and biocontrol by Fusarium oxysporum. © 2016 Society of Chemical Industry     

The Effect of Numerous Herbicides on the Germination of Orobanche aegyptiaca and Striga hermontheca

Abstract

Two hundred and thirty seven chemicals were tested to determine their effect on the germination of Orobanche aegyptiaca and Striga hermontheca. From their activity in these tests and a knowledge of their general properties the following are regarded as being the most promising for the pre-em. control of (1) Orobanche — oryzalin, dichlobenil, chlorthiamid, nitralin and chloramben. (2) Striga — 2, 4-D, MCPA and a range of other phenoxy compounds, chlorfenac, with MON 097, prynachlor, PH 40–21, PRB-8, RU 12068 and U 27658 showing the most interesting activity among the newer compounds.     

Selection of sorghum (Sorghum bicolor (L.) Moench) varieties resistant to the parasitic weed Striga hermonthica (Del.) Benth

Pot and field experiments were performed in Burkina Faso in 1987 and 1988 to evaluate the resistance of selected ‘low-stimulant’ sorghum (Sorghum bicolor (L.) Moench) varieties to the parasitic weed (Striga hermonthica (Del.) Benth. In a pot experiment, the variety IS-7777 supported the lowest number and had the latest emergence of Striga, compared with the other varieties tested. The varieties IS-14825, IS-6961, IS-7739, IS-14928 and IS-14975 also had signifi cantly lower numbers of emerged Striga per pot than the resistant control Framida. The resist ance of IS-7777 was confirmed in field experi ments, as was that of IS-7739, IS-6961 and IS-14928. However, the yield potential of these poorly adapted varieties was low in Striga-infested fields. The varieties IS-14975, IS–14825 and Seguetana Niarabougou exhibited a low susceptibility associated with a grain yield equivalent to that of the other varieties in farm fields infested by Striga. As Seguetana is already grown by Sahelian farmers, its use could be recommended in the absence of resistant varieties adapted to Sahelian agroclimatic conditions. The exceptionally high level of restance exhibited by IS-7777 could be exploited in studies on the genetics and mechanisms of resistance of the host plant to the parasite, as well as in sorghum improvement programmes.     

Variation in resistance to Orobanche crenata in species of Cicer

Crenate broomrape (Orobanche crenata) is a major constraint for legume cultivation in Mediterranean agriculture. Field trials, pot and in vitro experiments demonstrated that resistance to O. crenata is present in chickpea and wild species of Cicer. The resistance is the result of the combination of several mechanisms, including low induction of parasite seed germination and in some accessions, either a darkening at the infection site on the host root that prevents establishment, or a reduced development of established parasite tubercles.     

New insights concerning the ecology and the biology of Rhamphicarpa fistulosa (Scrophulariaceae)

Rhamphicarpa fistulosa (Hochst.) Benth. is a parasitic member of the Scrophulariaceae occurring sporadically on rice and other cereal crops in tropical Africa. Relatively little is known about this parasite, and some aspects concerning its life cycle and its impact on crops are reported in the present paper. The size, the shape and the seedcoat ornamentation of R. fistulosa are described and compared with those of Striga spp. The seeds do not require a host root exudate to stimulate germination but do require light. As in the case of Striga spp., they show a period of dormancy of at least 6 months. When the parasite roots come into close contact with a host root, they swell and develop haustoria, which form a direct xylem connection between host and parasite. In vitro and pot culture experiments establish that R. fistulosa is a facultative parasite, as it is able to complete its life cycle without a host plant. However, plants growing under these conditions are much smaller and produce only a few seeds. Field observations indicate that in some places, R. fistulosa can destroy cereals. The agronomic hazard represented by this member of the Scrophulariaceae is discussed.     

Foliar absorption and translocation of 14C-dicamba into host (pearl millet and cowpea) and parasite plants of the genus Striga

The foliar absorption and translocation of ¹⁴C dicamba were investigated to determine the potential of this chemical as a selective herbicide for Striga control. After application of the labelled herbicide to the host, the uptake, measured 5 days after foliar treatment, reached 46 and 72% for cowpea (Vigna unguiculata) and pearl millet (Pennisetum glaucum), respectively. A high percentage of the herbicide was translocated into Striga plants, particularly into S. gesnerioides. The fraction recovered in this species reached 51.2% of the amount absorbed 5 days after foliar application. The distribution patterns of the herbicide after 1 and 5 days suggest that dicamba might be used as an effective pre-emergence spray for Striga control. Selective application to the parasite leaves showed that the bulk of the radioactivity remained in the parasites, a very low percentage of the amount absorbed (1.6 and 2.5% in pearl millet and cowpea, respectively) being translocated into the host, suggesting that post-emergence application of dicamba might also be useful in the control of Striga. Absorption foliaire et transport du dicamba ¹⁴C à Pintérieur de la plante-hôte (petit mil et Vigna) leurs parasites du genre Striga L'absorption foliaire et le transport du dicamba ¹⁴C ont étéétudiés en vue de déterminer le potentiel de cette molécule comme desherbant sé1ectif contre le Striga. Après application de ('herbicide marqué sur 1'hôte, 1'absorption, mesurée 5 jours aprés le traitement foliaire atteignait 46% et 72% pour Vigna unguiculata et le petit mil (Pennisetum glaucum) respective-ment. Un taux élevé d'herbicide était transporté dans les plantes de Striga, en particulier dans S. gesnerioides. La part retrouvée dans cette espéce a atteint 51,2% de la quantité absorbée, 5 jours après I'application foliaire. Les modèles de distribution de 1'herbicide après 1 et 5 jours conduisent à penser que le dicamba pourrait être utilisé efficacement comme un herbicide de prélevée contre Striga. Des applications sélectives sur les feuilles du parasite ont montré que la majeure partie de la radioactivité restait dans les parasites, un très faible pourcen-tage de la quantité absorbée (1,6 et 2,5% dans le petit mil et le pois à vache, respectivement) étant transporté dans 1'hôte suggérant qu'une application de post levée de dicamba peut aussi être utilisée pour lutter contre le Striga. Blattaufnahme und Translokation von ¹⁴C-Dicamba bei Wirtspflanzen (Perlhirse und Kuhbohne) und parasitischen Pflanzen der Gattung Striga Die Blattaufnahme und Translokation von ¹⁴C-Dicamba wurden untersucht, um die Möglichkeiten zur selektiven Bekämpfung von Striga-Arten mit diesem Wirkstoff zu bestimmen. 5 Tage nach der Applikation des radioaktiv markierten Herbizids wurde bei der Kuhbohne (Vigna unguiculata (L.) Walp.) eine Aufnahme von 46% und bei der Perlhirse (Pennisetum glaucum (L.) R.Br.) 72% gemessen. Eine große Menge des Herbizids wurde in die Striga-Pflanzen transloziert, besonders Striga gesnerioides, bei der zu dieser Zeit 51,2% der absorbierten Menge gefunden wurden. Das Verteilungsmuster des Herbizids nach l und 5 Tagen läßt vermuten, daß Dicamba als ein wirksames Vorauflaufmittel zur Striga-Bekämpfung genutzt werden kann. Nach Applikation auf die Blätter der parasitischen Pflanzen verblieb die Radioaktivität größtenteils in diesen Pflanzen, und in die Wirtspflanzen wurde davon nur ein sehr kleiner Teil transloziert (1,6% in die Perlhirse, 2,5% in die Kuhbohne), so daßStriga-Arten wohl auch im Nachauflauf mit Dicamba bekämpft werden können.     

Integrated management of Striga hermonthica in sorghum using a mycoherbicide and host plant resistance in the Nigerian Sudano‐Sahelian savanna

Striga hermonthica is a major biotic constraint to sorghum production in Nigeria, sometimes causing total yield loss. Recommendations for Striga management often include the use of cultural and agronomic practices, herbicides and host plant resistance when available. The use of biological control has not been commercialized. Fusarium oxysporum (isolate PSM 197)‐based mycoherbicide was used in combination with selected sorghums (the Striga‐resistant cultivar Samsorg 40, and the Striga tolerant landrace Yar'ruruka) as an Integrated Striga Management strategy (ISM) in on‐farm trials in the Sudano‐Sahelian savanna of Nigeria. Crop stands were significantly (P = 0.05) higher in ISM compared with non‐ISM plots on which the mycoherbicide was not applied. Similarly, ISM plots had significantly (P = 0.05) lower Striga counts than non‐ISM plots. Striga emergence was reduced by ISM by around 95%. Sorghum yields were 49.6% higher where integrated management was used. Cost benefit analysis of the ISM package shows that use of the mycoherbicide increased the profitability of sorghum production on Striga‐infested soils. Farmers’ preferences monitored during and after the trials highlighted the need for careful selection and integration of control components into an ISM package.