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Striga gesnerioides (Willd.) Vatke Bas.: Buchnera gesnerioides Willd. Perennial herb, parasite of roots on various dicot species, in wooded savannah, grassy savannah, open forest, and thicket. Uses: medicinal., Published as part of Monteiro, Francisca, Costa, Esperança Da, Kissanga, Raquel, Costa, José Carlos & Catarino, Luís, 2022, An annotated checklist of the vascular flora of Quiçama National Park, Angola, pp. 1-67 in Phytotaxa 557 (1) on page 49, DOI: 10.11646/phytotaxa.557.1.1, http://zenodo.org/record/6985699

Striga gesnerioides is one of the major constraints to cowpea production in West Africa. In Burkina Faso, Striga is a national phenomenon despite the control measures proposed by research. This study aims to collect farmers' perceptions of S. gesnerioides. Thus, a survey was conducted among cowpea producers in 15 localities across the four agroclimatic zones of Burkina Faso. Data collected were related to farmers' ability to distinguish S. gesnerioides from Striga hermonthica, their perceptions of yield losses, local control strategies they use and the social utility of Striga. The study revealed a good knowledge of the pest by farmers. Farmers identified S. gesnerioides by its small height, its bushy growth habit and the haustorium that distinguishes it. They attributed 20 to 100% yield losses to the effects of the parasite. The most widely used indigenous control method is by manually uprooting the plants. Despite of its harmfulness to cowpeas, S. gesnerioides is used in traditional medicine to treat diabetes and curing animal’s wounds and urinary problems. Key words: Farmers’ perceptions, ethnobotanical survey, Striga gesnerioides, use.

Cowpea witchweed [Striga gesnerioides (Willd.) Vatke] is a primary constraint of cowpea [Vigna unguiculata (L.) Walp.] production in West Africa. Previously, seven S. gesnerioides races were classified based upon host specificity and genotypic profiling. Because race number and distribution are dynamic systems influenced by gene flow, genetic drift, and natural selection, a thorough investigation of S. gesnerioides diversity and the effectiveness of known sources of resistance in cowpea is needed to develop varieties with durable and broad-spectrum Striga resistance. In this study, we screened seven cowpea lines against 58 unique S. gesnerioides populations collected from across nine West African countries. Individuals from 10 S. gesnerioides populations were genotyped with simple sequence repeat (SSR) markers. We identified six races of S. gesnerioides based on their parasitism of the seven cowpea lines with known differential resistance genotypes. No cowpea line was resistant to all 58 Striga populations and none of the Striga populations were able to overcome the resistance of all seven lines. A novel race, SG6, of the parasite collected from Kudu, Nigeria, was found to overcome more cowpea resistance genes than any previously reported race. SSR analysis indicates that Striga populations are highly differentiated and genetic relatedness generally corresponds with geographic proximity rather than their host compatibility. Due to the dearth of broad-spectrum resistance found among Striga-resistant cowpea lines, there exists a need to stack multiple Striga resistance genes in order to confer broad-spectrum and durable resistance.

The increasing severity of Striga gesnerioides attacks on cowpea across West Africa has been related to its prolificity, seed mobility and longevity, and adaptation to aridity, in a context of agricultural intensification. To understand this fast extension, we analyzed (1) the distributions of the crop and the witchweed with ecological niche modeling and multivariate climate analysis, and (2) the chronological information available from collections and the literature. The ecoclimatic envelope of S. gesnerioides attacks on cowpea is the same as on wild hosts. Consistently, the modeled distribution of cowpea infestations is closely similar to the simple superposition of the parasite model (involving all hosts) and the crop model. Striga gesnerioides infestations are restricted to the driest component of the cultivated cowpea ecoclimatic niche, corresponding to the Sahelian and Sudano-Sahelian belts and the Dahomey gap. Thus, the parasite distribution, determined by its own requirements, does not constrain cowpea cultivation under Guinean climates. The spatial and temporal distributions of S. gesnerioides field infestations are consistent with an earlier impact on cowpea production in eastern West Africa, related itself to a similar trend in cowpea cultivation intensification from Niger, Nigeria and Benin to Burkina Faso and Ghana. Mali and Senegal were affected later, and literature reports of Senegalese strains of S. gesnerioides from the wild developing virulence on cowpea offer a model for the diffusion of witchweed parasitism by multilocal evolution, through host-driven selection, instead of epidemic diffusion. A contrario, in Côte d’Ivoire, cowpea is much less widespread, so the parasite has remained confined to the wild compartment. Thus, both historical and ecogeographic analyses refute the vision of S. gesnerioides as an invader. Instead, they point to the increasing importance and intensification of the crop, and the consequent loss of biodiversity, as the main drivers of the extension and diversification of its crop-specific strains.

Cowpea is a grain legume of major importance in sub-Saharan Africa where it is cultivated by smallholder farmers on poor soils and production is often constrained by the parasitic weed Striga gesnerioides. Experiments were conducted to assess the potential of rhizobium inoculation in mitigating Striga infestation and increasing cowpea productivity. We tested under basal P application and artificial S. gesnerioides inoculation the impact of cowpea genotypes (G) (nine Striga-resistant and 11 Striga–susceptible genotypes) and bradyrhizobium inoculation (N) (two bradyrhizobium strains USDA3384 and IRJ2180A, and uninoculated control) on Striga dynamics and cowpea yield. Additional treatments included N supplied as urea (with and without), and no input (i.e., soil inherent N and P) that served as negative check. A first experiment was carried out in potted sterile soils in the screen house excluding addition of N-fertilizers. Significant G x N interactions were observed in counts of nodule (P = 0.012), Striga attachment (P Striga counts were the lowest for resistant varieties with no emerged plants. Rhizobial inoculants depressed Striga counts with consistent differences found across cowpea genotypes. Inoculation with IRJ2180A performed the best against Striga attachment in resistant genotypes, and its emergence in susceptible genotypes. In the field trial, nodule numbers were lowest in cowpea without inputs (P Striga plants (P Striga while for susceptible ones, Striga emergence was the highest without any input addition. Significant G x N interaction was observed in cowpea grain yield (P Striga-resistant cowpea lines and elite bradyrhizobium inoculant under moderate application of P-based fertilizer could be a promising approach for mitigating Striga infestation and increasing productivity.

Striga gesnerioïdes est une plante parasite qui cause des dégâts importants sur le niébé et les méthodes de lutte testées restent insatisfaisantes. L’étude vise à mettre au point, une référence de technique d’association sésame-niébé pour contribuer à lutter efficacement contre Striga gesnerioïdes. À cet effet, un dispositif en Split-Plot est utilisé sur un terrain naturellement infesté par Striga gesnerioïdes. Trois comptages à des périodes différentes (42, 56 et 70 jours après semis) du nombre de plants de Striga gesnerioïdes émergés par poquet de niébé ont été réalisés. Ainsi, en association dans le même poquet (sésame + niébé), les variétés de sésame EF 146, HC 110, ICN 130, HB 168, Vgr 156 et EF 147 sont efficaces pour atténuer l’émergence de striga. En alternance de poquets (niébé et sésame), les variétés de sésame EF 146, HC 110, ICN 137, EF 147 et 38-1-7 sont efficaces contre striga. Et les variétés de sésame EF 146, Vgr 156, HC 108 et 38-1-7 ont montré leurs efficacités en alternance de lignes avec le niébé. EF 146 est la seule variété de sésame efficace dans toutes les trois mesures de protections. Ces résultats pourraient être vulgarisés au niveau des producteurs de niébé pour booster sa production au niveau national, voir mondial. Striga gesnerioïdes is a parasitic plant that causes significant damage to cowpea and the control methods tested remain unsatisfactory. The study aims to develop a technical reference of sesame-cowpea association to contribute to the effective control of Striga gesnerioïdes. For this purpose, a Split-Plot device is used on land naturally infested by Striga gesnerioïdes. Three counts at different periods (42, 56 and 70 days) of the number of emerged Striga gesnerioïdes plants per cowpea were made. Thus, in combination in the same plot (sesame + cowpea), the sesame varieties EF 146,HC 110, ICN 130, HB 168, Vgr 156 and EF 147 are effective in mitigating Striga emergence. In alternating rows (cowpea and sesame), the sesame varieties EF 146, HC 110, ICN 137, EF 147 and 38-1-7 were effective against striga. And the sesame varieties EF 146, Vgr 156, HC 108 and 38-1-7 showed their efficacy in alternating rows with cowpea. EF 146 is the only sesame variety that is effective in all three protective measures. These results could be disseminated to cowpea producers to boost its production at the national and even global level.

The parasitic weed, Striga gesnerioides , is a major constraint to cowpea production in sub-Saharan Africa. It causes significant yield reductions of cowpea, especially in dry areas. The objective of this study was to evaluate the response of 80 genotypes to Striga gesnerioides under natural infestation. The results showed significant variations in the resistance of cowpea lines to Striga; lines IT93K-693-2, IT99K-573-1-1 and IT98K-205-8 being free from Striga infestation; while lines 2491-171, 2472-154 and Suvita-2 supported few Striga shoots. The other lines supported more and varied numbers of emerged Striga shoots. The reduction of yield due to Striga infestation was more pronounced for the susceptible genotypes as compared to the resistant and tolerant lines. The high level of resistance observed in some breeding lines can be exploited in breeding cowpea for resistance to Striga . Principal Component Analysis (PCA) and clustering grouped the genotypes in three main clusters as follow: (i) high yielding and tolerant to Striga (ii) moderate yielding and resistant (iii) low-yielding and susceptible. Key words: Parasitic weed, Striga resistance

Background: The parasitic plant Striga gesnerioides (Willd) Vatke is becoming a threat to cowpea production in the three northern regions of Ghana (Derived Savanna, Southern Guinea Savanna and Northern Guinea Savanna. The objective of this study was to determine the extent of yield loss due to Striga in F3 progenies and their parental lines. A total of twelve cowpea genotypes were evaluated to ascertain the level of damage by S. gesnerioides. Results: The results indicated varietal differences with respect to Striga susceptibility in the genotypes studied. The susceptible varieties (Asomdwee and Hewale) showed an array of emerged Striga shoots. The F3 progenies (s52, s37, s147, s272) also exhibited the same trend. The resistance genotypes (IT99K-573-1-1 and GH3684), however, were totally devoid of Striga shoots. Similarly, some of the F3 progenies (r246, r286, r282 and r69) were completely without Striga shoot. Striga height was higher on susceptible genotypes than those that are moderately resistance. The results obtained from this study revealed a percentage reduction in pods per plant range between 45.12 and 49.53 %; grain yield reduction ranged between 78.22 and 87.17% on susceptible genotypes which indicated that Striga had greater influence on yield. Fodder yield was also significantly reduced between 70.59 and 73.03% in susceptible genotypes. There was a strong negative correlation (r = -0.724) between grain yield and days to Striga emergence. A significant negative correlation (r = -0.762) was also found between Striga shoot per plant and grain yield. Conclusion: Striga infestation reduced pods per plant to 49%, grain yield loss to 87% and fodder yield loss to 73%. This study has revealed potential F3 genotypes resistant to S. gesnerioides under pot experiment. The implication is that if susceptible genotypes are grown the farmer stand the chance of loosen everything to the parasite.

Witch weed (Striga gesnerioides) is a root parasitic weed of tobacco and cowpea in Sub- Saharan Africa. It is very difficult to control and host plant resistance is the most promising effective method affordable to small-scale farmers. This study was done to screen local tobacco genotypes for tolerance and resistance to Striga gesnerioides infection. Laboratory screening experiments were conducted during the 2016/17 season using fifteen local tobacco genotypes. The experiments were done using an Agar gel technique at the University of Zimbabwe, with treatments replicated four times in a Randomised Complete Block Design (RCBD). All tobacco genotypes significantly (p

Le niebe est une denree de base en Afrique subsaharienne. L’objectif de ce travail est d’identifier des lignees a haut rendement, tolerantes a la secheresse et resistantes a la race 1 de S. gesnerioides . Des lignees issues de la selection recurrente et des varietes temoins ont ete evaluees au Centre Ouest (condition maximale d’humidite) et au Nord (condition de stress hydrique) du Burkina Faso en 2014. Tous les genotypes ont montre une resistance a la race 1 de Striga et plusieurs lignees ont reussi a produire plus de 1300 kg/ha sur les deux sites. L’Analyse en Composantes Principales realisee sur la base des caracteres quantitatifs a permis d’identifier deux groupes. Le groupe 1 est compose par des individus precoces a rendement modere (Nafi, Gorom local, KVX˗61˗1 et Komcalle). Le groupe 2 est constitue par les genotypes extra precoces a rendement modere (C2˗6˗3, C2˗18˗2, C2˗27˗2, IT97K-499-35 et Yiis yande). © 2017 International Formulae Group. All rights reserved. Mots cles: Niebe, Striga gesnerioides , stress hydrique, rendement English Title: Evaluation of 15 genotypes of rain-fed cowpea [ Vigna unguiculata (L.) Walp.] In northern and central-western Burkina Faso English Abstract Cowpea is a staple food in sub-Saharan Africa. The objective of this work is to identify high yielding, drought tolerant and race 1 resistant lines of S. gesnerioides . The breeding lines of including some varieties were evaluated in field trial under drought stressed and non-stressed conditions in 2014. Results show that the breeding lines showed complete resistance to race 1 of Striga and many improved varieties are capable of producing over 1300 kg grain/ha. Biplot displays indicated that the genotypes could be grouped into two categories according to their cycle and yielding ability as indicated below: moderate yielding-early maturing (Nafi, Gorom local, KVX˗61˗1 et Komcalle) and moderate yielding extra-early maturing (C2˗6˗3, C2˗18˗2, C2˗27˗2, IT97K-499-35 et Yiis yande). © 2017 International Formulae Group. All rights reserved. Keywords: Cowpea, Striga gesnerioides , drought, yield

Drought and weed parasite Striga gesnerioides(Willd.)Vatke, are major constraints to cowpea production in sub-Saharan Africa. The purpose of this study was to examine the response of four cowpea (Vigna unguiculata(L.)Walp.)cultivars, VITOCO, VITA5, IT87D-10-10, and IT98K589-2 to water deficit, to a weed parasite S. gesnerioides and to determine the effect of this weed parasite on these cowpea cultivars under water deficit conditions. Pot experiment was conducted in a greenhouse condition under artificial infestation at the Agronomic Experimentation Station of Lomé. The experimental design was a split-split-plot design with three replications of two levels of S. gesnerioides;(presence and absence) in main plot, four water regimes; (periodic watering of 5, 10, 15 and 20 days) in sub-plot, and the cultivars in sub sub-plot. Data were collected on yield components (number of seed per pod, number of pod per plant and seeds weight per plant). Data collected on parasitic plantdate of emergence and its rate of emergence per pot. Water deficit tolerance was evaluated by the rank summation index (RSI).The results showed that the water régimes of 10 and 15 days had significant depressive effect on all yield components. The number of S. gesnerioides emerged per pot ranged from 10.20 (VITOCO) to 48.60 (IT98K589-2). In addition, the infestation of S. gesnerioides showed a significant reduction of all yield components evaluated in all tested cultivars. Therefore, no cultivar proved to be resistant, nor tolerant to S. gesnerioides.The overall rankings of the evaluated cultivars in terms of growth and yield parameters studied revealed that the cultivar IT98K-589-2 showed the best adaptive response in drought condition. The results also revealed that, the significant negative effect of water deficit on the seeds weight per plant is exacerbated by the S. gesnerioides infestation.

Striga gesnerioides is a root hemiparasite that primarily parasitizes dicotyledonous species, including cowpea ( Vigna unguiculata L.) and other legumes. Based on the differential resistance response of various cultivars, landraces, and breeding lines, it has been proposed that several distinct races of cowpea-parasitic S. gesnerioides exist in West Africa. In this study, we used amplified fragment length polymorphism profile analysis to examine the genetic variability within and among populations of cowpea-parasitic S. gesnerioides within the suspected distribution range of a particular race, and statistical clustering methods to define the phenetic relationships of the various races in West Africa. Our data indicate that genetic variability within and among populations of each of the previously recognized races of cowpea-parasitic S. gesnerioides is extremely low. On the basis of genotypic profile and host differential resistance responses, 2 previously unknown races were identified. Of the 7 races now identifiable, races SG1 (from Burkina Faso) and SG5 (from Cameroon) are the most closely related, and SG4 (from Benin) and SG3 (from Niger/Nigeria) are the most divergent. SG6, a new race of the parasite identified in Senegal, was found to be the most genetically similar to SG4 from Benin. We also demonstrate that a hypervirulent isolate of the S. gesnerioides from Zakpota, in the Republic of Benin, is genotypically distinct from other populations of SG4, thereby warranting designation as a separate race, which we called SG4z. To further support our race classification scheme, we identified a group of molecular markers that effectively discriminate each of the various races. Finally, we show that an isolate (designated SG4i) of the wild legume Indigofera hirsuta –parasitic S. gesnerioides is genetically distinct and significantly diverged from the various races of cowpea-parasitic S. gesnerioides. Our data suggest that both geographic isolation and host-driven selection are critical factors defining race formation in S. gesnerioides in West Africa.

Pot and laboratory experiments were performed in order to elucidate the genetics of resistance of three cowpea (Vigna unguiculata (L.) Walp.) resistant sources to two biotypes of the parasitic weed Striga gesnerioides (Willd.) Vatke (witchweed). B301, Suvita-2 and IT82D-849 were crossed to susceptible cultivars. Roots of each plant of parental, F1, F2, BC1 and BC2 populations were washed free of soil and examined closely for S. gesnerioides attachment. Data on resistant and susceptible cowpea plants were analyzed using the chi-square test to ascertain the goodness of fit to different genetic ratios. Segregation patterns indicate monogenic dominant inheritance of resistance to both S. gesnerioides biotypes in B301. Suvita-2, which is susceptible to the biotype from Maradi, Niger, showed segregation patterns that indicate monogenic dominant inheritance of resistance to S. gesnerioides biotype from Cinzana, Mali. Results also indicate monogenic dominant inheritance of resistance to S. gesnerioides biotype from Cinzana in IT82D-849. However, the inheritance of resistance to the biotype from Maradi would be monogenic and recessive in this line. These results suggest that the resistance of all three sources would be easy to transfer to promising breeding lines.

Background Cowpea, Vigna unguiculata L. Walp., is one of the most important food and forage legumes in the semi-arid tropics. While most domesticated forms of cowpea are susceptible to the root parasitic weed Striga gesnerioides, several cultivars have been identified that show race-specific resistance. Cowpea cultivar B301 contains the RSG3-301 gene for resistance to S. gesnerioides race SG3, but is susceptible to race SG4z. When challenged by SG3, roots of cultivar B301 develop a strong resistance response characterized by a hypersensitive reaction and cell death at the site of parasite attachment. In contrast, no visible response occurs in B301 roots parasitized by SG4z. Results Gene expression in the roots of the cowpea cultivar B301 during compatible (susceptible) and incompatible (resistant) interactions with S. gesnerioides races SG4z and SG3, respectively, were investigated at the early (6 days post-inoculation (dpi)) and late (13 dpi) stages of the resistance response using a Nimblegen custom design cowpea microarray. A total of 111 genes were differentially expressed in B301 roots at 6 dpi; this number increased to 2102 genes at 13 dpi. At 13 dpi, a total of 1944 genes were differentially expressed during compatible (susceptible) interactions of B301 with SG4z. Genes and pathways involved in signal transduction, programmed cell death and apoptosis, and defense response to biotic and abiotic stress were differentially expressed in the early resistance response; at the later time point, enrichment was primarily for defense-related gene expression, and genes encoding components of lignifications and secondary wall formation. In compatible interactions (B301 – SG4z), multiple defense pathways were repressed, including those involved in lignin biosynthesis and secondary cell wall modifications, while cellular transport processes for nitrogen and sulfur were increased. Conclusion Distinct changes in global gene expression profiles occur in host roots following successful and unsuccessful attempted parasitism by Striga. Induction of specific defense related genes and pathways defines components of a unique resistance mechanism. Some genes and pathways up-regulated in the host resistance response to SG3 are repressed in the susceptible interactions, suggesting that the parasite is targeting specific components of the host’s defense. These results add to our understanding of plant-parasite interactions and the evolution of resistance to parasitic weeds.

The parasitic flowering plants Striga gesnerioides (Willd.) Vatke and Alectra vogelii (Benth.) are formidable cowpea production constraints in the West and Central African savanna. The two parasites cause substantial yield reduction in cowpea in the dry savannas. A field study was conducted to screen some of the cowpea breeding lines that have been developed for resistance to Striga and Alectra under natural infestation. Results showed significant variations in the susceptibility of genotypes to infestations. The cowpea lines B301, IT03K-338-1 and IT99K-573-2-1 were consistently free of emerged Striga and Alectra shoots in both years while IT98K-1092-1 and IT97K-205-8 were resistant to Striga but supported some emerged Alectra shoots. Other lines supported varying numbers of emerged Striga and Alectra shoots. The combined effect of Striga and Alectra resulted in low yield of the susceptible cultivars compared with most of the resistant cowpea lines. The differential response to Striga and Alectra confirmed that the genes controlling these parasites are non-allelic and independent of each other. A strong negative correlation was observed between grain yields and Striga and Alectra counts. The cowpea breeding lines identified with a high level of resistance to both Striga and Alectra infestation indicate the possibility of breeding cowpea varieties that combine resistance to both parasites. Key words: Cowpea, Striga, Alectra, Comparative responses, screening, breeding lines, genotypes.

Striga gesnerioides (Willd) Vatke is a significant constraint to cowpea production in the dry savannas of sub-Saharan Africa. Yield losses caused by S. gesnerioides in these regions are estimated in millions of tons annually and the prevalence of Striga soil infestation is steadily increasing. Conventional breeding efforts have developed some cowpea lines with Striga resistance as well as other important agronomic traits but it is time-consuming and difficult to pyramid favorable traits. The use of marker-assisted selection (MAS) makes it easier to select plant traits and reduce the time needed to develop new varieties. The potential of Fast Technology for Analysis (FTA) as an effective technology for sampling and retrieval of DNA from plant tissue and their subsequent molecular analysis was assessed in the laboratory. DNA was successfully recovered from the leaf tissues of cowpea pressed into the FTA ® Classic card and the DNA obtained from the FTA papers was found to be suitable for molecular analysis by PCR-based techniques. The marker efficiency of Sequence Characterized Amplified Region (SCAR) marker MahSe2 and C42B was 93% in detecting SG3 resistance. This study demonstrated that the application of MAS using FTA technology has the potential to put the breeding process on a fast track and increase the efficiency of breeding activities. Key word: Marker assisted selection, Striga gesnerioides , race, FTA ® PlantSaver Card, PCR, tissue prints, DNA.

A large-scale continuous system for recovery of root exudates from millet and cowpea was developed and tested extensively. Large quantities of germination stimulants were exuded into the medium flowing through the plant trays, which could be demonstrated by germination of seeds of three species of angiospermous parasitic plants, Alectra vogelii, Striga gesneriodes, and witchweed. Recovery of root exudates was affected by adsorption on the macroreticular polymer resin XAD-4 followed by desorption with methanol. Furthermore, indications were found that germination inhibitors are released into the medium. Subsequent testing confirmed the quantitative release of the germination stimulants as well as a large number of other compounds. Nomencla- ture: Alectra vogelii Benth.; cowpea, Vigna unguiculata (L.) Walp. 'Saunders Upright'; millet, Sorghum vulgare (L.) 'Haygrazer'; Striga gesnerioides (Willd.) Vatke #3 STRGE; witchweed, Striga asiatica (L.) Kuntze # STRLU.

An in vitro growth system was used to determine the virulence of two samples of Striga gesnerioides from Zakpota in southern Benin. Cowpea variety B301, previously considered resistant to all races of S. gesnerioides, was susceptible to both samples of the parasite. Two other cowpea varieties, 58–57 and IT81D-994, were totally resistant. Resistance in 58–57 was associated with a hypersensitive necrosis of infected roots, whilst IT81D-994 supported production of small S. gesnerioides tubercles with stems which failed to develop. Striga gesnerioides from southern Benin is the fourth race of the parasite to be identified, and the first with virulence on variety B301. The implications for breeding cowpeas with resistance to S. gesnerioides are discussed.

In field trials conducted at Samaru (11 11 07 36'E) in 2003 and 2004 wet seasons in Northern Guinea Savannah of Nigeria, Variety B301 and derivatives of its crosses with IT84S 2246-4 (IT90K-59 and IT90K-76 did not support Alectra emergence. Varieties IT89KD-245-1 and IT89KD 245, both of which are derivatives of B301 and local variety Kananado supported low emergency of Alectra. Inspite of high infestation by Alectra, and very low pod number, Kano 1696 produced acceptable grain yield of 830 kg/ha. Cowpea varieties IT82D- 849 and SUVITA-2 known to be resistant to Striga gesnerioides, exhibited moderate susceptibility to Alectra Both TVX3236 and SAMPEA-7 supported high Alectra infection with consequent high susceptibility to the parasite. All the varieties tested including B301 had lower grain yield than VITA-3. Keywords: Cowpea, Alectra vogelii Resistance/Tolerance Guinea Savannah

Tests with 18 growth regulators and chemicals revealed that the cytokinins [zeatin, kinetin, and 6-benzylaminopurine (BAP)], ethylene, and sodium hypochlorite stimulate germination of cowpea witchweed seeds at various concentrations. Witchweed seeds preconditioned in different concentrations of sodium hypochlorite for 3 wk had germination rates of 25 to 89% after incubation in distilled water, 10−5M solution of kinetin, 50 mg L−1of 2-chloroethylphosphonic acid, and exudates from cowpea roots. Witchweed seeds preconditioned in distilled water and subsequently incubated in distilled water did not germinate.

Summary In glasshouse experiments in the United Kingdom, Striga gesnerioides-resistant cowpea varieties, Suvita-2 and 58–57, were assessed alongside a susceptible variety for their responses to seventeen samples of S. gesnerioides from four West African countries. The susceptible variety was attacked by all samples, while Suvita-2 was resistant to samples from Burkina Faso and Mali, and 58–57 was resistant only to samples from Burkina Faso. At least three physiological groups of the parasite can be distinguished: samples from Burkina Faso attacking the smallest range of cowpea varieties; those from Mali being intermediate; those from Niger and Nigeria attacking all the cowpea varieties. A sample from Cameroon behaved slightly differently and may represent a fourth type. A cowpea line from Botswana, B.301, selected for its field resistance to Alectra vogelii proved resistant to all Striga populations to which it was exposed, including those from Niger and Cameroon.

Summary: 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. Resume: Un systeme de culture in vitro pour etudier le comportement de S. gesnerioides vis a vis du niebe a ete mis au point. Les racincs de jeunes plantes de la dolique de C. sont repandre au dessus d'un papier filtre en fibres de verre dans un plateau peu profond de matiere plastique et un nombre connu de graines de Striga germees est place sur la surface de racines du niebe. Ceci permet de quantifier le schema d'infeslalion par le parasite. Le bon acces a la relation hote-parasite permet que le processus entier d'infection soil aisement surveille et les tissus preleves pour des etudes cytologiqucs. Ces observations ont montre pour la premiere fois que le contact des radicules de S. gesnerioides avec les racines holes stimulc le developpement d'un chevelu radiculaire et un renflement du bout de ces radicules. Ensuite la penetralion des racines du niebe par le Striga apparail localisee et cause de tres petits dommages aux racines holes. Les tubercules renfles du parasile ne se developpent a la surface des racines qu'apres que le centre de l'hote a ete penetre par les cellules envahissanles de Striga. Ce systeme de culture est approprie pour l'etude des mecamsmes de resistance de I'hote et pour cribler rapidement des plasmidcs du niebe comme nouvelles sources de resistance au parasite. Les varietes resistantes du niebe sont la meilleure solution pour lutter contre ce parasite. Zusammenfassung: Es wurde ein Pflanzenwuchssystem zur in-vitro-Untersuchung des Verhaltens von Striga gesnerioides an der Kuhbohne entwickelt. Die Wurzeln junger Kuhbohnen-Pflanzen wurden in einer flachen Plastikschale auf Glasfaserfilterpapier ausgelegt, und eine bestimmte Anzahl gekeimter Striga-Samen wurde auf die Oberflache der Wurzeln gelegt. Auf diese Weise lies sich der Infektionsprozes quantifizieren. Durch den einfachen Zugang zu den Wirt-Parasit-Verbindungen konnte der gesamte Infektionsprozes leicht beobachtet und Gewebe fur zytologische Untersuchungen entnommen werden. Es konnte zum ersten Mai beobachtet werden, das durch den Kontakt der Keimwur-zeln von Striga gesnerioides mit den Wirts-wurzeln die Entwicklung von Wurzelhaaren und an den Keimwurzein ein Anschwellen der Spitze stimuliert wurde. Auserdem zeigte sich. das beim Durchdringen der Kuhbohnen-Wurzeln durch Striga an den Wirtswurzeln nur ein sehr kleiner Schaden verursacht wird. Die gesch-wollenen Tuberkeln des Schmarotzers auf der Wurzeloberflache entwickelten sich erst, nachdem der Zentralzylinder der Wirtswurzeln von den Striga-Haustorien durchwachsen worden war. Dieses Pflanzenwuchssystem erlaubt die angemessene Untersuchung des Mechanismus der Resistenz der Wirtspflanze und eine schnelles Screening resistenten Zell-materials der Kuhbohne zur Gewinnung neuen resistenten Materials gegen diese parasitische Pflanze. Resistente Kuhbohnen-Sorten bieten die beste Voraussetzung fur die Bekampfung dieses Schmarotzers.

Significant efforts have been made to develop cowpea (Vigna unguiculata (L.) Walp.) varieties resistant to Striga gesnerioides in Burkina Faso. Despite these efforts, the resistant genotypes developed still express differential responses to Striga gesnerioides in different zones of the country. This suggests existence of intraspecific variability within the parasite. The objective of this study was to assess the intraspecific variability of cowpea genotypes to Striga gesnerioides infection in Burkina Faso. Ten cowpea varieties were screened over two consecutive years, under artificial infestation with 30 ecotypes of Striga seeds at Kamboinsé research station, in a screenhouse in Burkina Faso. Cowpea varieties used included Moussa local, Komsaré and KVx404-8-1, which are susceptible to all Striga ecotypes; and varieties B301, IT93K-693-2 and IT82D-849, which are free from all Striga ecotypes infestation. Cowpea varieties Tiligré, 524B, local Gorom and Niizwè had specific reactions depending on the ecotypes. The study highlights the existence of varietal specificities according to the geographical origin of Striga gesnerioides seeds. The structuring of the intraspecific diversity showed five biotypes, of which three were clearly identified as SG1, SG5 and SG Kp races; and two biotypes could not be identified. Although this study did not allow for a clear determination of the racial affiliation of the two new biotypes, it offers the possibility of developing new strategies to control Striga by focusing on the selection of resistant varieties based on regional specificities of Striga races in each agricultural zone.