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1.
S.O. EL  HIWERIS 《Weed Research》1987,27(5):305-311
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.  相似文献   

2.
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.  相似文献   

3.
The ability of Fusarium oxysporum (PSM 197), a potential mycoherbicide for control of Striga hermonthica, to control different Striga species (S. hermonthica, S. asiatica and S. gesneroides) and another parasitic weed, Alectra vogelli, was investigated under glasshouse conditions. Significant reductions in the total number of emerged plants of S. asiatica (91.3%), S. gesneroides (81.8%) and S. hermonthica (94.3%) were achieved in the presence of F. oxysporum (PSM 197). The pathogen only caused a reduction of 8.5% in A. vogelli. This high susceptibility of the three Striga species provides a possible opportunity to control these parasites simultaneously with this mycoherbicide.  相似文献   

4.
The parasltie flowering plants, Striga species, represent the largest biological constraint to cereal and legume crop production in sub-Saharan Africa. Eighty-three percent of Striga worldwide (35 species) occurs in Africa. Among them, Striga hermonthica causes the greatest damage. The IITA's scientists began research on breeding maize for horizontal resistance to Striga in 1982. By 1995 a comprehensive approach to combat Striga on maize had been developed and demonstrated. This included the development of a simple field infestation technique, the discovery of durable resistance genes, genetic studies of resistance genes and the formation of many resistant varieties (hybrids and synthetics) with high grain quality, high grain and stover yields and a combined resistance to major biotic and abiotic stresses. Multilocation testing and subsequent seed multiplication of the resistant varieties was carried out by national programmes in Benin, Burkina Faso, Cameroon, the Ivory Coast, Ethiopia, Ghana, Nigeria, and Togo. Striga-resistant maize varieties show horizontal resistance not only to S. hermonthica, but also to another species, Striga asiatica. Based on the results of a 15 year research, an integrated approach using resistant varieties and cereal-legume intercropping or rotation is recommended as a sustainable and permanent solution to combat Striga in Africa. This horizontal resistance package, with a combined resistance to other biotic stresses, could be applicable not only to Striga problems in other crops such as sorghum, millet, rice and cowpea, but also to other parasitic weeds, such as Orobanche species. This paper reviews and discusses why, approximately a century's research work on parasitic weeds, has not led to a major research breakthrough.  相似文献   

5.
Striga seeds were extracted from soils collecled in Mali and the viahility of these seeds was estimated. Striga seeds were found in 45 of 46 samples taken from 23 fields. Siriga hermonthica (Del.) Benth. growmg on the host crop millet, was present at all 46 sites sampled. The a size uf the Striga seedbaiik measured lo a depth of 15 cm was estimated to be 38 800 m -2 of surface area (geometnc mean 11 500). The average number of S. hermonthica plants observed per millei hill was 8.83 (geometric mean 3.89) or 13.98 m-2 (gcometrie mean 5.69 m-2). Higher crop hill densities tended to result in higher densities of emerged S. hermonthica per hill. The relationship between seeds m-2 and S. her-monhica plants m-2 was fitied to a reetungular hyperbola and used to reassess an existing model of S. herniouhica control.  相似文献   

6.
The parasitic angiosperms, Striga hermonthica and Striga asiatica, severely constrain cereal production in sub-Saharan Africa by causing huge losses in grain yield. Understanding the diversity of Striga populations is important because it allows identification of races or biotypes thus improving chances of breeding success. Amplified fragment length polymorphism (AFLP) analysis was used to study genetic diversity among 17 populations of S. asiatica and 24 populations of S. hermonthica from Kenya. A total of 349 DNA fragments ranging from 51 to 500 bp were obtained from four EcoRI and MseI primer combinations. Genetic distances for S. asiatica populations ranged from 0.009 to 0.116 with a mean of 0.032. S. hermonthica populations had a genetic distance that ranged from 0.007 to 0.025 with a mean of 0.015. Only two clusters were found in S. asiatica populations whereas no apparent structure was evident in S. hermonthica populations. There was no evidence of isolation by distance for the two species. Although the low genetic diversity suggests Striga is relatively uniform across the populations studied, it is possible that pathogenicity and virulence genes may be located in genomic regions that were not sampled. The data, however, does not provide evidence to support diversification of both Striga species in the region where the study was conducted.  相似文献   

7.
Under glasshouse conditions, the ability of Fusarium oxysporum isolate Foxy 2, a fungal pathogen isolated from Striga hermonthica, to control S. asiatica and S. gesnerioides, was investigated on potted plants. In the experiment, the target weed of the fungus, S. hermonthica, was included as a standard. In the present study, S. asiatica was the only species that, besides S. hermonthica showed high susceptibility to Foxy 2. This susceptibility was demonstrated by almost complete prevention of emergence of the parasite. In contrast, S. gesnerioides did not show any susceptibility at all. The susceptibility of two Striga species to the fungus provides an opportunity for simultaneous control of both parasites in those regions where they are co‐existing (e.g. Tanzania and Kenya).  相似文献   

8.
Nematodes     
Abstract

Studies were carried out on farms to evaluate potential control practices which could be constituted into a package of recommendations for the control of Striga hermonthica in the Gambia. ICSV 1002, a variety of sorghum, was identified as being relatively more tolerant to Striga and to the common insect pests of sorghum. Spot treatment of emerged Striga shoots with 2% solution of product paraquat using a pistol‐grip hand sprayer was found to control Striga without stimulating regrowth, improved yields and was more acceptable and cost‐effective than handpulling of the shoots in early millet and sorghum. Where there might be objections to the use of paraquat because of its toxicity hazards, a mixture of 2,4‐D (1 % soln.) plus glyphosate (1 % soln.) or 2,4‐D (2% soln.) was a useful substitute. A tentative control package consisting of ICSV 1002, spot spraying of Striga shoots with paraquat, and side dressing of urea fertilizer at 30 kg N/ha at 4 w.a.p. was tested at two sites against farmers’ practice on pilot scale. Infestation of Striga was reduced and yields were increased by 119% and 37% by the package at the two sites.  相似文献   

9.
Striga hermonthica is a parasitic weed that poses a serious threat to the production of economically important cereals in sub‐Saharan Africa. The existence of genetic diversity within and between S. hermonthica populations presents a challenge to the successful development and deployment of effective control technologies against this parasitic weed. Understanding the extent of diversity between S. hermonthica populations will facilitate the design and deployment of effective control technologies against the parasite. In the present study, S. hermonthica plants collected from different locations and host crops in Kenya and Nigeria were genotyped using single nucleotide polymorphisms. Statistically significant genetic differentiation (FST = 0.15, P = 0.001) was uncovered between populations collected from the two countries. Also, the populations collected in Nigeria formed three distinct subgroups. Unique loci undergoing selection were observed between the Kenyan and Nigerian populations and among the three subgroups found in Nigeria. Striga hermonthica populations parasitising rice in Kenya appeared to be genetically distinct from those parasitising maize and sorghum. The presence of distinct populations in East and West Africa and in different regions in Nigeria highlights the importance of developing and testing Striga control technologies in multiple locations, including locations representing the geographic regions in Nigeria where genetically distinct subpopulations of the parasite were found. Efforts should also be made to develop relevant control technologies for areas infested with ‘rice‐specific’ Striga spp. populations in Kenya.  相似文献   

10.
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.  相似文献   

11.
Striga hermonthica and S. gesnerioides pose serious threats to cereal and cowpea production, endangering peoples' livelihoods on the Abomey plateau, Benin. A 2-year joint experiment was undertaken with farmers in two hamlets to investigate the potential of managing sowing dates of cowpea, sorghum transplanting, and trap cropping as ways of increasing agricultural production and reducing Striga damage. Early sowing of cowpea failed due to dry spells. Late sowing reduced cowpea yield due to water deficiency at the end of the growing season. Transplanting sorghum seedlings raised in fertilised or Striga-free nurseries doubled or tripled cereal yield and substantially reduced S. hermonthica infestation compared to direct early-sown sorghum. Transplanting sorghum from plant hills to fill gaps was unsuccessful. Trap crops such as cowpea and groundnut increased subsequent maize yield. Trap cropping had only a small effect on S. hermonthica infestation. The very poor soils in Somè central were a major constraint upon yield improvement to acceptable levels even after the introduction of the new crop (and Striga) management methods.  相似文献   

12.
Thidiazuron at 0.1 to 10 mg 1?1 induced concurrent germination and haustorium initiation in Striga asiatica (L.) Kuntze and S. hermonthica (Del.) Benth, but it had no effects on S. gesnerioides (Willd.) Vatke. Both millet and sorghum strains of S. hermonthica were equally responsive. The response of Striga seeds to thidiazuron increased with conditioning. Early applications of the compound induced some germination, but had adverse effects on the conditioning process. Induction de la germination des graines de Striga par le thidiazuron Le thidiazuron de 0,1 à 10 mg 1?1 a induit de façon conjointe le germination et l'initiation d'haustoria chez Striga asiatica et S. hermonthica, mais n'a pas eu d'effet sur S. gesnerioïdes. Les souches de S. hermonthica liées au millet et au sorgho ont un comportement équivalent. La réponse des graines de Striga au thidiazuron a augmenté par conditionnement préalable. Des applications précoces de produit ont induit quelques germinations, mais ont eu des effets contraires sur Ie processus de conditionnement. Einleitung der Samenkeimung bei Striga-Arten durch Thidiazuron Mittels Thidiazuron-Lösungen von 0,1 bis 10 mg 1?1 konnten eine gleichzeitige Keimung und Ausbildung der Haustorien bei Striga asiatica (L.) Kuntze und S. hermonthica (Del.) Benth. herbeigeführt werden, nicht jedoch bei S. gesnerioides (Willd.) Vatke. Der Rispenhirsen-und der Sorghum-Typ von S. hermonthica reagierten in gleichem Maße. Konditionierung der Striga-Samen förderte die Wirkung von Thidiazuron. Frühe Anwendung des Wirkstoffs führte zu einer geringen Keimung, beeinträchtigte jedoch die Konditionierung.  相似文献   

13.
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.  相似文献   

14.
The physiological and biochemical mechanisms of organogenesis in Equisetum arvense have not been clarified yet. However, high concentrations of nitrogen have been shown to exert an inhibitory effect on in vitro tuber formation in E. arvense. The aim of this study was to clarify the influence of the form of nitrogen in a medium on in vitro organogenesis in E. arvense. Single‐node segments of E. arvense rhizomes were cultured in the test medium. The NH4‐N and NO3‐N concentrations of the test medium, respectively, were adjusted by adding NH4H2PO4 and KNO3 to the basal medium. The basal medium was a nitrogen‐free, modified form of White's medium. Vegetative shoots were newly formed in the test tubes for concentrations of NO3‐N and NH4‐N that exceeded 56 mg L?1. However, no rhizome was formed at NH4‐N concentrations exceeding 28 mg L?1. The number of newly formed tubers decreased at an NH4‐N concentration of 28 mg L?1 and no tuber was formed at NH4‐N concentrations exceeding 56 mg L?1. In summary, although the presence of NO3‐N in the medium did not inhibit in vitro rhizome or tuber formation in E. arvense, the presence of NH4‐N in the medium exerted a strong inhibitory effect on the in vitro formation of both of these organs.  相似文献   

15.
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.  相似文献   

16.
Striga hermonthica (Del.) Benth is a parasitic weed that is damaging major cereal crops in sub-Saharan Africa (SSA). Although Striga is recognised as an agricultural scourge, there is limited information available indicating the extent of its growth and spread as impacted by the changing climate in Kenya. This study investigated the impact of current climate conditions and projected future (2050) climate change on the infestation of Striga hermonthica in the western Kenya region. Specifically, the study aimed to predict Striga hermonthica habitat suitability in five counties in the western Kenya region through using the maximum entropy (MaxEnt) model and bioclimatic, soil, topographic and land use, and land cover (LULC) variables. Striga hermonthica geolocations were collected and collated and ecological niche models were developed to determine the habitat suitability. The results showed that approximately 1767 km2 (10% of the total study area) is currently highly suitable for Striga hermonthica occurrence. The future projections showed a range between 2106 km2 (19% of the total study area) and 2712 km2 (53% of the total study area) at the minimum carbon (RCP 2.6) and the maximum carbon emission scenarios (RCP 8.5) respectively. Elevation, annual precipitation, LULC, temperature seasonality and soil type were determined to be the most influential ecological predictor variables for Striga hermonthica establishment. The study revealed the importance of using climate, soil, topographic and LULC variables when evaluating agricultural production constraints such as Striga's prevalence. The methodology used in this study should be tested in other Striga affected areas.  相似文献   

17.
Prevention of seed input to the seedbank of Striga hermonthica‐infested fields is an important objective of Striga management. In three consecutive years of field experimentation in Mali, Striga reproduction was studied for 10 sorghum genotypes at infestation levels ranging from 30 000 to 200 000 seeds m?2. Host resistance was identified as an important determinant of Striga reproduction, with the most resistant genotypes (N13, IS9830 and SRN39) reducing Striga reproduction by 70–93% compared with the most susceptible genotype (CK60‐B). Seedbank density had a significant effect on Striga seed production. Higher seedbank density resulted in more Striga plants, which led to increased intra‐specific competition and consequently a reduced level of reproduction per plant. For the most susceptible sorghum genotypes, density dependence also occurred in the earlier belowground stages. Striga reproduction continued beyond harvest. At the high infestation level just 8% of the total reproduction was realised after harvest, whereas at the low infestation level 39% was attained after harvest. Even though host‐plant genotype plays a significant role in Striga reproduction, calculations indicated that only at very low infestation levels the use of the most resistant genotype was able to lower the Striga seedbank.  相似文献   

18.
Ethephon (2-chloroethylphosphonic acid), which generates ethylene, stimulated the germination of pre-conditioned seeds of Striga hermonthica when it was added to the alkaline Gezira clay soil at concentrations of 2.5 to 30 mg kg?1. As little as 5 min contact with treated soil was enough to stimulate germination. Ethephon in soil did not cause germination of unconditioned seeds for periods of up to 12 days and also had an adverse effect on seed germination when such seeds were given a second ethephon exposure after a storage period which was adequate, in untreated soil, to give the necessary pre-conditioning. Ethephon activity persisted in air-dry soil but declined over a 14 day period in moist soil. In the field ethephon at 0.6 to 4.8 kg ha?1 decreased the number of Striga shoots and increased sorghum height and flowering.  相似文献   

19.
Erwinia soft-rot is an important disease of many ornamental potted crops and is one of the most limiting factors in greenhouse calla lily (Zantedeschia spp.) production. Experiments were conducted to test the effect of phosphorous added to soil-less mixes or to nutrient solutions used for irrigation on soft-rot caused by Erwinia carotovora subsp. carotovora (Ecc). Soft-rot incidence increased to 51% when soil-less mix was amended with superphosphate in comparison to regular soil-less mix (no superphosphate added) (31%). In contrast, addition of phosphorous in the nutrient solution met the phosphorous needs of the plant without enhancing soft-rot. Plant height, fresh mass, and number of flowers per plant were greater in calla lilies irrigated with nutrient solution containing phosphorous than no phosphorous treatments. Similar results were obtained in tests conducted in a commercial greenhouse with larger sample size. No statistical differences were found between tubers sprayed with water (control) or with a 0.5 mM solution of KH2PO4 in laboratory experiments to determine the effect of phosphorous on tuber root development. In other experiments, tubers were sprayed with either water, a bacterial cell suspension 1 × 102 cfu ml–1, a solution of 0.5 mM KH2PO4, or a suspension of bacteria in KH2PO4. The results from these tests showed a significant increase of soft-rot development in tubers treated with the suspension of Ecc prepared in a solution of KH2PO4 relative to other treatments. Further laboratory tests indicated that enzymatic activity (polygalacturonase and pectate lyase) of Ecc increased when grown in the presence of phosphorous. These experiments suggest that increased soft-rot in the presence of phosphorous is due to increased virulence of Ecc.  相似文献   

20.
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.  相似文献   

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