Hermonthica Populations Research Articles

Variability Effect of Witchweed [Striga hermonthica(Del.) Benth.]Populations on the Performance of [Sorghum bicolor) cv. ‘Abu sabeen’ in Sudan

Field surveys and a green house experiment were conductedduring season 2009/2010 to investigate variability and host specificity ofwitchweed Striga hermonthica populations. The field surveys wereconducted in S. hermonthica endemic areas in Gadarif, Gezira andKordofan to collect seeds from striga plants growing under their respectivehosts. A total of fifteen S. hermonthica populations were collected.Twelve S. hermonthica populations, were collected from under sorghumand three. were collected from under millet. Laboratory and green houseexperiments were undertaken at the horticulture nursery, Faculty ofAgricultural Sciences, University of Gezira, Sudan, to test the viabilityand infectivity of seeds of witchweed populations on sorghum, cultivar“Abu-sabeen”, a highly susceptible cultivar. Data collected weretransformed as necessary and were statistically analysed. Results showedthat all S. hermonthica seed populations displayed high germination %ranging from 87.0 % to 92.3 %, regardless of the area, location and thehost crop. Capsules per plant, shoot dry weight and underground plantletsof emergent striga were highest on the respective host. It is noteworthythat some of the millet striga populations displayed limited emergence at60 days after crop emergence on sorghum and produced capsules.S. hermonthica populations significantly reduced growth and yield ofsorghum. However, the magnitude of the damage attained by eachpopulation was highest on the respective host, thus indicating theexistence of inter-crop specialization and probably the existence of twostrains of S. hermonthica, one specific to sorghum and the other to millet.These findings may provide clues on the complexity of breeding sorghum

Population genetic structure and marker-trait associations in East and West African Striga hermonthica with varying phenotypic response to Fusarium oxysporum f.sp. strigae isolates Foxy-2 and FK3.

To examine the genetic basis for the variable susceptibility of Striga hermonthica from differing zones of sub-Saharan Africa to Fusarium oxysporum f.sp. strigae (Fos) isolates Foxy-2 and FK3, 10 S.hermonthica populations from Eastern and Western Africa were phenotyped for their susceptibility response to Foxy-2 and FK3, and then genotyped with 22 simple sequence repeat (SSR) markers. There is low genetic differentiation between East African and West African S.hermonthica populations (i.e. the proportion of the total genetic variance contained in the subpopulation relative to the total genetic variance, FST =0.012, P<0.05), but intermediate genetic differentiation (FST =0.143, P<0.01) underlies the S.hermonthica groups that are differentiated by their phenotypic responses to Fos isolates. An expressed sequence tag SSR (EST-SSR) marker Y53 (P<0.01) and a genomic SSR marker E1009 (P<0.05) were associated with the S.hermonthica class susceptible to Foxy-2 and FK3 (groupA). A divergent S.hermonthica class, consisting of groups with intermediate susceptibility to Foxy-2 (groupB) and susceptibility to either FK3 (groupC) or Foxy-2 (groupD), showed no marker-trait association, instead demonstrated linkage disequilibrium decay. Owing to point substitutions and insertion-deletion mutations, the unique, protein-coding nucleotide sequence at the E1009 locus in groupA was partly dissimilar to groupB, but was totally distinct from groupsC and D. These findings implied that the inconsistent effectiveness of a Fos isolate is better explained by genomic variation in S.hermonthica, rather than by S.hermonthica sampling zones.

Soil Maize Cultivar-related Challenges on Striga hermonthica Infested Fields in Western Kenya

Maize production in Western Kenya is constrained by Striga hermonthica and declining soil fertility. Integrated Striga Management (ISM) packages have been proposed. An ISM field experiment assessed combination of 4 maize varieties with 5 levels of soil fertility amendments. Imazapyr Resistant (IR) maize and local yellow seed Shipindi had highest germination percentages of 90% and 81% respectively, compared to commercial white seed Duma and local white seed Rachar. Duma had significantly large plants in terms of leave size and plant height; and taking least time to silking and tasseling while producing heaviest cobs and grains per plant. Synthetic fertilizer (DAP+CAN) was associated with the least germination percentage, but produced the largest plants with many leaves, took the shortest time to silking, and produced highest cob weight and grain weight, with very low S. hermonthica infestations regardless of the maize varieties. Cattle manure (CM) and water hyacinth compost containing cattle manure culture (HCM) and Effective Microbes™ (HEM) had the highest S. hermonthica population per unit area. Maize grown with water hyacinth compost containing Effective Microbes™ (HEM) positively influenced cob weight than those receiving cattle manure (CM) and the controls; while being associated with the highest numerical increase in grain yield/area. Alternative soil fertility interventions based on these observations are therefore proposed.

Genetic diversity and virulence of Striga hermonthica from Kenya and Uganda on selected sorghum varieties

Joel KA, Runo S, Muchugi A. 2018. Genetic diversity and virulence study of Striga hermonthica from Kenya and Uganda on selected sorghum varieties. Nusantara Bioscience 10: 111-120. Parasitic weeds pose a severe problem in agricultural production, causing massive crop losses in many regions of the world and especially Africa. One example to be considered the most significant biological constraint to food production in sub-Saharan Africa (SSA) is Striga hermonthica, the most widespread among the Striga species in the semi-arid tropical African zones. The wide geographical distribution set conditions for genetically structured populations. The genetic variations among the weed populations allow for the quick breakdown of resistance in crops hence making control of the weed difficult. Efficient and effective control of S. hermonthica demands knowledge on inherent genetic variability within local and regional races of the weed. However, the genetic diversity and virulence of S. hermonthica ecotypes in Kenya and Uganda on selected sorghum varieties remain unknown. This study aimed at evaluating the genetic diversity among seven S. hermonthica populations from locations in Kenya and Uganda using 5 primer sets of Expressed Sequence Tags-Simple Sequence Repeats (EST-SSR). The genetic diversity was moderate as shown by the Nei’s genetic distance values. AMOVA measured low genetic differentiation among the populations. This study also investigated twelve sorghum varieties for their response to S. hermonthica infection. The result demonstrated that the varieties resistance responses to S. hermonthica varied widely. The phenotype of resistant interaction was characterized by the inability of the weeds haustoria to penetrate the sorghums root endodermis due to severe necrosis and in rare cases the parasites radicle growing away from the host root. The resistant sorghum varieties were the Asareca W2, Asareca AG3, N13 and the Wild-type which had low mean number of S. hermonthica plantlets growing on their roots, while the most susceptible varieties were Sap 027, Epurpur which had the highest mean number of S. hermonthica plantlets growing on their roots. There was a highly significant difference in the means of the number of Striga growing on the roots of sorghum varieties, Striga dry biomass and S. hermonthica length between the susceptible and resistant ones. This knowledge holds unique potentiality since resistant sorghum germplasm tested will be sourced and targeted to the seven specific geographical areas where virulence of the particular S. hermonthica populations was characterized.

Density‐independent reproductive success of the hemiparasitic plant Striga hermonthica, despite positive and negative density‐dependent phases

AbstractThe hemiparasite Striga hermonthica is a major constraint to smallholder farmer livelihoods and food security in sub‐Saharan Africa. A better understanding of its life‐cycle can help developing more effective management strategies. Here, we studied density dependence in S. hermonthica on Sorghum bicolor. We exposed two genotypes of S. bicolor that differed in the level of tolerance and resistance to S. hermonthica to a range of seed densities of the parasite. We evaluated multiple host and parasite performance parameters through periodic, destructive harvests and related these to the initial seed density using model selection. Initially, the probability for attachment was positively density‐dependent, suggesting facilitation of new infections. However, at host maturity, S. hermonthica infection probability showed strong negative density dependence, indicating severe competition, in particular in the early developmental stages. Although parasite shoot dry weight showed a strong negative density dependence at host maturity, flower production per parasite exhibited positive density dependence again, suggesting compensation. The two host genotypes had similar responses to increased parasite densities, indicating differences between the genotypes in tolerance but not resistance. Consequently, despite density dependence in life‐cycle components, the per capita reproductive output of S. hermonthica, R0 (flowers seed−1) was density‐independent. Apparently, management of the hemiparasite can neither benefit from a negatively density‐dependent bottleneck, nor from a positively density‐dependent Allee effect. The most promising suggestion to obtain S. hermonthica population decline (R0 &lt; 1) and long‐term control is to increase host shading by growing a vigorous, competitive crop.

Genetic diversity and population structure of Striga hermonthica populations from Kenya and Nigeria

SummaryStriga 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.

Identification of Striga hermonthica-Resistant Upland Rice Varieties in Sudan and Their Resistance Phenotypes.

Rice has become a major staple cereal in sub-Saharan Africa. Currently, upland rice cultivation is expanding particularly in rainfed areas where the root parasitic weed Striga hermonthica, a major constraint to cereal production, is endemic. Laboratory, pot, and semi-controlled open air experiments were performed to evaluate resistance of selected rice varieties in Sudan to a resident S. hermonthica population. In the laboratory, 27 varieties were screened for post-attachment resistance using the rhizotron technique. Varieties displaying high post-attachment resistance, Umgar, NERICA5, and NERICA13 together with NERICA4, NERICA18, and Nipponbare, a lowland rice variety, were further evaluated for performance and Striga resistance in pot and semi-controlled open air experiments and for germination inducing activity in a laboratory. In addition, comparative studies on reaction of Umgar, Kosti1 and Kosti2, released varieties for commercial production in Sudan, to the parasite were performed in two pot experiments. In the pot experiments Umgar and NERICA5, consistently, sustained the lowest Striga emergence (<2.2 Striga plants per pot), while NERICA13 and NERICA4 supported 1.8–5.7 and 8.7–16.4 Striga plants per pot, respectively. In an artificially Striga-infested field, number of emergent Striga plants per 10 rice hills, at harvest, was 2.0, 2.0, 4.8, 13.5, 13.3, and 18.3 on Umgar, NERICA5, NERICA13, NERICA4, NERICA18, and Nipponbare, respectively. Striga had no adverse effects on total above-ground parts and panicle dry weight in Umgar and NERICA5. Germination-inducing activity of root exudates, at 14 days after sowing onward, was markedly lower for Umgar than for NERICA5, NERICA13, NERICA4, and NERICA18. Based on these findings, Umgar has both pre and post-attachment resistance to a resident Striga population in Sudan. Kosti1 and Kosti2 did not exhibit Striga-resistance at the same level as Umgar. Further the resistance of NERICA5, a variety reported to be endowed with a broad spectrum resistance to Striga species and ecotypes, at least to one resident Striga population in Sudan was clearly indicated.

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

SummaryThe 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.

Fusarium oxysporum f. sp. strigae strain Foxy 2 did not achieve biological control of Striga hermonthica parasitizing maize in Western Kenya

The production of maize, a major staple food crop in sub-Saharan Africa is being constrained by the parasitic weed Striga hermonthica. The fungus Fusarium oxysporum f. sp. strigae (Foxy 2) that causes fusarium wilt of Striga in Ghana, West Africa, is being considered for biological control of the weed in Western Kenya. The present study investigated the efficacy of F. oxysporum f. sp. strigae (Foxy 2) for S. hermonthica management in Western Kenya. Research was conducted in post-entry quarantine (PEQ) facilities at Alupe, Busia, Homabay, Kibos and Siaya field stations for two seasons. Each PEQ was a split-plot, with 4main blocks each having 6 treatment subplots. The treatments included seeds of two S. hermonthica-susceptible maize varieties, either coated with Foxy 2 using gum Arabic, gum Arabic alone, or left untreated. Data was collected over seven sampling periods on S. hermonthica population per plant, percentage of those that were wilting, and the severity of wilting. Maize plant growth parameters assessed included duration to 50% anthesis and 50% silking, plant height, number of leaves, stover and cob weights, and maize yield per hectare. Statistical analysis was done using SAS 9.1 software. Data on S. hermonthica population were analyzed by χ2-test using Proc Genmod (Poisson); while the other parameters were analyzed by Proc Mixed using study location, season and blocks as random effects, and the sampling periods as repeated effects. All the assessed parameters were similar between plants grown from seeds inoculated with F. oxysporum f. sp. strigae (Foxy 2), those coated with gum Arabic, and the ones without any coating. These parameters were also not different between the maize varieties. There are varying reasons for the disparities between results on F. oxysporum f. sp. strigae (Foxy 2) obtained in this Kenyan study, and those from researches outside this country. In conclusion, F. oxysporum f. sp. strigae strain Foxy 2 is predominantly safe on maize growth, but its efficacy in controlling S. hermonthica was not evident on the tested Kenyan soils.

Variation for host range within and among populations of the parasitic plant Striga hermonthica

Striga hermonthica is an angiosperm parasite that causes substantial damage to a wide variety of cereal crop species, and to the livelihoods of subsistence farmers in sub-Saharan Africa. The broad host range of this parasite makes it a fascinating model for the study of host-parasite interactions, and suggests that effective long-term control strategies for the parasite will require an understanding of the potential for host range adaptation in parasite populations. We used a controlled experiment to test the extent to which the success or failure of S. hermonthica parasites to develop on a particular host cultivar (host resistance/compatibility) depends upon the identity of interacting host genotypes and parasite populations. We also tested the hypothesis that there is a genetic component to host range within individual S. hermonthica populations, using three rice cultivars with known, contrasting abilities to resist infection. The developmental success of S. hermonthica parasites growing on different rice-host cultivars (genotypes) depended significantly on a parasite population by host-genotype interaction. Genetic analysis using amplified fragment length polymorphism (AFLP) markers revealed that a small subset of AFLP markers showed 'outlier' genetic differentiation among sub-populations of S. hermonthica attached to different host cultivars. We suggest that, this indicates a genetic component to host range within populations of S. hermonthica, and that a detailed understanding of the genomic loci involved will be crucial in understanding host-parasite specificity and in breeding crop cultivars with broad spectrum resistance to S. hermonthica.

Genetic Diversity ofStriga hermonthicaPopulations in Ethiopia: Evaluating the Role of Geography and Host Specificity in Shaping Population Structure

Striga hermonthica, a root hemiparasitic Orobanchaceae, severely constrains grain production in sub-Saharan Africa. Host specificity and geography may play important roles in shaping the population structure of S. hermonthica, with the Rift Valley potentially presenting a significant barrier to dispersal. Genetic diversity was assessed in 12 S. hermonthica populations from locations in Ethiopia. Of these, seven populations were parasitic on sorghum, two each on tef and maize, and one on finger millet. Genetic variation was detected using four amplified fragment length polymorphism (AFLP) primer combinations. After correcting for repeatability, 385 fragments were detected across all primer combinations. The percentage of polymorphic loci was relatively high, ranging from 53.2% to 76.4%. Expected heterozygosity ranged from 0.168 to 0.279. Genetic differentiation between populations was relatively high, and all populations were significantly different from each other. FST values ranged from 0.032 to 0.293 and averaged 0.146. Genetic differences between populations could not be attributed to host specificity. Instead, geography was the main determinant of population structure. There was a correlation between geographic and genetic distance. A significant portion of the genetic variance could be apportioned on either side of the Rift Valley (5%; ). Also, a significant geographic barrier was identified in the southern portion of the sampled region.

Genetic Diversity of a Parasitic Weed, Striga hermonthica, on Sorghum and Pearl Millet in Mali

Eleven populations of witchweed, Striga hermonthica, were collected in four regions of Mali and investigated with 12 microsatellite markers. Extensive genetic diversity was observed, with most plants heterozygous for most markers. Allelic diversity was broadly distributed across populations with little genetic differentiation and large amounts of gene flow. Nearby fields of pearl millet and sorghum were found to have indistinguishable witchweed populations. Some population structure was apparent, but did not correlate with the local environment or host genotype, suggesting that seed transportation or other human-driven variables act to differentiate central Malian S. hermonthica populations from southern Malian populations.

Long-term management of the parasitic weed Striga hermonthica: Strategy evaluation with a population model

To increase sorghum yields in areas in Africa that are heavily infested with the root parasite Striga hermonthica, crop varieties are being bred whose roots emit fewer exudates that stimulate S. hermonthica seeds to germinate. Because S. hermonthica has a persistent seedbank, it is important to anticipate the long-term effects of such breeding efforts on the seedbank dynamics. This study reports the results of analyses conducted with a population model for S. hermonthica based on existing and earlier published models and data. The essential innovation is an explicit modelling of density-dependent feedback, which was included at different points in the life cycle. Sensitivity analyses showed that density-dependence reduced the impact on the equilibrium seedbank density of life cycle parameters at stages preceding the density-dependent process. The implication is that intervention early in the parasite life cycle through, for instance, breeding for low exudate emission of the cereal host, carries the risks of maintaining or increasing S. hermonthica seedbanks, and selection for S. hermonthica populations responsive to the new varieties. Only crop varieties with very low production of germination-stimulant will be effective in the long run. The best breeding strategy is to select for crop varieties that inhibit S. hermonthica development or growth at stages later in the life cycle or that affect the parasite at multiple stages simultaneously. The most effective management strategy is to use control measures that cause a reduction in seed production, viability of newly produced seed, or seed survival in the soil, or to use a combination of measures that affect the parasites at multiple stages. Despite considerable knowledge gaps regarding the basic demography of S. hermonthica, the model proved useful in identifying points in the S. hermonthica life cycle that are of particular interest for designing intervention strategies. In-depth studies on the demography of S. hermonthica and on the location(s) of density-dependence in the parasite's life cycle are needed.

Genetic diversity of Striga hermonthica and Striga asiatica populations in Kenya

SummaryThe 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.

Population structure, genetic diversity and host specificity of the parasitic weedStriga hermonthica (Scrophulariaceae) in Sahel

Seed proteins of individual plants from 14 populations ofStriga hermonthica growing on sorghum, millet, maize and wild grasses in Burkina Faso, Mali and Niger were studied using gel electrophoresis in order to assess the population structure and genetic diversity of the parasitic weed. The relative intensity of the different bands within a pattern was used to depict the genotypic constitution of each sample. Genotypic frequencies conformed to Hardy-Weinberg expectations in 13 populations out of 14 for the two loci that were interpreted. Heterozygote deficiencies could be the result of the Wahlund effect. The genetic divergence between populations appears to be low for bothAdh andGot loci. Thus, the physiological specialization for a particular host could be a recent phenomenon. A low host specificity ofS. hermonthica populations could affect the efficiency of introducing new resistant cultivars as a control measure against the parasitic weed.

Effect of rate and time of nitrogen fertilizer application on &lt;i&gt;Striga hermonthica&lt;/i&gt; infestation in field-grown maize

The effects of urea and sulphate of ammonia applied at 0, 90, 120, 150 and 180 kg N ha-1 (from 1989 to 1992) and the time and rate of N application (1992) on the severity of Striga hermonthica infestation and maize yield were studied in order to compare the two sources of N fertilizer, commonly available to farmers in Ghana, in reducing S. hermonthica infestation, and to determine the rate and time of application that would minimise the deleterious effect of Striga on maize. The experiments were carried out under natural field infestations on farmers' fields (6-10 locations each year) in the Guinea Savanna zone of Ghana and replicated three times at each location on plots 5 m long and 3.6 m wide. In 1989 and 1992, higher S. hermonthica population density was recorded when urea was applied compared to sulphate of ammonia. However, there were no differences in Striga population density between the two sources of nitrogen from 1990 to 1991. Applying N at either 4 or 6 weeks after planting (WAP) maize did not affect the number of emerged Striga shoots. The rate of nitrogen applied did not influence the emergence of Striga from 1989 to 1991 as compared to 1992 when Striga population declined with increased rate of nitrogen fertilizer. Maize grain yield was unaffected by the source of nitrogen applied from 1989 to 1991. Similarly, applying N fertilizer at 4 or 6 WAP did not affect maize grain yield in 1992. However, the application of sulphate of ammonia resulted in higher maize yield compared to urea in 1992. Maize grain yield increased with increased nitrogen rate up to 90 kg ha-1 beyond which no appreciable increase was observed. A minimum of 90 kg N ha-1 is therefore required for any meaningful reduction in the deleterious effects of Striga on maize. In addition, to reduce the population of Striga in maize, it is essential to apply N fertilizers early. Ghana Jnl agric. Sci. Vol.30(2) 1997: 127-133

A fungal pathogen with potential for biocontrol ofStriga hermonthica (Scrophulariaceae)

Fusarium equiseti (Corda) Saccardo (IMI Number 311922b) was isolated from diseasedStriga hermonthica (Del.) Bentham parasitic on sorghum in the Nuba Mountains Rural Development Project, Kordofan, Sudan in November 1986. Symptoms of the disease consisted of progressive blackening and drying of the leaves and flowers. The disease caused 50% mortality ofS. hermonthica populations in two areas.