18 Records out of 22207 Records

Understanding resistance in inter-specific rice cultivars to the parasitic witchweed Striga

Author: Cissoko, Mamadou

Awarding University: University of Sheffield, England

Level : PhD

Year: 2012

Holding Libraries: DA. H1c 62-11517 ; Institute of Commonwealth Studies Library ;

Subject Terms: Striga ; Rice ; Oryza sativa ; Oryza glaberrima ; Striga hermonthica ; Striga asiatica ; Genetics ; Weeds ;

Abstract:

Both cultivated rice species, Oryza sativa (L.) and Oryza glaberrima (Steud.), are grown in Africa. To take advantage of superior traits from each species, AfricaRice Center and partners developed inter-specific rice cultivars called NERICA (NEw RICe for Africa) for rain-fed upland ecosystems. NERICA rice cultivars showed different susceptibilities to both S. hermonthica and S. asiatica species under controlled environment conditions. Some cultivars showed good broad-spectrum resistance against several Striga ecotypes and species whilst others showed intermediate resistance or were very susceptible. In addition, some cultivars showed resistance to a particular ecotype of Striga but were susceptible to others. The phenotype of a resistant interaction was often characterized by necrosis at the host parasite interface and an inability of the parasite to penetrate the host root endodermis. In general, the most resistant NERICA cultivars grew better than the very susceptible cultivars although even a small number of parasites caused a reduction in above ground host biomass. There was however, genetic variation for tolerance to Striga (the ability to grow and yield well in the presence of Striga) amongst the NERICA cultivars. The NERICA cultivars were also grown in field trials at Kyela in Tanzania (under S. asiatica infestation) and at Mbita Point in Kenya (under S. hermonthica infestation) in 2010 and 2011 to determine the impact of environment on the expression of resistance. The resistance of the NERICA cultivars against S. hermonthica and S. asiatica, in the field, was broadly similar to that observed in the laboratory although there were some exceptions. These results allow us to recommend particular cultivars for Striga-infested regions but they also illustrate the necessity of understanding the genetic basis of resistance to different ecotypes of Striga for breeding of durable resistance (and pyramiding of appropriate resistance genes) in host cultivars adapted to different rice agro-ecosystems in sub-Saharan Africa. Sixty four lines of an inter-specific CSSL population and the parent cultivars O. glaberrima MG12 and O. sativa Caiapo were phenotyped for resistance to S. hermonthica. MG12 showed good resistance to S. hermonthica whilst Caiapo was very susceptible. The CSSLs showed a range of susceptibility to the parasite, however, only two CSSLs showed the same strong resistance phenotype as MG12. Graphical genotyping and a Quantitative Trait Loci (QTL) analysis revealed a large QTL on chromosome 12 (designated STR12.1) which explained at least 80 % of the variation for resistance in the population and suggests that resistance to S. hermonthica (in MG12) is due to one (or a few genes) of major effect. This finding opens the way for the identification of candidate Striga resistance genes (through fine mapping approaches) and their transfer to farmer-preferred cultivars via marker assisted breeding.

Use of RNA interference and overexpression of purple acid phosphatase genes in management of parasitic plants

Author: Alakonya, Amos Emitati

Awarding University: Kenyatta University, Kenya

Level : PhD

Year: 2011

Holding Libraries: Kenyatta University Moi Library ;

Subject Terms: Cuscuta pentagona ; Striga hermonthica ; Orobanche aegyptiaca ; Parasites ; Genes ; Plants ;

Abstract:

Parasitic plants are major contributors to food insecurity in poverty stricken Sub Saharan Africa; To date, there is no effective parasitic plant control strategy that has been adopted by the majority of small scale farmers in the region leading to continued parasite spread and hence food insecurity. This study evaluated a variety of strategies against the parasitic plants Cuscuta pentagona, Striga hermonthica and Orobanche eaegyptica. The efficacy of RNA interference and intercropping with phosphorus efficient species was evaluated against C. pentagona and S. hermonthica. Further the effect of overexpressing purple acid phosphatases genes in tomato on 0. eaegyptica management was also evaluated. First, this study established that C. pentagona KNOX genes were involved in haustoria development. Targeting C. pentagona KNOX genes by interspecific RNA silencing through transgenic Nicotiana tabaccum as the host caused haustoria distortion and suppressed C. pentagona growth. Contrary to the results obtained in C. pentagona KNOX gene silencing study, targeting of the C. pentagona plasma membrane H+-ATPase through transgenic Medicago sativa did not suppress C. pentagona nor silence the H+ATPase gene. Instead, the parasite elicited a hypersensitive reaction and changed its mode of obtaining nutrients from symplastic to apoplastic transfer. In addition, this study showed that intercropping of maize with a P fixing legume Lupinus albus does not mobilize enough phosphorus in the rhizosphere for access by maize although it enhances cereal biomass accumulation and suppression of S. hermonthica emergence. Furthermore, it was shown that intercropping L. alb us and maize does not affect arbuscular mychorrhiza fungi colonization in maize roots. Of further interest was the confirmation that soil phosphorus level and arbuscular mychorrhiza fungi colonization have an inverse relationship in S. hermonthica tolerant and susceptible maize and sorghum cultivars evaluated. Finally, the overexpression of purple acid phosphatases from L. albus and Medicago truncatula in tomato resulted in low Orobanche emergence, enhanced root branching, improved tomato vigor and low arbuscular mychorrhiza fungi colonization. It was concluded that RNA interference, intercropping of maize with phosphorus efficient species like L. albus and overexpression of purple acid phosphatases from L. albus and M truncatula can reduce parasitic plant infestation and establishment. These findings lay the foundation for further studies in food crops like maize and Sorghum which have been greatly impacted by Striga.

Efficiency and effectiveness of dissemination pathways : a case study of push-pull technology for stemborers and striga weeds control in western Kenya

Author: Murage, Alice Wakukira

Awarding University: Egerton University, Kenya

Level : PhD

Year: 2011

Holding Libraries: Kenya Agricultural Research Institute Headquarters Library ;

Subject Terms: Stem borers ; Stem borers ; Chilo partellus ; Busseola fusca ; Striga hermonthica ; Striga asiatica ; Farmers ; Homa Bay District ; Kisii District ; Busia District ; Bungoma District ; Agricultural Extension work ;

Abstract:

Food security in Kenya is potentially challenged by increased infestation of maize fields by cereal stemborers (mainly Chilo partellus Swinhoe and Busseola fusca Fuller) and parasitic Striga weeds (mainly Striga hermonthica (Del.) Benth. and Striga asiatica (L.) Kuntze). The conventional control measures for these pests have had limited acceptance by smallholder farmers in the region due to various socio-economic and environmental effects. The 'push-pull' technology (PPT), developed by the International Centre of Insect Physiology and Ecology (ICIPE) together with other collaborators, has been well evaluated by smallholder farmers as an effective method for controlling the two pests. However, this technology is relatively knowledge intensive, thus realization of maximum adoption will depend on how well-trained farmers are, via effective and efficient dissemination pathways. The information on efficiency and effectiveness of dissemination pathways is scanty in literature. This study therefore sought to fill this gap in order to proffer better targeting of resources in an efficient dissemination strategy. Both primary and secondary data were used in this evaluation. A total of 491 randomly selected respondents from Homabay, Kisii, Busia and Bungoma districts were interviewed, and secondary data were obtained from project records in ICIPE-Mbita. Data were analysed using: a weighted score index; an ordered probit model for pathway preference ranking; a two limit tobit for pathways' effects on adoption; a duration model for pathways' effects on the speed of adoption; and Data Envelopment Analysis (DEA) for efficiency analysis. The results from the weighted score index show that field days (FD) were the most preferred dissemination pathway, followed by farmer field schools (FFS) and farmer teachers (FT). The tobit and duration model results show that FD had the highest impact on the level and intensity, and the speed of adoption, respectively, whereas the DEA results show that FD was relatively more efficient compared to FFS and FT in the short run; but in the long run, FTs were more efficient. Considering that the pathways are not mutually exclusive, it is imperative to account for the complimentary roles of the various pathways in strengthening the uptake of PPT technology. The dissemination pathways would be more effective if the target population is well segmented and appropriate pathways utilised for the various farmer segments. The findings of this study contribute to the framework for ICIPE and other research institutions to examine both their human and financial strategies in order to invest in dissemination strategies that are relevant, efficient and effective.

Analytical determination of the effects of phosphatic fertilizers and manure on maize yields in acidic soils in Kisii and Rachuonyo districts

Author: Ademba, Jacob Sospeter

Awarding University: Egerton University, Kenya

Level : MSc

Year: 2009

Holding Libraries: Kenya Agricultural Research Institute Headquarters Library ;

Subject Terms: Maize ; Zea mays ; Soil fertility ; Soil acidity ; Fertilizers ; Manures ; Striga hermonthica ; Kisii Central District ; Rachuonyo District ;

Abstract:

Maize production in sub-Saharan Africa remains low and the yields are on the decline. This has been attributed to a variety of factors which include soil nutrient depletion and Striga infestation. Soil phosphorous, nitrogen and. Striga hermonthica are the major constraints to maize production in Nyanza Province of Kenya. The yields are typical of low input systems ranging below 1.0 t ha-I against a potential of5.0 t ha-I per season. In an attempt to overcome these constraints, field trials were conducted at two on-farm sites, Bototo in Kisii Central district and Kabondo in Rachuonyo district, in Nyanza Province of Kenya. The trials were conducted during the long and short rains seasons in 2007. The study investigated the effects of phosphatic fertilizers and manure on nutrient uptake, nutrient use efficiency, maize yields and soil nutrients content at harvest in both sites. A Randomized Complete Block Design (RCBD) was used with the farmers as replicates. Farmers in Bototo plant H614 variety while those in Kabondo plant H513 maize variety. Plots were top dressed with Calcium Ammonium Nitrate (CAN) fertilizer at a uniform rate of 30 kg N ha,' Diammonium Phosphate (DAP), Minjingu Rock Phosphate (MRP) and Triple Super Phosphate (TSP) fertilizers were applied at a rate of 60 kg ha' P~5 and farmyard manure (FYM) at 10 t ha'. One rate of P (60 kg ha' P205) was applied on all the P sources and a no P treatment (check) plus lime only treatment was included in determining the effects due to the applied P in the acidic soils. Complete soil chemical analysis was done in all the plots. To assess the effects of phosphorus fertilizers and manure and estimate the nutrient content and uptake of major nutrients, plant and soil samples were analyzed using standard methods. There were significant (P:s 0.01) crop growth vigor response to the fertilizers and manure due to treatments at both sites. There were significant (P:s 0.01) grain yield, total dry matter yield and harvest index responses to phosphate fertilizers and manure treatments at both sites. Phosphate fertilizers and manure treatments had significant (P:S 0.01) effects on Striga emergence at both sites. Striga emergence correlated weakly with phosphate fertilizers and manure treatments and strongly with grain yield at both sites. Nutrient uptake and removal by the crop significantly (P:S 0.01) increased due to fertilizers and manure application, with a corresponding reduction in the total soil N, P, K, Ca and Mg. Phosphate fertilizers and manure application significantly (P:S 0.01) increased available soil phosphorus, agronomic phosphorus use efficiency (APUE) and physiological phosphorus use efficiency (PPUE) in both sites. The results indicate that phosphate fertilizers and manure applications are essential to improve maize yield, nutrient phosphorus use efficiency and the applied nitrogen reduced the impacts of Striga hermonthica damage to maize yields.

Breeding investigations of finger millet characteristics including blast disease and striga resistance in western Kenya

Author: Oduori, Chrispus O A

Awarding University: University of KwaZulu-Natal, South Africa

Level : PhD

Year: 2008

Holding Libraries: Kenya Agricultural Research Institute Headquarters Library ;

Subject Terms: Finger millet ; Eleusine coracana ; Striga ; Genetics ; Food security ; Crop diseases ;

Abstract:

Finger millet (Eleusine coracana (L.) Gaertn. ssp. coracana) is an important food, food security and cash crop in eastern and southern Africa where small-scale farmers grow it in low input farming systems. The crop has food security, nutritional, cultural, medicinal, and economic value with high industrial potential. Little research and hardly any breeding have been done on the crop leading to low yields and low production. A project was therefore implemented in western Kenya during 2004-2007 seasons to investigate the possible breeding contributions to enhance productivity and production of the crop. The research comprised a social survey, germ plasm evaluation, appraisal of ethrel as a chemical hybridising agent (CHA), genetic analysis of yield, and resistance to blast and Striga, and breeding progress in developing new finger millet varieties. A participatory rural appraisal (PRA) was conducted in three districts during 2006 to position finger millet (FM) in the farming systems, production constraints, and variety diversity and farmer preferences. The PRA established the high rating the peasant farmers gave to finger millet among crop enterprises, using it for food, cash, brewing, ceremonies and medicinal purposes. Farmers cultivated many varieties ranging from five to nine in a district, but each district had its own popular variety. Farmers used the following criteria to select new cultivars: high yield potential; early maturity; resistance to blast disease, Striga, birds, drought, and lodging; large head size, dark grain colour, and good taste. This probably indicated the willingness of farmers to adopt new varieties. Farmers identified constraints to production as blast disease, Striga, wild FM, birds, rats, termites, lack of market, labour shortage, and low yield. The farmers' variety selection criteria and production constraints underscored the need to improve finger millet varieties. Evaluation of 310 accessions for trait variability and association conducted during 2005 long rain (LR) season at two sites revealed wide variation among the accessions for yield and secondary traits. The best accessions grain yield was above the yield potential of 5,000- 6,OOOkg ha' reported in other environments. Accessions KNE 072 (7,833kg ha'), GBK 028463 (7,085kg ha'), GBK 029661 (6,666kg ha') and FMBT ACC#42 (6,566kg ha') were outstanding. The data showed the opportunity to select for yield directly because of its wide variability but indirect selection could also be used to exploit seedling vigour as shown by its high correlation to yield and direct and indirect positive effects on yield through plant height and single plant yield in path analysis. The wide genetic variability among the genotypes for several traits indicated high potential to breed new and better finger millet varieties. Ethrel (2-chloro-ethyl-phosphonic acid) was studied for its efficacy as a chemical hybridising agent on FM both under greenhouse and field conditions. The greenhouse study led to an 8x8 diallel crossing of six western Kenya elite plus two exotic varieties at 1,500 and 2,000ppm concentrations at success rates of 0.19-8.63%. Application of 1,500ppm- 2,000ppm ethrel at DS 45 in the field resulted in emasculation of 15-38% without causing female infertility and adverse effects on yield and maturity period. However, ethrel significantly reduced plant height and ear exertion by 25 and 50%, respectively. There were no significant interactions between factors. Ethrel could, therefore, enable hybridisation for breeding purposes. Studies of genetic control of yield and important secondary traits of the six western Kenya elite varieties using Fs lines showed additive gene effects influenced yield, finger branching, neck and head blast, days to 50% flowering, ear shape, and days to physiological maturity, underscoring potential to generate superior varieties. Overdominance gene effects influenced plant height, lodging, and plant stand establishment. D

Studies on desmodium species for the allelochemicals involved in striga suppression

Author: Guchu, Salome Muthoni

Awarding University: University of Nairobi, Kenya

Level : PhD

Year: 2007

Holding Libraries: University of Nairobi, Chiromo Library ;

Subject Terms: Desmodium uncinatum ; Striga hermonthica ; Chemistry ;

Abstract:

The fodder legumes Desmodium uncinatum and D. intortum suppress the growth of Striga hermonthica (witch-weed) via an allelopathic mechanism that involves Striga germination stimulants and post-germination growth inhibitors. In this study, the root extracts (dichloromethane, acetone and methanol) from the two Desmodium species were investigated for Striga germination stimulation and post-germination radicle growth inhibition activities. The less polar extract (dichloromethane) showed Striga germination stimulation activity of over 40% at 10 ppm, but did not show any post-germination radicle growth inhibition at the same concentration. On the other hand, the polar extracts (acetone and methanol) were found to exhibit post-germination radicle growth inhibition activities of over 45% at 10 ppm. Chromatographic separation of the dichloromethane and acetone extracts of D. uncinatum roots yielded eleven compounds. These include, two pterocarpans [1,9- dihydroxy-3-methoxy-2-methylpterocarpan (uncinacarpan, 1) and 3,9-dihydroxy-lmethoxy-2-(3-methylbut-2-enyl)pterocarpan (edudiol, 2)], two isoflavanones [5,7- dihydroxy-2',3' ,4' -trimethoxy-6-(3-methylbut-2-enyl)isoflavanone (uncinanone D, 3) and 5,4' -dihydroxy-7,2' -dimethoxy-6-methylisoflavanone (uncinanone E, 4)], three abietane diterpenes [7 -oxo-15-hydroxydehydroabietic acid (5), 7a-hydroxycallitrisic acid (6) and 7, 15-dihydroxy-8, 11, 13-abietatrien-18-oic acid (7)]. a phytosterol [sitosterol (8)], a pentacyclic triterpene [Iupeol (9)], a long chain fatty acid [hexadecanoic acid (10)] and a Lla vune-C-glycoside [vitexin (11) J. Among these compounds, uncinacarpan (1), uncinanone D (3) and uncinanone E (4) are novel. The dichloromethane and acetone extracts of D. intortum roots afforded five compounds, four isoflavanones [7,2',4'-trihydroxy-2',2'-dimethylpyrano[5,6:6,7]isoflavanone (intortunone, 12), 5,7,2',4' -tetrahydroxyisoflavanone (dalbergioidin, 13), 5,7,2',4' -tetrahydroxy -6-(3- methylbut-2-enyl)isoflavanone (uncinanone A, 14) and 4',5'-dihydro-5' ,2' ,4'trihydroxy-5'-isopropenylfurano-(2',3':7,6)isoflavanone (uncinanone B, 15)] and an abietane diterpene [7-oxodehydroabietic acid (16)]. Intortunone (12) is a novel compound. The isolated compounds were characterized by use of a combination of spectroscopic techniques (UV, IR, MS, ID- and 2D-NMR) and by chemical derivatization. The isoflavanones, intortunone, dalbergioidin and uncinanone B from D. intortum were found to exhibit weak Striga germination stimulation activities (below 25% at 10 ppm) whereas the flavone-C-glycoside, vitexin was found to mildly inhibit the postgermination radicle growth of Striga by 37 % at 100 ppm.

Ex-ante economic evaluation of the herbicide coated maize in the control of striga in Western Kenya.

Author: Ngare, Lucy Wangare

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 2005

Holding Libraries: University of Nairobi Upper Kabete Library ;

Subject Terms: Crops ; Maize ; Crop diseases ; Pest control ; Striga ; Herbicides ; Weeds ;

Abstract:

ABSTRACT NOT AVAILABLE

Effects of coppicing and non-coppicing improved fallow species on soil inorganic nitrogen and Striga hermonthica in western Kenya

Author: Mavuthu, Abednego Kiwia

Awarding University: Moi University, Kenya

Level : MSc

Year: 2005

Holding Libraries: World Agroforestry Centre Library ;

Subject Terms: Agriculture ; Agroforestry ; Soils ; Crops ; Nitrogen ; Striga hermonthica ; Western Kenya ;

Abstract:

ABSTRACT NOT AVAILABLE

Ascertaing metabolic pathway sites in Orobanche aegyptiaca that can be inhibited using anti-metabolites in vitro

Author: Mgutu, Allan Jalemba

Awarding University: Kenyatta University, Kenya

Level : MSc

Year: 2004

Holding Libraries: Kenyatta University Moi Library ;

Subject Terms: Weeds ; Weed control ; Striga ; Orobanche aegyptiaca ; Biochemistry ;

Abstract:

Some parasitic angiosperms cause considerable damage to food and fodder plants resulting in very low yield or none at all. The pernicious root parasites Striga and Orobanche are among the most devastating weeds and are not effectively controlled due to various reasons. The principal interest of this study was the biochemical understanding of the growth and development processes of the weeds. In this study, biochemical pathways of Orobanche aegyptiaca that can be inhibited with anti-metabolites were investigated using in vitro experimental systems. In vitro cultures of Orobanche aegyptiaca were established both on solid and liquid media with potential use in bioassays and biochemical studies. A modified MS medium composition was adopted as most suitable and consisted of a 10-fold reduction in ammonium nitrate. The medium was further supplemented with 2 mg/L 2,4-dichlorophenoxy acetic acid and 0.1 mg/L kinetin as plant growth regulators and standard MS vitamins. The effect of anti metabolites inhibiting amino acid, fatty acid, carotenoid, cellulose and folate biosyntheses, photosynthesis and tubulin polymerization were determined by measuring the growth of the in vitro tissues and elongating radicles. Branched chain amino acid biosynthesis was the most sensitive pathway to inhibition among all the investigated biosynthesis pathways. Glutamine biosynthesis and/or ammonium assimilation was equally sensitive to inhibition in the in vitro tissues. The significance of amino acid biosyntheses in Orobanche aegyptiaca was shown when the activities of the specific enzymes were also found to be quite sensitive to inhibition by the same anti-metabolites. Acetolactate synthase in branched chain amino acid biosynthesis was effectively inhibited by all the ALS targeting anti-metabolites used i.e. chlorsulfuron (IC5o 1.0 nM), imazapyr (IC5o 0.88?M) and imazaquin (IC5o 1.97 ?M). Despite the common inhibitory activity, imazaquin was completely ineffective on the radicles. Glutamine synthetase was sensitive to glufosinate when partially purified (IC5o 9.1 ?M). Cellulose biosynthesis was sensitive to inhibition by dichlobenil in callus tissues (IC5o0.1 nM) and elongating radicles (IC5o 10 nM) only. Cell suspensions seemed to have developed the ability to grow without real cell walls. Inhibitors of microtubulin polymerization were only effective in inhibiting growth of callus tissues. Folate biosynthesis was mildly sensitive to inhibition by sulfadiazine and asulam possibly due to a competent folate recycling system and/or sufficient stored reserves. Inhibition of fatty acid, carotenoid and plastoquinone/tocopherol biosyntheses, and photosynthesis, had little effect on growth of the tissues.

Interactions between Striga hermonthica (fel.) benth (scrophulariaceae) and stemborer Chilo partellus (swinhoe) (lepidoptera : pyralidae) on Maize plant (Zea mays L.)

Author: Mohamud, Mohamed Hassan

Awarding University: Kenyatta University, Kenya

Level : PhD

Year: 2004

Holding Libraries: Kenyatta University Moi Library ;

Subject Terms: Maize ; Crop diseases ; Striga hermonthica ; Chilo partellus ; Pest control ; Weeds ;

Abstract:

A study on the interactions between Striga hermonthica (Del.) Benth, and stemborer [Chilo partellus (Swinhoe) (Lepidoptera: pyralidae)] on maize plant (Zea mays L.) hybrid (511) was carried out at ICIPE Mbita Point Research and Training Centre (MPRTC) situated on the shores of Lake Victoria in Western Kenya. Maize is the staple food in this area and is grown by small-scale farmers. C. partellus, is one of the serious pests of the maize plant whereas S. hermonthica is a parasitic weed. Both the borer and the weed are among the major factors limiting maize production and infest a large area of Western Kenya within the Lake Victoria basin. This study was to investigate the interactions between striga and borer on maize plant. Studies on C. partellus infestation levels in the S. hermonthica infested / uninfested maize fields was carried out within MPRTC during both long and short rain seasons of the year 2000. Results showed that there was a positive correlation between borer leaf damage and striga plants, and also there was a negative correlation between striga weeds and maize plant height as well as yield. Investigations on various infestation density levels of S. hermonthica and C. partellus on maize plants were carried out in the laboratory and screen house. These involved the effect of the striga infested maize plants on oviposition, biology and behaviour of C. partellus. Results indicated that the mean number of eggs laid by the moths was higher on the high striga infested maize plants than on the low and medium striga infested, and the control. Effect of the striga infested maize plants on larval arrest, settling, feeding, food assimilation, growth and development were also studied. There was no significant difference on the mean number of C. partellus larvae arrested on maize plants in 3 and 5 days after infestation; neither on those settled on maize leaf cuts in 4, 8 and 24 hours after infestation. Results from these studies also showed that larvae consumed less leaf cuts and stem segments from the striga infested maize plants than they did on those from the control maize plants. The least larval food assimilation also occurred on the high striga infested maize plants. The shortest larval development period was recorded on the control (uninfested) maize plants. Percentage pupation was also significantly higher on the uninfested maize plants compared to the medium and high striga infested maize plants. In order to achieve sound knowledge on maize and striga interactions further studies on the influence on maize growth should be carried out. There is also need to carry out further studies on oviposition preference of C. partellus moths on striga infested maize plants.