11 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.

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.

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

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.

Molecular basis of Striga hermonthica resistance in some Kenya maize cultivars.

Author: Kariuki, Silas

Awarding University: Egerton University, Kenya

Level : MSc

Year: 2000

Holding Libraries: Egerton University Library ;

Subject Terms: Striga hermonthica/Maize/Molecular biology/ ;

Abstract:

ABSTRACT NOT AVAILABLE

Studies on witchweed [Striga hermonthica (Del.) Benth] seed longevity under different management systems in Kenya.

Author: Odhiambo, G D

Awarding University: University of Reading, England

Level : PhD

Year: 1998

Holding Libraries: Index To Theses ;

Subject Terms: Agriculture ; Striga hermonthica ; Farm management ; Seeds ;

Abstract:

Studies were conducted under laboratory conditions at the University of Reading and in the field in western Kenya in the period between 1991 and 1997 on some aspects of S. hermonthica seed dynamics in the soil with special reference to the effects of adding organic materials and fertilizer N to soil and the effect of S. hermonthica handpulling. In the long term studies, S. hermonthica seed populations in the soil declined considerably at one site in Kibos but remained relatively stable at another site in Homabay. S. hermonthica seed numbers were not decreased by adding maize stover alone at both sites. There was a small decrease in seed numbers at Homabay by adding nitrogen while a combined addition of maize stover and fertilizer N were more effective. In short term studies (6 seasons) at Ebukanga, seed numbers were also decreased with the best treatment being addition of farmyard manure combined with fertilizer N. S. hermonthica handpulling decreased seed numbers at Kibos and Homabay. S. hermonthica seed numbers and S. hermonthica plant emergence were more weakly and positively correlated at Kibos compared to Homabay. Striga handpulling reduced the number of emerged S. hermonthica plants at Homabay while at Kibos this occurred only when seed numbers were large. S. hermonthica emergence was not affected by organic materials and fertilizer N at Kibos in the long term studies while in the short term S. hermonthica emergence was higher. At Homabay, 80 kg N ha-1 as fertilizer N or combining organic amendments with fertilizer N to provide 30 kg N ha-1 reduced S. hermonthica plant emergence. At Ebukanga, combining composted manure with fertilizer N to provide 50 kg N ha-1 was more effective in reducing S. hermonthica emergence than stover combined with 25 kg N ha-1. S. hermonthica handpulling reduced seed numbers and to some extent, emerged S. hermonthica plants. However, better maize yield was only obtained with improved soil fertility at both Kibos and Homabay. In the long term studies at Homabay, combining maize stover with fertilizer N slightly depressed maize yield due to immobilization while combining 80 kg N ha-1 with S. hermonthica handpulling gave better maize yield.

Isolation and bioassay of Striga hermonthica seed germination from non-host crops and yield testing for control efficacy.

Author: Ariga, Emmanuel Safary

Awarding University: University of Nairobi, Kenya

Level : PhD

Year: 1996

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Striga hermonthica ; Biochemistry ;

Abstract:

ABSTRACT NOT AVAILABLE