152 Records out of 22207 Records

Molecular detection of viruses associated with passionfruit (passiflora edulis sims) woodiness disease, monitoring and management of Aphid vectors in Kenya

Author: Ngeranwa, Dora C Kilalo

Awarding University: University of Nairobi, Kenya

Level : PhD

Year: 2012

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Passiflora edulis ; Cowpeas ; Mosaic virus ; South African passiflora virus ; Crop diseases ;

Abstract:

Passionfruit (Passiflora edulis Sims) is an important economic crop in the world as an income earner and for food and nutrition security. Among the biotic stresses constraining production, woodiness disease is important causing economic losses wherever passionfruit is grown worldwide. In Kenya, passionfruit is a source of income to many small scale farmers. Although viral diseases are reported to be present in Kenya, there is limited,information on the causal agents and the relationship with aphid species found in passionfruit agroecosystem. This study was undertaken to identify the causal agents of woodiness disease, incidence and distribution; monitor and identify the potential aphid vectors, determine virus transmission ability of the aphid species present in the orchards and to evaluate the effect of aphid repellant sources such as plastic reflective mulch to manage aphid vectors. A survey was undertaken in major passionfruit growing areas in the Rift Valley, Central and Eastern provinces of Kenya in 2008 and 2010. The area was stratified according to administrative districts and agroecozones from which 130 fields were selected along rural roads. Suspected passionfruit leaf samples collected were assayed using ELISA and RT-PCR techniques for detection and identification of the viruses. Sequence diversity for Cowpea aphid borne mosaic virus (CABMV) was determined. Experiments for monitoring aphid vectors and evaluating aphid repellant sources were laid out in randomized complete block design in two sites. The presence and abundance of aphids were monitored using yellow water pan traps. The aphids captured were counted and identified under a stereomicroscope and using a dichotomous key. The viruses were distributed widely with moderate to high incidence in all the passionfruit growing surveyed areas. The incidence was significantly (p<0.05) higher in the upper midland zones (82%) compared to the lower highland zones (50%). The most common virus had 45% incidence. Coat protein sequence analysis for the most common virus isolated from Kenya, was closely related to South African passiflora virus and CABMV. Based on sequence identity, the virus was identified as a strain of CABMV. There was a high homology of the amino acid sequences among the Kenyan isolates suggesting a low diversity with strain differences. Other viruses present were Cucumber mosaic virus (CMV) and an unidentified potyvirus.

Characterization and selection of Kenyan sweet potato (Ipomoea batatas L.) genotypes for sweet potato virus disease resistance and high dry matter

Author: Karuri, Hannah Wangari

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : Msc

Year: 2009

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Ipomoea batatases/Ipomoea batatas/Genetics/Crop diseases/Viruses/ ;

Abstract:

Sweet potato virus disease (SPVD) is a major constraint to sweet potato production in Kenya. In addition to SPVD, low production of sweet potato in Kenya is also due to lack of cultivars with consumer quality attributes such as high dry matter content. Use of resistant cultivars is the most effective means of controlling the disease. This study aimed at characterizing Kenyan sweet potato genotypes for SPVD resistance and high dry matter content using morphological and simple sequence repeat (SSR) markers. A total of 314 genotypes were collected, established in a screenhouse and evaluated for their reaction to SPVD using symptom severity. Severity of SPVD in each genotype was determined using a scale of 1-5; where 1= no symptoms and 5=very severe symptoms. Serological assays were done on 89 genotypes with a symptom severity score of between 1.00 and 1.50. Analysis of variance of the symptom severity scores showed that the genotypes responded differently (P < 0.001) to SPVD in the screenhouse. Twenty genotypes tested negative for both SPFMV and SPCSV and were considered resistant/tolerant to SPVD.Three hundred and fourteen genotypes were planted in the field and characterized using 42 morphological traits based on the CIP Research Guide 36 followed by cluster analyses of the scored traits using unweighted pair group method with arithmetic means (UPGMA). Tuber dry matter content was determined 5 months after planting in the field. Phylogenetic analysis using morphological descriptors grouped the genotypes into two major clusters. None of the clusters clearly distinguished the 20 resistant genotypes from the 294 susceptible ones. The tuber dry matter content significantly (P<O.OOI) varied among the sweet potato genotypes. Genotypes with highest and lowest tuber dry matter content were not distinguished from each other using DPGMA phenogram generated. This indicates that morphological markers are not reliable in identifying and classifying sweet potato genotypes into phenotypic groups based on their resistance to SPVD and high dry matter. Therefore, morphological markers supplemented with molecular markers need to be investigated for their potential application in identification of sweet potato genotypes with SPVD resistance and high dry matter content. Eighty nine sweet potato genotypes were selected following graft inoculation with SPVD-infected scions and characterized using 6 SSR primer pairs. The amplified DNA fragments were screened by capillary electrophoresis on the ABI 3730 genetic analyzer and analysed using the Genemapper v3.7 software. Cluster and principal component analysis (PCA) were done using NTSYS-pc version 2.11 T. Six primer pairs were highly polymorphic among the genotypes and polymorphic information content (PIC) varied from 0.33 to 0.81 with an average of 0.47. The number of alleles within the 89 genotypes across the 6 loci ranged from 10 to 17, with an average of 13.52. Cluster analyses showed Jaccard's coefficient from 0.5 to 1, with an average of 0.75 accounting for 50% variation among the 89 genotypes. The phylogenetic and PCA analysis clustered 89 genotypes into 2 main clusters and 5 subclusters. The dendrogram did not reveal any unique clustering of the sweet potato genotypes according to dry matter content or reaction to SPVD. The genetic differences among the SPVD resistant and high dry matter content genotypes revealed by the clustering into distinct groups suggest the presence of different sources of resistance to SPVD and high dry matter. This study therefore indicates that there is a high level of genetic diversity in sweet potato genotypes that are SPVD resistant and have high dry matter. These genotypes can be used as parents in breeding programmes aimed at improving the crop for the two traits

Identification of amplified fragment length polymorphism AFLP markers linked to maize streak virus MSV disease resistance genes

Author: Lagat, Martin Kipkogei

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2009

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ; Kenya Agricultural Research Institute Headquarters Library ;

Subject Terms: Crop diseases ; Maize ; Maize streak virus ;

Abstract:

Maize (Zea mays L.) is the most important cereal in Sub-Saharan Africa, where it is used as human food animal feed, raw material for various industrial products and as source of employment at various stages of production. In Kenya, lack or limited availability of maize is equated to hunger. Despite its significance, the average annual production remains lower than the average annual consumption. One of the contributors to low productivity of this important crop are diseases, particularly maize streak virus which causes up to 100% yield loss. The disease is difficult to control through conventional methods and therefore, use of resistant varieties is a more feasible method of managing it. However, the conventional methods of breeding and deploying resistant varieties take a long time, and are dependent on crop growth stage and prevailing environmental conditions. Thus, there is need for better tools and techniques such as DNA-based molecular marker assisted selection. The objective of this study was to map AFLP regions linked to maize streak disease resistance in two single crosses arising from inbred lines, OSU23i (resistant), CML 202 (resistant), and EM12-210 (susceptible). Phenotypic screening of the resistant parents revealed inbred line OSU23i was more resistant with mean score of 1.13, and CML 202 had a mean score of 1.21. The susceptible parent EM12-210 interestingly had a low mean score of 1.33 which was close to the resistant parents. The average F1 score was 1.5, which was close to the midparent value of 1.22. The average F2 score was 1.92, which, was 0.42 units less resistant than the F1 and 0.7 units less resistant than the mid-parent. The results indicated that there was incomplete dominance in the resistance inherited by the F2 progenies. To enhance stringency of selection, AFLP markers were mapped. Out of 9 primer combinations used, 8 produced scorable bands, ranging from 58- 69 per primer combination. All the scored bands were over 90% polymorphic. Out of the 8 primer combinations, the primer combination E-ACCIIM-CAC was chosen based on low heterozygosity and high allele frequency for the resistance allele. Marker trait association revealed very significant associations (r2>0.5 1; p<O.OOI) detected between loci 25 and 26, 25 and 29, 26 and 27, 26 and 29,42 and 51,43 and 52, 44 and 53, 45 and 54, and 46 and 55. Using the significance of LD procedure, 18-20 markers that accounted for 40-58% of the variation were selected as having significant association with MSV resistance. LD decayed within a map distance of 11.4 cM, with the resistant allele (A) decaying in 4.6 cM (40.4%), the susceptible allele (B) in 6.2 cM (54.5%), and the segregating allele (H) in 0.5 cM (0.6%) of the map distance. The average distance between linked loci was 4.6 cM. In cross EMI2-21O/CML202, allele A covered 22.6 cM which represented 39.6% of the genome, allele B covered 30.2 cM representing 53.1 %, and allele H covered 4.2 cM representing 7.3% of the map distance giving a total of 57 cM per individual linkage map. The number of recombination detected ranged from 11 to 31 with a mean of 23.3. Heterozygote segments detected by each locus ranged from 0 to 13. In cross EMI2-21O/OSU23i, allele A covered 23.5 cM which represented 41.2.6%, allele B covered 31.9 cM representing 56%, and allele H covered 1.6 cM representing 2.9% of the map distance giving a total of 57 cM per individual linkage map. The mean number of recombination detected was 21.7. The number of recombination ranged from 7 to 32, while heterozygote segments detected ranged from 0 to 7. The resistance allele (allele A) had higher frequencies in only 15 out of the 58 loci in both crosses. In the 15 loci, the levels of heterozygosity were low, indicating potential regions of resistance. Only 10 genotypes had higher frequencies for the resistant allele (A) in cross EM12- 210/CML202, and only 7 in cross EMI2-21010SU23. By combining phenotypic scores from artificial inoculation and ma

Host suitability and interspecific competition among the West African stemborer egg parasitoid Telenomus isis and other indigenous egg parasitoids in Kenya

Author: Anani, Yaovi Bruce

Awarding University: Kenyatta University, Kenya

Level : PhD

Year: 2008

Holding Libraries: Kenyatta University Moi Library ;

Subject Terms: Maize ; Crop diseases ; Pest control ; Butterflies and moths ; Chilo partellus ; Busseola fusca ; Telenomus isis ; Stem borers ;

Abstract:

In East and Southern Africa (ESA), the noctuid Busseola fusca and the exotic crambid Chilo partellus are among the most important lepidopteran stemborer pests of cereal crops. In western Africa, the scelionid egg parasitoids Telenomus busseolae and Telenomus isis are the most important biotic control agents of noctuid stemborers such as Sesamia calamistis and B. fusca. Telenomus isis had never been reported from ESA and was thus introduced into the International Centre of Insect Physiology and Ecology (ICIPE) laboratories in 2003 for possible release against B. fusca. This study aimed at assessing the potential of egg parasitoid, T Isis, as a biological control agent against B. fusca in ESA. Distribution and parasitism of noctuid stemborer eggs was assessed in some localities in Kenya. Busseolae fusca was the most prevalent species in high altitude areas (> 1500 m above sea level) but it co-existed with S. calamistis in mid altitude areas (500-1200 m above sea level). The highest egg parasitism rate (32.6%) was recorded in Kiboko with Telenomus busseolae dominated the egg parasitoid community followed by the trichogrammatid Trichogramma bournieri. Host acceptance and suitability were assessed using fifteen lepidopteran borer species. Only noctuid stemborers were successfully attacked by T. isis. Parasitism rate and developmental time significantly varied between the major borer species tested (S. calamistis, Sesamia botanephaga, and B. fusca) but no significant differences were observed in sex ratios (expressed as a proportion of female progeny). With increasing duration of host deprivation from 0 to 14 days, longevity for the three-stemborer species increased, whereas mean fecundity decreased, indicating resorption of eggs. The effects of temperature, humidity and host species on the bionomics of T. isis were studied. The lower and upper threshold for development were estimated at 10.6 to 36.5?C respectively, and the optimal temperature for development was between 30.5?C to 31.5?C for the three stemborer species and both two relative humidities. Furthermore, the effects of host species, host age and duration of host deprivation on the performance of Tr. bournieri, a polyphagous parasitoid of eggs of several cereal stemborer species in eastern Africa was evaluated as part of an interspecific competition study. The noctuids S. calamistis, S. nonagrioides and B. fusca, and the crambid Chilo partellus and pyralid Eldana saccharina were successfully parasitized by Tr. bournieri. Parasitism rate, number of progeny and developmental time of Tr. bournieri varied significantly among the host species. Sesamia calamistis and B. fusca eggs where the most suitable hosts, while E. saccharina was the least suitable host. While parasitism rate and the number of progeny tended to decrease with the age of host eggs, there were no significant differences in the sex ratio. Longevity of the parasitoid increased with increase in deprivation of hosts from 0 to 12 days. The mean lifetime fecundity per female decreased with increased of host deprivation increased, indicating resorption of eggs. In addition, oviposition behaviour of T. isis and two other indigenous parasitoids (T. busseolae and Tr. bournieri) were studied using S. calamistis, S. botanephaga and B. fusca as hosts to evaluate the degree of self-super, and superparasitism. Four distinct steps of behaviour were observed: foraging, palpitation with antennae on the eggs, insertion of ovipositor and egg marking. Walking and resting were observed less frequently than the other behaviours. On average, insertion of ovipositor took 2 to 3 minutes per female. Telenomus isis females responded pontualy to the calling virgin female moths indicating that the parasitoid uses pheromones to find the host eggs.

Screening for resistance to potato virus Y and potato virus X in potato salanum tuberosum L.

Author: Onditi, John O

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 2008

Holding Libraries: University of Nairobi Chiromo Library ;

Subject Terms: Salanum tuberosum ; Crop diseases ; Viruses ;

Abstract:

Studies were conducted at KARI-Tigoni and KARI-Marindas (Molo) with the aim of assessing the value of using varieties with Potato Virus Y (PVX) and Potato Virus X (PVX) resistance in preventing crop losses under the local (Kenyan) potato growing conditions and also to assess suitability of these PVY and PYX resistant clones as resistant parents for developing new potato varieties in Kenya. In the first study, seven PVY and PYX resistant clones from the International Potato Centre (CIP) Lima, Peru together with six local susceptible check varieties were subjected to natural virus infection over three cropping seasons during Short Rains (SR) 2005 at KARI-Tigoni and in both sites (KARI- Tigoni and Molo) during the Long Rains(LR) 2006 and SR 2006. ELISA tests conducted on the tuber samples at the end of every season indicated significant (P = 0.05) higher percentage of 40 - 100 % PVY and PYX infection in the susceptible check varieties and significant (P = 0.05) lower percentage of 0 - 5 % infection in the best resistant clones. The CIP clones experienced significant (P = 0.05) lower yield reduction ranging from 1.2 to 2.3 Tlha compared to the susceptible check varieties which had a higher yield reduction of 12.2 to 15.4 Tlha. Among the CIP clones evaluated, CIP 394905.8 was found to be the best in with standing virus related yield losses since instead of experiencing a yield reduction like other genotypes; it experienced yield increase ranging from 0.83 to 1.2 Tlha in both sites of the study. In the second experiment, five CIP resistant clones were crossed with two susceptible cultivars and the progeny seedlings obtained were subjected to PVY and PYX sap inoculation to screen for virus resistance in the seedlings. Successful development of berries from the crosses was higher (ranging from 18.6 % to 61.5 %) in the crosses conducted in the field under lower temperature ranges of 12 - 31?C, 14 - 20 ?C and 11 - 18?C compared to the crosses conducted in the glasshouses (0 - 3.7 %) under relatively higher temperature ranges of 21 - 36?C and 18 - 31 'C. Number of true potato seeds obtained from the crosses and planted in each of the crossing combinations ranged from 1253 to 1791 and percentage emergence of seedlings ranged from 65 % to 90 %. Among the CIP clones used as resistant parents, CIP clone 395438.1 was identified as the best with 2 single dominant genes for PVY and PYX resistance out of four (Ry Ry ry ry) and it produced 84 % of resistant progenies when crossed with susceptible cultivar Tigoni. The studies recommended the utilization of PVY and PYX resistant clones/varieties in reducing virus related crop losses and as parents for developing new virus resistant genotypes.

Adapting spraying regimes to two late blight resistant potato varieties and testing for metalaxyl resistance in phytophthora infestans

Author: Ngatia, Grace Wanjiru

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2008

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Pesticides ; Crop diseases ; Blight ; Phytophthora infestans ; Solanum tuberosum ;

Abstract:

Nine fungicide spray regimes were tested to complement the resistance of Asante (CIP 381381.20) and Tigoni (CIP 381381.13) potato varieties against late blight over two seasons at the KARl seed multiplication centre in Njabini (Latitude: 0? -44' 60 N, Longitude: 36? 40' 0 E). The nine treatments were based on different spray intervals and/or combinations of a systemic (Ridomil Gold) and contact (Dithane M45) fungicide. All the treatments reduced disease severity, increased yield and marginal net benefit substantially when compared to the unsprayed control treatment. The damage threshold treatment where Ridomil was sprayed at the onset of disease symptoms and then at 5, 10 and 15% disease severity, gave the best control of late blight for both varieties with a disease severity ranging from 12.7 to 15.2%. This treatment also gave the highest net benefit in season 2 of>Ksh.80,000 per hectare for both varieties. However, it also required the highest investment of Ksh. 9,880 per hectare. The one spray treatment, where Ridomil was sprayed only at the onset of symptoms, required the least investment of Ksh.l 026 and 1625 per hectare for season 1 and 2 respectively and gave the highest marginal rate of return which ranged from 1678 to 6794% for both varieties over both seasons. The two spray treatment, where Dithane M45 was sprayed at emergence and Ridomil sprayed at the onset of symptoms effectively complemented the host resistance of both varieties, as it satisfactorily suppressed the disease and gave additional marginal rates of return to The one spray treatment, ranging from 123 to 3164% with a minimal addition investment of less than Ksh.1 000 per hectare. The two spray treatment was found to be cost effective and therefore recommended to complement the resistance of Asante and Tigoni varieties. Potato leaf samples infected with P. infestans were collected in potato production zones of Meru and Nyandarua districts and isolated on 10% V8 agar supplemented with antimicrobial compounds. The sensitivity of isolates to metalaxyl was assessed by measuring the radial growth of the colony on 10% V8 agar amended with 0, 5 or l Ouug/ml of metalaxyl. Overall, 6% of the isolates were resistant to metalaxyl, 6% were intermediate and 88% were sensitive. The prevalence of isolates that grew in the presence of metalaxyl with growth of <40% of the control at 5 ug/ml was higher in the isolates obtained from the Nyandarua area than those from Meru. In addition, the LB2004 version of LATEBLIOHT, a mathematical model that simulates the effect of weather, host growth and resistance and fungicide use on the asexual development of P. infestans on potato foliage was used to simulate late blight disease for two potato varieties, Asante and Tigoni. Model predictions using general category parameters overestimated disease, perhaps due to inaccurate estimates of the fitness parameters. The fitness parameters were then calibrated using data collected from Njabini. The new parameters determined through calibration for Asante variety were: sporulation rate (SR) of 1.2 x 108 sporangia m-2 day' I , lesion growth rate (LOR) of 4 x 10-3 m day' I , latent period (LP) of 4.2 days and infection efficiency (IE) of 0.8 while for Tigoni variety the LOR was found to be 3.9 x 10-3 m day' I , SR was 1.175 x 108 sporangia m-2 day' I , LP was 4.2 days and IE was 0.8. When calibrated parameters for Asante and Tigoni varieties were used for simulation, model predictions fit the observed data.

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

Regeneration potential and transient expression of b-glucuronidase mediated via agrobacterium tumefaciens in immature embryos of Kenya maize genotypes

Author: Binott, Jayne Jebichii

Awarding University: Kenyatta University, Kenya

Level : MSc

Year: 2007

Holding Libraries: Kenyatta University Moi Library ;

Subject Terms: Maize ; Genetic engineering ; Genetically altered foods ; Crop diseases ;

Abstract:

Production of maize is constrained by both abiotic and biotic stress factors in the field and by post-harvest pest problems; the most important being the larger grain borer, Prostephanus truncatus (Horn) and maize weevil, Sitophilus zeamais. Developing insect resistance crop varieties through conventional plant breeding is elusive, expensive and time consuming due to the limited genetic variation within the maize genotypes as well as difficulty in maintaining quantitatively controlled traits such as insect resistant. However, by using genetic engineering tools, modified novel genes (e.g. from Bt or plant proteins) can be introduced into maize to produce transgenic maize that confer resistance to these insects pests. The present study investigated regeneration potential of Kenyan maize genotypes as a prerequisite to genetic transformation. Twelve parental inbred lines and their respective single cross hybrids were planted in Kiboko and Kabete and evaluated for callus induction, somatic embryo formation and subsequent plant regeneration. Embryos were excised from surface sterilized kernels harvested at different physiological stages namely 10, 15, 18, 21 and 24 days after pollination (DAP). They were used as explants to initiate callus on N6 induction media with varying levels of 2,4-D (020mg/L) supplemented with 2.87g/L proline, 0.1 g/L casein hydrolysate, 2g/L glycine, 30g/L sucrose and 3g/L gelrite. The pH was adjusted to 5.8 before autoclaving. The induction frequency of primary calli at 2mg/L 2, 4 D was genotype dependent. Callus induction ranged from 80-90% for hybrids and 50-80% inbred lines. Following two biweekly subculture, the embryogenic calli formation was initiated. Three types of calli were initiated: Type I accounted for 17.6%, type II 52.9% while the remaining 29.4% made up type 0. Using this system, somatic embryo competence was demonstrated in 6 inbred lines and 4 hybrids. However, plant regeneration was only achieved in 4 inbred lines and 3 hybrids. The frequency of shoot formation ranged between 4-40%. The development of this efficient and reproducible regeneration system sets a basis for genetic transformation via Agrobacterium tumefaciens. Six Agrobacterium strains carrying two types of plasmids (pBECK2000.4) and (pCAMBIA2301) were used to introduce Gus A (Gus) reporter gene encoding -(3-glucuronidase to maize embryogenic tissues. The expression of gus activity on transformed embryogenic tissues was evaluated by histochemical staining with X-Gluc. Gus staining revealed variation in both intensity and pattern of blue staining in embryos transformed with the same plasmid and bacterial strain. EHA105(pCAMBIA2301) AGL1(pBECK) revealed high infectivity across various genotypes. Fifteen days (15 DAP) was optimal embryo stage for gus expression while incubation for 24 hrs was appropriate for co cultivation stage. There was no gus activity in bacterial strains that were devoid of plasmid.

Incidence and composition of casual agents of root rots complex in common beans (Phaseolus vulgaris L.) and molecular characterization of Rhyctonici solconi isolates from Embu District, Kenya.

Author: Githinji, Thiong'o

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 2005

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Agriculture ; Crops ; Beans ; Crop diseases ; Phaseolus vulgaris ;

Abstract:

ABSTRACT NOT AVAILABLE

Ear rot and fumonisin B1 levels in self selected maize varieties at different harvest intervals in Western Kenya

Author: Alakonya, Emitati Amos

Awarding University: Kenyatta University, Kenya

Level : MSc

Year: 2005

Holding Libraries: Kenyatta University Moi Library ;

Subject Terms: Maize ; Crop diseases ; Mycotoxins ; Fusarium moniliforme ; Western Kenya ;

Abstract:

This study was aimed at carrying out a social economic and biological investigation on ear rot fungi, fumonisins and how they can be managed in maize in Western Kenya. During the study a Participatory Rural Appraisal (PRA) on farmer perceptions and practices in relation to maize ear not revealed that maize is the major crop in the region. Rotten maize is used for brewing, livestock feed, mixed with clean maize and sold during times of scarcity to consumers for maize meal. Maize ear rot was ranked as the most important crop protection constraint. Stalk borers and weevils were the most important field and storage pests respectively. The awareness of the health hazards associated with consumption of contaminated maize was limited among farmers and even extension staff in the two divisions. Evaluation of soil amendments in management of root infection by Fusarium moniliforme was evaluated in the greenhouse and field using several amendments. Non-amended soil acted as the control. The results revealed that different soil organic amendments had significant effects on the pathogenecity of F. moniliforme and plant performance. Goat manure had significant suppressive effects on root infection when used singly, but the effects were less than those obtained from a mixture of goat/Fym. Efficacy of various amendments were rated starting from the most to the least effective as follows; goat/Fym, neem/Fym, cotton, Fym, cott/Fym, sun/Fym, neem and sunflower respectively. In general organic amendments reduced the survival and infection of maize plants by F. moniliforme compared to controls. Use of soil amendments did not eliminate FB1 occurrence in maize when used at planting. The ear rot on-farm trial carried out in Tongaren and Malava divisions gave a broader assessment of the varieties in terms of response to natural infection to ear rot fungi and the actual farmers' practice under which these varieties are grown. The varieties revealed significant difference in percentage rotten grain, ear rot severity, yield of clean and rotten maize between the harvest intervals and also between varieties. Between 4th and 12th harvesting intervals the highest percentage rot was 40% in variety H622 and KSTP' 94 at 12th week harvest interval in Tongaren and Malava divisions respectively. Mycological analysis revealed that Fusarium spp were the most dominant ear rot fungi with F. moniliforme being the most prevalent fungi. Other ear rot fungi isolated but in low numbers included Stenocarpella spp, Aspergillus spp and Penicillium spp. The natural occurance of FB1 was investigated in four maize varieties at different harvest intervals by direct competitive ELISA method. From the maize samples analysed FB1 was found in 97.22% samples at levels ranging from 32ng/g to >5000ng/g the average concentration in clean maize, rotten maize all the sample analysed was 255ng/g, 2432ng/g and 1344ng/g respectively. It was established that FB1 is not just restricted to the rotten maize but also clean maize and that there is widespread occurance of the mycotoxin in maize from the two division. AFB1 occurred only in 4 samples out of the 72 samples analysed and ranged between 2.3ng/g to 4.1ng/g. All samples except for one were clean maize samples. The Fusarium moniliforme isolates produced FB1 in the range of 69ng/g to >5000ng/g. The study concluded that FB1 levels are higher than recommended and efforts to regulate the mycotoxin should be put in place in Kenya given that maize movement in Kenya is not restricted. It is now evident that people in W. Kenyan are exposed to higher levels of FB1 and there is need for farmer education and research towards low FB1 levels given the June 2004 mycotoxicoses in Eastern and Central Kenya