8 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.

A comparative assessment of SRI and conventional rice production in Mwea irrigation scheme, Kenya

Author: Matolo, Nyamai

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

Level : MSc

Year: 2012

Holding Libraries: Kenya Agricultural Research Institute Headquarters Library ;

Subject Terms: Rice ; Oryza sativa ; Mwea-Tebere Irrigation Scheme ; Irrigation ; Agricultural production ;

Abstract:

Rice (Oryza sativa L.) is an important food crop in Kenya's drive to attain food security and the alleviation of hunger. Yet the productivity of the crop remains low, leading to a huge national deficit. An exploratory field study was conducted to evaluate a system of rice intensification (SRI) that would increase water and crop productivities relative to the conventional production system. The effects of SRI on total water input and the yield of three rice varieties were investigated at the Mwea Irrigation Scheme (MIS) of Kenya. The experiment was a randomized complete block design (RCBD), laid out as a split plot with production system as the main plot factor (conventional, modified conventional, and SRI) and variety (Basmati 370, BW 196 and NERICA1) as the subplot factor. The component practices of the conventional system were: transplanting of 25 day-old seedlings, multiple seedlings per hill, 10 cm x 10 cm interplant spacing, continuous flooding, and hand weeding. In the modified conventional system interplant spacing was 25 cm x 25 cm, with all the other practices being similar to those of the conventional system. SRI was defined by: transplanting 14 day-old seedlings, single seedling per hill, 25 cm x 25 cm interplant spacing, intermittent irrigation by alternate wetting and drying (A WD), and a combination of hand weeding and use of a pushed rotary weeder. In all production systems, manure, basal nitrogen, phosphorus, potassium, and N-topdressing were applied at the rates of 400 kg/ha, 60 kg/ha, 60 kg/ha, 40 kg/ha and 70 kg/ha respectively. Data collected included rice grain yield and total water input per production system. Average grain yield was higher in SRI (14.85 t ha') compared to conventional production system (8.66 t ha') at P=0.006. Differences in yield between the modified conventional system and SRI were not statistically significant at (1=0.05. Compared to the conventional system, grain yield under SRI was increased by 70%, 80%, and 61 % for Basmati370, BW196 and NERICAI respectively. Total volume of irrigation was 111.02 m3, 94.7 m3 and 84.24 m3 for conventional, modified conventional and SRI systems respectively. SRI increased crop and water productivity in the MIS by 71 % and 90% respectively. The production practices of SRI had potential to improve rice productivity while saving on water. SRI improved the overall performance of rice regardless of the genetic characteristics, indicating that the production practices of the system were beneficial to plant growth. Reducing plant density through wider spacing as a modification of the current conventional practice has potential to increase yields in Mwea, as the yields under SRI and a modified conventional system were comparable. Further research to determine the optimum levels of SRI components for higher crop yields is recommended.

Competition between cultivated rice oryza sativa L. and the wild rice oryza punctata kotschy ex steud in Kenya

Author: M'Ringera, Jane Tei

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 2008

Holding Libraries: University of Nairobi Chiromo Library ;

Subject Terms: Oryza sativa ; Oryza punctata ; Rice ;

Abstract:

Rice is an important staple food for more than SO% of the world's population. Kenya rice production comes from cultivated rice (Oryza. Sativa L.) that meets 60% of rice demand. Cultivated rice in the coastal region of Kenya grows in competition with wild rice particularly, Oryza punctata Kotschy ex Steud This study examined the effect of competition on the growth performance from germination to maturity of cultivated (0. sativa) and wild (0. punctata) rice species. Two null hypotheses were formulated; (1) grown together or grown separately, O. sativa and O. punctata have the same germination rate, and (2) grown together or grown separately, O. sativa and O. punctata have the same growth performance. The study was carried out at Chiromo campus, University of Nairobi. Randomized complete block design with three replications of each treatment was used. Four treatments were used namely; O. sativa grown alone, O. sativa grown together with O. punctata, O. punctata grown alone and O.punctata grown together with O. sativa. Data were collected on; seed dormancy, germination rate, stern height, tillering ability, flowering rate, flag leaf area, leaf area index and above and below-ground dry mass. Data were analyzed using the statistical program SPSS version 14. Analysis of variance was carried out at S% significance level. Means separation was carried out by use of Student Newrnan-Keul's test. The growth curves for stern height and tiller number were found by regression using the least squares method. O. sativa (Basmati 370) had low seed dormancy that was easily broken by water treatment while O. punctata had high dormancy which was broken by completely dehusking the seeds. The two species were then germinated at 30?C. O. sativa grown together with O. punctata attained a mean germination rate of 7 seeds per day, which was significantly (p<O.OOI) higher than 6 seeds per day when planted alone. O. punctata grown together with O. sativa attained mean germination rate of 4 seeds per day, which was not significantly (p>0.05) different from 3 seeds per day when planted alone. For both species, the seeds from the mixture attained higher germinations than the monocultures. O. sativa was found to be a better performer than O. punctata in relation to germination. There was a significant (Pc O.OS) difference among the four treatments in relation to stern height, with mean heights as 84.20?2.07cm for O. sativa grown alone, 79.39?2.S7cm for O. sativa grown together with O. punctata, 116.00?13.63cm for O. punctata grown alone and 98.93?8.30cm for O. punctata grown together with O. sativa. O. sativa matured within 12Sdays while O. punctata matured within 108days. O. punctata produced significantly (p<O.OOI) more tillers than O. sativa whether grown alone or grown together with O. sativa. The mean (?SE) of the number of tillers per hill were 4.43?O.16 for O. sativa grown alone, 4.34?O.21 for O. sativa grown together with O. punctata, 9.07?1.82 for O. punctata grown alone and 5.74?2.09 for O. punctata grown together with O. sativa. Competition, therefore, significantly (p<O.OOI) lowered tiller production within each species. Whether grown together or grown separately, o. punctata flowered 21days earlier than O. sativa. The mean number (?SE) of the flowering tillers were; 1.30?O.05 for O. punctata grown alone, O.99?O.04 for O. punctata grown together with O. sativa, O.54?O.03 for O. sativa grown alone and 0.49?O.03 for O. sativa grown together with O. punctata. Competition, therefore, significantly (p<O.OOl) lowered the flowering rate of the two species. The monocultures attained significantly (p<O.OOl) higher flag leaf area compared to the mixtures. The mean flag leaf area (?SE) attained by each treatment were; 35.00?O.67 for O. sativa grown alone, 32.50?O.72 for O. sativa grown together with O. punctata, 26.lO?O.67 for O. punctata grown alone and 24.70?O.55 for O. punctata grown together with O. sativa. Competition, therefore, significantly (p<O.OOl)

The importance of wetland plant resources and agricultural products in the Nyando river wetlands, Kenya : a comparative study of papyrus and rice

Author: Omollow, Maurice Omondi

Awarding University: Moi University, Kenya

Level : MPhil

Year: 2003

Holding Libraries: Moi University Margaret Thatcher Library ;

Subject Terms: Nyando River, Kenya ; Wetlands ; Rice ; Oryza sativa ; Papyrus ; Cyperus papyrus ; Kisumu District ; Nyando District ; Socioeconomic factors ;

Abstract:

This study assessed the community perceptions of the importance of wetland plants, particularly papyrus (Cyperus papyrus) and compared it with that of agricultural products, mainly rice (Oryza sativa), in the Nyando River Wetlands, Kenya. The goal was to suggest better mechanisms for the sustainable management of the two resources and the wetlands. It was conducted among communities living in NRW area namely Nyando, Lower Nyakach and Kadibo Divisions of Kisumu and Nyando districts, from August 2000 to February 2001. Primary data was gathered using field observation, interviews, group discussions and questionnaires, administered to 120 randomly selected household heads. Secondary data was collected from published and unpublished materials. Results were analyzed using descriptive statistics. The community perceived papyrus to be important as a source of income, building material and production of handicrafts. Rice was viewed as a major source of family income and food. Majority, 65 (54.2%) respondents perceived rice to be more important, compared to 47 (39.2%) who perceived papyrus to be more important and 8 (6.7 %) who were undecided. This difference was significant (X2 = 42.5, P = 0.05, df=2). There was no significant relationship between demographic factors and respondents choice of product with more value. However, there was a significant relationship between respondents' choice and the physical characteristics of the wetland site in their locality (X2 = 10.76, P = 0.05, df=4). The mean monthly income from rice was Ksh. 3106 and Ksh. 2414 from papyrus mat making. The differences in monthly mean incomes from the two enterprises were insignificant [F. (6, 79) =0.651, P= 0.05). The study concluded that both papyrus and rice were important for the socioeconomic development of the community. However, unchecked harvesting of papyrus, fire outbreaks, poor farm management practices, lack of appropriate skills, limited financial resources, poorly developed infrastructure, marketing problems and land use and land ownership conflicts resulted in the mismanagement and degradation of the wetlands. To increase community incomes and strengthen wetland conservation, there is need to identify and promote sustainable uses of the wetlands based on community perceptions of the importance of the wetlands, raise their awareness of the importance of wetlands conservation by providing appropriate training, education, extension services, financial and technical assistance. The wetlands should be zoned for various land uses, community based organizations established and strengthened, co-ordination between stakeholders in wetlands use and management enhanced and a comprehensive wetland management policy developed. There is need to investigate the uses of other wetland resources, demonstrate their wise use, plan for their conservation and explore the possibilities of making Nyando River Wetlands a Ramsar Site. Key words: Community, Importance, Wise Use and Perception

Some effects of water deficit on rainfed landraces of rice (Oryza sativa L.) Indigenous to Kenya (drought resistance).

Author: Onyango, John Collins

Awarding University: University of Sussex, England

Level : DPhil

Year: 1989

Holding Libraries: University Microfilms International ;

Subject Terms: Plant growth ; Rice ; Oryza sativa ; Rain ;

Abstract:

Available from UMI in association with the British Library. Landraces of rice (Oryza sativa L.) have been selected by farmers over period of cultivation in regions of Kenya which are subject to drought. The response of some of these varieties to water deficit has been investigated with the aim of identifying the characteristics responsible for their field reputation for drought resistance. Three landraces (sindano buhari kr-35, matama kr-108 and mdadho kr-135) were compared with drought- susceptible and drought-resistant checks, ir-20 and ir-52 respectively. Experiments were conducted in controlled conditions, in glasshouses and the field. Water deficit was imposed either by restricting the watering regime, or by the use of polyethylene glycol 6000. When plants were grown and water deficit imposed by restricted watering, growth was reduced at low mean water potentials. Root growth was reduced more than shoot growth. Leaf water potential and stomatal conductance decreased, but the mean length of roots increased. All varieties however, including the checks, showed a similar pattern of response to water deficit suggesting that varietal differences in the control of water loss could not account for their differing performance under conditions of water deficit in the field. When plants were grown in the field, kr-35 was the most resistant to water deficit in terms of relative yield, and ir-20 the most sensitive. Visual observation of rooting pattern when the plants were excavated revealed that plants in well-watered soil had a large number of shallow roots. Withholding water resulted in a decrease in water potential in the upper regions of the soil profile and this was accompanied by a reduction in root biomass and a change in the proportion of roots at different depths. Kr-35 showed the least reduction in long roots, and ir-20 the greatest. Plants were grown in soil surrounded by a semipermeable membrane and immersed in solutions of controlled water potential. As the water potential was reduced, the number of long roots decreased dramatically in ir-20, but in kr- 35 the proportion of longer roots increased. Water uptake by mature roots, measured by micropotometry, was greater per unit length of root in kr-35 than in ir-20. Whole plant water use efficiency increased as the water potential of the nutrient solution was decreased, and kr- 35 was about twice as efficient in its use of water as ir-20. The results are discussed in relation to the characteristics which should be selected for rice varieties bred for rainfed cultivation.

Effect of seedling age and method of nitrogen application on plant deal total nitrogen content, yield of irrigated lowland rice (oryza sativa L.)

Author: Maobe, Samson N

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1988

Holding Libraries: University of Nairobi Upper Kabete Library ;

Subject Terms: Agriculture ; Crops ; Rice ; Oryza sativa ; Fertilizers ; Nitrogen ;

Abstract:

ABSTRACT NOT AVAILABLE

Mechnanisms of drought tolerance and its effects on yield of upland rice oryza sativa L. varieties grown in Kenya

Author: Onyango, John Collins

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1985

Holding Libraries: National Council for Science and Technology Library ; University of Nairobi Chiromo Library ;

Subject Terms: Plant growth ; Rice ; Oryza sativa ; Drought ;

Abstract:

Landraces of rice (Oryza sativa L.) have been selected by farmers over period of cultivation in regions of Kenya which are subject to drought. The response of some of these varieties to water deficit has been investigated with the aim of identifying the characteristics responsible for their field reputation for drought resistance. Three landraces (sindano buhari kr-35, matama kr-108 and mdadho kr-135) were compared with drought- susceptible and drought-resistant checks, ir-20 and ir-52 respectively. Experiments were conducted in controlled conditions, in glasshouses and the field. Water deficit was imposed either by restricting the watering regime, or by the use of polyethylene glycol 6000. When plants were grown and water deficit imposed by restricted watering, growth was reduced at low mean water potentials. Root growth was reduced more than shoot growth. Leaf water potential and stomatal conductance decreased, but the mean length of roots increased. All varieties however, including the checks, showed a similar pattern of response to water deficit suggesting that varietal differences in the control of water loss could not account for their differing performance under conditions of water deficit in the field. When plants were grown in the field, kr-35 was the most resistant to water deficit in terms of relative yield, and ir-20 the most sensitive. Visual observation of rooting pattern when the plants were excavated revealed that plants in well-watered soil had a large number of shallow roots. Withholding water resulted in a decrease in water potential in the upper regions of the soil profile and this was accompanied by a reduction in root biomass and a change in the proportion of roots at different depths. Kr-35 showed the least reduction in long roots, and ir-20 the greatest. Plants were grown in soil surrounded by a semipermeable membrane and immersed in solutions of controlled water potential. As the water potential was reduced, the number of long roots decreased dramatically in ir-20, but in kr- 35 the proportion of longer roots increased. Water uptake by mature roots, measured by micropotometry, was greater per unit length of root in kr-35 than in ir-20. Whole plant water use efficiency increased as the water potential of the nutrient solution was decreased, and kr- 35 was about twice as efficient in its use of water as ir-20. The results are discussed in relation to the characteristics which should be selected for rice varieties bred for rainfed cultivation.

Studies on the growth of lowland paddy (Oryza sativa L.) with special reference to stand establishment and weed control.

Author: Auma, Elmada Odenya

Awarding University: University of Ceylon, Sri Lanka

Level : MSc

Year: 1971

Holding Libraries: Egerton University Library ;

Subject Terms: Rice ; Oryza sativa ; Plant growth ; Weeds ;

Abstract:

ABSTRACT NOT AVAILABLE