3 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.

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.

The effect of type, time and rate of multipurpose tree (MPT) mulch application on maize (Zea mays) performance under Striga asiatica infestation.

Author: Gomba, A

Awarding University: University of Zimbabwe

Level : MSc

Year: 2000

Holding Libraries: World Agroforestry Centre Library ;

Subject Terms: Maize ; Striga asiatica ; Plant growth ; Composting ; Crop diseases ;

Abstract:

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