Browsing by Author "Rwegasira, Gration M."

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Mapping of quantitative trait loci (QTL) related to yield, nut quality and plant size of cashew (anacardium occidentalel)
(2017) Mzena, Geradina P.; Kusolwa, Paul M.; Rwegasira, Gration M.; Yao, Nasser K.
Improvement of yield, nut quality and plant size in cashew is a complex process through conventional technique. It takes at least 9-12 years to develop new varieties, this causes inadequate supply of improved planting materials to farmers. To overcome this limitation, we need to use marker-assisted selection. However, to date, MAS in cashew breeding has been hampered by the absence of markers linked to yield, nut quality and plant size. This study aimed at identifying quantitative trait loci associated with yield, nut quality and plant size. To map QTL a genetic linkage map with 761 single nucleotide polymorphism markers was developed using F2 population of cashew derived from ATA19/250 × Cook05. The linkage map consisted of 21 linkage groups covering 2230cM with an average marker distance of 3.3cM. The F2 progenies were evaluated for yield, number of nuts, nut weight, number of kernels, kernel weight, plant size, canopy diameter and percentage outturn in three seasons namely 2013, 2014 and 2015. A total of 13 QTLs were mapped on 8 linkage groups which explained 25.6 - 56% of the total phenotypic variation. The identified QTLs will speed up the development of high-yielding varieties with good nut quality through marker assisted selection
Relationship between symptoms expression and virus detection in cassava brown virus streak-infected plants
(Canadian Center of Science and Education, 2012) Rwegasira, Gration M.; Rey, Chrissie M. E.
Diagnosis of Cassava brown streak disease (CBSD) has for long been based on foliar and root symptoms expression on infected plants. Variability in patterns of symptoms expression between varieties and seasons however, has meant that symptom-based diagnostics are unreliable. The current study established the relationship between symptom expression on cassava plants and the infection with Cassava brown streak virus (CBSV) using RT-PCR diagnostic tool. It was established that manifestation of CBSD-like symptoms (particularly the foliar chloroses and necrotic blotches) may not be an absolute indication of CBSV-infection. Only 67% of tested samples were both foliarly symptomatic and infected by the virus. About 22% of samples were free from CBSV despite being foliarly symptomatic and 7% were CBSV-infected but foliarly symptom less. Some CBSV-infected plants did not exhibit any foliar symptoms although had root necroses. A few CBSV-free plants were regenerated from infected cuttings in one of the four tested cultivars, Albert. Five out of fifteen (33%) plants cv. Albert were symptom less and two out of the five (40%) were CBSV-free. The findings from this study suggest that symptoms-based diagnosing for CBSV infections is unreliable. As some of CBSV-infected plants tend to be considered CBSV-free due to lack of the disease symptoms, the scenario might have contributed to unlimited spread of CBSD through latently-infected planting materials.
Studies on the Influence of Altitude on Abundance of Fall Armyworm (Spodoptera Frugiperda (Je Smith)) (Lepidoptera: Noctuidae) in Tanzania
(Society for Science and Education, 2023-08-25) Mbemba, Kiva F.; Rwegasira, Gration M.; Tryphone, George M.
Fall armyworm (FAW) (Spodoptera frugiperda) is one of the most devastating polyphagous field crop pests in many parts of the world, including Tanzania. Influence of altitude on the abundance of S. frugiperda was studies by using Pheromone (Frugilure S. frugiperda, Chemtica international, S.A) embedded cup traps. The study was conducted along sites of Mt. Uluguru slopes including; SUA (525 masl), Mlali (579 masl), Mgeta (1050 masl) and Nyandira (1691 masl) located in Morogoro Region, Tanzania. A total of 16 cup traps (four at each site equidistantly arranged at 100 m apart) were used. Weather data were recorded using Hygrocron i-button hung on a tree at equidistant from the four traps. Data on S. frugiperda counts and weather variables were recorded weekly for duration of six months from January to June 2020. Results showed that S. frugiperda was abundantly recorded across he tested altitude albeit at varied abundance. There was significant difference (p < 0.001) among altitude on S. frugiperda abundance, whereby at low altitude, S. frugiperda abundance was high compared to medium and high altitude. Rainfall had positive correlation on S. frugiperda abundance (r = 0.16, r = 0.04) for SUA and Mlali and negative correlation (r = -0.44) and (r = -0.03) for Mgeta and Nyandira. Temperature had positive correlation (r = 0.21) on S. frugiperda abundance at Nyandira while SUA (r = -0.03), Mlali (r = -0.35) and Mgeta (r = -0.28) had negative correlation. Relative humidity for all four locations showed negative correlation with S. frugiperda abundance. Thus, appropriate and effective management practices of S. frugiperda should be considered throughout maize production areas and across crop production seasons regardless of the altitude.
Studies on the influence of altitude on abundance of fall armyworm (spodoptera frugiperda (Je Smith)) (lepidoptera: noctuidae) in Tanzania
(Society for Science and Education, 2023-08-25) Mbemba, Kiva F.; Rwegasira, Gration M.; Tryphone, George M.
Fall armyworm (FAW) (Spodoptera frugiperda) is one of the most devastating polyphagous field crop pests in many parts of the world, including Tanzania. Influence of altitude on the abundance of S. frugiperda was studies by using Pheromone (Frugilure S. frugiperda, Chemtica international, S.A) embedded cup traps. The study was conducted along sites of Mt. Uluguru slopes including; SUA (525 masl), Mlali (579 masl), Mgeta (1050 masl) and Nyandira (1691 masl) located in Morogoro Region, Tanzania. A total of 16 cup traps (four at each site equidistantly arranged at 100 m apart) were used. Weather data were recorded using Hygrocron i-button hung on a tree at equidistant from the four traps. Data on S. frugiperda counts and weather variables were recorded weekly for duration of six months from January to June 2020. Results showed that S. frugiperda was abundantly recorded across he tested altitude albeit at varied abundance. There was significant difference (p < 0.001) among altitude on S. frugiperda abundance, whereby at low altitude, S. frugiperda abundance was high compared to medium and high altitude. Rainfall had positive correlation on S. frugiperda abundance (r = 0.16, r = 0.04) for SUA and Mlali and negative correlation (r = -0.44) and (r = -0.03) for Mgeta and Nyandira. Temperature had positive correlation (r = 0.21) on S. frugiperda abundance at Nyandira while SUA (r = -0.03), Mlali (r = -0.35) and Mgeta (r = -0.28) had negative correlation. Relative humidity for all four locations showed negative correlation with S. frugiperda abundance. Thus, appropriate and effective management practices of S. frugiperda should be considered throughout maize production areas and across crop production seasons regardless of the altitude.