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Articles by M.G. Kinyua
Total Records ( 6 ) for M.G. Kinyua
  M.J. Mahasi , R.S. Pathak , F.N. Wachira , T.C. Riungu , M.G. Kinyua and J.W. Kamundia
  The objective of this study was to analyze the simple correlation coefficients in order to understand the pair-relations and carry out a path analysis to determine direct effects. Character associations between yield components can be used as the best guide for successful yield improvement by indirect selection. Thirty-six safflower accessions were evaluated for phenotypic traits at 4 locations namely Katumani, Kinamba, Lanet and Naivasha for two long rain seasons in two years. The experimental design was a Partially Balanced Lattice design with 3 replications. Path analysis of yield components revealed that components with the highest correlation to yield also had the highest direct effect to yield i.e., primary branches, capitula/plant, effective capitula, seeds/capitula and 100 seed weight. Two approaches can be suggested in selecting genotypes for specific traits to improve seed yield in safflower: Select genotypes with high number of seeds/capitulum, which is directly responsible for seed weight of capitulum as is evident from the high positive correlation between the two. Alternatively select genotypes with high 100 seed weight as this has a high significant (p ≤ 0.05) positive association with seed yield. Generally simple correlations differed at the same location every year. The high correlation and direct effects of number of capitula/plant, effective capitula/plant and seeds/capitulum on seed yield suggests selection for these components will improve seed yield in safflower.
  M.J. Mahasi , R.S. Pathak , F.N. Wachira , T.C. Riungu , M.G. Kinyua and J.K. Waweru
  The objective of this study was to evaluate GxE interactions and yield stability in multi environmental trials across wide ecological locations in Kenya. Thirty-six safflower accessions were evaluated for phenotypic traits at 4 locations namely Katumani, Kinamba, Lanet and Naivasha for two long rain seasons in two years using 7 yield components. The experimental design was a Partially Balanced Lattice design with 3 replications. Analysis of variance (ANOVA) and Principal Component Analysis (PCA) were applied for evaluation of GxE interaction, genotype classifications and stability. The ANOVA showed highly significant differences (p<0.01) among genotypes and locations as well as significant GxL and LxY interactions for all yield components. The first 3 PC accounted for 79% of the total variability in morphological traits. Classification based on the first three principal components showed accessions from Asia (46, 20, 44, 19, 51, 57, 58, 41, 1, 2, 52) tended to group together however a misclassification was found where they also grouped with those of Chinese, Mexican, American and Australian origin. Analysis of GxE interaction could serve in identification of high yielding genotypes with stable performance. Different genotypes reacted differently to varying seasons as indicated by the high significant GxE interaction hence environmental effects are important in understanding plant growth and should be given consideration in safflower breeding programs.
  J.N. Oggema , M.G. Kinyua and J.P. Ouma
  Embryogeneic callus induction and subsequent differentiation is accomplished by application of suitable growth regulators and controlling conditions during culture. The growth regulator, 2,4-D is one of the most effective auxin for calli induction in sweet potato (Ipomoea batatas (L.) Lam.), however the optimum concentration varies with individual cultivars. The optimum 2,4-D level for the local sweet potato cultivars has not been determined yet it is important in multiplication of planting material and transformation procedures. To determine the optimum 2,4-D concentration that produced embryogenic calli early and in high frequencies for local Kenyan sweet potato cultivars Mugande, SPK004, Kemb10, Japon tresmesino and Zapallo, leaf explants were cultured in vitro on MS basal medium supplemented with six concentrations of 2,4-D (0, 0.5, 1.0, 2.0, 3.0 and 5.0 mg L-1), set as a factorial treatment arranged in a Completely Randomized Design (CRD), replicated three times. For each treatment four parameters were considered: Mean number of days taken to form calli, calli weight, calli diameter and calli strength. The results established significant (p<0.05) differences in cultivar responses to 2,4-D levels. Calli induction was effective when supplemented at low levels of 0.5 mg L-1 as high levels above 3.0 significantly reduced the quantity and quality of embryogenic calli that was formed. Low levels of 2,4-D should be used for local Kenyan sweet potato cultivars as the number of days taken to form calli reduced and calli incidences increased.
  J.N. Oggema , J.P. Ouma and M.G. Kinyua
  The development of a reliable plant regeneration protocol in sweet potato forms the basis for sweet potato (I. batatas) genetic improvement. The success in production of the transgenic sweet potato is dependent on the reliability and efficiency of the regeneration protocol to produce somatic embryos capable of forming whole plants. The effect of direct and indirect embryogenesis on in vitro plant regeneration was studied and thereafter a suitable tissue culture protocol for 5 locally adapted Kenyan sweet potato cultivars Mugande, SPK004, Kemb10, Japon tresmesino and Zapallo established. Embryogenic calli was induced directly and indirectly from sweet potato leaf explants and auxiliary buds cultured on MS medium supplemented with 2,4-D (0, 0.5 and 1.0 mg L-1). Absisic acid was added to induce embryo maturation and when the hormone levels were reduced these embryos began to differentiate into shoots before whole plants were regenerated. For each treatment the number and days taken to form shoots, roots and plants that were regenerated were counted and used as a selection index of an efficient sweet potato regeneration protocol for the locally adaptable Kenyan cultivars. The test cultivar had a significant (p≤0.05) effect on both direct and indirect embryogenesis. The use of indirect embryogenesis was beneficial for the local Kenyan sweet potato cultivars as more calli formed hence ensuring higher plant regeneration and increased mass propagation of in vitro plants while direct embryogenesis took a shorter time to form shoots and roots but fewer plants were regenerated.
  P.K. Kimurto , M.G. Kinyua , J.B.O. Ogolla , J.M. Macharia and P.N. Njau
  A better understanding of factors limiting and/or regulating grain yield can provide an opportunity to identify and then select for traits that increase the efficiency of water use and yield under drought stress conditions. The main objective of this study was to assess response of some bread wheat genotypes to varying moisture levels in a tropical environment. In two experiments, twelve bread wheat cultivars were evaluated under the rain shelter in the year 2002 at three simulated moisture regimes (210, 240 and 270 mm). Cultivars differed in their response (p<0.001). The differential responses of the cultivars were mainly due to differences in Evapotranspiration Rates (ET), Harvest Index (HI), kernel number and seeds/head (p≤0.001). Although early seedling vigor and biomass accumulation ensures drought escape, it is affected by early-seedling stage drought because genotypes can’t recover later with supply of water. Other traits identified for selection were longer flag leaf and longer growth cycles. The study provides evidence that under moisture stress, adaptive traits contribute significantly to superior performance and during selection, yield potential and adaptive traits need to be combined, because neither alone will provide superior germplasm or explain superior performance. There was sufficient intraspecific variation in these morphological attributes to suggest their use as selection tools.
  J.N. Malinga , M.G. Kinyua , A.W. Kamau , J.K. Wanjama , J.O. Awalla and R.S. Pathak
  Recent development of virulent (Diuraphis noxia (Kurdjumov) (Homoptera: Aphididae) (RWA) biotypes is a challenge to insect resistance breeding programs. The aim of this study was to detect the existence of biotypes within two Russian wheat aphid populations sampled from Njoro and Timau locations of Kenya. Ten clones were raised from each population and used in population increase studies, virulence tests on different wheat cultivars and Amplified Fragment Length Polymorphic (AFLP) DNA fingerprinting assays. Results of two population increase tests indicated that aphid survivorship was high on Njoro biotype with mortality being concentrated at the end of the maximum life span. Timau biotype had low survivorship with mortality concentrated early in the cycle. Timau biotype had fewer progeny and lower estimates of intrinsic rate of natural increase on susceptible bread-wheats. Results of virulence tests showed that no clear virulence trend was recorded on the biotypes but Njoro biotype was appreciably more virulent on some resistant wheats than Timau biotype. One AFLP primer pair, E-AAC/M-CAC, gave amplified and polymorphic DNA fingerprints and more than one RWA genotype were identified among clones of Njoro and Timau biotypes. The study shows the existence of more than one biotype and/or genotype present within tropical RWA populations.
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