Browsing by Author "MUNYIRI SHELMITH WANJA"

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PHENOTYPIC CHARACTERIZATION OF SELECTED LOCAL MAIZE LANDRACES FOR DROUGHT TOLERANCE BASED ON FLOWERING STRESS, AND THEIR RESISTANCE TO LARGER GRAIN BORER (Prostephanus truncatus) IN KENYA
(Chuka University, 2008-10) MUNYIRI SHELMITH WANJA
Maize is staple food in Kenya and is grown in almost all agro-ecological zones. The average maize yield in the highlands is about 3.5 t/ha while that for the arid and semi arid (ASALs) low altitude areas is less than 1.3 t/ha. Arid and semi arid areas constitute about 82% of the total land area and supports about 20% of the country’s human population. The demand for more food culminating from the population increase and the migration of people from high potential areas to semi arid lowlands has led to maize growing in marginal areas. Kenya’s ASALs are home to the very rural poor who practice subsistence farming as a livelihood. Local landraces of maize are an important livelihood resource in these areas. The objective of the study was to characterize selected Kenyan local maize landraces for drought tolerance and resistance to larger grain borer in storage. The characterization for drought tolerance was carried out using secondary traits that exhibit high heritability for drought tolerance such as grain yield, anthesis-silking interval (ASI), tassel size, ears per plant and leaf rolling. The experiment was laid out in a lattice design (unbalanced) each with sixty-four maize genotypes. A second experiment to evaluate drought tolerance was conducted for landraces that exhibited favorable tolerance characteristics. This experiment was laid out in a split plot (RCBD) design with water levels (water stressed and unstressed, at flowering) as the main plots and germplasm as the sub plots. Irrigation was withheld one week to tasseling and resumed forty days later in water stressed plots. The wellwatered plots had continuous irrigation. The field experiments were carried out at KARIMasongaleni field station in Kibwezi district, which falls under agro-ecological zone VI. Among the characters evaluated, a low ASI (1-6 days) was associated with a high level of drought tolerance and low yield losses under moisture stress. Drought stress resulted in 17% to 81% relative grain yield losses. Germplasm GBK-032419, DT/BT/1470.DT and GBK-034659 exhibited lowest grain yield losses of 28%, 22% and 17% while KTL N 70140-4, KTL N 10162- 1 and Makueni Dry Land Composite (control) exhibited high grain yield losses of 81%, 70% and 68%, respectively. However, Katumani inbred lines DT/BT/1917.DT and DG/BT/2443.DT, though exhibiting the shortest ASI of about 1 day experienced about 50% grain yield loss under moisture stress. In general, an increase in number of ears per plant, 100-seed weight, increased plant height, high shelling %, reduced leaf rolling and low ASI were associated with yield increases under water stress. Germplasm that exhibited favorable drought tolerance characteristics were CML-492, DT/BT/1917.DT, DT/BT/1470.DT, DG/BT/2443.DT, GBK044593, GBK-032419, GBK-032423, GBK-34659, KTL N 701104 and GBK-032357. The most vii susceptible germplasm (ASI between 12-17 days) were KTL N 70133-3, KTL N 10168-1, Katumani Composite B, Makueni Dry Land Composite, KTL N 10168-2, GBK-043227, GBK034711 and GBK-027054. The germplasm that exhibited drought tolerance characteristics were further evaluated for resistance to larger grain borer (LGB) damage in storage. This experiment was done at CIMMYT field laboratory-Kiboko. Samples were laid out in complete randomized design and replicated three times. Although no absolute resistance existed, most landraces exhibited higher levels of resistance to LGB than the control variety H614. The germplasm with the highest resistance level was CML-492, while GBK-043731 had the lowest level. Germplasm CML-492, DT/BT/1971.DT, DT/BT/1470.DT, DG/BT/2443.DT, GBK-044593, GBK-032419, GBK-032423, GBK-34659 and GBK-032357 exhibited tolerance to drought and also resistance to LGB relative to control H614. Katumani Composite B, though exhibiting susceptibility to drought, had a high level of resistance to LGB than most local landraces. It was concluded that some Kenyan local landraces exhibit drought tolerance characteristics and also resistance to LGB. According to factor analysis, the phenotypic characteristics evaluated for drought tolerance accounted for 68% of the total variation.
RESISTANCE TO THE SPOTTED STEM BORER AND AFRICAN MAIZE STEM BORER IN TROPICAL MAIZE
(Chuka University, 2014-05) MUNYIRI SHELMITH WANJA
In sub-Saharan Africa (SSA), maize (Zea mays L.) is the staple food for about 50% of the population. However, lepidoptera stem borer poses a major threat to sustained food sufficiency in SSA causing annual yield losses of 15% and particularly in Kenya where they cause losses estimated at 13.5%. The potential to manage insect pests using host-plant resistance exists, but has not been adequately exploited. The goal of this study was to determine the resistance levels in tropical maize to the African (Busseola fusca Fuller) and the spotted stem borer (Chilo partellus Swinhoe) to support breeding efforts for improved maize productivity. Specific objectives were; i) Determine the variability in resistance to spotted and African stem borers in tropical maize; ii) Investigate the mechanisms of resistance in CIMMYT tropical maize inbred lines and; iii) Map the quantitative trait loci (QTL) associated with resistance to C. partellus and B. fusca stem borers using a tropical maize population. Two hundred and ninety five (295) germplasm which included 120 inbred lines, 75 landraces, 100 hybrids and open pollinated varieties (OPVs) were evaluated for two seasons at the Kenya Agricultural Research Institute (KARI)-Kiboko and KARI-Embu field stations. Data were recorded on leaf damage on a 1-9 scale, number of stem borer exit holes, stem tunnel length (cm) and grain yield. A selection index was computed using the damage traits leaf damage, number of stem borer exit holes and cumulative tunnel length to categorize genotypes into resistant and susceptible categories. Germplasm with selection index of below 0.8 were regarded as highly resistant, 0.8-1.00 as moderately resistant, 1.0-1.2 as moderately susceptible and above 1.2 as highly susceptible. Evaluations for mechanisms of resistance were carried out for two seasons at KARI-Kiboko on 120 inbred lines. Data were recorded on leaf toughness, stem penetrometer resistance, trichome density and pith sugar content. To map the QTL for stem borer resistance, a population of 203 F2:3 individuals were developed between 2009 and 2011. Field evaluations were carried out at six sites, three for each stem borer species. Data were recorded on leaf damage, number of stem borer exit holes and cumulative tunnel length as putative stem borer resistance traits. The mapping population was genotyped with 152 single nucleotide polymorphism (SNP) molecular markers. Phenotypic data were subjected to ANOVA using PROC GLM of SAS 2007 and means separated using Fisher’s protected LSD (P<0.05). Variability for resistance to maize stem borers was identified in the genotypes evaluated. Top ten highly resistant landraces against C. partellus were GUAT 1050, GUAT 280, GUAT 1093, GUAT 1082, GUAT 1014, CHIS 114, GUAT 1034, GUAT 1038, CAQU 321 and GUAN 34. Topmost highly resistant commercial hybrids and OPVs to C. partellus were DH01, PH1, ECA-STRIGOFF-VL-102-#-, KDV1-1-#, KDV1-2- #, and PH3253 while, KDV1-3-#, EEQPM-8-EA-#, DH02, KDV1-2-#, DKC8053, POOL15QC, KDV1-1-#, WH403, EEQPM-9-EA-#, and PH4 were highly resistant to B. fusca among others. Open pollinated varieties KDV1-1-#, KDV1-2-#, KDV1-3-#, EEQPM-8-EA-#, POOL15QC and EEQPM-9-EA exhibited high resistance to both stem borer species. Most CIMMYT MBR lines exhibited high resistance levels, with CKSBL10008, CKSBL10005, CKSBL10025, CKSPL10273 and CKSBL10027 being the top five highly resistant lines to B. fusca and CKSBL10039, CKSBL10025, CKSBL10026, CKSBL10014 and CKSBL10004 the top five highly resistant to C. partellus. Dual and high resistance to both stem borer species was found in CIMMYT MBR lines CKSBL10025, CKSBL10026, CKSBL10027, CKSBL10034, CKSBL10014 and CKSBL10039 among other inbred lines. Trichome density was the best mechanism in discriminating genotypes into resistant and susceptible categories, followed by leaf toughness and stem sugar content in that order. Number of stem borer exit holes and cumulative tunnel length were the most consistent traits in assessing resistance. A linkage map spanning 1248.01 cM on 10 chromosomes with an average 8.21cM was constructed. Several QTL for putative resistance traits were detected on chromosomes 1, 2, 3, 4, 5, 6, 7 and 9 based on data from both individual sites and different species. In the combined B. fusca sites analysis, one QTL for stem tunnelling was revealed on chromosome 4 (LOD 2.86) while in the C. partellus combined sites, one QTL for reduced stem tunnelling on chromosome 4 (LOD 2.81), and another QTL for reduced number of borer exit holes was revealed on chromosome 5 (LOD 2.53). Individual sites analyses revealed five QTL for reduced stem tunnelling, three for stem exit holes and two for leaf damage. Phenotypic variances explained by each QTL ranged from 6 to 10% suggesting a need to validate these QTL using a larger population and in different environments. Variability for resistance against maize stem borers was identified and germplasm identified as highly resistant are recommended as novel sources of resistance for stem borer resistance breeding in SSA. Information on resistant commercial hybrids and OPVs should to be disseminated to farmers in the relevant ecologies for adoption to curb grain yield losses. Trichome density, leaf toughness and stem sugar content could be adopted as satisfactory indicators of resistance mechanisms and used for pyramiding of resistance genes for high and durable resistance. Quantitative trait loci for the three putative resistance traits were detected in the CIMMYT tropical population studied. Overall, this study identified new sources of resistance to spotted and African stem borers in tropical maize germplasm that could be used as new varieties and/or used as sources of resistance in breeding for resistance to stem borers.