Different Agro-ecological Zones In Kenya Research Articles

Species-Site Suitability Assessment of Bamboo and Its Detailed Study in Different Agroecological Zones of Kenya

The site suitability assessment of Bamboo in Kenya was studied for diverse agroecological zones (AEZs) comprising one indigenous and fifteen exotic bamboo species in nine different AEZs of Kenya. Three bamboo clumps from each species that were at least five years old were assessed to accurately capture data on growth performance and yield. Soil samples collected at 0–30 cm depth from different areas varied considerably. The proportion of soil varied across the bamboo planting sites (F(1,11) = 24.94; p < 0.001), soil pH in the planting sites varied significantly (F(1,11) = 13.92; p < 0.001), and soil bulk densities had different results (F(1,11) = 13.92; p < 0.001). The lowest bulk density (0.61 ± 0.01) was recorded in Kakamega (UM1), while the highest (1.63 ± 0.01) was reported in Gede. Data on characteristics of clumps and internode length and wall thickness integrated through GenStat statistical software using ANOVA entail a huge variation in growth performance for each bamboo species across planting sites. Morphological characters were also studied in detail. The mean height, diameter, and stocking density were comparatively lower even in elevated zones that were only 200 m below its natural range. This resulted in an extremely low yield, which is not viable for economic investment. The species is unsuitable for plantation establishment outside its natural range of 2300 m–3200 m above the sea level (a.s.l.). Plantation below this range will not dissipate but will not attain a healthy growth. The primary use will be restricted for ornamental and conservation purposes such as scaffolding, roof construction, and fabrication of basic household furniture.

Field Screening of Elite Cassava (Manihot esculenta) Mutant Lines for their Response to Mosaic and Brown Streak Viruses

Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD) have been major limiting biotic factors to the productivity of cassava farming in Kenya. Development of resistant cassava varieties is most effective way. The study was to determine response of elite cassava lines to CBSD and CMD under field conditions on different agro-ecological zones in Kenya. Screening was done under hot-spot field conditions where five lines together with their parents were evaluated in Randomized Complete Block Design with three replications at University of Eldoret (UoE), Solai and Marakwet sites in Kenya. Severity assessment done on 1-5 rating scale where 1 very resistant and 5 most susceptible. Elite cassava lines had significant differences in their response (p < 0.05) to CBSD and CMD. Additionally, genotypes, site and time interval were also significant (p < 0.05). The three elite lines (CAS1, CAS2 and CAS3) had better tolerance to both diseases compared to their parents (KME3 and KME4) with KME4 showing visible brown rings on the root typical of CBSD The elite lines CAS1, CAS2 and CAS3 identified to have better adaptability to both CBSD and CMD could be further exploited in breeding for new cassava varieties for Kenya and other countries in the region with similar ecology.

Field evaluation of glutathione and glutamic acid as host marking pheromones for control of Tephritid fruit flies in a mango orchard in Kenya.

Tephritid fruit flies are a major constraint to the global production of horticultural crops. In Africa, an array of native and alien invasive fruit fly species represents a key challenge to the horticultural industry. In an effort to develop a safer management tool for these pests, we previously identified glutathione (GSH) and glutamic acid (GA), as the host marking pheromones (HMPs) of Ceratitis cosyra and Ceratitis rosa, respectively. Here, we report on the effectiveness of these compounds (GSH and GA) in reducing natural fruit fly population infestations in mango orchards. Mango trees at two different agroecological zones in Kenya were sprayed with HMPs, and the fruits sampled periodically and assessed for fruit fly emergence. Fruit fly emergence data were compared to two controls, the positive control using spot spraying of food bait (SS), and the negative control using water (W). The two HMPs and SS substantially decreased fruit fly emergence from the sampled mangoes. GSH and GA treated mangoes showed reduced C. cosyra and C. rosa infestation by ~70-75% relative to control (W), and with variation noted in the pheromone applied and the recovered fruit fly species. The adult emergence in pheromone-treated plants compared favorably with the positive control SS. However, the HMPs had little impact on reducing Bactrocera dorsalis infestation of mangoes. The decrease in fruit fly emergence in sampled mango fruits from HMP treated trees corroborate previous laboratory results and support the prospect of using HMPs in the management of African fruit fly species. © 2022 Society of Chemical Industry.

Evaluation of vegetable pigeonpea [Cajanus cajan (L.) Millsp] genotypes for yield stability

BackgroundVegetable pigeonpea is an important food security crop in the marginal dry areas of the Eastern region of Kenya. The adaptation and stability of vegetable pigeonpea genotypes across different agro-ecological zones in Kenya are not adequately determined. The objective of this study was to evaluate the yield stability and adaptability of genotypes: KAT 60/8, MZ 2/9, ICEAP 00554, ICEAP 00557 and KIONZA based on additive main effects and multiplicative interactions (AMMI) and Genotype plus genotype by environment (GGE biplot) analysis.MethodsEvaluation of vegetable pigeonpea Genotypes was conducted at Kiboko, Katumani and Kambi ya Mawe research stations located in Eastern region and University of Nairobi Field station in central region of Kenya. The genotypes were planted in a Randomized Complete Block design (RCBD), replicated three times at all sites. Rainfall at Kiboko and Kabete were supplemented with irrigation, using sprinklers, for a total of 38 times, providing 832 mm of water. The crop was protected from pests by the application of broad-spectrum, non-systemic, pyrethroid alpha-cypermethrin and dimethoate, after field scouting. All other agronomic and cultural practices were done as recommended for each location.ResultsCombined analysis of variance (ANOVA) at six environments revealed highly significant (P < 0.01) variations in G × E interactions for yield (Kg/ha), 100 Seed mass (g/100 seed), days to flower and maturity (P < 0.05). AMMI model for grain yield interaction principal components analysis (IPCA), explained 96.5% of the total yield variation. The cultivar MZ 2/9 and KAT 60/8 recorded a lower IPCA1, indicating a wider adaptation and stability. Kambi ya Mawe, Katumani and Kiboko had higher IPCA1, indicating greatest interactive environments and adapted genotypes. Kambi ya Mawe, was the most ideal location for evaluating pigeonpea genotypes. While KIONZA was the most ideal genotype for yield performance, MZ 2/9 and KAT 60/8 were most stable with a wider adaptation.ConclusionKIONZA should be used as a reference genotype, while Kambi ya Mawe would be the most ideal location for testing the vegetable pigeonpea genotypes in breeding research. Increased deployment of stable pigeon pea cultivars, MZ 2/9 and KAT 60/8 would enhance food security in the dry areas of Eastern regions of Kenya. These genotypes need to be promoted with farmers for wider adoption in the Eastern region of Kenya.

Physicochemical Profile of Essential Oils Obtained from Chia (Salvia hispanica L.) Seeds Grown in Different Agro-Ecological Zones of Kenya

The chia seed samples were purchased from farmers in five locations in three agro-ecological zones in Kenya. The oil was obtained by cold pressing and physicochemical properties were determined; the fatty acid profile was determined by Gas chromatography. The mean oil yield from pressing was 16%, the refractive index of chia seed oil at 25 °C ranged from 1.4811 to 1.4832, specific gravity ranged from 0.9616 to 0.9629, acidity index and free fatty acids content ranged from 0.0345-0.0808 mg KOH/g oil, and 0.1736-0.4061%, respectively. The matter in volatiles ranged from 0.047-0.086%. The saponification value ranged from 162.1969–183.3791 milligrams (mg) of potassium hydroxide (KOH) per gram (g) of chia seed oil. The differences in refractive index, acidity index, free fatty acids, specific gravity, and saponification value, were statistically significant at (P&lt;0.05). The α-linolenic (C18:3) and linoleic acids (C18:2) were the dominant fatty acids in chia seed oil and they varied with regions. The levels α-linolenic (C18:3) and linoleic acids (C18:2) ranged from 53.32-64.04% and 19.37-22.87%, respectively. The levels of oleic, linoleic, and linolenic fatty acids in chia seed oils from different regions were statistically significant at (P&lt;0.05). The study recommended the cultivation of chia seed in agro-ecological zones II and III where higher yields and higher content of linoleic and linolenic fatty acids were reported, consumption of chia seed oil as edible oil, and substitution of marine oils with chia oil as potential sources of polyunsaturated fatty acids.

Physicochemical Profile of Essential Oils Obtained from Chia (Salvia hispanica L.) Seeds Grown in Different Agro-Ecological Zones of Kenya

The chia seed samples were purchased from farmers in five locations in three agro-ecological zones in Kenya. The oil was obtained by cold pressing and physicochemical properties were determined; the fatty acid profile was determined by Gas chromatography. The mean oil yield from pressing was 16%, the refractive index of chia seed oil at 25 °C ranged from 1.4811 to 1.4832, specific gravity ranged from 0.9616 to 0.9629, acidity index and free fatty acids content ranged from 0.0345-0.0808 mg KOH/g oil, and 0.1736-0.4061%, respectively. The matter in volatiles ranged from 0.047-0.086%. The saponification value ranged from 162.1969–183.3791 milligrams (mg) of potassium hydroxide (KOH) per gram (g) of chia seed oil. The differences in refractive index, acidity index, free fatty acids, specific gravity, and saponification value, were statistically significant at (P<0.05). The α-linolenic (C18:3) and linoleic acids (C18:2) were the dominant fatty acids in chia seed oil and they varied with regions. The levels α-linolenic (C18:3) and linoleic acids (C18:2) ranged from 53.32-64.04% and 19.37-22.87%, respectively. The levels of oleic, linoleic, and linolenic fatty acids in chia seed oils from different regions were statistically significant at (P<0.05). The study recommended the cultivation of chia seed in agro-ecological zones II and III where higher yields and higher content of linoleic and linolenic fatty acids were reported, consumption of chia seed oil as edible oil, and substitution of marine oils with chia oil as potential sources of polyunsaturated fatty acids.

English

Papaya is one of the most important fruits crops of Kenya. However, in the recent past, papaya productivity and quality have been limited by lack of high quality seeds. Most producers depend on farmer selected and imported seeds for propagation. However, this is not satisfactory since few farmers can afford imported seeds due to their high price. On the other hand, most of the farmer selected seeds give rise to trees with inferior fruit quality and are susceptible to diseases. The above mentioned challenges necessitated the development of new Jomo Kenyatta University of Agriculture and Technology (JKUAT) papaya lines with superior qualities to help boost fruit production. So far, the new JKUAT papaya has been evaluated only at JKUAT main campus in Kiambu County. This study evaluated the performance of newly developed JKUAT papaya lines (Line 1, 5, 6 and 7) in different agro-ecological zones of Kenya. The study sites were JKUAT (upper midlands zone), Nkubu (upper highlands zone), KALRO Mwea (upper midlands zone) and Mitunguu irrigation scheme (upper highlands zone). The results on morphological, fruiting and biochemical quality showed significant differences. The total number of fruits varied significantly where line 1 had the lowest number (84 fruits) in JKUAT and the highest number was recorded in line 5 (134 fruits) in KALRO, Mwea. The fruit weight varied significantly and ranged from 1.2 kg in line 5 in JKUAT to 2 kg in line 7 in KALRO Mwea. The total soluble solids (TSS) varied significantly from 8.3% in line 7 in KALRO Mwea to 13.7% in line 5 from Nkubu. The results revealed that new lines had good productivity and they should be commercialized in Kenya. However, there is a need to determine the performance of the newly developed papaya lines under heat and water stress conditions. Key words: Agro-ecological zones, fruit quality, fruit yield, morphology, papaya lines.

The Influence of Weather on the Occurrence of Aflatoxin B1 in Harvested Maize from Kenya and Tanzania.

A study was conducted using maize samples collected from different agroecological zones of Kenya (n = 471) and Tanzania (n = 100) during the 2013 maize harvest season to estimate a relationship between aflatoxin B1 concentration and occurrence with weather conditions during the growing season. The toxins were analysed by the ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method. Aflatoxin B1 incidence ranged between 0–100% of samples in different regions with an average value of 29.4% and aflatoxin concentrations of up to 6075 µg/kg recorded in one sample. Several regression techniques were explored. Random forests achieved the highest overall accuracy of 80%, while the accuracy of a logistic regression model was 65%. Low rainfall occurring during the early stage of the maize plant maturing combined with high temperatures leading up to full maturity provide warning signs of aflatoxin contamination. Risk maps for the two countries for the 2013 season were generated using both random forests and logistic regression models.

Genetic Diversity of Aphid (Hemiptera: Aphididae) Species Attacking Amaranth and Nightshades in Different Agro-Ecological Zones of Kenya and Tanzania

Aphids are major pests of African indigenous vegetables. Information on the genetic diversity and the role of host crop and environmental differentiation in their diversity in East Africa is scanty. The knowledge on genetic diversity is a critical component in the development of sound and sustainable integrated pest management strategy, from detection to control. A portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene was used to characterise the species of aphids on amaranth and nightshades at different agro-ecological zones of Kenya and Tanzania. Aphid samples were collected in localities growing the vegetables in low, mid and high altitude agro-ecological zones. Total DNA was isolated and amplified using universal barcoding primers targeting the 5′ end of the COI barcode region. Nucleotide sequences of the COI barcode, using the Basic Local Alignment Search Tool model, found high homology to four species of aphids: Myzus persicae, Aphis fabae, Aphis craccivora and Macrosiphum euphorbiae. Three subspecies of the A. fabae were also detected. Intraspecific diversity depicted M. euphorbiae having the lowest value, while A. fabae showed the highest diversity. Interspecific diversity between A. fabae and A. craccivora was the lowest while between A. craccivora and M. persicae it was the highest. The phylogenetic tree showed each species clustering together irrespective of the host crop or site where collected. Principal component analysis and haplotype network analyses confirmed these results. Low genetic diversity revealed by COI suggests that the environment or host crop contribute less to the genetic diversity of aphids in both countries.

Catechins and Plain Black Tea Parameters Variations in Selected Tea Growing Agro-Ecological Zones in Kenya

Over 60% of tea in Kenya is produced by smallholder tea farmers distributed in the East and West of the Rift Valley. With all smallholder tea farmers using the same production technologies including planting materials, the quality of tea from different agro-ecological zones should be the same. However, black teas attract different prices. This study compared levels of leaf quality, catechins, and polyphenols in green leaf and quality parameters of black tea from twelve factories in three different agro-ecological zones in Kenya and assessed the relationships between the green leaf quality parameters and black tea quality parameters. The catechins contents, the black tea quality parameters, and sensory evaluations changed (p less than or equal to0.05) between the factories and with an agro-ecological zone of production. All black teas had high antioxidant activities, which differed (p less than or equal to0.05) across the factories and zones. Despite the use of same agronomic inputs in the smallholder tea growing zones in Kenya, the quality of resultant black teas was largely influenced by the environmental factors in the different regions. It is therefore not possible to produce black teas of the same quality across the country. Despite the variations, all regions exhibited high levels of black tea quality parameters and sensory evaluation, re-affirming the Kenyan smallholder black teas are of high quality. The high antioxidant activities suggest possible beneficial pharmacological activities from consumption the teas. The green leaf quality (leaf count) were significantly (p less than or equal to0.05) correlated with black tea brightness and all sensory evaluation parameters, demonstrating high benefits from good plucking standards. Green leaf gallic acid, epigallocatechin, epicatechin, epigallocatechin gallate, and total catechins levels were related (p less than or equal to0.05) to black tea total polyphenols and all sensory evaluation parameters. In addition, the green leaf caffeine, epicatechin, epigallocatechin gallate, and total catechins influenced (p less than or equal to0.05) theaflavins in black tea. These green leaf parameters are therefore key drivers of Kenyan plain black tea quality.

A comparative evaluation of quality and sensory characteristics of ‘Apple’ mango fruits produced under different agro-ecological zones in Kenya

A comparative evaluation of quality and sensory characteristics of ‘Apple’ mango fruits produced under different agro-ecological zones in Kenya

Liriomyza Leafminer (Diptera: Agromyzidae) Parasitoid Complex in Different Agroecological Zones, Seasons, and Host Plants in Kenya.

Liriomyza leafminers (Diptera: Agromyzidae) are severe pests of vegetables and ornamentals worldwide. Previous studies revealed low leafminer parasitism across different agroecological zones in Kenya. The present paper reports on the composition of leafminer parasitoids at different elevations, in different seasons, and on different host crops. Surveys were conducted monthly from January to November 2012, and nine parasitoid species were recovered. Total mean parasitism in the study sites was 31.23 ± 1.03% from a total of 20 different vegetable Liriomyza-infested crops belonging to seven families. Diglyphus isaea (Walker) (Hymenoptera: Eulophidae), Phaedrotoma scabriventris, a newly released parasitoid, and Opius dissitus Muesebeck (Hymenoptera: Braconidae) were the most abundant at all elevations, accounting for 67.3, 18.6, and 9.2% of total parasitoids, respectively. Elevation, season, and host crop significantly affected the parasitoid species present and their abundance. Diglyphus isaea was more abundant at the high- and mid-elevations at all seasons compared with the low-elevation, whereas the lower-elevation favored higher abundance of P. scabriventris and O. dissitus during the long rainy season compared with the high- and mid-elevations at all seasons. Of all the host crops surveyed, parasitoids were more abundant on tomato, local kidney bean, snow pea and French bean than other crops. The total parasitism rate observed in this study suggests a considerable improvement in leafminer parasitism compared with previous surveys in Kenya. The implications of these findings for leafminer management in vegetable and ornamental production in Kenya are discussed.

Identification of aphid (Hemiptera: Aphididae) species of economic importance in Kenya using DNA barcodes and PCR-RFLP-based approach.

Aphids are among pests of economic importance throughout the world. Together with transmitting plant viruses, aphids are capable of inflicting severe crop production losses. They also excrete honeydew that favours the growth of sooty mold which reduces the quality of vegetables and fruits and hence their market values. Rapid and accurate identification of aphids to the species level is a critical component in effective pest management and plant quarantine systems. Even though morphological taxonomy has made a tremendous impact on species-level identifications, polymorphism, morphological plasticity and immature stages are among the many challenges to accurate identification. In addition, their small size, presence of cryptic species and damaged specimens dictate the need for a strategy that will ensure timely and accurate identification. In this study, polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based on mitochondrial cytochrome c oxidase subunit I gene and DNA barcoding were applied to identify different aphid species collected from different agro-ecological zones of Kenya. Three restriction enzymes RsaI, AluI and Hinf1 produced patterns that allowed unambiguous identification of the species except Aphis craccivora and Aphis fabae. Analyses of the barcode region indicated intraspecific and interspecific sequence divergences of 0.08 and 6.63%, respectively. DNA barcoding identified all species, including the morphologically indistinguishable A. craccivora and A. fabae and separated two subspecies of A. fabae. Based on these results, both PCR-RFLPs and DNA barcoding could provide quick and accurate tools for identification of aphid species within Aphididae subsequently aiding in effective pest management programmes and enhance plant quarantine systems.

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The cassava green mite (CGM), Mononychellus progresivus Doreste, causes serious leaf damage on cassava leading to low root yield in the dry savanna regions of Africa. A study to compare effectiveness of the predatory phytoseiid Typhlodromalus aripo (De Leon), an acaricide abamectin, an insecticide chlorpyrifos and fertilizer in management of CGM was carried out in various agro-ecological zones of the eastern dry low-midlands at Katumani (LM4), Kiboko (LM5), the cool upper midlands at Embu (UM2) and the warm humid coastal lowlands at Mtwapa (CL3) of Kenya. The acaricide abamectin was found most efficacious in controlling CGM at all agro-ecological zones. Further, the results revealed that the exotic phytoseiid T. aripo was effective in suppressing population densities of CGM by 45% in the dry-hot midlands (Kiboko) and 64% in the warm-humid coastal climatic zone, but the predator could not persist in the cool midlands. However, in the same cool midlands, high amounts of rainfall led to low CGM density of less than 20 mites per leaf, amid the presence of the indigenous phytoseiid Euseius fustis (Pritchard & Baker). Increase in CGM density was positively correlated to the warm and hot dry environment at the plots at Kiboko and Katumani. In the irrigated and wetter sites T. aripo increased with the increase in relative humidity in the environment at Kiboko and Mtwapa. Abamectin spray was the best option in suppressing CGM densities in the dry lowland zones. Similarly, soil fertility input led to higher yield in the sandy soils of low coastal and eastern midlands. High CGM densities did not result in low yield as other environmental factors such as soil fertility, and temperature influenced the final root yield. These findings give insight on the management options of the CGM pest in the different agro-ecological zones in Kenya and similar regions of Africa.

Genetic Variability and Correlation Studies of Grain Yield and Related Agronomic Traits in Maize

A total of fourty two maize hybrids produced through a full diallel mating design and seven parental inbred lines were evaluated in three sites located at different agro-ecological zones in Kenya to determine the genetic parameters governing the inheritance of grain yield and related agronomical traits. The genetic parameters studied among the traits included the mean performance, genotypic variances, phenotypic variances, genotype by environment variances, broad sense heritability and phenotypic and genotypic correlation coefficients. Significant differences were recorded for all traits studied thereby revealing the diversity of the maize genotypes. The grain yield and days to maturity which showed high heritability had low genotypic variances suggesting the involvement of non-additive gene action which could be utilized through heterosis breeding. Ear height and plant height showed the highest heritability and high genotypic variances suggesting the preponderance of additive gene action. Grain yield was positively and strongly correlated with ear height and plant height. The tall plants with high ear placement gave better yields and this could be attributed to the high dry matter accumulation function carried out by the high number of leaves possessed. The positive relationships observed in this study imply that the desirable traits in these hybrids could be exploited in further breeding activities for the development of composites and synthetics for the resource constrained maize farmers who cannot access hybrid seeds every year.

Analysis of Genotype x Environment Interaction for Grain Yield in Maize Hybrids

Maize is an important staple crop for millions of people in Sub-Saharan Africa. The crop grows in a wide range of environmental conditions. The present study was performed to analyze the genotype-by-environment (G×E) interaction for grain yield of fourty two single cross hybrids grown in three environments located at different agro-ecological zones of Kenya. The maize genotypes were grown in randomized complete block design with three replicates in 2006 and 2007. Grain yield data of the single cross hybrids was analysed using the additive main effects and multiplicative interaction (AMMI) and GGE biplot methods. The additive main effects and multiplicative interaction model (AMMI) analysis of variance (additive main effects) showed significant effects for genotypes, environment and the genotype by environment interaction. The total proportion contributed by environment and G x E interaction accounted for 78% and 10% of the total variation. The results also showed that 64.5% of the total variation was contributed by the environment while the genotype and interaction was associated with 20.7% and 10.3% of the total variation, respectively. The most stable genotype in the high yielding group in this study was CML312/TZMI 711 (X20), followed by genotypes TZMI 102/CML384 (designated as X33), and CML312/TZMI 712 (X21). The genotype CML312/TZMI 711 (designated as X20) could be used for broad selection since it was found to be the most ideal genotypes with both high mean yield and high stability. In the biplot analysis, X20 was also close to the origin, had the shortest vector from the ATC and with large PC1 scores (high mean yield) and small (absolute) PC2 scores (high stability) implying it had the least contribution to genotype by environment interaction (GEI). Through the stability analysis, the superior genotypes identified could also be used as references for genotype evaluation and also included in further testing in both early and later stages of selection.

Yield Selection within Coffea arabica cv. Ruiru 11

Aims: This study was aimed at identifying high yielding Ruiru 11 sibs in varying growing conditions. The study also intended to measure the extent to which cherry yields of Ruiru 11 are affected by the environment. Study Design: Randomized Complete Block Design with three replications. Place and Duration of Study: The study was conducted in three different agro-ecological zones in Kenya namely Mariene in Meru County, Kisii near Kisii town in Kisii county and Koru in Kericho County between November 2008 and September 2011. Methodology: Thirty four (34) Ruiru 11 sibs, all of which are resistant to Coffee Berry Disease and Coffee Leaf Rust, were evaluated in this study alongside two entries of SL28, a cultivar susceptible to the two diseases. One entry of SL28 was sprayed with copper fungicides to control, while the other SL28 entry was not sprayed with any fungicides. Planted at a spacing of 2m by 2m, each entry had 12 trees per plot per rep, giving a total of 1296 plants per experiment per site. Cherry yield recording was done during the peak harvesting period of May to July at Mariene and July to September at Koru and Kisii. The data was subjected to Analysis of Variance (ANOVA) using XLSTAT version 2012 statistical software and effects declared significant at 5% level. Results: Significant (P = .05) yield differences among Ruiru 11 sibs were obtained in all Research Article American Journal of Experimental Agriculture, 3(1): 76-88, 2013 77 years of evaluation at Koru but only in 2011 at Kisii and Mariene. There was a greater discrimination between sibs at Koru, followed by Kisii and then Mariene. Year effect was highly significant (P < .001) and equally distinguished in all sites but year x sib interactions were significant (P = .05) only at Kisii. Combined analysis for all environmental combinations showed highly significant (P < .001) differences between sibs, environments and their interaction. Environments made a greater contribution (42.6%) to the variation compared to sibs (7%). The interaction term also made a significant contribution (18.7%). The best sibs per site and those adapted to contrasting environments were identified. Conclusion: The expression of high yield variation among Ruiru 11 sibs is a sign of high potential of intra-selection within the cultivar for yield improvement. Identified sibs can be recommended to farmers and also exploited in future breeding programmes for improvement of Ruiru 11 productivity and agronomic adaptability. The occurrence of significant sib by environment (G x E) interactions was an indication that the best improvement strategy should be a multi-site selection.

Diversity and abundance of wild host plants of lepidopteran stem borers in two different agroecological zones of Kenya

A survey was carried out between 2004 and 2005 in two ecologically different locations, Kakamega and Muhaka to assess diversity and abundance of wild host plants of lepidopteran stem borers as compared to maize plots during the cropping and non-cropping seasons. Kakamega in Western Kenya is characterized by a Guineo-Congolian rain forest mosaic and Muhaka at the Kenyan coast by a Zanzibar Inhambane mosaic with secondary grassy and woody vegetation. In Kakamega, wild host plants and maize covered 2 and 43% of the surveyed area. No variation in diversity and relative abundance of wild host plants was observed between both the cropping and non-cropping seasons. In Muhaka, the diversity and relative abundance of wild host plant species differed between seasons, with the Shannon Weaver Index (H) of 1.67 and 0.95 for cropping and non-cropping seasons, respectively. Similarly in this location, wild host plant cover varied between cropping (23%) and noncropping (17.9%). During both seasons, this was higher than the maize cover, with 10.7% and 0% for the cropping and non-cropping seasons, respectively. For both localities, the implication of the differences found in the abundance and diversity between the cropping and non-cropping seasons is discussed.

Genetic Diversity of Phaeoisariopsis griseola in Kenya as Revealed by AFLP and Group‐specific Primers

AbstractGenetic diversity of 50 Phaeoisariopsis griseola isolates collected from different agroecological zones in Kenya was studied using group‐specific primers and amplified fragment length polymorphism (AFLP) markers. Group‐specific primers differentiated the isolates into Andean and Mesoamerican groups, corresponding to the two common‐bean gene pools. Significant polymorphisms were observed with all the AFLP primer combinations used, reflecting a wide genetic diversity in the P. griseola population. A total of 207 fingerprints was generated, of which 178 were polymorphic. Cluster analysis of the polymorphic bands also separated the isolates into the two groups defined by group‐specific primers. All the isolates examined were grouped into three virulence populations; Andean, Afro‐Andean and Mesoamerican, and their genetic diversity measured. On average, greater diversity (91%) was detected within populations than between populations (9%). The genetic distance between Andean and Mesoamerican populations was higher (D = 0.0269) than between Andean and Afro‐Andean (D = 0.0095). The wide genetic diversity reported here has significant implications in breeding for resistance to angular leaf spot and should be taken into consideration when screening and deploying resistant bean genotypes.

Etiology, effect of soil pH and sweetpotato varietal reaction to Alternaria leaf petiole and stem blight in Kenya

Leaf petiole and stem blight disease is commonly encountered on sweetpotato in Kenya. A study was carried out to confirm the causal agent of the disease in different agro-ecological zones of Kenya and determine the importance of soil pH as well as field conditions on disease development. Diseased leaf and vine tissues were collected and pathogen isolated. The Kabete, Kakamega, Busia (Alupe), and Kabondo isolates were identified as Alternaria bataticola while the Kisii isolate was identified as Alternaria alternata. Pathogenicity and virulence of different isolates of A. bataticola and A. alternata were investigated under greenhouse conditions. Within 4 - 6 days following artificial inoculation, and depending on sweetpotato cultivar, the fungus produced characteristic symptoms typical of Alternaria leaf petiole and stem blight. All the isolates were pathogenic and differences in virulence depended on isolate source and conidial concentration. The Kabete isolate was more virulent than Kakamega, Kabondo and Alupe isolates, whose virulence did not differ significantly from each other (P Key Words: Alternaria bataticola, A. alternata, virulence, Ipomoea batatus, Kenya (African Crop Science Journal 2001 9(1): 287-292)