Solomon I. Shibairo

Postharvest moisture loss characteristics of carrot (Daucus carota L.) cultivars during short-term storage

Abstract Differences in moisture loss characteristics among carrot cultivars Imperator Special 58, Gold Pak 28, Caro-pride, Paramount, Eagle, Celloking, Top Pak and Caro-choice during short-term storage at 13 °C and at either 80% or 35% relative humidity were investigated. Experiments were conducted over two years with an early and late harvest in each year. Moisture loss was significantly greater when carrots were stored at low relative humidity compared to high relative humidity. Consistent cultivar differences in moisture loss characteristics were observed only in the late-harvested carrots at low relative humidity. Cultivars with higher specific surface area and relative electrolyte leakage, and lower water and osmotic potentials exhibited high moisture losses. Regression analysis, however, showed that moisture loss differences among cultivars were mainly associated with the specific surface area of the root.

Influence of preharvest water stress on postharvest moisture loss of carrots (Daucus carota L.)

SummaryTo understand the relationship between preharvest water stress and postharvest moisture loss, carrot cvs Eagle and Paramount were grown in muck soil in 6 1 pots (eight carrots per pot) in a greenhouse at the University of British Columbia. The plants were watered to field capacity every second day for 5.5 months prior to receiving 100,75,50 and 25% field capacity water stress treatments (for 4.5 weeks), henceforth referred to as low, medium, high and severe water stress respectively. Postharvest moisture loss of carrots stored at 13μC and 32% relative humidity was monitored every second day for three weeks. The percent moisture loss was low in the low water stressed, and high in the severely water stressed carrots of both cultivars. Root crown diameter, weight, and water and osmotic potentials decreased, whereas specific surface area and relative solute leakage increased with increasing preharvest water stress. The results show that carrots adjust to water stress by lowering water and osmotic poten...

The Physico-Chemical Characteristics and Some Nutritional Values of Vegetable Amaranth Sold in Nairobi-Kenya

Twenty one major supermarkets and ten independent green grocers in the city of Nairobi were surveyed for types of vegetable amaranths sold and their post harvest handling. The nutrient composition of the vegetables was also analyzed. In addition, information on three other traditional leafy vegetables (TLVs) namely, Cleome gynandra, Solanum nigrum, and Vigna unguiculata was obtained. All the vegetables were sold in bundles of average weight 0.45 kg. The edible fraction per bundle averaged 38.9%. Chemical analyses showed that vegetable amaranth had a moisture content of 85.5%, therefore a dry matter content of 14.5%. Expressed on dry matter basis, the mean total ash content was 19.2%, crude protein content 26.1% and the crude fiber content 14.7%. The mean ascorbic acid content was 627 mg/100 g, zinc content 5.5m g/100 g and iron content 18 mg/100 g. The men nitrate content was 732.5 mg/100 g, total oxalates 5830 mg/100 g and soluble oxalates 3650 mg/100 g, while the lead content averaged 1.03 mg/100 g. The study concludes that vegetable amaranth has potential as popular vegetable in the diets of Kenyans to significantly contribute to provision of micronutrients, particularly iron and zinc.

Potassium nutrition and postharvest moisture loss in carrots (Daucus carota L.)

SummaryThe effect of potassium (K) nutrition on the shelf life of carrots (Daucus carota L., cv. Paramount) was studied using a hydroponic system involving rockwool slabs as an inert support. Carrots were grown for 192 d under greenhouse conditions and with 0, 0.1,1.0,10 and 15 mM K supplied in the nutrient medium. Increase in K concentration in the nutrient medium up to 1 mM decreased postharvest moisture loss. Carrot root weight and tissue K concentration increased, and water potential, osmotic potential and relative solute leakage decreased with increasing K concentration up to 1 mM. Concentrations greater than 1 mM had little or no additional effect on postharvest moisture loss, root water and osmotic potentials and relative solute leakage. Root weight did not increase above 10 mM K. The best subset model obtained by backward stepping and the optimum Mallow’s coefficient showed that carrot root weight and relative solute leakage accounted for most of the variation in moisture loss. Root weight correla...

Genetic Diversity of Kenyan Potato Germplasm Revealed by Simple Sequence Repeat Markers

International potato germplasm (Solanum tuberosum L.) has been long introduced to and bred in Kenya and the accumulated Kenyan Solanum germplasm is unique in its geographical and climatic ranges of adaptation to tropical highlands. However, little is known about the genetic diversity of these improved Solanum accessions. A representative set of 48 potato accessions grouped as farmer varieties, local genotypes and modern varieties was selected and studied using the simple sequence repeat (SSR) technique. Twenty-two SSR primer pairs were applied and 122 polymorphic bands were scored. The frequencies of polymorphic bands ranged from 0.02 to 0.98 and averaged 0.35. The proportion of total SSR variation occurring among four origin categories (International Potato Centre (CIP), Europe, Kenya and Unknown) of accessions was 6.32%; between accessions introduced before and after 1980 4.79%; and among three germplasm classes of accessions 4.36%. Accessions from the CIP displayed more SSR variation than those from Europe. More SSR variation was detected in the accessions introduced/bred after 1980. The modern varieties displayed slightly more diversity than the farmer varieties and local genotypes. Some dominant groups of accessions largely from CIP and Europe were found, but these groups were not distantly separated. Both the genetically most distinct accessions and the possibly genetically related accessions were identified. These results not only demonstrate the considerable genetic variation harbored in the Kenyan potato germplasm, but also are significant for developing effective strategies of acquiring genetically diverse germplasm and for selecting genetically distinct potato materials to widen the Kenyan improved gene pool.ResumenDesde hace tiempo se ha introducido y mejorado germoplasma internacional de papa (Solanum tuberosum L.) en Kenia y el germoplasma acumulado de Solanum Keniano es único en sus amplitudes de adaptación geográfica y climática a altiplanos tropicales. No obstante, poco se sabe sobre la diversidad genética de estas introducciones mejoradas de Solanum. Se seleccionó y estudió, utilizando la técnica de una secuencia simple de repetición (SSR), un juego representativo de 48 introducciones agrupadas como variedades de los productores, genotipos locales y variedades modernas. Se aplicaron veintidós pares de iniciadores SSR y se registraron 122 bandas polimórficas. Las frecuencias de bandas polimórficas variaron de 0.02 a 0.98 con un promedio de 0.35. La proporción de la variación total de SSR que se presentó entre cuatro categorías por origen (Centro Internacional de la Papa CIP, Europa, Kenia y desconocido) de las introducciones, fue 6.32%; entre las introducciones hechas antes y después de 1980 fue de 4.79; y entre tres clases de accesiones de germoplasma, de 4.36%. Las introducciones del CIP mostraron más variación de SSR que las de Europa. Se detectó más variación de SSR en las accesiones introducidas o mejoradas después de 1980. Las variedades modernas mostraron ligeramente más diversidad que las de los productores y que los genotipos locales. Se encontraron algunos grupos dominantes de introducciones, mayormente del CIP y Europa, pero estos grupos no estaban distantes en separación. Se identificaron tanto a las introducciones genéticamente más diversas como a las que posiblemente estaban genéticamente relacionadas. Estos resultados no solo demuestran la considerable variación genética con la que se cuenta en el germoplasma de papa Kenyano, sino que también es significativo para el desarrollo de estrategias efectivas en la adquisición de germoplasma diverso genéticamente y para seleccionar materiales de papa genéticamente distintos para ampliar el acervo genético mejorado de Kenia.

The population structure of wild sorghum species in agro-ecological zones of Western Kenya

There is need to understand the genetic structure of wild sorghums that grow alongside cultivated traditional sorghum varieties in order to assess the potential effect of crop genes in wild populations. In this study, 175 wild sorghum samples were collected from 13 agroecological zones (AEZs) from three counties in Western Kenya and genotyped using microsattelite markers. Crop alleles were observed in wild sorghum populations. The range of allelic frequencies varied from low (˂0.4), to moderate (0.4-0.7) and to high (0.7) in the AEZs. Wild sorghum populations had moderate to high expected heterozygosity (HE) values of between 0.453 in LM1 to 0.715 in LM2. Differences in the magnitude of diversity was significant in the counties (Busia HE = 0.59 – 0.71; Homabay HE = 0.58-0.68 and Siaya HE = 0.45-0.59) but not distinct among the AEZs. Whole population FIS, FST and FIT values were low at 0.15, 0.16 and 0.29, respectively indicating low level of inbreeding, low genetic differentiation of the population and low to moderate deviation from Hardy–Weinberg (HW) equilibrium respectively. The deviation from HW equilibrium was significant in some wild populations from Siaya and Busia. Intra-population diversity (HS) was larger than inter-population diversity (DST) in 13 populations from the sampled AEZs, indicating the importance of gene flow between populations of wild sorghums. Heterozygosity values under mutation drift equilibrium (HEQ) varied under infinite allele model (IAM), two–phase model (TPM) and the step wise mutation model (SMM). However, significant population bottlenecks were absent in the wild sorghums. Presence of significant geographic county clusters and lack of significance on AEZ clusters indicate that human activities have had more influence on the distribution and diversity of wild sorghums than the prevailing climatic conditions. Efforts towards physical and genetic containment of crops genes need to be enhanced for successful ecologically sensitive confined field trials and future adoption of transgenics in cropping systems. Keywords: Diversity, Sorghum bicolor , Sorghum halepense , Sorghum sudanense , microsatellite loci. Abbreviation: AEZ, Agro-ecological zone; DST, inter-population gene diversity; FIS, fixation index; FIT, index of deviation from HW equilibrium; FST, degree of population differentiation; GST, proportion of inter-population gene diversity; HE, expected heterozygosity; HEQ, heterozygosity values under mutation drift equilibrium; HO, observed heterozygosity; HT, total gene diversity; IAM, infinite allele model; SMM, stepwise mutation model; TPM, two-phase model; LM, lower Midlands; UM, upper midlands; HB, Homabay; SY, Siaya; BU, Busia counties; SSR, simple sequence repeats.

Effects of Early and Late Harvest on Agronomic Performance and Stability of Late Blight Resistant (R-gene Free) Potato Genotypes

Late blight is an important constraint to potato production and genotype resistance is an effective disease control mesure. Ten late blight resistant potato genotypes (R-gene free) were assessed for yield performance and stability at early (90 days) and late harvest (120 days) at two locations in Kenya during two years. Significant differences (P ≤ 0.05) in area under disease progress curves (AUDPC) were detected among potato genotypes. Resistant genotypes free of R-genes had significantly (P ≤ 0.05) higher yield at late than early harvest, perhaps due to increased tuber bulking period. The rank of genotypes for AUDPC, late blight resistance, and tuber yield varied across seasons and locations (environment). Additive main effects and multiplicative interaction (AMMI) analysis of tuber yield and late blight resistance resulted in significant (P ≤ 0.05) effects of genotypes (G) and environments (E). The proportion of genotypic variance was larger than the environmental variance and the G × E interactions. For tuber yield, the G, E, and G × E interactions accounted for 42.9, 39.6 and 17.5%; and 53.4, 29.7, and 16.9% at early and late harvests, respectively. For AUDPC, G, E, and G × E accounted for 80.2, 5.0, and 14.8%; as well as 82.3, 4.6, and 13% for early and late harvests, respectively. The resistance of potato genotypes without R-genes varied. Selective deployment of resistant genotypes can improve potato tuber yield.

Effects of nitrogen and phosphorus fertiliser on growth and yield of ironweed ( Vernonia galamesis )

ABSTRACT Ironweed (Vernonia galamensis) is a promising new crop for industrial oil but information on its response to fertiliser is scanty. A field experiment was conducted at the University of Nairobi Field Station farm during 2 seasons (January to May 1998, season 1 and March to August 1998, season 2) to determine the effects of nitrogen (N) and phosphorus (P) fertiliser rates on growth, photosynthetically active radiation (PAR) interception and seed yield of 2 Vernonia galamensis cultivars (ethiopica and gibbosa). N was applied at 0, 75 and 150 kg N/ha, and P at 0, 45 and 90 kg P2O5/ha. The experiment was a 2 × 3 × 3 factorial laid out in a randomized complete block design with 3 replications. N and P application significantly increased total dry matter (TDM), photosynthetically active radiation (PAR) interception and leaf area index (LAI) of both varieties in late vegetative and reproductive stages. Gibbosa had consistently higher TDM, LAI, PAR and was taller compared to ethiopica throughout the growing season. Average seed yield of gibbosa was 2.3 times higher than that of ethiopica in both experiments. The highest TDM, LAI and seed yields were obtained at the highest N and P levels. Gibbosa had a significantly higher number of capsules/plant but a lower harvest index (HI) compared to ethiopica.