Jane Ambuko

Carotenoid profiling of the leaves of selected African eggplant accessions subjected to drought stress

Abstract African eggplants (Solanum aethiopicum and S. macrocarpon) are among the most economically important and valuable vegetable and fruit crops. They are a major source of biologically active nutritional substances and metabolites which are essential for plant growth, development, stress adaptation and defense. Among these metabolites are the carotenoids which act as accessory pigments for photosynthesis and precursor to plant hormones. Though African eggplants are known to be resistant to various abiotic stresses, the effect of these stresses on secondary metabolites has not been well defined. The objective of this study was to establish the effect of drought stress on carotenoid profiles of nineteen African eggplant accessions selected based on leaf and fruit morphological traits. Stress was achieved by limiting irrigation and maintaining the wilting state of the crops. Fresh leaves were sampled at different maturity stages; before stress, 2 weeks and 4 weeks after stress for carotenoid analysis. The fresh harvested leaf tissues were immediately frozen in liquid nitrogen and ground. Analysis was carried out using a Dionex HPLC machine coupled to Photo Array Detector and Chromeleon software package (Thermo Fisher Scientific Inc, Waltham, Massachusetts, USA). Major carotenoids viz;. Xanthophylls (neoxanthin, violaxanthin, zeaxanthin and lutein) and carotenes (β–carotene and α–carotene), phytofluene, lycopene, phytoene as well as chlorophylls (chlorophyll‐b and Chlorophyll‐a) were targeted. The carotenoids increased with maturity stage of the crop. Although the stressed crops reported significantly decreased amount of carotenes, chlorophylls, neoxanthin and violaxanthin, the concentration of zeaxanthin increased with stress whereas lutein had no significant change. Chlorophyll‐a was significantly high in all the control accessions. Two accessions reported significantly higher contents of carotenoids as compared to the other accessions. The results of this study indicate that water stress has significant impact on the concentration of some carotenoids and photosynthetic pigments. This will definitely add value to the study of stress tolerance in crops.

Variation of Nutritional and Anti-Nutritional Contents in Finger Millet (Eleusine coracana (L.) Gaertn) Genotypes

Variation in nutritional and anti-nutritional contents among six finger millet genotypes was determined. Improved finger millet genotypes Gulu-E and FMV-1 from Kenya Agricultural Research Institute, KNE-479 and KNE 1034 from International Crops Research Institute for Semi-Arid Tropics (ICRISAT) and local landraces Ateso and Nyaikuro, were compared. There was no significant (p>0.05) difference in calcium (Ca), iron (Fe) and zinc (Zn) contents among the genotypes. Genotypes Ateso and Gulu-E had the highest crude fat contents while KNE-479 had the lowest. Genotypes KNE-479 and Nyaikuro had the highest crude protein content. Lowest crude protein contents were observed in genotypes Gulu-E and Ateso. Genotype Ateso followed by FMV-1 and Nyaikuro had high isoleusine, leusine, methionine, threonine and cysteine amino acid contents. High levels of phenylalanine were observed in genotypes Nyaikuro and Ateso. Ateso had the highest P- hydroxybenzoic, sinapic and syringic acids, while Nyaikuro had high ferulic and vanilic acids. Except for genotype KNE-479 with highest sinapic acid contents, the ICRISAT developed genotypes had the lowest anti- nutritional contents. Anti-nutrients tannins, vanilic acid and ferulic acid were negatively correlated to Fe and Zn contents. Therefore when selecting finger millet for Fe and Zn the levels of anti-nutritional contents need to be considered.

Metabolomic analyses to evaluate the effect of drought stress on selected African Eggplant accessions

BACKGROUND Drought stress is one of the main abiotic stresses that affect crops. It leads to biochemical changes that can have adverse effects on plant growth, development and productivity. African eggplants are important vegetable and fruit crops reported to adapt and thrive well under drought stress. The diversified metabolites arising due to stress have not been well defined. A gas chromatographic-mass spectrometric metabolomic approach was applied to characterize the effect of drought stress on metabolites at different stages of growth. Nineteen accessions were selected for analysis and drought was imposed by withholding water until soil moisture reached 60% field capacity. Fresh leaf tissues were sampled before stress, 2 and 4 weeks after stress and metabolite profiling done. RESULTS Significant changes in metabolite content were observed, and potentially important metabolites with respect to stress responses were characterized. Proline, glutamate, sucrose, fructose and tricarboxylic acid cycle metabolites were shown to be positively correlated with stress. Principal component analysis showed a clear discrimination between the different accessions, growth stages and stress/control conditions. CONCLUSION The results illustrate that drought stress has a significant impact on the concentrations of some metabolites, such as amino acids, sugars and organic acids, which may contribute to drought stress effects and tolerance.

Efficacy of 1-methylcyclopropene in purple passion fruit (Passiflora edulis Sims) as affected by dosage and maturity stage

The study was conducted to determine the efficacy of two 1–MCP application regimes (2 ppm for 24 hours and 4 ppm for 12 hours) to extend the shelf life of passion fruits. The fruits were harvested at two stages of maturity (stage 1 and 2) based on peel colour. After 1–MCP treatments, the fruits were kept at ambient room conditions (25 ± 1°C and RH 60 ± 5%) to ripen. Physiological and physicochemical changes associated with fruit ripening, including ethylene evolution, respiration rate, weight loss, peel colour, total soluble solids and total titratable acidity were evaluated every 2 or 3 days from six fruits which were randomly sampled from each of the treatment combinations. 1–MCP treatments significantly (p < 0.05) delayed or reduced the rate of most of the ripening changes irrespective of the harvest maturity. Overall, based on the physiological and physicochemical changes observed, 1–MCP treatments prolonged the postharvest shelf life of passion fruits harvested at stage 1 and 2 by 3 and 4 days respectively.

Effect of drying methods on the retention of bioactive compounds in African eggplant

Abstract African eggplants (Solanum aethiopicum L.) are a rich source of bioactive compounds and functional constituents that are beneficial to human health. However, the short shelf life of these vegetables can be a major cause of postharvest losses especially during peak harvesting season. Drying is one of the most convenient technologies for the production of shelf stable food products. However, drying can lead to considerable loss of the available bioactive compounds due to thermal degradation depending on the drying method and temperature conditions. This study investigated the effect of four drying methods (solar, oven, vacuum, and freeze) on the retention of total phenolics, beta‐carotene, antioxidant capacity, and lycopene in five African eggplant (S. aethiopicum) accessions (sangawili, manyire green, S00047A, AB2, and aubergine blanche). Samples were dried up to ~10% moisture content. The fresh and dried samples were analyzed for total phenolic content, antioxidant capacity, beta‐carotene content, and the lycopene content. In the fresh state, beta‐carotene, total phenolic content, and free radical scavenging activity ranged between 14.75 ± 0.50 and 29.50 ± 0.77 mg/100 g db, 751.21 ± 1.73 and 1,363.95 ± 2.56 mg/100 g GAE db, and 99.58 and 325.61 mg/ml db IC 50 value, respectively. The accession S00047 showed highest total phenolic content and lowest IC 50 value in the fresh samples. The results also showed that total phenolic content, antioxidant capacity, and beta‐carotene contents were significantly (p < .05) affected by drying method and drying temperature with freeze‐drying presenting the highest retention. Overall, 36.26%s–95.05% (total phenolics) and 31.44%–99.27% (beta‐carotene) were retained during freeze‐drying. Lycopene was only detected in the dried samples of the accession manyire green but absent in all the fresh samples of all the accessions. This study demonstrates that freeze‐drying was the most effective in retaining the highest bioactive compounds in African eggplants.

Heritability Analysis and Phenotypic Characterization of Spider Plant (Cleome gynandra L.) for Yield

Knowledge on phenotypic diversity among existing spider plant accessions is a milestone in the improvement of spider plant, which is a highly nutritious indigenous vegetable in Kenya. A study involving agronomic and morphological characterization of 49 spider plant accessions assembled from East and South Africa was carried out at the University of Nairobi Field Station for two seasons in a randomized complete block design with three replications. Phenotypic data was collected on growth habit, flower, petiole, leaf and stem colour, petiole, leaf and stem hairiness, number of leaves per plant, plant height, number of primary branches, leaf length and width, single leaf area, and chlorophyll content according to FAO descriptors with modifications. Data was analyzed using both DARwin software V6 and Genstat Version 14. We observed significant differences among the traits implying great genetic variability among the evaluated spider plant accessions. The high genetic variation was further validated using the Unweighted Pair Group Method with Arithmetic mean (UPGMA) clustering method with stem and flower colour as key traits. The 49-spider plant accessions were clustered into 2 major groups, each consisting of Kenyan and South African accessions. Stepwise regression revealed that plant height had the most influence on yield in terms of number of leaves per plant. We also observed high heritability for several traits including days to flowering (91%), number of leaves per plant (99%), plant height (99%), number of primary branches (94%), chlorophyll content (94%), and single leaf area (87%). Our results reveal the high genetic variation between different spider plant accessions, especially from different regions of Africa that could be further exploited to improve productivity in the plant. The high heritability of most of the yield related traits is promising for improving yield in the crop through direct selection.

Incidence of Jelly Seed Disorder in ‘Tommy Atkins’ and ‘Van Dyke’ Mangoes as Affected by Agro-Ecological Conditions in Kenya

Jelly seed disorder is one of the major problems in mango production in Kenya as well as other mango producing countries in the world. This problem manifests itself through breakdown of tissues around the seed of the affected fruits resulting in unmarketable fruits. Although the exact cause of jelly seed in mango is unknown, some reports indicate that the condition could be due to imbalance related to Ca, Mg, N and K supply to the fruit. To establish the extent of this problem in Kenya, a study was conducted in 2013 in three major mango producing counties located in different agroecological zones namely Embu, Murang’a and Meru. Three farms with homogenous trees of “Tommy Atkins” and “Van Dyke” mangoes were randomly selected per county. Soil and mango leaf analysis were carried out to determine the nutrient status. Rainfall and temperature data were also recorded during the study period. At harvest time, 50 tree-ripe fruits of each variety were randomly sampled from 25 trees per site and sliced along the endocarp to expose the seed then visually examined and scored for the incidence of jelly seed using Galan Sauco scale. Soil analysis showed Original Research Article Njuguna et al.; IJPSS, 11(5): 1-9, 2016; Article no.IJPSS.26447 2 that, Meru vertisol and lithosols soils had higher Ca, Mg, K content compared to Murang’a eutric Nitisol soils and Embu ferralic arenosal soils. Similarly, mango leaves and fruits sampled from Meru county had higher Ca, Mg and K contents than those from Murang’a and Embu. Fruits (both varieties) from Embu county showed higher incidents of jelly seed that those from Murang’a and Meru county. Significantly higher jelly seed incidents were reported in ‘Van Dyke’ compared to ‘Tommy Atkins’ mangoes. It can therefore be concluded that incidences of jelly seed depend on the variety as well as agro-ecological zone where the mangoes are produced.