| dc.description.abstract | Vegetable nightshades, widely consumed in East and West Africa, are priority African Indigenous Vegetables (AIVs) earmarked for promotion through research and development due to their potential nutritional and economic benefits to marginal and nutritionally vulnerable populations. Several constraints associated with nightshades were addressed in this study under the objectives-: to collect germplasm of vegetable African nightshades in Western Kenya for conservation and research; identify the species and characterize their genetic diversity using morphological and molecular markers; evaluate nutritional and steroidal glycoalkaloid (SGA) content, and yield under different spacing regimes and N-fertilizer rates. Germplasm was collected in seven districts based on agro-ecological zonation and ethnic composition. Ninety accessions were characterized using a descriptor list with 4 7 morphological traits; 25 representative accessions selected for characterization using amplified fragment length polymorphism (AFLP) markers. Morphological and AFLP characterization datasets were subjected to cluster analysis in R. For yield evaluation experiments, 90 accessions were raised in nurseries and transplanted to 6xl m plots at 50x50 cm spacing in a 3-replicate randomized complete block design (RCBD); and leaf, berry and seed yield collected at 2-week intervals. Evaluation of yield responses to spacing and N-fertilization was conducted by subjecting 11 selected accessions to four different spacing regimes (20x50, 40x50, 60x50 and 80x50 cm) and four urea rates (control, 60 kg/ha, 90 kg/ha and 120 kg/ha) respectively. Nutritional value was determined using 25 representative accessions as follows-: water content by oven-drying 10 g leaf samples for 72 hrs at 60°C; crude protein by multiplying total N ( determined with a carbon-nitrogen-sulphur analyzer) with Kjeldahl conversion factor (6.25); and mineral content by nitric acid digestion and inductively coupled plasma- optical emission spectrometry. SGAs were extracted from leaves and determined with high performance liquid chromatography (HPLC) and mass spectrometry. HPLC method was validated by comparing spiked and un-spiked extracts using standard SGAs. Data from yield evaluation, spacing and N-fertilization, nutritional and SGA content experiments were subjected to ANOV A using CoStat software. Three ploidy levels and six species were identified, including one diploid (S. americanum), four tetraploids (S. villosum, S. tarderemotum, S.jlorulentum and S. grossidentatum) and one hexaploid (S. scabrum) . S. scabrum, S. villosum and S. tarderemotum were cultivated in western Kenya, while S. jlorulentum and S. grossidentatum leaves were collected from volunteer plants. S. tarderemotum was popular among the Kuria, Luo and Kisii while S. villosum was popular among the Kalenjin. S. scabrum had the highest morphological diversity with six clusters; S. villosum had two and other species had one each, but S. tarderemotum and S. jlorulentum formed a single cluster. AFLP results agreed with morphological characterization (r = 0.80), but reduced S. scabrum to four clusters and resolved S. tarderemotum and S. jlorulentum. S. scabrum produced the highest leaf, berry and seed yields of up to 75.96 t/ha, 151.81 t/ha and 8.91 t/ha respectively. Leaf yield increased significantly with increasing plant density, but berry and seed yields differences were non-significant. Berry and seed yield increased significantly with applied N but leaf yield differences were non-significant. Nightshades contained high levels of crude protein, Ca and K, B, Cd, Cu, Fe, Mn, Mo, Ni and Zn. S. tarderemotum, S. villosum and S. scabrum had higher nutritional value compared to others. Solamargine and solasonine were the principle SGAs (95 .6- 100% total SGAs). Solamargine was the major SGA in all species except S. grossidentatum, where solasonine was more abundant. Trace amounts of solanine and tomatine were also detected. Total SGA levels in nightshade leaves ranged from 78.97 to 168.85 mg/kg fresh weight, and were lower than the upper recommended intake level of200 mg/kg fresh weight. | en_US |