Determination of ploidy among yam (Dioscorea spp.) landraces in Kenya by flow cytometry

Yam (Dioscorea spp.), a traditional crop in Kenya has not undergone improvement and little has been done to understand its genetic background. The taxonomy and phylogeny of the local landraces has not been fully studied. The main cultivated species is Dioscorea minutiflora Engl. Others found with low distribution are Dioscorea alata L., Dioscorea bulbifera L. and Dioscorea odoratissima Pax. Flow cytometry was used to estimate the ploidy level of 155 accessions of Kenyan yam including two checks, TDr.18544 a tetraploid and TDc.98136 an octoploid from International Institute of Tropical Agriculture (IITA), Nigeria. Also included in the study were Dioscorea dumetorum Pax, Dioscorea asteriscus Burkill and Dioscorea schimperiana Kunth which are yam wild relatives. Leaf samples were harvested from the field genebank and nuclei extracted using an extraction buffer (Partec GmbH, Munster Germany). Plant nuclei were isolated and stained with propidium iodide then analyzed in a flow cytometer. Seven ploidy levels of 3x (11.4%), 4x(37.5%), 5x(29.2%), 6x(14.6), 7x(3.1%); 8x(3.1%) and 10x(0.6%) were observed. Tetraploids (4x) formed the highest proportion followed by pentaploids (5x). The highest ploidy, decaploid, (10x), was found in D. odoratissima Pax, a conspecific form of Dioscorea preahensilis found under cultivation in two farms in Western Kenya. No diploids were observed in the study. Ploidy level was not associated with geographical habitat of the landraces while farmer-named varieties were not associated with ploidy levels. The findings generated new knowledge and form a basis for future yam research and improvement in the country. Further work is required to establish the phylogeny of Kenyan yam landrace

Fumonisin contamination of maize (Zea mays) in aflatoxin ‘hot’ zones in eastern province of Kenya

Natural Fusarium and fumonisin contamination were evaluated in 86 stored maize samples and correlated to damaged kernels (%). Maize samples were collected from selected farmers in Aflatoxin ‘hot’ zones of Eastern province. Samples were collected from Kitui and Kibwezi districts in May to June 2008. Fusarium species were isolated and identified using morphological characteristics at Mycology Laboratory, Kenya Medical Research Institute. Fumonisinquantification was done using ELISA (RIDASCREEN ® ELISA test kit (Art. No.: R3401) at Bora Biotech, Nairobi. Colony Forming Unit (CFU) counts indicated that apart from Aspergillus a common contaminant in maize, Fusarium species infestation was also high. The most common species being F. verticillioides isolated at (39.9 %) in the two districts. Other isolated Fusarium species included, F. proliferatum (15.1 %), F. solani (9.0 %), F. anthophilium (9.0 %), F. oxysporium (15.1 %), and F. Lateritium (12.1 %). Damaged kernels analysed in this study included insect infestation, mouldy kernels, and off coloured kernels. Results showed up to 20 % of the grains were damaged in some samples. Contamination with fumonisin toxin was observed to be high. Most of the samples exceeded 1 mg / kg the maximum tolerable levels recommended by the European commission. Fusarium species count and fumonisin levels showed positive correlation (p < 0.05). In addition, there was a positive correlation between damaged kernels (%) and Fusarium species count (p < 0.05). Positive correlation was also observed between damaged kernels (%) and Fusarium species count (p < 0.05). In general, F. verticillioides and F. proliferatum were isolated in samples with the highest percentage of kernel damage and highest fumonisin concentrations. These findings indicate wide spread infestation and contamination of maize by Fusarium species and fumonisin toxins. It is apparent that apart from aflatoxins contamination there is also high level of fumonisin exposure in the high risk population necessitating urgent intervention measures to curb the long term health consequences in the population. Keywords: Fusarium spp, Mycotoxin, Fumonisin, Zea maize, Aflatoxin ‘Hot’ zone

Development of Early Maturing Fusarium Wilt Resistant Pigeonpea Cultivars

Most of the East African pigeonpea ( Cajanus cajan (L.) Millsp) landraces are tall (up to 3.5 m), late maturing (10-12 months), low yielding and susceptible to Fusarium wilt ( Fusarium udum Butl.), one of the most serious fungal diseases in the region. Breeding populations were created by hybridization of the local landraces and early maturing, small and brown seeded Indian genotypes in 1984 and 1985. Selection for reduced height, early maturity, grain yield, seed colour and size, and resistance to Fusarium wilt was conducted for seven generations. Selected lines were evaluated at two Fusarium wilt infested plots for two years and also in a wilt infested soil in a glasshouse. Ten lines that were resistant or tolerant to Fusarium wilt, early maturing, short in height, high yielding and with large, white/beige seeds were finally selected. High positive significant correlations (r = 0.87** and 0.62**) between glasshouse and two field sick plot disease ratings were observed

Development of Early Maturing Fusarium Wilt Resistant Pigeonpea Cultivars

Most of the East African pigeonpea ( Cajanus cajan (L.) Millsp) landraces are tall (up to 3.5 m), late maturing (10-12 months), low yielding and susceptible to Fusarium wilt ( Fusarium udum Butl.), one of the most serious fungal diseases in the region. Breeding populations were created by hybridization of the local landraces and early maturing, small and brown seeded Indian genotypes in 1984 and 1985. Selection for reduced height, early maturity, grain yield, seed colour and size, and resistance to Fusarium wilt was conducted for seven generations. Selected lines were evaluated at two Fusarium wilt infested plots for two years and also in a wilt infested soil in a glasshouse. Ten lines that were resistant or tolerant to Fusarium wilt, early maturing, short in height, high yielding and with large, white/beige seeds were finally selected. High positive significant correlations (r = 0.87** and 0.62**) between glasshouse and two field sick plot disease ratings were observed

Evaluating Diversity Among Kenyan Papaya Germplasm Using Simple Sequence Repeat Markers

Papaya is an important fruit crop, produced in Kenya for local consumption and export. Despite a history of varietal introductions, no attempts concerned on developing varieties suited to Kenyan conditions have been documented. The objective of this study was to provide information on the diversity of germplasm available in Kenya, as a precursor to systematic plant breeding program. Forty two papaya accessions were collected from farmers’ fields located in Coast, Rift Valley, Western, Nyanza, Central and Eastern provinces. Genetic diversity was determined using seven simple sequence repeat (SSR) markers, computing allelic richness and frequency, expected heterozygosity and cluster analysis. Results indicated that the markers were highly polymorphic among the accessions, with polymorphic information content (PIC) varying from 0.75 to 0.852 with an average of 0.81. The genetic similarity among the 42 papaya accessions ranged from 0.764 to 0.932 with an average of 0.844 showing that most papaya accessions used in this study were closely related. About 96.9% of the pair-wise comparisons among papaya accessions exhibited genetic similarity greater than 0.802, while less than 4% (3.1%) showed genetic similarity lower than 0.802. The phylogenetic analysis grouped the 42 accessions into two main clusters A and B. Cluster A had four sub-clusters while cluster B had one cluster. Accessions from Coast, and some from Rift Valley Provinces, presented the highest variation, being scattered throughout the tree, with little or no differentiation from most accessions, whereas some accessions from Coast regrouped in clusters A (iv) and B. The genetic differences among the accessions revealed by the formation of distinct clusters suggest significant genetic variability emanation from varying sources of the papaya germplasm in Kenya. Although the level of genetic diversity revealed by SSR markers in this study is sufficient to distinguish between breeding lines for varietal protection, the rather narrow genetic diversity demonstrated indicates the need to introduce new germplasm or use other techniques such as mutation and genetic engineering to provide breeding materials for the future improvement of papaya in Kenya

Genetic diversity and population structure of Eritrean pepper (Capsicum species) as revealed by SSR markers

Pepper (Capsicum spp.) is one of the most important vegetable crops and the most widely used spice worldwide including Eritrea. Diversity studies are an essential step for crop breeding and improvement. Therefore, the objectives of the study were to determine the diversity and population structure of local Eritrean pepper collected from farmers and research institutions and to evaluate the relatedness of the Eritrean pepper with accessions obtained from five other countries. A total of 407 individual pepper plants from 150 seed samples were evaluated using 28 SSR markers. The results showed that varieties maintained in situ by farmers were heterogeneous. Diversity parameters indicated extensive genetic variation among the Eritrea genotypes. The 28 markers revealed a total of 352 alleles with an average of 13 alleles per marker. Mean Polymorphic Information Content was 0.62 and, mean Observed Heterozygosity was 0.41. The analysis of molecular variance showed only 10% variation was among populations, 30% among individuals within populations and 60% within individuals. This can be explained by the high mean number of effective migrants (2.25) that ranged from 1.01 to 10.45 among populations indicating movement of germplasm among farmers in different geographic and agro-ecological regions. A factor analysis, neighbour joining clustering and the model based clustering (Structure) classified the 407 individuals into 3 groups. However, in the model based clustering; increasing the number of populations to 4 (K=4 ) caused all non-Eritrean genotypes to fall in a separate cluster suggesting availability of potentially rich diversity within the Eritrean populations justified by the large number of private alleles observed