Genetic Diversity of Cocoyam In Kenya Possessing such rare attributes such asyielding 30-60 tons/ha, being rich in minerals and vitamins and very low instarch grains, cocoyam remains a very indispensable yet neglected food cropespecially for predominantly malnourished rural households in Kenya.The future of cocoyamdepends on selection of high yielding, good quality genotypes as well asdevelopment of low cost technologies that will enhance its sustainableproduction.
(National Academy of Sciences, 1975)The genetic diversity as revealed by morphological, cytological and DNA basedstudies suggest that diversity is low with the existence of two distinct genefamilies with no distinct allelic difference between wild and cultivated types (A. & P., 1978) (Obidiegwu, Kendabie, Obidiegwu, & Amadi, 2016) The limitedgenetic diversity within cultivated gene pools threatens sustainableproduction. Breeding againstdisease focus on Taro leaf blight (TLB) caused by Phytophthora colocasiae, andfive viruses namely Dasheen mosaic virus (DsMV), Colocasia bobone disease virus(CBDV), Taro bacilliform virus (TaBV), Taro vein chlorosis virus (TaVCV), andTaro reovirus. When TaBV combines with CBDV it causes AlomaeBo bone disease,and is the most damaging taro viral disease (Obidiegwu, Kendabie, Obidiegwu, & Amadi, 2016). The most important disease in Africa isthe cocoyam root rot disease (CRRD), caused by the oomycete Phthium myriotylum.
Selection of economicimportant traits can become much more efficient when the desired expression ofthe most important plant characteristics such as yield, eating quality anddisease resistance are associated with DNA based markers (Anna, 1995). DNA- based markershave become methods of choice in genetic diversity studies, as they analyzevariation at DNA level. (Rao, 2004).This excludes all environmental influences and time specificity, since analysiscan be performed at any growth stage using any plant part and requires onlysmall amounts of material. (Mueller & Wolfenbarger, 1999)Accessing the diversity within Kenyan germplasm will beachieved through the use of available SSR markers and SNP markers. There afterwhich available sequence information will be invaluable in development ofmarkers for use in selection thorough marker assisted selection for acceleratedbreeding.
(Mueller & Wolfenbarger, 1999) METHODOLOGYSamples for DNA extraction will be collected in the field during germplasmcollection by use of FTA cards (GE Healthcare, 2010) and also bystoring the samples in silica for future use.Flinders TechnologyAssociates (FTA TM ) is a simple technology that reduces the steps of DNAcollection, transportation, purification and storage and consequently, reducingthe cost and time required to process a DNA to the final step of purified DNAready for down stream application (Mbogori, Kimani, Lagat, & Danson, 2006)FTA cards with the DNA will be washed with FTA reagents (GE Healthcare, 2010)and used forPCR.This will be particularly useful while running the PCRfor detection of diseases affecting cocoyam. If need be extraction of DNA fromcocoyam dried leaf tissues stored in silica will be achieved by use of amodified CTAB extraction protocol by including a phenol extraction step. PCR will be done with available Simple Sequence Repeat(SSR)markers primers for the diseases under study.
Relevant primer sequences will beused to synthesize the primers needed and subsequently used for PCR analysis.These molecular primers for the respective diseases under study will be used toscreen germplasm to be used for mass propagation of the planting through tissueculture. Extracted genomic DNA will be sent for SNP (singlenucleotide polymorphism) sequencing and resultant SNP sequencing data cleanedand used for diversity studies of the germplasm. The software STRUCTURE will beused for analysis of SNP data for diversity and be used to draw the relationshiptaxonomy figures.
SNP sequence data is valuable because it is amiable toseveral analyses including multiple sequence alignment and RNA sequence analysis,and also for use in development of molecular markers.