Genetic Diversity of Cocoyam In Kenya
Possessing such rare attributes such as
yielding 30-60 tons/ha, being rich in minerals and vitamins and very low in
starch grains, cocoyam remains a very indispensable yet neglected food crop
especially for predominantly malnourished rural households in Kenya.
The future of cocoyam
depends on selection of high yielding, good quality genotypes as well as
development of low cost technologies that will enhance its sustainable
production. (National Academy of Sciences,
The genetic diversity as revealed by morphological, cytological and DNA based
studies suggest that diversity is low with the existence of two distinct gene
families with no distinct allelic difference between wild and cultivated types (A. & P., 1978) (Obidiegwu,
Kendabie, Obidiegwu, & Amadi, 2016) The limited
genetic diversity within cultivated gene pools threatens sustainable
disease focus on Taro leaf blight (TLB) caused by Phytophthora colocasiae, and
five viruses namely Dasheen mosaic virus (DsMV), Colocasia bobone disease virus
(CBDV), Taro bacilliform virus (TaBV), Taro vein chlorosis virus (TaVCV), and
Taro 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 is
the cocoyam root rot disease (CRRD), caused by the oomycete Phthium myriotylum.
Selection of economic
important traits can become much more efficient when the desired expression of
the most important plant characteristics such as yield, eating quality and
disease resistance are associated with DNA based markers (Anna, 1995). DNA- based markers
have become methods of choice in genetic diversity studies, as they analyze
variation at DNA level. (Rao, 2004).
This excludes all environmental influences and time specificity, since analysis
can be performed at any growth stage using any plant part and requires only
small amounts of material. (Mueller & Wolfenbarger, 1999)
Accessing the diversity within Kenyan germplasm will be
achieved through the use of available SSR markers and SNP markers. There after
which available sequence information will be invaluable in development of
markers for use in selection thorough marker assisted selection for accelerated
breeding. (Mueller & Wolfenbarger, 1999)
Samples for DNA extraction will be collected in the field during germplasm
collection by use of FTA cards (GE Healthcare, 2010) and also by
storing the samples in silica for future use.
Associates (FTA TM ) is a simple technology that reduces the steps of DNA
collection, transportation, purification and storage and consequently, reducing
the cost and time required to process a DNA to the final step of purified DNA
ready for down stream application (Mbogori, Kimani, Lagat, &
FTA cards with the DNA will be washed with FTA reagents (GE Healthcare, 2010)and used for
This will be particularly useful while running the PCR
for detection of diseases affecting cocoyam. If need be extraction of DNA from
cocoyam dried leaf tissues stored in silica will be achieved by use of a
modified 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 be
used to synthesize the primers needed and subsequently used for PCR analysis.
These molecular primers for the respective diseases under study will be used to
screen germplasm to be used for mass propagation of the planting through tissue
Extracted genomic DNA will be sent for SNP (single
nucleotide polymorphism) sequencing and resultant SNP sequencing data cleaned
and used for diversity studies of the germplasm. The software STRUCTURE will be
used for analysis of SNP data for diversity and be used to draw the relationship
taxonomy figures. SNP sequence data is valuable because it is amiable to
several analyses including multiple sequence alignment and RNA sequence analysis,
and also for use in development of molecular markers.