In vitro regenerability and transformability of selected Kenyan cassava (manihot esculenta crantz) genotypes
Wanyonyi, Christine Nakhumicha
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Cassava (Manihot esculenta Crantz) is a valuable source of calories especially in countries where malnutrition is widely spread and ranks fourth as a source of food calories, after rice, maize and wheat. Cassava is a root crop that is rich in starch but low in protein and is widely used as food, animal feed and raw material in industries. Some of its undesirable traits include susceptibility to diseases and pests, high cyanogenic glucoside content, low protein content in roots and low shelf life after harvest. Attempts to improve these traits in cassava by conventional breeding face challenges of high outcrossing, high heterozygosity and low fertility. Therefore, the application of genetic transformation to introduce agronomically useful traits would greatly compliment classical breeding approaches. The objective of this study was to determine the regenerability and test for transformability of selected Kenya cassava genotypes. Three genotypes (Ex-ndolo, Karibuni and Shibe) were collected from coastal and eastern agroecological zone based on their traits which are high yielding and early maturity and maintained at the Kenyatta University Plant Transformation Laboratory glasshouse. Sterile plants were established in vitro and maintained on media containing Murashige and Skoog salts with vitamins, (30g/l sucrose and 3.0g/l gel rite) and used as source of explants. Picloram and 2, 4-D were used to induce somatic embryos using leaf and stem explants. The results indicated callus induction varied between 82.67-86.3% for picloram and 6].41 -78.13% for 2,4- dichlorophenoxyacetic acid (2, 4-D) for concentrations 4mg/l, 6mg/l, 8mg/1 and lOmg/1 using stem and leaf explants while varying the photoperiod. Somatic embryo frequency was 31.95-81.48% for leaf explants and 19.65-42.83% for stem explants. Embryogenic calli was matured on media supplemented with different concentration of 6-Benzylaminopurine, c-naphthaleneacetic acid and gibberellic acid before being transferred to regeneration media. Ex-Ndolo was highly responsive to the maturation media and formed shoots when the embryos originated from leaf explants for both 2, 4-D and picloram were matured. There were significant differences in GUS assay frequencies between experiment done after infection and that done after eight weeks in all the three genotypes when subjected to Agrobacterium tumefaciens-mediated transformation. The results from this study will provide a platform for scientists to introgress genes of agronomic interest.