Effect Of Irradiation And Colchicine On Callus And Somatic Embryo Formation In Cassava (Manihot Esculenta Crantz)

ABSTRACT

A study was conducted to assess the mutagenic effect of gamma radiation on sprouting and height in four local cassava accessions.The four cassava accessions were assessed for their callus induction and somatic embryo formation ability from leaf lobes from gamma irradiated stakes as well as colchicine treated leaf lobes on different concentrations of plant growth regulators, incorporated into Murashige and Skoog, (1962) (MS) basal medium. The cassava accessions were irradiated at 0, 32, 35, 45 and 50 Gy and planted in pots filled with loamy soil. The height of the shoots was measured with rule after sprouting. The leaf lobes were collected from the shoots and cultured on MS medium supplemented with 8 mg/l 2,4-D and 16 mg/l Picloram. Another set of leaf lobes were treated with 0.0, 0.05, 0.1, 0.2, 0.25 g/l colchicine for one hour and thereafter cultured on MS medium supplemented with 8 mg/l 2,4-D and 16 mg/l Picloram as described above. Callus induction from leaf lobes in 45 and 50 Gy were significantly (p≤0.05) affected by the irradiation. However, callus induced from leaf lobes in 32 and 35 Gy were not significantly (p≤0.05) affected by the irradiation. On the other hand, Callus induction from leaf lobes in 0.1-0.25 g/l colchicine were significantly (p≤0.05) affected by the mutagenic treatment whereas callus induced from leaf lobes in 0.05 g/l colchicine was not significantly (p≤0.05) affected. Callus induced on 8 mg/l 2,4-D and 16 mg/l picloram gave the best response in Ankrah and all control tested while Tomfa recorded the least. Colchicine at a concentration of 0.05 g/l and radiation dose of 32 Gy treatments gave the best response of callusing. Callus induction decreased with increasing colchicine concentration and gamma irradiation. Callus derived from irradiated and colchicine leaf

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lobes appeared soft but friable and tiny, compact, respectively, predominately with creamy to brown colouration.Calli obtained were sub-cultured on embryo regeneration medium consisting of MS supplemented with 0.01mg/l NAA and 0.1 mg/l BAP. There was no plantlet regeneration. Instead, embryo formation and prolific root was observed in cases where there was no embryo. Similarly, somatic embryo formation was significantly (p≤0.05) different among the accessions. No response to callus formation was observed in 0.25 g/l colchicine treatment after 30 days. Among the four accessions evaluated, Ankrah was the most promising accession in terms of callus induction frequency and somatic embryo formation ability. The results presented in this thesis clearly show that, sprouting in all accessions decreased as the dose of irradiation increased. Gamma irradiation had significantly (p≤0.05) effected height of cassava plant but this varied among all accessions.. Also, among the four accessions studied Ankrah and Tuaka were the most promising accession in terms of callus induction and somatic embryo formation ability.