Abstract
The effect of different concentrations of thidiazuron (TDZ), benzyl amino purine (BAP), kinetin and 2,4-dichlorophenoxy acetic acid (2, 4-D) on callus induction in three elite cassava cultivars (agric-rouge, atinwewe and agblehoundo) was evaluated. Leaf explants harvested from greenhouse-grown cassava were sterilised using different concentrations of commercial bleach commonly called Jik (3.85% NaOCl) at different time intervals. The highest number (94%) of clean explants was obtained when 2% (v/v) Jik was used for 15 min. The explants were cultured in half MS media supplemented with different growth regulators TDZ, BAP, kinetin 2, 4-D, 100 mg/l myo inositol, 2% sucrose and gelled with 0.3% phytagel. Callus formation was observed from the cut edges of the leaves in all cultivars after 10 days in medium supplemented with TDZ, 12 days in BAP medium, and 15 days in kinetin medium. There were significant (p < 0.05) differences in callus formation among all cytokinins types and concentrations. However, there were no significant differences in callus formation in different 2,4-D concentrations. All 2,4-D concentrations produced 100% callus in all the cultivars. However, 2,4-D at 2 µM significantly produced the highest (2.48±0.30) callus weight in cultivar atinwewe. Furthermore, simple sequence repeats (SSR) and sequence-characterized amplified region of the induced calli on TDZ and 2,4-D media indicated the loss of CMD2 gene among induced calli compared to the mother plants. Key words: Cassava, simple sequence repeats (SSR) and sequence-characterized amplified region (SCAR), genetic stability, callus, cytokinins, auxins.
Highlights
Cassava (Manihot esculenta Crantz) is the most important root crop in the tropics and ranks fourth after rice, wheat and corn as a source of calories for human consumption (Acedo and Labana, 2008)
After 15 days the highest (97%) number of clean explants was obtained when the explants were sterilized in 2% Jik for 15 min and this sterilization procedure was used in all the subsequent experiments
Callus induction was first observed in all cultivars after ten days in medium supplemented with TDZ, 12 days in benzyl amino purine (BAP) medium, and 15 days in kinetin medium
Summary
Cassava (Manihot esculenta Crantz) is the most important root crop in the tropics and ranks fourth after rice, wheat and corn as a source of calories for human consumption (Acedo and Labana, 2008). In Benin, cassava is consumed by more than 54% of the population in different ways as raw or after processing into gari, chips or tapioca (MAEP, 2013) This is an indication of its importance as food security crop and Sessou et al 1045 poverty alleviation in the country. Cassava mosaic disease (CMD) are the most economically important and may lead to yield losses of 20 to 95% (Fauquet et al, 1990; Hahn et al, 1989) Due to these constraints, the average crop yield in Benin is low (15.55 tonnes per hectare) compared to the global yield of 90 tonnes (FAOSTAT, 2017). The cultivars contain CMD2 gene which is dominant monogenic resistance locus (Fondong, 2017) The propagation of those cassava cultivars in the field by farmers is by cuttings and few works have been done for in vitro culture (Cacaï et al 2012, 2013). There is need to evaluate alternative propagation methods that are fast and tissue culture offers a feasible option
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