INDUCED MUTATION IN SWEET POTATO AIMED AT IMPROVED QUALITY AND DROUGHT ADAPTATION

• Main Author: Malebana, Mmapaseka Elizabeth
• Other Authors: Dr SM Laurie
• Format: Others
• Language: en-uk
• Published: University of the Free State 2014
• Subjects: Department of Plant Sciences
• Online Access: http://etd.uovs.ac.za//theses/available/etd-10292014-124540/restricted/

Induced mutation was incorporated into the South African sweet potato breeding programme to improve elite cultivars for yield, drought adaptation and nutritional quality. Three cream-fleshed cultivars namely Ndou, Monate and Mokone were selected, propagated in vitro and subjected to gamma ray mutagenesis from a 60Co source at SANBS. Radio-sensitivity tests were done on three node cuttings used as explants to determine optimum dosages for bulk irradiation. Data was subjected to regression analysis and calculated LD50 values were 64 Gy for Ndou, 38 Gy for Monate and 55 Gy for Mokone. Variation observed in lethal dosages highlighted the importance to test each genotype or plant material for sensitivity before mutagenic treatment. Bulk irradiation was done at respective optimum dosages and explants were propagated in vitro up to M1V4 and M2V5 stages to dissolve chimeras and obtain stable mutations. Three mutant populations comprised of 8 207 mutant plants were generated. These mutant plants were screened in the glasshouse for phenotypic/morphological changes visible to the naked eye. Mutant plants with changes in leaf shape, vine colour, fused veins, abaxial vein pigmentation, chlorophyll variegation on leaves and root flesh colour from cream to pale orange/yellow, were observed. After screening, 410 mutant plants (4.99%) with phenotypic changes were identified from the generated mutant populations. Mutant plants/lines derived from the cultivar Ndou were further subjected to vegetative drought and heat tolerance screening in the glasshouse. Two experiments were conducted and these mutant lines were evaluated for drought tolerance and drought and heat tolerance respectively. Thirteen mutant lines with improved drought and heat tolerance, when compared to Ndou, were identified from the first experiment. Further drought screening procedures will be conducted to confirm these results. Field evaluation trials were established to evaluate Ndou mutant lines. These were first evaluated in an initial evaluation trial at Lwamondo using single plants established from seedlings in a non-balanced completely randomised design. Mutant lines with three replicates each were harvested, data was collected on root yield and samples were taken and freeze dried for mineral and total starch content analyses. No mutant line had significantly improved root yields compared to Ndou. Thirteen mutant lines with significantly improved Mn and six mutant lines with significantly improved Mg contents compared to Ndou were identified. Total starch contents were significantly higher in four mutant lines than that of Ndou. Non-significant variations were observed in Zn and Fe contents between mutant lines and the control. Promising mutant lines were further identified and evaluated in a replicated preliminary yield evaluation trial at Towoomba. Top cuttings were used to establish the trial. Data was collected on marketable yield, unmarketable yield, total yield, root-flesh colour and dry mass content. Two mutant lines, M96 and M95, had improved total yields of 33.01 t ha-1 and 30.02 t ha-1 respectively compared to Ndou with 22.96 t ha-1. Dry mass contents were also improved in two mutant lines M47 (30.33%) and M28 (29.38%) compared to the control Ndou (27.00%). Root flesh colour changes were identified phenotypically in M224 and M6 with changes from cream to pale orange/yellow. All mutant lines will be subjected to advanced yield and nutrient evaluations including β- carotene quantification to identify mutant lines with improved yield, drought adaptation and enhanced nutritional contents to address food security and micronutrient deficiency in SA.