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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-10292014-124540 |
| Date | 29 October 2014 |
| Creators | Malebana, Mmapaseka Elizabeth |
| Contributors | Dr SM Laurie, Prof MT Labuschagne, Dr A van Biljon |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-10292014-124540/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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