a) Frost damage caused by freezing stress is a major problem for potato
growers in some parts of South Africa. In this study two South African potato
cultivars, Darius and BP1, were compared for yield loss due to freezing stress
during the late vegetative, early reproductive and late reproductive growth
stages. The cultivars were subjected to temperatures of -2°C and -4°C for three
and six hours. Significant genotype x treatment interactions were observed for
stem and leaf damage in both cultivars. Genotype x treatment interactions were
also significant for yield and some of the yield components. The cultivars were
shown to be the most sensitive to freezing stress during the early reproductive
growth stage, followed by the late reproductive growth stage. BP1 was identified
to be more sensitive to freezing stress in the early and late reproductive growth
stages. Stem damage was positively associated with tuber number, whereas
leaf damage correlated with tuber mass.
b) Electrophoretic separations of proteins were done to study the polymorphisms
as a result of freezing stress at -2°C and -4°C for three and six hours. The plants
were treated during the late vegetative, early reproductive and late reproductive
growth stages. The freezing treatments caused large variability in the protein
profiles of Darius. Various new protein bands developed while others
disappeared. Differences in the intensity of the bands were also recovered. A
protein band of approximately 29/33 kDa developed consistently at -2°C
treatment during the early reproductive growth stage. Plants subjected to -4°C
for three and six hours developed protein bands of approximately 40/49 kDa
during the three growth stages tested.
c) In this study fourteen selected C1 progenies of a Caren x Bravo cross with the
two parents were included, subjected to freezing temperatures of -4°C for four
hours to study the heritability of potato yield under freezing stress conditions.
The plants were treated during the early reproductive growth stage (the most
sensitive growth stage). Freezing stress (-4°C) treatment during the early
reproductive growth stage reduced potato yield, tuber diameter, tuber mass and
number of tubers significantly. Significant genetic variability was found among
offspring for leaf damage, yield, tuber diameter, tuber mass and number of tubers
under freezing stress conditions. Tuber diameter (r=0.56), tuber mass (r=0.86)
and number of tubers (r=0.75) were significantly correlated with yield for
percentage damage caused by freezing stress. The freezing treatment had no
significant effect on the correlation coefficients between potato yield and yield
components. Relatively high broad sence heritabilities were recorded for potato
yield (h2 =0.74) tuber diameter (h2=0.91), tuber mass (h2=0.87) and number of
tubers (h2=0.79).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-06132007-113521 |
| Date | 13 June 2007 |
| Creators | Venter, Carien |
| Contributors | Prof CS van Deventer |
| 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-06132007-113521/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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