Maize is an economically important crop in Africa including South Africa. To
maintain and produce maize varieties with specific agronomic traits and qualities,
management is required in the form of identity preservation (IP). Identity
preservation is becoming increasingly important with the advent of modern
biotechnology. The purpose of IP is to minimize gene flow of which the principal
factor is pollen movement.
Maize pollen movement has been previously studied measuring out-crossing,
measuring pollen concentrations and computer modelling. In this study, genotypic
detection of trapped pollen as well as the phenotypic observation of out-crossing
was used. Field trials were performed at two geographic locations in South Africa
and spatial as well as temporal isolation was used to ensure that surrounding
maize production did not influence the result of this study.
It was determined that although various methods of pollen preservation were not
effective to maintain pollen DNA integrity, storage in CTAB buffer proved
successful for up to nine months for PCR analysis. An inexpensive pollen trapping
system was devised using Tween 20 coated on glass slides. From pollen trapping
experiments it was determined that maize pollen, with a specific genotype, could
be detected at up to 400 m from the source even though the pollen load on the
traps was low. Phenotypic evaluation of out-crossing revealed a very high incidence (between
22.3 and 39.1%) of out-crossing between yellow and white adjoining maize rows,
and decreased to 1% at a distance of 25 m, and thereafter was an average of
0.36% up to 81.6 m. The two geographic locations were not significantly different
in terms of out-crossing data. The analysis of out-crossing data over distance,
determined that distance is not solely responsible for the pattern of out-crossing.
The analysis of weather data taken during the flowering period indicated that
temperature and relative humidity were not significantly different across the
different locations. However, wind differed significantly between the different
locations with more relevant wind, regarding the orientation to maize plots, in
Delmas than in Lichtenburg.
Low levels of out-crossing were detected using PCR that would otherwise have
remained undetected. The 35S promoter from the Bt gene was detected at 0.12
and 0.9%, respectively, across the different locations, in sampled cobs of white
maize up to a distance of 2 m. The quantification of the Bt gene in yellow hybrid
seed was consistent with expected values, taking the development of the yellow
maize parent into consideration.
During the course of this study different areas of research were identified that have
not been addressed adequately in this or other studies, this includes, in hind sight,
several ways in which the experimental design of this study could have been
improved. The assessment of the impact of individual environmental variables on
pollen longevity warrants a more detailed study. The correlation between pollen DNA viability and fertilisation potential should be further investigated. It would also
be useful to have included data over multiple years but was not possible due to the
time constraints of an M.Sc.
In conclusion, this study has determined that maize pollen of a specific genotype
can be detected at 400 m from its source and that even though out-crossing
declines rapidly up to 25 m, out-crossing events average 0.36% up to 81.6 m.
Out-crossing is determined by distance in conjunction with environmental factors,
making geographic specific data important for region specific identity preservation
requirements. This study makes an important contribution to available data on
pollen movement, as no other published data is available for South Africa.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09062005-080914 |
| Date | 07 September 2005 |
| Creators | Chetty, Lukeshni |
| Contributors | Dr CD Viljoen |
| 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-09062005-080914/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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