One of the biggest constraints to the expansion of the walnut industry in South Africa, is the
availability of good quality and cost effective plant material. Since walnuts are more difficult to
propagate vegetatively than most fruit and nut species, controlled conditions are required to
ensure grafting success. Hot callus grafting is a bench grafting procedure subjecting grafted
trees to controlled, elevated temperature and humidity, and has been implemented successfully
in several countries to increase grafting success of walnut. Until now, hot callus grafting has not
been investigated as a possible walnut propagation method in South Africa. The present study
assessed method of heat supply and time of grafting, as important factors determining grafting
success of two walnut cultivars grafted onto Juglans regia rootstocks under hot callus conditions.
Although neither method of heat supply provided definite superior grafting success, localized
heating of graft unions in a heated trench, gave more consistent results than heating the entire
grafted tree in a heated room. Both methods seemed promising, since acceptable grafting
success was obtained in some instances with both the heated trench and room. Post-grafting
shoot growth on the other hand, was significantly higher for the heated trench than for the room.
Both methods did, however, result in trees of a suitable size for orchard establishment after only
one growing season. Results further indicated that exposure to increased temperature for a
period of 25 days is more than sufficient for callus development of walnut, and very little is
gained by heating grafted trees for longer. Earlier grafting, before the onset of bud break of
cultivar and/or rootstock, generally resulted in improved grafting success and drastically
increased shoot growth during the first growing season, providing grafted trees of saleable size
in a shorter time. There were no clear differences regarding callus formation, grafting success or
survival between the two cultivars evaluated, âChandlerâ and âSerrâ. As expected, more vigorous
post-grafting growth was observed for âSerrâ, since it is the more vigorous grower of the two. A
separate hot callus grafting trial, using Paradox rootstocks, also indicated that the type of
rootstock utilized in hot callus grafting may impact grafting success. More consistent results were obtained with all four cultivars grafted onto this hybrid rootstock, than with J. regia
rootstocks in the preceding trial. For both J. regia and Paradox rootstocks, survival of trees
through the first growing season was still unacceptably low, although results were comparable to
that of other studies. Since results were available for a single season only, conclusions should
be regarded as preliminary. Nevertheless, findings clearly illustrated the potential value of hot
callus grafting as propagation method for walnut in South Africa and lay a foundation for the
establishment of propagation guidelines using this approach.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09172009-160603 |
| Date | 17 September 2009 |
| Creators | van Zyl, Lukas C |
| Contributors | Dr GM Engelbrecht, Me A Bothma-Schmidt |
| 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-09172009-160603/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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