Summary:
The future mass propagation of elite families of Pinus patula by cuttings is a realistic
method of deployment if the short-term performance of cuttings and seedlings are
confirmed at harvesting. This will impact significantly on the future outlook of forestry in
South Africa as softwood yields are improved substantially through the introduction of
material of high genetic value in commercial plantings. This, however, will require
significant changes in future silviculture and other management practices as foresters and
plantation staff learn to regenerate, maintain, and schedule the harvesting of cutting
stands according to a different set of demands as a result of the change in plant type.
Contrary to operational experience, cutting survival was similar to seedling survival in all
field studies. This indicates that factors other than those that were studied and reported
on, such as planting techniques, may be contributing to mortality. Also, due to the
different root structure of cuttings they may be more fragile. The similar survival
observed in these trials, therefore, may have been due to the close supervision given to
the planting operations by the research staff. Although survival was similar, both plant
types survived unacceptably poorly in the majority of studies with an average stocking of
approximately 50% at one year. It is therefore anticipated that commercial stands will
require several blanking operations in order to achieve an acceptable stocking in excess
of 85% by the following planting season. The reduction in expected profitability as a
result of blanking costs, delayed establishment, and the loss of improved genetic plant
material, indicates that this is an area that still requires further research irrespective of
what plant type is being planted.
The pathogen, Fusarium circinatum, was commonly isolated from the planting stock
before and after planting in two studies. Due to its virulent nature, it was assumed that
mortality on the trees on which F. circinatum was isolated was principally due to this
pathogen. At planting all plants were observed to be healthy and free of disease
indicating that this pathogen maybe carried from the nursery to the field in a cryptic form,
either inside or outside the plant tissue , which results in the death of the newly planted
tree. In two field studies, where F. circinatum was commonly isolated, the application of
Benomyl fungicide and to some extent the biological control agent Trichoderma
harzianum at planting appeared to improve survival although this improvement was not
significant. Laboratory studies, designed to determine alternatives to Benomyl fungicide,
indicated that three fungicides (Octave, Folicur and Tilt), three sterilants (Sporekill®,
Prasin®and Citex®) , as well as a biological control agent (T.harzianum), were all highly
successful in controlling F. circinatum colony growth in vitro. It is recommended that
these products undergo nursery testing , where the plant material is inoculated with F.
circinatum spores, in order to test their efficacy and possible phytotoxicity in vivo before
commercial application.
Post-planting survival was also affected by site climate . Greater temperature extremes, as
well as lower humidity and less rainfall resulted in poor survival. Plant dimension at
planting was found to interact with site quality where it was a significant factor on a poor
quality site. Optimal cutting dimensions at planting was a root collar diameter of 2.8 - 3.2
mm, and a stem height greater than 7 cm at planting for cuttings produced in cavities
90 ml in volume. Optimal seedling dimensions at planting were a root collar diameter of
1.8 - 2 mm, and a stem height of 10 - 15 cm for seedlings produced in cavities 80 ml in
volume.
In a separate study, plant morphological criteria influenced medium-term growth, where
greater root mass and thicker cutting root collar diameters at planting improved field
growth performance for seven years after planting. A greater root mass at planting was
achieved by raising cuttings in containers that could support greater medium volume.
From the study it was concluded that cuttings should be raised for an approximate period
of 9 months in container cavities no smaller than 80 ml in volume and possess an oven-dry
root mass of 0.3 - 0.5 g at planting. In addition to similar survival, the cuttings in this
study grew either similarly to, or in some cases out-performed, the seedlings that were
used as a control.
Several other published studies indicate that hedge maturation poses the greatest threat to
the success of softwood cutting deployment. This is especially true in clonal forestry and
methods to maintain juvenility, such as cold storage of shoots and cryopreservation,
require further research before clonal plantations of P. patula can be realised. In the
studies carried out on family hedges in this report, the effect of donor hedge maturation
was found to influence nursery management practice and the characteristics of rooted
cuttings. The nursery data indicates that rooting efficiency, root system quality, and stem
size and form, all decline with increasing hedge age particularly from two years after the
date of sowing. A decline in root system quality was particularly apparent and was
observed prior to a decline in rooting efficiency. If field trials indicate poorer
performance from older hedges , it may be necessary to determine whether the causes are
purely ontogenetic, morphological, or both before drawing final conclusions about hedge
longevity. Until such results are known, it is recommended that P. patula cuttings should
be propagated from seedling donors maintained as hedges , approximately 15 cm high, for
a period not more than three years from the date of sowing. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/4474 |
| Date | January 2005 |
| Creators | Mitchell, Richard Glen. |
| Contributors | Zwolinski, Janusz., Jones, N., Coutinho, T. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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