Browsing by Author "Coutinho, Teresa Ann."

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Factors affecting the successful deployment of Pinus patula as rooted cuttings.
(2005) Mitchell, Richard Glen.; Zwolinski, Janusz.; Jones, Nicky B.; Coutinho, Teresa Ann.
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.
Studies on the expression of resistance of Coffea selections to Hemileia Vastatrix.
(1990) Coutinho, Teresa Ann.; Rijkenberg, Fredericus Hermanus Johannes.
Physiological races of Hemileia vastatrix in southern Africa were identified. Prevalent races were I (2.2%), II (88.9%) and III (2.2%). Six samples could not be identified. Twelve biotypes of race II were distinguished. In some cases, the biotypes only occurred in specific regions. It was established, using fluorescence microscopy, that, in some cases, the percentages of germinated urediospores that did not form appressoria, appressorium formation over stomata, and aborted appressoria, were significantly different between susceptible and resistant selections of the host, and non-hosts. The sequence of events leading to successful infection was investigated using scanning electron microscopy (SEM). When a stoma is encountered by a germ tube tip a uniquely shaped appressorium forms over one end of the stomatal slit. A distinct appressorial foot is wedged within the stomatal vestibule. In coffee, a torpedo-shaped substomatal vesicle initial (SSVI) develops bilaterally from the apex of the infection wedge, While in bean, the infection wedge protrudes into the substomatal chamber. The substomatal vesicle (SSV), at 48 hours post inoculation (hpi) is anchor-shaped. Haustorial mother cells are formed on stubby primary infection hyphae which curve back onto subsidiary cells. No differences in appearance of these structures were noted between resistant and susceptible coffee selections. A much-branched mycelium ramifies through the intercellular spaces of the mesophyll cells 96hpi. In bean, the SSV began to collapse 48hpi. Bayfidan ® only slightly suppressed fungal development on the leaf surface. However, within susceptible tissue, this systemic fungicide had an effect on the morphology of the fungus. Extracellular material accumulated on the SSVI and the SSV. The SSV appeared swollen, and disruptions in the vesicle wall was noted. The discovery of teliospores on locally infected trees led to a SEM study on their structure, development and germination. Infection structure formation on the leaf surface, latent period, reaction score and urediosorus concentration differed between susceptible coffee leaves of different ages. Generally, mature leaves are more susceptible than very young or old leaves. A range of fungicides, mainly systemics, were tested in the field on naturally infected coffee trees. Various epidemiological and climatic factors influence rust development in the field. The role of these factors at the fungicide site and in commercial coffee-growing regions of southern Africa was evaluated.