O glifosato e o oxifluorfen têm sido os principais herbicidas para controle de plantas invasoras em plantações florestais. Neste contexto, constituíram em objetivos do presente estudo avaliar as taxas de degradação e de lixiviação de glifosato e oxifluorfen em Latossolo Vermelho-Amarelo Distrófico psamítico, manejados no sistema de cultivo mínimo, florestados com eucalipto. Para tal, foi conduzido um experimento em condições de campo, na Estação Experimental de Ciências Florestais de Itatinga, ESALQ/USP (Itatinga - SP), sendo as análises realizadas no Laboratório de Resíduos de Pesticidas e Análises Cromatográficas (LARP/USP). Aplicou-se o glifosato (1440g i.a. ha-1) e oxifluorfen (960g i.a. ha-1) em três repetições na dosagem recomendada (4,0 L./ha-1) para condição de campo. A dissipação dos herbicidas foi avaliada por cromatografia. Foram analisadas amostras de serapilheira, solo e solução do solo. Para a avaliação dos teores de herbicidas na serapilheira e no solo foram realizadas amostragens 3 dias antes da aplicação dos herbicidas na testemunha e, nos demais tratamentos, no dia da aplicação 0, 1, 3, 7, 15, 30, 60 e 93 dias após a aplicação dos herbicidas. Foram amostradas a serapilheira e as seguintes camadas de solo: 0-1, 1-2, 2-4, 4-6, 6-10, 10-15 e 15-30 cm. Para avaliar a lixiviação dos herbicidas, amostras de solução do solo foram coletadas em lisímetros ativado por gravidade (sem tensão) e outro por vácuo (com tensão). O lisímetro ativado por gravidade foi instalado sob a serapilheira, 15, 50 e 100 cm de profundidade e o outro lisímetro foi instalado 15, 50, 100 e 300 cm. Para avaliar a fotodegradação do oxifluorfen foram instaladas parcelas na sombra (sombrite a 80%). A meia-vida do glifosato no solo sem serapilheira foi de 10 dias e no solo sob serapilheira, de 47 dias. Sua lixiviação no solo sob serapilheira foi 36% menor do que no solo sem serapilheira. Devido a este efeito, os riscos de contaminação de solos manejados no sistema de cultivo mínimo são menores. A concentração do glifosato decresceu enquanto a do seu metabólito (AMPA) aumentou durante as duas primeiras semanas após sua aplicação. E tais resíduos foram detectados na solução do solo após 8 dias de sua aplicação, a 15 cm de profundidade. A meia-vida de oxifluorfen no solo sem serapilheira foi de 25 dias e no solo com serapilheira sua meia-vida foi reduzida para 13 dias. O oxifluorfen no solo com serapilheira lixiviou até 5cm e no solo sem serapilheira até 8cm. Em ambas as situações as concentrações foram muito baixas. O teor de oxyfluorfen sob sombra foi sempre maior do que sob pleno sol, comprovando sua fotodegradabilidade. / Glyphosate and oxyfluorfen have been the main herbicides used for the control for the weed control in forest plantations. In this context, to evaluate the degradation and the leaching of glyphosate and oxyfluorfen in red-yellow latosols (oxisol) under minimum cultivation of the soil and planted with eucalyptus were the objectives of the present study. To do so, an experiment was carried out under field conditions in the Experimental Forest Science Station at Itatinga, ESALQ/USP (Itatinga - SP). The analyses were performed under laboratory conditions at LARP/USP - a laboratory of pesticide residues and chromatographic analyses. Oxyfluorfen was applied (960g a. i. ha-1) in (three repetitions) at the recommended dosage (4.0 L./ha-1) for the field conditions. Glyphosate (1440g a. i. ha-1) and oxyfluorfen (960g a. i. ha-1) were applied in three repetitions at the recommended dosage (4.0 L./ha-1) for the filed condition. The dissipation of the herbicides was evaluated by means of chromatography. Samples of litter, soil and soil solution were analyzed. In order to evaluate the herbicide rates in litter and in soil, samplings were performed three days before the herbicides application in the control and, in the other treatments, at the day of application (0), and at 1, 3, 7, 15, 30, 60, and 93 days after the application. litter and the following soil layer were sampled: 0-1, 1-2, 2-4, 4-6, 6-10, 10-15, and 15-30 cm deep. In order to evaluate the herbicides leaching, samples of soil solution were collected in lisimeters activated by gravity (without tension) and by vacuum (with tension). The lisimeter activated by gravity was installed under the litter at 15, 50, and 100 cm deep; the other was installed at 15, 50, 100, and 300 cm deep. In order to evaluate the photodegradation of oxyfluorfen, the plots were installed under shade (shading net at 80%). The half-life of glyphosate in soil without litter was 10 days and in soil under litter was 47 days. The leaching of glyphosate in soil under litter was 36% smaller than in soil without litter. Because this effect, the risk of contamination of soils that have minimum cultivation are small. The concentration of glyphosate decrease while concentration of your principal metabolite (AMPA) increase during the first two week after application. Glyphosate was found in soil solution 8 days after application up to 15cm deep. The half-life of oxyfluorfen in soil without litter was 25 days and in soil under litter was 13 days. Oxyfluorfen was found at 5 cm deep in soil with litter and at 8 cm deep in soil without litter. In both situations the concentration was very low. Along the experiment, oxyfluorfen under shade was always higher than under sun, this proves the photo-degradation.

An abundance of waste products from the forestry industry (sawdust and paper pulp) lead to the concept of using them as growing media for high value crops on a field scale. However, management of subsequent weed growth posed a problem as the impact of these novel media on the performance and fate of herbicides was unknown. Three aspects of sawdust and paper pulp waste were examined and compared to two cropping soils, viz. their effect on herbicide behaviour with regard to crop selectivity, weed control efficacy and the environmental fate of selected chemicals. Cropping species such as lettuce and onions were more susceptible to alachlor and chlorpropham in sawdust than in paper pulp. The two cropping soils evaluated (Horotiu sandy loam and Mangateretere silt loam) tended to be intermediate although the former was often close to the sawdust and the latter to the paper pulp in terms of herbicide phytotoxicity to the crop plants. For the less water soluble herbicide pendimethalin, the differences in crop selectivity in the different media were not significant. The effect of the media on the efficacy of weed control was evaluated through plant species with a much lower tolerance to the herbicides evaluated in contrast to the above species. For these plants the efficacy of the herbicides was generally lower in both the sawdust and paper pulp than in the two soils. The effect was more pronounced with the more soluble alachlor, where efficacy was reduced by factors of 5 – 10, compared to pendimethalin where efficacy reduction was by factors of 0 – 3. The two high organic media had contrasting effects on the various environmental behaviour indices evaluated. Herbicide adsorption as quantified by distribution coefficient (Kd) was higher in the two novel media compared to both the Horotiu and Mangateretere soils. However, when the Kd was normalised to organic carbon (Koc), there was less variation amongst the media indicating that organic matter is an important factor in controlling sorption in these media. However, despite the high level of adsorption in the sawdust, herbicides were most prone to leaching in this medium. Conversely the paper pulp tended to be more retentive while the two soils were intermediate. The degradation as quantified by half-lives (t½) of the herbicides was generally slower in the two novel media, probably reflecting the higher sorption in these two media but also due to the lower level of microbial activity in the sawdust and paper pulp. The study shows that herbicide behaviour in these carbon based media differs significantly from that expected from soil organic matter, mainly due to the non-humified nature of the organic matter in the media and its poor biological activity.

This study investigated methods to reduce herbicide application through improved targeting of weeds, thereby also reducing damage to pastures. The focus was to evaluate and improve wiper and spot-spraying application techniques for pasture herbicides as they reduce chemical use by treating just the weed. Wiper application of herbicides was shown to be a useful technique for controlling Californian thistles. In one trial, a stem reduction of over 90% when assessed 10 months post application was achieved with a double pass of clopyralid, metsulfuron and glyphosate when the plants were treated at the post-flowering stage and were vigorously growing. A double pass was superior to a single pass for glyphosate and triclopyr/picloram, but not for clopyralid and metsulfuron. Subsequent trials produced poor results possibly because of the stressed condition of the thistles and their growth stage as well as lack of consistency in wiper output and operator differences. Despite wiper applicators usually being selective, some damage to pastures was observed in the field, and from a series of experiments it was concluded that rain falling soon after wiper application was the likely cause of pasture damage. An innovative and highly sensitive technique using a spectrophotometer was developed to measure herbicide output from wiper applicators. A spectrophotometer could accurately measure clopyralid concentrations as low as 0.02 g active ingredient in a litre of water. The Eliminator and Rotowiper outputs were found to be highly variable while the Weedswiper was more consistent although it applied less herbicide than the other two wipers. Spot spraying experiments confirmed that glyphosate and metsulfuron create bare patches by damaging both grass and clover while clopyralid and triclopyr/picloram only eliminate clover. However, metsulfuron patches stayed bare for much longer while glyphosate ones quickly filled up with weeds and clover. Ingress of clover stolons appeared to be more important than re-establishment from seed in the recovery of patches. The bigger the damaged patch, the higher the likelihood of recolonisation by opportunistic weeds. Bioassay studies found that over-application of clopyralid and triclopyr/picloram provided residual activity up to 18 and 30 weeks, respectively, thereby potentially preventing re-establishment of white clover. The negative effects on clover seedlings from metsulfuron ranged from 3 to 6 weeks for standard and high rates, respectively, with a stimulatory effect on seedlings thereafter for up to 18 weeks. Dose-response curves for the application of metsulfuron and triclopyr/picloram into the centre 5% versus full plant coverage of Scotch thistle and ragwort rosettes showed that application of herbicide to the centre 5% was as effective at the same concentration and greatly reduced the risk of damage to pasture.

Plant form is a compromise between resource gathering, reproduction and the tolerance to physical demands of the abiotic and biotic environment. In an agricultural field in addition to the natural factors causing stress, humans also introduce physical and mechanical stresses, and chemical pesticides into the environment. Many of these factors are hazardous, since they represent stresses to which plants are unable to develop defense mechanisms. However, weeds have persisted in the agricultural environment despite the efforts to eradicate them. They have adapted to environmental changes such as crop rotation and have developed tolerance to stressors like pesticides in very short periods of times (less than 10 years), much less time than normally expected for evolutionary responses to occur. Perhaps a key to why weeds persist in stress-dominated habitats is the way they compromise between yield and survival. The mechanisms that explain which process is relevant in the control of seed production or seedling growth relate to the ecophysiology of the individual plants. However, trade-offs between plants physiological functions will have implications at both population and community levels. Climate change, air pollution and water scarcity are examples of environmental stresses that particularly affect agriculture. Herbicides are a major technological tool for agriculture and are responsible, at least in part, for significant increases in crop production during the last quarter of the century. The research presented in this dissertation was developed to understand the extent that individual responses to multiple environmental stresses can be extrapolated to population-level responses in an annual weed species. The specific objectives were to assess (1) the impact of three anthropogenic stresses (herbicide, UVB light and ozone) and their interactions on individual Italian ryegrass ontogeny and reproduction and (2) the potential evolutionary effect of these stresses and combinations on changes in population size and structure over time. Plants were capable of growth and reproductive compensation under the studied stresses. Stress factors with similar biochemical mechanisms had different effects at the individual plant and population levels of organization. Compensation occurred at all levels of organization: as individuals modifying growth and allocation to different organs and as populations modifying birth, and death rates and density dependent responses. The ability to compensate sometimes decreased with the number of stress factors (e.g. herbicide and UVB). In other cases, compensation ability increased with the number of stress factors (e.g. ozone and herbicide). / Graduation date: 2004

Glyphosate (N-(phosphonomethyl)glycine, PMG, H3L) is a widely used organophosphorous herbicide. It interacts with metal ions and mineral surfaces, which may affect its mobility, degradation and bioavailability in the environment. However, these interactions are far from fully understood. This thesis is a summary of five papers discussing the complexation of PMG with metal ions in aqueous solution and the adsorption of PMG and/or Cd(II) on different mineral surfaces. The complexation of PMG with the metals Cd(II) or Al(III) in aqueous solution was investigated with macroscopic and molecular scale techniques. Potentiometric titration data were combined with EXAFS, ATR-FTIR and NMR spectroscopic data to generate solution equilibrium models. In the PMG-Cd(II) system, only mononuclear complexes were formed, while both mono and binuclear complexes were observed in the PMG-Al(III) system. EXAFS, ATR-FTIR, and XPS measurements showed that PMG adsorbs to the surfaces of goethite (α-FeOOH), aged γ-alumina (γ-Al2O3) and manganite (γ-MnOOH) through one oxygen of its phosphonate group to singly-coordinated surface sites. Surface complexation models consistent with these spectroscopic results were fit to adsorption data using the 1pK reaction formalism. Electrostatic effects were accounted using either the Extended Constant Capacitance Model (ECCM) or the Basic Stern Model (BSM), and the charge of the surface complexes was distributed over the different planes. The formation of the surface complexes was described according to the following reactions: ≡MeOH(0.5-) + H3L <=> ≡MeHL(1.5-) + H2O + H+ ≡MeOH(0.5-) + H3L <=> ≡MeL(2.5-) + H2O + 2H+ The coadsorption of PMG and Cd(II) on the surfaces of goethite and manganite results in the formation of ternary mineral-PMG-Cd(II) surface complexes, as suggested from EXAFS results. Previous EXAFS measurements have also established the coordination geometries for the binary goethite-Cd(II) and manganite-Cd(II) surface complexes. In addition to the surface reactions in the binary mineral-Cd(II) and mineral-PMG systems, a single ternary complex with the stoichiometry ≡MeLCd(OH)(1.5-) was sufficient to explain coadsorption data: ≡MeOH(0.5-) + H3L + Cd2+ <=> ≡MeLCd(OH)(1.5-) + 3H+ It was concluded that the affinity of PMG for the three mineral systems decreases within the series: goethite > aged γ-Al2O3 > manganite. The formation of the ternary surface complex is more significant on goethite surfaces than on manganite surfaces.

Amphibians develop in aquatic environments where they are very susceptible to the effects of pesticides and other environmental contaminants. Glyphosate-based herbicides are widely used and have been shown to affect survival and development of tadpoles under laboratory conditions. The goal my thesis is to determine if agriculturally relevant exposure to Roundup WeatherMax®, a herbicide formulation containing the potassium salt of glyphosate and an undisclosed surfactant, influences the survival and development of wood frogs tadpoles (Lithobates sylvaticus) under both laboratory and field conditions. In the field, experimental wetlands were divided in half using an impermeable curtain so that each wetland contained a treatment and control side. Tadpoles were exposed to two pulses of this herbicide at environmentally realistic concentration (ERC, 0.21 mg acid equivalent (a.e.)/L) and predicted environmental concentrations (PEC, 2.89 mg a.e./L), after which survival, growth, development, and expression of genes involved in metamorphosis were measured. Results indicate that exposure to the PEC is extremely toxic to tadpoles under laboratory conditions but not under field conditions. Results from both experimental conditions show sublethal effects on growth and development, and demonstrate that ERC of glyphosate-based herbicides have the potential to alter hormonal responses during metamorphosis. My secondary objectives were to compare the effects of Roundup WeatherMax® to the well-studied Vision® formulation (containing the isopropylamine (IPA) salt of glyphosate and POEA), and to determine which ingredient(s) are responsible for the sublethal effects on development. Survival, growth and gene expression results indicate that Roundup WeatherMax® has greater toxicity than Vision® formulation. Contrary to my prediction, results suggest that, under realistic exposure scenarios, POEA is not the sole ingredient responsible for the observed developmental effects. However, my results demonstrate that chronic exposure to the POEA surfactant at the PEC (1.43 mg/L) is extremely toxic to wood frog tadpoles in laboratory. As part of the Long-term Experimental Wetlands Area (LEWA) project, this research contributes to overall knowledge of the impacts of glyphosate-based herbicides on aquatic communities.

Investigations into the biology and control of the annual grassy weed Bromus pectinatus Thunb. were conducted at the National Plant Breeding Station, Njoro, Kenya, from 1982 to 1984. Pot growth of B. pectinatus was influenced by soil type and microclimate, but not by seed origin. B. pectinatus was germinated and grown in amended and untreated soils ranging in pH from 3.05 to 8.13. Soils with a pH near 3 could not support growth or germination of B. pectinatus. B. pectinatus grew best on a soil of pH 6.55 and when soil pH influenced germination the optimum soil pH was 6.0. Exposure to light inhibited the germination of B. pectinatus seeds. Germination of B. pectinatus seed was most rapid at a 17 C temperature. Germination of dormant B. pectinatus seeds was enhanced by seed hull removal or pricking the lemma or removing the rachilla segment. Germination of B. pectinatus seed in the soil was unaffected by depth of burial, whereas, emergence was reduced to 35, 19, 11, 4 and 0% from depths of 0, 1, 2, 4 and 8 cm, respectively. There was a relationship between field emergence of B. pectinatus and the precipitation pattern. After-harvest germination of B. pectinatus seed indicated that there was an innate dormancy in hulled seed which persisted for 8 months. Field measurements were used to develop an equation which related yield loss in wheat with B, pectinatus infestation. Delayed sowing of wheat and barley into a B. pectinatus infested site resulted in yield reductions that were correlated with length of delay. Replacement series studies were conducted using varying proportions of wheat : B. pectinatus and rapeseed : B. pectinatus. Rapeseed / canola was unaffected by B. pectinatus interference. A spatial interference study determined that B. pectinatus interfers with wheat mainly above ground. The herbicides isoproturon, pendimethalin and oxadiazon were found to be ineffective against B. pectinatus, The herbicides triallate, chlorsulfuron, metribuzin, trifluralin and EPTC achieved limited control of B, pectinatus. Superior control of B. pectinatus was achieved using fluazifop-butyl at 0.25 kg/ha and fenthiaprop-ethyl at 0.12 kg/ha, in rapeseed / canola. / May 1986

Ionisable pesticides can be partially ionised within the range of natural soil pH and this strongly influences their reactivity in soils. This group includes important, worldwide contaminants of groundwater and surface waters. It is essential that their specific behaviour is recognised within risk assessment procedures. Experiments were carried out with ten pesticides (six acids and four bases) and nine arable soils (range in pH, texture and organic matter content) to advance the understanding and prediction of the behaviour of ionisable pesticides in soils. The main conclusions can be summarised as follows:<br />• Adsorption of ionisable pesticides tends to be stronger in soils with lower pH and containing more organic carbon. A regression equation including Log D (lipophilicity corrected for pH), the soil organic carbon content and a pesticide descriptor was selected to predict the adsorption of acids. The behaviour of bases was more complex and approaches specific to each compound seem to be required.<br />• There were some marked differences between the soils in their ability to degrade the different ionisable pesticides. The lack of consistent behaviour renders a global approach to prediction of degradation unrealistic. Distinct types of behaviour could however be distinguished according to the main route of degradation.<br />• Significant correlations between sorption and degradation were only observed for three pesticides out of ten, with faster degradation in soils with stronger sorption.<br />• A centrifugation technique was used to measure adsorption at realistic soil moisture contents and provides a robust characterisation of the fraction of pesticide available for leaching. Time-dependent adsorption was also assessed.<br />The increase in adsorption between one and seven days was not directly related to the level of adsorption although it was more important in soils containing more organic carbon.<br />Although specific interactions between pesticides and soils are still not fully understood, these results provide the basis for a more robust analysis of the behaviour of ionisable pesticides in the environment.

Le développement de la culture du sorgho de saison sèche, qui concerne l'ensemble du bassin du lac Tchad, constitue la dynamique agraire la plus visible de ces dernières décennies dans les plaines de l'Extrême-Nord Cameroun. La plante est repiquée dans des terres argileuses plus ou moins inondables, difficilement cultivables en saison des pluies, et accomplit son cycle à partir de la réserve en eau du sol. Le traitement herbicide, introduit récemment, est utilisé de façon croissante compte tenu des avantages à la fois agronomiques pour accélérer la préparation des parcelles et maîtriser certaines adventices vivaces, et économiques en réduisant légèrement les coûts par rapport à l'emploi de manoeuvres salariés. Un travail de recherche est apparu opportun pour accompagner les agriculteurs concernant l'adaptation de ce changement technique vers une utilisation la plus modérée possible des herbicides. Notre démarche associe deux approches agronomiques : l'une consiste à cerner les problèmes que les agriculteurs doivent résoudre à travers l'analyse et la formalisation des règles de décision pour la conduite de la culture ; l'autre à évaluer de nouvelles règles de décision liées à l'utilisation de l'herbicide sur l'élaboration du rendement de sorgho et l'évolution de la flore. La combinaison de ces deux formes de connaissances agronomiques permet de conseiller les agriculteurs sur l'insertion judicieuse d'une nouvelle technique dans leurs systèmes de culture, en valorisant au mieux leurs savoirs et leurs savoir-faire. La démarche s'appuie sur des enquêtes fines à l'échelle de l'exploitation agricole et des expérimentations "systèmes de culture" en parcelles paysannes, dans deux terroirs de référence. L'analyse révèle l'importance de l'hétérogénéité inter et intra-parcellaire du sol, sur laquelle l'agriculteur s'appuie pour enchaîner les opérations afin de repiquer dans de bonnes conditions d'humidité du sol malgré la lenteur des tâches culturales et un créneau réduit de réalisation de l'implantation. Dans la majorité des situations pédoclimatiques, la réserve hydrique du sol constitue le principal facteur limitant de la culture. La concurrence des mauvaises herbes se révèle limitante dans les terrains les plus humides en particulier lors des années de bonne pluviométrie. Dans ces conditions climatiques et d'enherbement, le traitement herbicide offre des gains de rendement d'au moins 20 % et parfois beaucoup plus dans les zones inondables où prolifèrent certaines adventices vivaces. Dans les situations à dominante de graminées annuelles, le désherbage chimique ne permet pas d'augmentation de production et ne devrait être envisagé que comme une solution d'ajustement ponctuelle pour éviter à l'agriculteur de prendre du retard dans l'implantation de sa sole, en particulier lors des années les plus sèches. Les résultats ont permis de préciser les règles de décision liées à la mise en oeuvre du traitement : localisation des traitements et modulation des doses en tenant compte de l'hétérogénéité des milieux cultivés; alternance de l'utilisation d'herbicide avec le mode de préparation habituelle selon le scénario climatique. Cette démarche, mise en oeuvre dans le cadre d'un projet de développement, contribue à l'enrichissement de services d'appui et de conseil aux exploitations familiales à l'échelle régionale, notamment pour orienter les agriculteurs vers des principes de gestion intégrée de l'enherbement et limiter les effets négatifs de l'innovation sur l'environnement et l'emploi en milieu rural.

Progress in tree biotechnology initially trailed behind agricultural crops due to their long life cycle, difficult tissue culture and regeneration protocols, and their abundance in natural forests. However, rapid global deforestation rates, together with an increased world demand for pulp, paper and timber products, have prompted scientific and commercial focus to improve genetic timber stocks. South Africa, a tree-poor country (where indigenous forests are protected), has relied almost solely on exotic plantations to meet its demand for timber. A pioneer study investigating the feasibility of using direct (biolistic) and indirect (Agrobacterium-mediated) methods for gene transfer was undertaken in Pinus patula Schiede et Deppe, a Mexican softwood and a forerunner for saw timber, pulpwood and paper in the South African forest industries. The aim of the transformation methods was to impart herbicide resistance to the trees. This was achieved via the introduction of a bar-GUS pAHC25 cassette under the control of the ubiquitin promoter. To provide target material for transformation, two in vitro micropropagation pathways were used: somatic embryogenesis and organogenesis. Both embryonal suspensor masses (ESM) and somatic embryos at various stages of development were initially used as target explants for the biolistic study using an established in vitro protocol. A stepwise selection was implemented in order to allow transformed (particularly bombarded) cultures the opportunity to regenerate under selection pressure using MSG3 maintenance medium supplemented with BASTA® herbicide at 1 mg l ¯¹ followed by 3 mg l¯¹ active ingredient at the next subculture. Biolistic transgene delivery was more efficient when sorbitol was included in the pre-bombardment medium enabling use of higher vacuum and shooting pressures, without lowering the regeneration potential of ESM significantly. Bombarded material from two genotypes (Lines 2 and 3) was regenerated to produce mature somatic embryos using an optimized regeneration regimen. The indirect study with Agrobacterium tumefaciens (LBA4404), transformed with the pAHC25 vector via triparental mating or heat shock, used a variety of target tissues including: mature somatic embryos, ESM and mature zygotic embryos (MZE's) - a novel in vitro system for P. patula. The Agrobacterium-mediated method resulted in optimized decontamination conditions using a combination of liquid MSG3 (or sterile dH₂O for mature embryos) supplemented with 500 mg l ¯¹ cefotaxime, with rotation, and sterile 65 mm Whatman No. 3 filter paper stacks, which avoided excess filtering and stress to transformation material. Further efforts to aid regeneration during the indirect study included L-proline post-transformation, though no mature somatic embryos were regenerated at the conclusion of the Agrobacterium-mediated study. Recovery of transformed ESM in both studies was best during the active growth phase 4-6 d after subculture. Regeneration with good somatic embryo potential was an exigent aspect in both transformation studies. Expression of positive histochemical GUS activity in all transformed material was confirmed by polymerase chain reaction (PCR) analysis indicating that Pinus patula tissue was amenable to transformation. A new bar PCR regime was implemented in P. patula. In the biolistic study, a higher transformation efficiency of bar amplicons (53%) than GUS amplicons (45%) was observed, reflecting their non-linked status on the pAHC25 transformation vector. This is the first report of biolistic transformation of P. patula that will allow for the production of transgenic ESM. The production of transgenic P. patula holds great promise for commercial development in the South African forestry industry. The application of transgenic trees in the timber industry is numerous but the aims most relevant to P. patula include wood modification and disease resistance to pathogens like pitch canker fungus. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.