Orientador: Rosana Marta Kolb / Banca: Catarina dos Santos / Banca: Luis Octávio Regasini / Resumo: Atualmente, há esforços crescentes para o desenvolvimento de alternativas de manejo de plantas daninhas, devido ao aumento de espécies resistentes aos herbicidas e às preocupações ambientais. Mesmo que não se possa eliminar o uso de herbicidas convencionais, sua utilização pode ser reduzida pela descoberta de compostos bioativos, mais efetivos e/ou com menor toxicidade ao ambiente do que as moléculas que vem sendo usadas. O cinamaldeído e a curcumina são moléculas naturais que apresentam diversas atividades biológicas, e as chalconas são precursoras de flavonoides, que apresentam atividade alelopática, influenciando o desenvolvimento das plantas. Visando prospectar novos herbicidas, foi avaliado o potencial fitotóxico do cinamaldeído, da curcumina e de diferentes estruturas de chalconas metoxiladas. Inicialmente, foi feita triagem de 17 chalconas com bioensaio de desenvolvimento inicial com alface, para selecionar a mais promissora, e que seria testada com daninhas (seis espécies). Estas foram tratadas com 5 mL de solução 1 x 10-3 mol L-1 de cinamaldeído, curcumina ou 3,4-dimetoxichalcona (BC-18); como controle negativo e positivo usou-se água destilada e glifosato (componente ativo do Roundup®), respectivamente. Os comprimentos da raiz e parte aérea foram avaliados quando as plântulas dos controles negativos atingiram aproximadamente 5 cm. Todos os compostos induziram a inibição do crescimento quando comparados ao controle negativo, afetando a raiz e a parte aérea das plântu... (Resumo completo, clicar acesso eletrônico abaixo) / Absctract: Currently, there is increasing effort to develop weed management alternatives due to the increase of herbicide resistant species and environmental concerns. Even if the use of conventional herbicides cannot be eliminated, their use can be reduced by the discovery of bioactive compounds, more effective and/or with less toxicity to the environment than the molecules that are being used. Cinnamaldehyde and curcumin are natural molecules that exhibit various biological activities, and chalcones are precursors of flavonoids, which have allelopathic activity, influencing the development of plants. Aiming to prospect new herbicides, the phytotoxic potential of cinnamaldehyde, curcumin and different methoxylated chalcone structures was evaluated. Initially, 17 chalcones were screened in bioassay of initial development of lettuce, to select the most promising one, and tested with weeds (six species). These were treated with 5 mL of 1 x 10-3 mol L-1 solution of cinnamaldehyde, curcumin or 3,4-dimethoxychalcone (BC-18); as negative and positive control, distilled water and glyphosate (Roundup® active component) were used, respectively. The root and shoot lengths were evaluated when the seedlings of the negative controls reached approximately 5 cm. All the compounds induced growth inhibition when compared to the negative control, affecting the root and shoot of the seedlings. Cinnamaldehyde showed higher phytotoxic activity than glyphosate in five species, whereas curcumin showed greater inhibition in one species and glyphosate-like inhibition in two other species. BC-18 showed greater phytotoxicity than glyphosate in three species and glyphosate-like activity in other two species... (Complete abstract click electronic access below) / Mestre

Orientador: Edivaldo Domingues Velini / Banca: Caio Antonio Carbonari / Banca: Luciano Soares de Souza / O atual sistema produtivo de cana-de-açúcar deixa quantidades variáveis de palhada na superfície do solo capaz de provocar supressão de algumas espécies de plantas daninhas, além de modificar as características químicas, físicas e biológicas dos solos. Portanto objetivou-se avaliar o efeito de diferentes quantidades de palha de cana-de-açúcar na emergência de plantas daninhas relevantes para a cultura da cana-de-açúcar, além de produzir informações necessárias para conduzir estudos complementares visando determinar a natureza dos efeitos observados. Para tanto, foram conduzidos três estudos de campo em três épocas distintas do ano avaliando-se os efeitos de diferentes quantidades da palha de cana-de-açúcar (0; 2,5; 5; 10; 15 e 20 t ha-1) sobre o regime térmico do solo em diferentes profundidades e sobre a emergência de nove espécies de plantas daninhas (Ipomoea grandifolia, Ipomoea nill, Ipomoea quamoclit, Brachiaria decumbens, Bidens pilosa, Euphorbia heterophylla, Panicum maximum, Ipomoea hederifolia e Merremia aegyptia) aos 7, 14, 21, 28, 35 e 42 dias após a semeadura (DAS). Os experimentos foram conduzidos em blocos casualizados com quatro repetições. A presença da palha sobre o solo alterou o regime térmico, reduzindo a amplitude térmica do solo, principalmente em menores profundidades. A palha reduziu a emergência de plantas daninhas e a intensidade do efeito é dependente da espécie e da quantidade do resíduo sobre o solo. A interferência da palha reduzindo a germinação de plantas daninhas foi pouco dependente da época do ano e das condições climáticas, sendo possível estabelecer modelos gerais relacionando a quantidade de palha com a porcentagem de emergência, quando a variável dependente foi expressa em porcentagem dos valores observados no tratamento sem palha.... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The sugarcane has great economic importance to the country. Even in the face of technological advances in the cultivation of sugarcane, interference from weeds still cause many losses. After the adoption of mechanized harvesting the weed management has become more complex, mainly due to varying amounts of straw left on the soil surface. In addition to the suppression effect by some weed species, the straw of sugarcane can also modify the chemical, physical and biological properties of soils. Therefore the aim of this study was to evaluate the effect of different amounts of straw sugarcane germination of weed relevant to the culture, as well as producing information necessary to conduct further studies in order to determine the nature of the effects observed . For that, we conducted three field studies that evaluated the effects of quantities of straw between 0 and 20 t ha-1 on the soil thermal regime and the emergence of nine species of weeds. Three experiments were conducted to the field at different times of the year. The experimental design was randomized blocks, with six treatments and four replications, totaling 24 installments. The treatments consisted of volumes of dry straw cane sugar (0, 2.5, 5, 10, 15 and 20 t ha-1). Each plot consisted of 4 m long and 3 m wide, totaling 12 m². In each were opened three trenches of 1 m2 and 5 cm deep, for sowing of approximately 100 seeds of nine species of weeds. In each trench was used three kinds, the first being Bidens pilosa, I... (Complete abstract click electronic access below) / Mestre

Silverleaf nightshade (Solanum elaeagnifolium), a perennial broadleaf weed, has become a serious pest in many semi-arid areas of the world. Control of silverleaf nightshade is confounded by its ability to produce thousands of viable seeds from a single mother plant, a deep and well-developed root system and the ability to propagate vegetatively from creeping lateral roots, root fragments and from rhizomes. Exacerbating factors are longevity of its propagules in soil, particularly under adverse environmental conditions. Currently, in South Africa, it is one of the more serious weeds in cotton (Gossypium hirsutum L.) production, where its interference results in remarkable loss of product quantity and quality. Research has been done on the competition aspect of silverleaf nightshade with cotton but there is a serious lack of information on the allelopathic aspect. In this study, a series of experiments that included laboratory and glasshouse experiments were conducted to evaluate the allelopathic interference of silverleaf nightshade on early growth of cotton. Cotton seeds were exposed to silverleaf nightshade extract solutions or planted in soil into which silverleaf nightshade leaf material or ripe berries were incorporated. In all the experiments attempts were made to avoid or to reduce, at least, the influence of factors that could be potentially confounding. In this regard, PEG-6000 was used to evaluate the sensitivity of crop parameters to the osmolality of test solutions in order to ensure that osmotic inhibition was not a confounding factor in the bioassays where the biological activity (phytotoxicity) of plant extracts were assessed. Competition for growth factors was the other major potentially confounding factor that was considered throughout, and steps were taken to negate its influence. Germination and early seedling growth of cotton cultivars Sicala, CA 223, Siokra V15, Tetra and Delta Opal were inhibited by test solutions (silverleaf nightshade extracts) and by soil-incorporated residues of silverleaf nightshade. Inhibitory effects of silverleaf nightshade solutions were observed when either a layer of filter paper or a thin layer of soil or quartz sand was used as substrate. In both laboratory and pot experiments, it appeared that cotton cultivar Sicala was the most sensitive to allelochemicals contained in extracts and residues of silverleaf nightshade. This finding of differential tolerance of crop cultivars towards allelochemicals contained in a weed is a rare occurrence in allelopathy research. Berries of silverleaf nightshade were generally more inhibitory to cotton than leaf material. For both types of plant material used, residues lost their inhibitory effect over time, probably as decomposition of allelopathic compounds in soil progressed. Information obtained from this study can be viewed as knowledge that contributes to the bridging of the gap between identification and isolation of allelochemicals from silverleaf nightshade, and confirmation of silverleaf nightshade allelopathy under natural conditions. Experiments involving soil as growth medium, in particular fieldwork, are needed to verify the validity of these findings under natural conditions. / Dissertation (MSc(Agric) Agronomy (Weed Science))--University of Pretoria, 2007. / Plant Production and Soil Science / MSc(Agric) / unrestricted

Silverleaf nightshade is a serious problem weed in many semi-arid regions of the world. Although many research efforts have been devoted to this weed’s interference with crop species, possible chemical interference (allelopathy) has not been thoroughly investigated yet. In the present study, allelopathic potential of silverleaf nightshade foliage was assessed by means of germination bioassays. Preliminary experimentation was necessary to evaluate procedures of the bioassay method to be used, as many different approaches are described in literature. Water infusions and crude water-soluble extracts of silverleaf nightshade foliage inhibited germination and root growth of cotton and lettuce respectively. Osmolalities of the infusions or extracts used were not inhibitory to germination or root growth of either cotton or lettuce. Preliminary exploration of the nature of the chemical substances implicated in this phytotoxic activity suggests that more than one compound is involved. This includes an alkaloid, a saponin and several flavonoidic constituents, implying the presence of a synergistic effect for crude extracts. An anatomical study was conducted in an attempt to link the allelopathic potential of silverleaf nightshade foliage to specific cells or structures in the leaves. It was considered that glandular trichomes, abundant on both leaf surfaces, might harbour phytotoxic secondary metabolites. It was furthermore speculated that stellate trichomes with intrusive basal cells observed to reach the vascular bundles, might be involved in excreting alkaloids contained in the vascular bundle sheath onto the leaf surface. The results of this study represent the first step in showing the allelopathic potential of silverleaf nightshade and laid a foundation for continuing with field studies and more in-depth chemical analyses. / Dissertation (MSc (Agric) Horticulture)--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

Cover crops not only improve soil conditions, but can also suppress weed growth. In a field experiment the influence of two cover crops, Secale cereale (stooling rye), and Lolium multiflorum (annual ryegrass), on the growth of Zea mays (maize) and C. esculentus (yellow nutsedge) was compared to the latter crop and weed’s growth at three control treatments which involved weed residues left on the soil surface, application of herbicides and weed control by hoeing. Maize emergence and growth were delayed in the presence of residues of both cover crop species, especially in annual ryegrass residues. C. esculentus growth was significantly inhibited in the area between the maize planting rows by the cover crops for the first 14 days after maize emergence, but this growth suppressing effect diminished after 28 days. In a controlled environment study, the influence of the same cover crops, together with Avena sativa (oats) and three cultivars of annual ryegrass were evaluated. Maize and C. esculentus growth were suppressed, especially by the root residues of the cover crops with the annual ryegrass cultivar ‘Midmar’ being the most suppressive. Chemical analysis of the leachate of root residues indicated the presence of phenolic acids and benzoxazolin-2(3 H)-one (BOA). It is suggested that weed growth could be reduced by the allelochemicals leached from cover crop residues but in order to achieve prolonged, effective weed control the combination of mulch retained on the soil surface and the application of herbicides will required. In an integrated weed management approach a possible reduction in the type and number of herbicide applications required for effective weed control, could be implemented. / Thesis (PhD)--University of Pretoria, 2012. / Plant Production and Soil Science / unrestricted

Laboratory and greenhouse experiments were conducted to evaluate the allelopathic effects of the extracts and residue Arctotis arctotoides (L.f.) O. Hoffm on selected vegetable crops. The study aimed to address the following specific objectives to (i) examine the ultra structures of the leaf of A. arctotoides using the Scanning Electron Microscope (SEM), (ii) carry out comprehensive qualitative and quantitative phytochemical analysis of the root and shoot materials of the plant, (iii) investigate the allelopathic activities of the root and shoot aqueous extracts of A. arctotoides at concentrations of 10, 8, 6, 4 and 2 mg/ml on germination, radicle and plumule growth of cabbage, carrot, tomato and spinach, (iv) evaluate the inhibitory effects of the dried shoot residue of the plant at 10, 20 and 40 g kg-3 of soil (treatments B, C and D) and the control (treatment A) on the morphology, growth and chlorophyll pigment content of tomato and cabbage transplants at 1, 2, 3 and 4 weeks after transplanting and (v) assess the effects of the dried shoot residue of A. arctotoides on the yield, nutrient uptake by the leaves of tomato and cabbage at 4 and 12 weeks after transplanting. Finally, to analyze the residual mineral content of the soils with tomato and cabbage transplants at 12 weeks after transplanting. The the SEM revealed that anisocytic stomata and glandular trichomes (GTs) were numerous on the abaxial than the adaxial surfaces of A. arctotoides. The non glandular trichomes (NGTs) were also present on both surfaces but lesser on the abaxial. Morphologically, the GTs were peltate, uniseriate and globular head while the NGTs were cylindrical and filamentous with variable number of cells at the basal portion. The energy dispersive X-ray spectroscopy of some crystals showed that Na+ Mg2+ and Ca2+ were the major constituents of the crystal deposit found around the GTs and stomata. The results of the phytochemical composition of the root and shoot extracts of A. arctotoides confirmed the occurrence of alkaloids, flavonoids, phenolics, saponnins, tannins and triterpenes as the common constituents. In addition, cardiac glycosides and steroids were also detected in the shoot of the A. arctotoides. Quantitative estimation of the chemical constituents of the crude extracts further revealed that the alkaloid content in the root higher (0.97 percent) than the shoot (0.64 percent). The quantity of flavonoids detected in the shoot (1.02 percent) was more than that observed in the root (0.35 percent). Others (phenolics and tannins) were marginal in the two plant parts. The results of the inhibitory effects of the root and shoot aqueous extract at the varying concentrations showed that root extract at 10 mg/ml considerably reduced the germination of cabbage, carrot, tomato and spinach seeds by 84.0, 83.2, 72.8 and 37.4 percent respectively. Incubation of the shoot extract at the same concentration resulted in 100 percent inhibition of cabbage and carrot seed germination whereas those of tomato and spinach were suppressed by 91.5 and 61.2 percent respectively. The two extracts at the varying concentrations also had a significant reduction on the radicle and plumule growth of the four vegetables. Addition of the shoot residue to the soil showed massive chlorosis, necrotic lesions and wilting of tomato and cabbage leaves under treatments C and D at 2 weeks after transplanting. The number of leaves, leaf area, dry shoot and root weight of the two vegetables grown in the amended soils were also drastically reduced. The inhibition percentages due to the addition of the three concentrations of A. arctotoides dried shoot residue on the dry shoot weight at 4 weeks after transplanting were 38.6, 45.5 and 70.3. for tomato and 57.5, 73.3 and 87.5 percent for cabbage. Similarly, the declines in the dry root weight of 61.3, 82.9.4 and 83.4 percent for tomato as well as 53.1, 54.7 and 67.2 percent for cabbages were recorded for the two vegetables under treatment B, C and D during the period. The results further showed that the dry fruit yield and shoot weight of tomato under the treatments B, C and D decreased with increase in shoot residue concentrations of A. arctotoides. Relative to treatment A, no significant differences were recorded in the dry head weight of cabbage under the residue treated groups. The reductions in the fruit yield and fresh head weight caused by treatments C and D were 37.2 and 84.8 percent for tomato and 30.9 and 72.4 percent for cabbage. The findings on the mineral contents in the leaves of the two vegetables revealed significant differences in the uptake of N, Mg, Na, Cu and Fe by tomato leaves. The concentrations of N, K, Na and Zn in cabbage leaves also differed. However, the P content was relatively constant in the leaves of the two vegetables at 4 and 12 weeks after transplanting. At 12 weeks after transplanting, the Fe content in soils with tomato and cabbage treatments C and D was greatly enhanced in comparison with the other nutrients. The residual N, P and Zn detected in soils planted to cabbage were similarly equal among all the groups including the control. Thus, under the greenhouse experiment, Arctotis arctotoides (L.f) O. Hoffm has been shown to contain some phytotoxic chemical compounds in its root and shoot materials. The compounds either singly or collectively have demonstrated some inhibitory potentials on the germination, growth and yields of cabbage, carrot, tomato and spinach evaluated in this study.

No information is available on the role of allelopathy in crop rotation systems of the Western Cape Province of South Africa, where more than 100 000 ha are under threat from herbicide-resistant rye grass. A study which investigated the use of allelopathic properties for the suppression of rye grass hybrid type (Lolium multiflorum x perenne) was undertaken. These objectives were accomplished by: a) exploring the use of allelopathic properties of crop residues for rye grass suppression; b) evaluation of the role of allelopathy from seeds, seedlings, roots and above-ground plant material of rotational crops; c) assessing the distribution of genetic and morphological variability of rye grass and d) determining the interactions among micro-organisms and allelopathic root leachates from rotational crops and rye grass. In the field trials, growth inhibitory or stimulatory effects were observed on crops exposed to the residues of others. Medic suppressed the weed type rye grass. The radicle length of rye grass was inhibited by seed leachates from wheat and lupine. Growth inhibition from lupine seed and seedling leachates was evident in rye grass radicle length and cumulative germination percentage. Morphologically, 50% of the total number of specimens was classified as rigid rye grass, 48% as the hybrid, namely L. multiflorum x perenne and 2% as perennial rye grass. The wide genetic and morphological variation detected in rye grass may be due to high genotypic plasticity and hybridisation for producing the weed type L. multiflorum x perenne. The faster growth rate of rye grass on Langgewens soil treated with barley root leachates was revealed by Principal Component Analysis (PCA) as a probable association with growth-promoting soil micro-organisms. Crop cultivars and weeds may modify the soil micro-organism populations to their advantage and to the disadvantage of other species by the release of root exudates that apparently differ in composition between plant species. The effect on microbial communities varied with source of exudates and between soils. / Thesis (PhD)--University of Pretoria, 2011. / Plant Production and Soil Science / unrestricted

Please read the abstract in the 00front part of this document. / Dissertation (MSc Agric (Weed Science))--University of Pretoria, 2001. / Plant Production and Soil Science / Unrestricted

Investigations were carried out into the allelopathic potential of the invasive alien annual Himalayan Balsam (Impatiens glandulifera Royle) using a series of bioassays, including ones developed or adapted for this study. They were evaluated for their suitability to detect three of the four main modes of allelochemical release, namely leaching, exudation and decomposition. Assays which involved the measurement of lettuce radicles and hypocotyls gave reliable results and allowed a range of different Impatiens material, both living and dead, to be assessed and ranked according to the allelopathic effects demonstrated. Attempts were made to isolate resource competition from allelopathy using separately grown but connected donor and receiver plants and a density dependent design where single I. glandulifera plants were grown in pots with variable numbers of receiver plants. Results proved inconclusive. Initial experiments showed that the allelopathic potential of I. glandulifera varied according to the organ from which the material was derived. Pods, leaves and stems produced the greatest inhibition of lettuce seedlings. Effects on germination were not significant at most of the concentrations tested. Live roots of I. glandulifera plants produced pronounced orange staining of the agar into which they were placed and showed clear evidence of distance dependent inhibition of lettuce radicles. Effects were limited to growth rather than germination of the test plants. Germinating I. glandulifera seeds caused a significant inhibition of lettuce radicle elongation when the two species were grown together in an agar medium. The inhibitory effects increased significantly with increasing exposure time. Increasing I. glandulifera seedling number also produced significant reductions in lettuce radicle length. Dormant seeds, by contrast, stimulated growth. Dead seeds did not produce significant changes to the growth of the test plants. When rhizosphere soil was gathered from pot grown I. glandulifera plants, the results were mixed. Initial samples inhibited growth, whereas those collected from dying plants over a period of weeks stimulated growth. Further experimentation is required before the indications of allelopathic interactions demonstrated here can be applied to the behaviour of wild populations of I. glandulifera.

Invasive woody shrubs are a problem when they displace native species and threaten habitats, especially those that harbor rare or endangered species. They not only compete with native plants, but also alter habitat and food that many organisms depend upon. Invasive plants undergo a release from their specialist predators in the nonnative range, providing them advantages over native species. Because modes and pathways of how invasive species spread are not fully understood, predicting spread and implementing restoration ecological controls remain inexact. Due to the lack of comparative studies on woody shrubs, especially invasive privets, we understand very little about conditions affecting their invasiveness. A study was conducted near Dallas, Texas to determine if privet has allelopathic properties that influences growth of native plants. Soil nutrients and other analyses were made and compared between field plots supporting privet, plots in which privet has been removed, and plots where privet has not been observed. In some field plots, natives were planted under the three previously mentioned conditions, and their survival and condition were monitored to evaluate effects of privet on their establishment and growth. It was found that Chinese privet did hinder seed germination in red mulberry, soapberry and beautyberry and root formation in beautyberry cuttings. The soil in the sites were found to be normal for bottomland forests that endured two flooding events within one year.