The aim of this project was to provide sound scientific underpinning for the development of new weed management strategies in sugar cane by exploring competition from the major weeds, and explaining the different mechanisms of weed interference from Paspalum paniculatum and P. urvillei. Critical periods of weed control (CPWC) were studied in six field trials. In ratoon cane, CPWC with natural weed infestations started between 228 and 916 growing degree days (GDD), and ended between 648 and 1311 GDD, depending on the site and cane variety. These results represented a maximum CPWC of 12 to 28 weeks after harvest (WAH). In plant cane, the CPWC started earlier (6 WAP) and was longer than those in ratoon cane. Relative competitiveness ‘q’ values of eight common weed species showed that sugar cane was a stronger competitor than most of the weeds tested. The adverse effect of weed competition in sugar cane is not experienced before several weeks following weed emergence. Weeds transplanted 10 WAP caused no significant change in cane yield response as compared to those transplanted 4 WAP. Paspalum paniculatum was often found to be more competitive than P. urvillei, although the latter produced more leaf area and grew taller to intercept more light within the canopy. This indicated that other mechanisms of weed interference were involved and competition for light was more important during the earlier (tillering) growth stages. Root competition was shown to be as important as shoot competition. Root competition effects were observed several weeks after imposing competition, suggesting that it was more important than competition for light in the post-tillering phase. Application of root exudates from the two grasses to sugar cane confirmed an allelopathic effect on the root biomass of sugar cane. One chemical identified in the leachates from both Paspalum species for the allelopathic effects was 2-propenoic acid, 3-(4-methoxyphenyl). The main implications of the above findings for the Mauritian sugar industry would involve a change in the timing of application of herbicides. A new tank-mix consisting of trifloxysulfuron + ametryn and amicarbazone has been found to meet this objective. This strategy will enable a saving of at least one herbicide treatment per season. / Thesis (PhD)--University of Pretoria, 2011. / Plant Production and Soil Science / unrestricted

The fairy circles are an intriguing and unexplained feature of the pro-Namib in Namibia and northwestern parts of South Africa. The presence of hundreds of almost circular patches where no plants grow were first mentioned in scientific literature in 1971 and since then scientists have tried to find an explanation for the origin of these circles. Although there are many hypotheses regarding the origin of these circles not one of these can explain the existence of these circles satisfactory. In this study several aspects of the fairy circles were investigated to improve the characterization of the phenomenon. Total element analysis of the soil from the different microhabitats (inside the circle, on the edge of the circle and between the circles, referred to hereafter as the matrix) and at different depths in these microhabitats were performed by inductively coupled plasma mass spectrometry (ICP-MS) and analyzed by principal component analysis (PCA). No patterns emerged regarding the concentration of the elements in the respective microhabitats. The occurrence of vesicular arbuscular mycorrhizae (VAM) in the roots of plants collected from the different microhabitats was also investigated. It was shown that VAM occurred in most of the roots of plants collected in the matrix and on the edge but no VAM were found in plants collected inside the circles. The succulent plant Euphorbia damarana has also been implicated in the origin of the circles. The presence of germination inhibiting compounds in this species was investigated. No such compounds were found. The extracts of it inhibited the growth of radicles of lettuce seeds at a concentration of 25 mg/ml. Bio-assays were also performed on soil collected in the different microhabitats using a dominant grass of the area, Stipagrostis uniplumis, as bioindicator. The fresh an dry shoot mass of plants harvested from soil collected on the edge and in the matrix grew much better than the shoots grown in soil collected from the inside of the circles (p = 0.0007). The dry shoot mass showed the same trend as the fresh shoot mass. The fresh root mass showed a marked increase in the roots collected from soil on the edge of circles when compared to plants grown in soil collected from the inside and the matrix (p = 0.013). There was a significant difference in the length of shoots measured in plants grown in the soils collected from the different microhabitats with the shoots measured from plants grown in the soil collected from the edge showing stimulation in growth when compared to the plants grown in soil from the matrix and inside the circles (p = 0.00004). The difference in shoot length between grasses grown in soil collected from the edge and the matrix was also significant (p = 0.00004) with the edge samples showing a stimulation in growth. / Dissertation (MSc)--University of Pretoria, 2008. / Plant Science / unrestricted

Renewed interest in hemp (Cannabis sativa L.) for cannabinoid production has highlighted critical knowledge gaps for growers. The impacts of weed interference on hemp yield are largely unstudied despite causing serious economic losses in most cropping systems. Furthermore, understanding factors determining cannabinoid content of hemp will be crucial for effective production. To evaluate the effects of weed competition on hemp yield and cannabinoid content, hemp growing in plasticulture was subjected to competition from 5, 3, 1, or 0 waterhemp (Amaranthus tuberculatus (Moq.) Sauer) plants. Hemp biomass and cannabinoid content were not significantly affected by weed competition. Yields in weedy and weed-free treatments were generally comparable, although unexpectedly high variation limited the ability to detect subtle differences between treatments. Waterhemp biomass was significantly reduced by competition from hemp in comparison to hemp-free controls. Suppression of weed growth by hemp and lack of significant yield loss from weeds suggests that hemp can be highly competitive and grown successfully without herbicides in certain circumstances. Abundance and documented phytotoxicity of hemp secondary metabolites suggest a potential for allelopathic activity. While incorporated hemp residue was not more effective than a maize control at reducing plant growth, hemp residue and extracts effectively inhibit seed germination. A laboratory assay showed that crude extracts of hemp can reduce the germination of a Brassica napus L., a bioindicator. Furthermore, a greenhouse experiment showed that small amounts of hemp residue on the soil surface can effectively reduce and delay the germination of waterhemp. Together, these results show that hemp residue has the potential to be incorporated with a practice such as chaff-lining for enhanced control of germinating weed seeds.

Growth media recycling during algae cultivation is necessary to increase the efficiency and reduce the cost of biofuel production from algae feedstocks. Without recycling media, the cost of algae based biofuel production would be prohibitively high and large scale algae based biofuel production would not be economically viable. The ratio of media recycled to media wasted assumed for algae farms is generally calculated to maintain salt concentrations below growth inhibitory levels, ignoring the influence of secondary metabolites which might decrease productivity. Secondary metabolites, which include allelopathic or auto-inhibitory biological contaminants, might lead to the accumulation of growth-inhibiting compounds in recycled media used in algae production. Chlorella sorokiniana (strain DOE1412) was a leading algae biofuel feedstock candidate and has not previously been evaluated for inhibitor production. To test the effects of water recycling on the growth of DOE1412, media was recycled through multiple rounds of algae cultivation. DOE1412 was grown in modified BG11 culture media until reaching the end of linear growth phase, at which point the biomass was removed, nutrients replenished to their initial concentrations, and the recycled culture media used for a subsequent round of growth. The culture media was recycled through five rounds of growth with cultures grown on recycled media compared to controls grown on freshly prepared growth media. Biomass density was monitored via optical density and the specific and productivity growth rates were used to quantify the extent of inhibition. Exploratory work was performed with the goal of identifying potential inhibitory substances produced by DOE1412 during cultivation. Samples of recycled media were analyzed for polyunsaturated fatty acids which have been demonstrated to be inhibitory. The carbohydrates content of used media was analyzed to assess the amount of organic materials shed by DOE1412 into recycled media during growth. The log phase growth rate (day-1) of DOE1412 was inhibited by 3±2%, 8±1%, 10±2%, and 18.6±0.9% when grown in media recycled 1-4 times, respectively, with a 99% level of confidence that inhibition was observed in each round of regrowth. The productivity growth rate (OD750/day) of DOE1412 was not inhibited in media recycled 1-3 times. The productivity growth rate of DOE1412 was inhibited by 13±3% when grown in media recycled 4 times with a 99% level of confidence that inhibition was observed. Zinc was found to accumulate in the recycled media to potentially toxic levels (>0.09 mg/L), therefore it is uncertain if the observed inhibition was due to an accumulation of inhibitory secondary metabolites or the accumulation of zinc. Two inhibitory polyunsaturated acids, linoleic and linolenic acid, were identified in media recycled 4 times. The carbohydrate content of recycled media fluctuated between 8-10% of total fixed carbon in media recycled 1-3 times and increased to 18% in media recycled 4 times. However, changes observed in media recycled 4 times may have been due to improper storage of used media.

No description available.

The aim of this study is to elucidate factors that effect growth of Sarcina lutea and Bacillus subtilis, exposed to the growth inhibitor SDS (Sodiumdodecylsulfat). Agar diffusion experiments revealed repeated, concentric zones of inhibition and stimulation upon exposure to Sodiumdodecylsulphate or to Amoxicillin. Temperature, nutrient concentration and inhibitor concentration were controlled. Formation of successively repeated zones of inhibition, stimulation, inhibition and stimulation is discussed: •The extension of the primary inhibition zone is due to the concentration of applied Sodium dodecyl sulphate.•Immediately outside the primary inhibition zone the bacteria have access to diffusing nutrients that have not been consumed in the primary inhabitation zone.•In zones of dense bacterial growth the bacteria may produce inhibiting substances, affecting growth of bacteria in adjacent zones.•In zones of dense bacterial growth the nutrients will soon become depleted, thus affecting bacteria in adjacent zones.

Corals, the foundation species of tropical reefs, are in rapid global decline as a result of anthropogenic disturbance. On many reefs, losses of coral have coincided with the over-harvesting of reef herbivores, resulting in ecosystem phase-shifts from coral to macroalgal dominance. It is hypothesized that abundant macroalgae inhibit coral recovery and recruitment, thereby generating ecological feedback processes that reinforce phase-shifts to macroalgae and further diminish reef function. Notwithstanding, the extent to which macroalgae directly outcompete coral, the mechanisms involved, and the species-specificity of algal-coral competition remains debated. Moreover the capacity for herbivores to prevent vs. reverse ecosystem phase-shifts to macroalgae and the roles of herbivore diversity in such phenomena remain poorly understood. Here I demonstrate with a series of field experiments in the tropical Pacific and Caribbean Sea that multiple macroalgae common to degraded reefs directly outcompete coral using chemical warfare, that these interactions are mediated by hydrophobic secondary metabolites transferred from algal to coral surfaces by direct contact, and that the outcomes of these allelopathic interactions are highly species-specific. Using field observations and experiments in the tropical Pacific, I also demonstrate that the process of herbivory attenuates the competitive effects of allelopathic algae on corals by controlling succession of algal communities, and that the herbivore species responsible for macroalgal removal possess complementary tolerances to the diversity of chemical defenses deployed among algae, creating an essential role for herbivore diversity in reversing ecosystem phase-shifts to macroalgae. Lastly, I demonstrate with field experiments in the tropical Pacific that algal-coral competition simultaneously induces allelochemicals and suppresses anti-herbivore deterrents in some algae, likely due to trade-offs in the productions of defense metabolites with differing ecological functions. Together, these studies provide strong evidence that chemically mediated competitive and consumer-prey interactions play principal roles in coral reef degradation and recovery, and should provide resource managers with vital information needed for effective management of these ecologically and economically important but threatened ecosystems.

Thesis (MScAgric (Agronomy))--Stellenbosch University, 2008. / The development of herbicide resistance in weeds is one of the major factors hampering profitable crop production worldwide. In South Africa resistance to herbicides in weeds is also a big problem, in particular in the Winter Rainfall Region of the country. The lack of sufficient different mode of action herbicide groups that can be rotated in these conditions necessitate the implementation of integrated weed management programmes to curb the development and spread of herbicide resistance. One of the alternative physical weed management strategies is to maximize crop competition to the weed population. One aspect of such a strategy is to plant crop cultivars that have greater interference potential than others.

Nesta tese, organizada em capítulos, são apresentados diferentes estudos sobre processos que afetam a história de vida, o potencial de dispersão, as preferências do assentamento larval e o recrutamento efetivo do coral invasor Tubastraea coccinea. No primeiro capítulo, demonstra-se que plânulas produzidas por T. coccinea são capazes de sofrer metamorfose e agregar-se em grupos de até oito pólipos ainda na coluna d´água, sem que ocorra previamente assentamento larval. Nesta seção, foi avaliada também a sobrevivência de propágulos para testar se diferentes níveis de agregação possibilitam uma extensão do período planctônico e, portanto, um aumento do potencial de dispersão. Os resultados obtidos mostram que pólipos natantes sobrevivem mais que plânulas, provavelmente por serem capazes de se alimentar e, assim, suprir a alta demanda energética associada à natação e à procura de um substrato favorável para o assentamento. Grupos de dois ou mais pólipos sobrevivem mais que pólipos solitários. Porém, a mortalidade não diferiu entre agrupamentos pequenos (2-3 pólipos) e grandes (4-8 pólipos), o que sugere que existe um limite para o tamanho ótimo dessas colônias pelágicas. A maioria dos grupos de pólipos que se mantém nadando na coluna d´água (80%) permanece viva após seis meses, o que sugere que a capacidade de sofrer metamorfose no ambiente pelágico e formar colônias de pólipos planctônicos é uma característica chave na história de vida da espécie, incrementando o potencial de dispersão, a conectividade entre populações e a capacidade de colonização de novos ambientes. No segundo capítulo, é caracterizada primeiramente a distribuição espacial de colônias adultas e pólipos fundadores do coral T. coccinea sobre substratos rochosos com diferentes orientações. Para isso, foi avaliada a consistência desses padrões para duas escalas espaciais, uma pequena (de dezenas de metros) e outra intermediária (de unidades de quilômetros). Posteriormente, estudaram-se as preferências durante o assentamento larval e os padrões de recrutamento sobre superfícies com diferentes orientações através de experimentos de campo e laboratório. O objetivo principal desta secção foi determinar se os padrões de distribuição de recrutas e colônias adultas podem ser explicados por processos que ocorrem durante etapas larvais ou pós-larvais iniciais. Os resultados indicam que tanto a flutuabilidade das larvas quanto o comportamento ativo de natação, não relacionado com condições de luminosidade, são fatores que determinam claramente o padrão de distribuição do coral. Como parte desse padrão, observou-se que a densidade de recrutas juvenis é maior em substratos orientados para baixo, sendo quase nula nas superfícies orientadas para cima. Com exceção da quase ausência de indivíduos sobre áreas orientadas para cima, existem diferenças substanciais entre a distribuição de recrutas e adultos para as demais orientações, principalmente para superfícies verticais. Essas diferenças podem estar relacionadas com o escoamento costeiro, o qual é intenso na região de estudo e pode causar depósito excessivo de sedimentos sobre superfícies positivas, inibindo o desenvolvimento de colônias deste coral. Por outro lado, interações competitivas com outras espécies de corais azooxantelados poderiam ser a causa da diminuição da abundância de T. coccinea em substratos negativos. No terceiro e último capítulo desta tese avaliou-se o potencial de interação de Tubastraea coccinea com espécies representativas de uma comunidade bentônica do litoral norte do Estado de São Paulo, recentemente invadida. Amostragens no campo, visando estimar a densidade de recrutas juvenis de T. coccinea sobre diferentes tipos de manchas formadas por organismos incrustantes, foram usadas para obter uma primeira inferência sobre o potencial de facilitação, ou inibição, do recrutamento. Os cnidários Carijoa riisei, Parazoanthus sp e Obelia dichotoma afetaram negativamente o recrutamento do coral sol, enquanto que algas incrustantes coralináceas facilitaram o recrutamento e podem facilitar a colonização do coral. O papel da mediação alelopática foi avaliado a partir de experimentos de laboratório, nos quais foram medidas diferentes componentes do assentamento larval em função da exposição das larvas a extratos brutos de várias espécies acompanhantes. Os testes mostraram a ocorrência geral de alelopatias negativas, as quais em alguns casos levaram apenas à inibição do assentamento, mas em outros à rápida mortalidade das larvas, sugerindo a ação de metabólitos tóxicos. Adicionalmente, foram realizados estudos comparativos de comunidades com a presença, ou ausência, do coral invasor, considerando fatores relevantes para a sua ocorrência, como a orientação do substrato. As comunidades invadidas por T. coccinea tendem a apresentar maior riqueza e equitatividade. A invasão no local de estudo é relativamente recente, pelo que os resultados encontrados devem estar mais relacionados a diferenças na susceptibilidade dessas comunidades à invasão, do que a eventuais efeitos das colônias do coral sol desenvolvidas nas mesmas. Se for assim, o estabelecimento do coral sol no litoral do Estado de São Paulo poderá implicar em uma perda significativa da diversidade biológica de substratos consolidados rasos. Os dados obtidos nesse estudo, abordando aspectos relevantes da vida pelágica e bentônica de T. coccinea, constituem um acervo de informação que poderá subsidiar planos de controle e monitoramento da espécie invasora, contribuindo ao estabelecimento de critérios de gestão de áreas de conservação. / In this thesis, organized in chapters, we present studies on the processes affecting the life history, dispersal potential, larval settlement preferences, and effective recruitment of the invasive coral Tubastraea coccinea. In the first chapter we report, for the first time, that larvae produced by the sun coral may metamorphose and aggregate in the water column without previous settling on any substrate. We then compared the survival of different types of propagules to test whether alternative development pathways allow longer pelagic life, and thus higher dispersal potential. Our results show that single-polyps live longer than planulae, probably because they can feed and sustain minimal metabolic activity. Clustered polyps live longer than solitary polyps, as expected if per capita polyp mortality rates are similar between these categories. However, mortality rate did not differ between small (2-3 polyps) and large (4-8 polyps) clusters, indicating that, in overall conditions, polyp performance attain a maximum at intermediate aggregations, setting an eventual adaptive upper limit to cluster size. In our experiment, over 80% of swimming colonies remained alive for a period exceeding six months. We conclude that pelagic metamorphosis and cluster formation may be an important mechanism allowing connectivity among populations and the colonization of new habitats. Moreover, founder individuals resulting from pelagic polyp aggregation can generate greater genetic variability in benthic developing colonies. In the second chapter, we first characterized spatial distributions of adult colonies and single-polyp recruits of the invasive azooxanthellate coral Tubastraea coccinea over substrates of different orientation, and evaluated their consistency at both small (several tens of meters) and intermediate (a few km) spatial scales. We then assessed, through field and laboratory experiments, larval preferences and relative settlement and recruitment rates on surfaces with different orientations to determine whether processes taking place during the larval and early post-larval stages could help explain the distribution patterns of recruits and adult colonies. Results suggest that larval passive buoyancy and active larval behavior, unrelated to light conditions, determine a clear settlement distribution pattern, in which the density of settlers is highest at undersurfaces and almost nil at upward facing horizontal substrates. Except for an almost absence of settlers, recruits and adult individuals on upward facing horizontal habitat, there is substantial mismatch between the distribution of settlers and that of recruits and adult colonies. The latter were also common in vertical substrates in the field. We speculate that coastal runoff at the study area and subsequent sedimentation may inhibit coral development on flat upward facing habitat, and that competitive interference and pre-emptive interactions with native azooxanthellate corals could constrain abundance of T. coccinea in underface horizontal habitat. In the third and final chapter of this thesis, the interactions of representative species of the benthic community of the north shore of São Paulo state with the exotic coral, recently introduced at the study site, were evaluated. Field surveys of the density of juvenile recruits of T. coccinea on different types of patches formed by fouling organisms allowed us to detect the effect of competitor species that inhibit coral recruitment. The Cnidarians Carijoa riisei, Parazoanthus sp and Obelia dichotoma negatively affected the juvenile recruitment of the sun coral. Conversely, it was observed that the recruitment of this scleractinian is considerably greater on several other species (chiefly fouling coralline algae), which act as facilitators and promote coral colonization. The role of allelopathic interactions mediating larval settlement was investigated through a settlement experiment using extracts of different companion species. Results indicated a general negative allelopathic response, either limited to settlement inhibition or leading acute mortality, the latter suggesting toxic effects. We also conducted comparative studies of communities with and without the invasive coral, considering other factors that could influence coral occurrence, such as substratum orientation. Species richness and evenness were general higher in invaded communities. The sun coral invasion is relatively recent in the study area and, therefore, these results are probably related to differences in the susceptibility of these assemblages to be invaded, rather than eventual effects of established colonies on them. If this is so, the establishment of T. coccinea in São Paulo state may lead to a significant loss of biological diversity in shallow rocky habitat. Our data give a full account of relevant aspects of the pelagic and benthic life of this invasive coral, and constitute a collection with no precedence that may subsidize plans of control and monitoring of this invasive species, contributing to the establishment of criteria used in the management of conservation areas.

A agricultura moderna exige que as operações de manejo das plantas daninhas sejam economicamente viáveis, e principalmente seguras em termos de minimização da contaminação ambiental. A preocupação sobre a utilização intensiva de herbicidas sintéticos tem sido debatida constantemente, de tal forma que pesquisas têm sido desenvolvidas estrategicamente para a descoberta de novas moléculas herbicidas, baseadas em produtos naturais, para aplicação direta como agente de controle ou utilização indireta como aleloquímico. O solo é habitado por uma grande variedade de microrganismos, sendo que a maioria deles não foi estudada e identificada até o momento, conseqüentemente muitas pesquisas ainda podem ser desenvolvidas com o objetivo de explorar metabólitos secundários produzidos por estes microrganismos. Sendo assim, foi desenvolvida a presente pesquisa com o objetivo de testar e desenvolver uma fase inicial na seleção e descoberta de microrganismos do solo (actinomicetos) com potencial de produção de compostos fitoinibitórios. O método geral de seleção constituiu-se na coleta de amostras de solo de 0-20 cm de profundidade, a partir de áreas com diferentes sistemas de manejo e/ou vegetação. Estas amostras de solo foram então submetidas ao isolamento de actinomicetos (10 g de solo de cada amostra) através da diluição em série e plaqueamento em meio seletivo. Foram isoladas e cultivadas em meio líquido glicerina-caseína 103 colônias, sendo que, a solução de metabólitos acelular foi obtida por centrifugação e filtragem. A partir das soluções contendo os metabólitos foi conduzido um teste de germinação (screening primário) através de bioensaios de laboratório, utilizando como plantas teste pepino (Cucumis sativa) e sorgo (Sorghum bicolor). Com o objetivo de verificar a concentração do meio de cultura que exerceria o mínimo de efeito na germinação e crescimento/desenvolvimento das plântulas, foi realizado um teste de germinação com o meio de cultura sem os metabólitos microbiológicos, sendo avaliado através de análise de regressão dos resultados obtidos. O screening secundário foi realizado em condições de câmara-de-crescimento e consistiu na aplicação do meio de cultura acelular em condições de pré e pós-emergência das plantas de pepino e sorgo. Os screenings primário e secundário resultaram na seleção de sete microrganismos produtores de composto fitoinibitórios, estes utilizados para condução do experimento em condições de casa-de-vegetação, sendo aplicadas as soluções de metabólitos em condições de pré e pós-emergência das plantas de pepino, sorgo, picão-preto (Bidens pilosa) e capim colchão (Digitaria ciliaris). A conclusão principal desta pesquisa foi de que o método para seleção de isolados de actinomicetos, com potencial de produção de fitotoxicinas é adequado, e pode ser utilizado em um programa de descoberta de novos compostos com potencial herbicida, no entanto, os resultados obtidos não permitiram isolar actinomicetos com suficiente potencial fitoinibitório, para ser utilizado de forma direta em um programa de manejo de plantas daninhas na agricultura. / The modern agriculture requires that the weed management practices are economically feasible, and mainly safe for the minimization of the environmental contamination. The concern on the intensive use of synthetic herbicides has been debated constantly, in such way that researches have been developed strategically for the discovery of new herbicides molecules, based on natural products, either for direct application as control agent, or for indirect use as allelochemical. The soil is colonized by a great variety of microorganisms, however most of them were not studied and identified at the moment, consequently many researches still can be done, with the objective of exploring secondary metabolites produced by these microorganisms. Therefore, it was developed this research with the objective of testing and developing a initial process in the selection and discovery of soil microorganisms (actinomycetes) with potential of producing phytoinhibitory compounds. The general method used in the research consisted of soil sampling at 0-20 cm depth, from areas that had been cultivated with different cropping systems and/or vegetation. These soil samples were submitted to actinomycets isolation (10 g of soil per sample) through series dilution in selective medium. It was isolated and cultivated in liquid casein-glycerin medium 103 colonies, being the no cellular metabolite solution obtained by centrifugation and filtration. From the solutions containing the metabolites it was conducted a germination test (primary screening) through a laboratory bioassay with test plants of cucumber (Cucumis sativus) and sorghum (Sorghum bicolor). Objectifying to verify each of the cultivation medium concentrations that would cause the minimum effect on germination and growth/development of seedlings, it was also conducted a germination test with medium without the microbial metabolites, being evaluated through regression analysis results. The secondary screening was done in the growth chamber conditions, and consisted of application of no cellular medium in pre and post emergence conditions of the plants of sorghum and cucumber. The primary and secondary screening resulted in the selection of seven microorganisms producers of phytoinhibitory compounds, these used to conduct an experiment in the greenhouse, being sprayed the metabolic solutions in pre and post emergence conditions of cucumber, sorghum, Bidens pilosa and Digitaria ciliaris. The main conclusion of the research was that the method used for actinomycets selection and isolation, with potential of phytotoxins production is adequate and can be used in a new compounds discovery program with potential herbicide effects; however the results obtained did not allow isolating actinomycets with enough phytoinhibitory potential to be directly used in a program of weed management in agriculture.