Aldo Merotto

Competição por recursos do solo entre ervas daninhas e culturas

Engenheiro Agronomo, Aluno do Programa de Pos-graduacao em Fitotecnia, UFRGS.RESUMOA competicao entre plantas e um processo impor-tante tanto em comunidades naturais quanto em ambientes agri-colas. O impacto vegetativo das ervas daninhas em agroecossis-temas e considerado competicao se houver reducao no montantede recursos disponiveis para a cultura e, neste contexto, o desen-volvimento das raizes influencia na competitividade e na sobrevi-vencia das plantas. Uma planta que apresenta sistema radicalbem desenvolvido em extensao e em comprimento tem sido asso-ciada com aumento na habilidade competitiva devido ao maiorpotencial de absorcao de agua e nutrientes. A competicao entreos sistemas radicais das ervas daninhas e das culturas interferetanto na disponibilidade de agua e nutrientes quanto nas intera-coes por luz, na parte aerea. Entretanto, somente ocorrera com-peticao quando a zona de deplecao das raizes da cultura e daservas daninhas se sobreporem. A intensidade de competicao entreraizes das ervas e da cultura pelos recursos abaixo da superficiedo solo dependera do tipo e da disponibilidade dos recursos e daespecie vegetal e de sua capacidade em desenvolver sistemaradical extenso, com diâmetro reduzido e com ampla area super-ficial.Palavras-chave: interferencia, agua, nutrientes, habilidadecompetitiva, sistema radical.SUMMARYCompetition between plants is an important processas much in natural communities as in agricultural environments.The impact of weeds in agroecossystems is refered as competitionif there is a reduction in the amount of resources available for thecrop and, in this context, root development influences plantcompetitivity and survival. A plant which presents a welldeveloped root system in extension and in length has beenassociated with increased competition hability due to a greaterabsorption capacity of water and nutrients. Competition betweenroot systems of weeds and crops interferes in water and nutrientsavailability, as well as in interactions for light in the aerialsystem. However, competition will only occur when depletionzone of crop and weed roots has surpassed themselves. Intensityof competition between roots of weeds and crops by undergroundresources will depend on type and availability of resource, and onplant species, and capacity to develop an extensive root system,with a reduced diameter and a high surface area.Key words: interference, water, nutrients, competitive hability,root system.

Cross-Resistance to Herbicides of Five ALS-Inhibiting Groups and Sequencing of the ALS Gene in Cyperus difformis L.

Resistance to ALS-inhibiting herbicides in Cyperus difformis has evolved rapidly in many rice areas worldwide. This study identified the mechanism of resistance, assessed cross-resistance patterns to all five chemical groups of ALS-inhibiting herbicides in four C. difformis biotypes, and attempted to sequence the ALS gene. Whole-plant and ALS enzyme activity dose-response assays indicated that the WA biotype was resistant to all ALS-inhibiting herbicides evaluated. The IR biotype was resistant to bensulfuron-methyl, orthosulfamuron, imazethapyr, and propoxycarbazone-sodium and less resistant to bispyribac-sodium and halosulfuron-methyl, and susceptible to penoxsulam. ALS enzyme activity assays indicated that resistance is due to an altered target site yet mutations previously found to endow target-site resistance in weeds were not detected in the sequences obtained. The inability to detect resistance mutations in C. difformis may result from the presence of additional ALS genes, which were not amplified by the primers used. This study reports the first ALS gene sequence from Cyperus difformis. Certain ALS-inhibiting herbicides can still be used to control some resistant C. difformis biotypes. However, because cross-resistance to all five classes of ALS-inhibitors was detected in other resistant biotypes, these herbicides should only be used within an integrated weed management program designed to delay the evolution of herbicide resistance.

Resistência de amendoim-bravo aos herbicidas inibidores da enzima acetolactato sintase

ABSTRACTWild poinsettia resistance to acetolactate synthase inhibitor herbicides The continuous weed control withherbicides of only one site of action selectsbiotypes resistant to these herbicides. Fourexperiments were conducted in greenhouse ofUFRGS, Brazil, to confirm the occurence of wildpoinsettia ( Euphorbia heterophylla ) biotypesresistance to herbicides inhibitors of acetholactatesynthase (ALS), and to determine whether therewas cross resistance to herbicides with other siteof action. A biotype from Passo Fundo - RS wasresistant to imazethapyr, whereas a biotype fromPorto Alegre - RS was susceptible to thiscompound. The biotype from Passo Fundo wasresistant to the following ALS-inhibitors:imazapyr, imazaquin, imazethapyr, chlorimuron,nicosulfuron, metsulfuron e flumetsulan. Thisbiotype was not resistant to herbicides fromthe following modes of action: EPSPsinhibitors, auxin agonists, fotossystems I and IIinhibitors, and PROTOX inhibitors. Theconfirmation of resistance to ALS inhibitorsin biotypes from Nao-me-Toque, Passo Fundoand Rio Pardo suggests a wide spread of wild

Período crítico para controle de Brachiaria plantaginea em função de épocas de semeadura da soja após dessecação da cobertura vegetal

ABSTRACT - This study was conducted to evaluate the impact of soybean seeding time aftercover crop desiccation on the control of alexandergrass ( Brachiaria plantaginea ) and to quantifythe influence of weed control timing on soybean yield. The experimental design used was asplit-plot, in randomized blocks, with four replications. The treatments consisted of soybeanseeding times (1 and 10 days after desiccant application – DAD), arranged as main plots, andtimes of Alexandergrass control (11, 17, 24, 31, 38, and 45 days after soybean emergence –DAE – for seeding performed 1 DAD, and 8, 15, 22, 29, 36, and 42 DAE for seeding performed10 DAD), arranged as subplots. For each soybean seeding time, a check with Alexandergrasschemical control was included during all crop season. Grass weed control was attained throughapplication of the herbicide clethodim at 120 g ha -1 . Levels of Alexandergrass control, at soybeanharvesting time, varied between 90 and 99%, considering all treatments. There were reductions

Bioensaios para diagnóstico da resistência aos herbicidas imidazolinonas em arroz

Red rice is the most troublesome weed in rice paddy fields. Herbicide resistant rice cultivars allow red rice control through the herbicides imidazolinones. However, imidazolinone resistant red rice biotypes have occurred in several rice paddy fields. The aim of this study was to develop rapid methods to identify imidazolinone resistant rice plants at different stages of rice plant development. The rice cultivars IRGA 422 CL, SATOR CL and PUITA INTA CL were used as well-known resistant cultivars, and IRGA 417 as a well-known susceptible check. The seed, seedling, and tiller bioassays discriminated resistant and susceptible plants efficiently, being considered fast methods for herbicide resistance diagnosis in rice. The discriminatory concentrations between resistant and susceptible plants to the herbicides imazethapyr + imazapic for the seed, seedling and tiller bioassays were 0.01 mM, 4 mM and 3 mM, respectively. The use of these bioassays allows the identification of resistant individuals even during the rice crop season, and can be used to indicate the need of alternative measures to maintain the sustainability of red rice control in fields cultivated with herbicide resistance cultivars.

Evolutionary and social consequences of introgression of nontransgenic herbicide resistance from rice to weedy rice in Brazil

Several studies have expressed concerns about the effects of gene flow from transgenic herbicide‐resistant crops to their wild relatives, but no major problems have been observed. This review describes a case study in which what has been feared in transgenics regarding gene flow has actually changed biodiversity and peoples lives. Nontransgenic imidazolinone‐resistant rice (IMI‐rice) cultivars increased the rice grain yield by 50% in southern Brazil. This increase was beneficial for life quality of the farmers and also improved the regional economy. However, weedy rice resistant to imidazolinone herbicides started to evolve three years after the first use of IMI‐rice cultivars. Population genetic studies indicate that the herbicide‐resistant weedy rice was mainly originated from gene flow from resistant cultivars and distributed by seed migration. The problems related with herbicide‐resistant weedy rice increased the production costs of rice that forced farmers to sell or rent their land. Gene flow from cultivated rice to weedy rice has proven to be a large agricultural, economic, and social constraint in the use of herbicide‐resistant technologies in rice. This problem must be taken into account for the development of new transgenic or nontransgenic rice technologies.

Período anterior ao dano no rendimento econômico (PADRE): nova abordagem sobre os períodos de interferência entre plantas daninhas e cultivadas

This work hypothesizes economic aspects, such as weed control cost and grain price, should be used as criteria to determine weed interference periods in the crops to support weed control decisions. The weedy period based on such parameters was termed weedy period prior to economic loss (WEEPPEL). A mathematical model was developed based on the abovementioned economic aspects, model parameters were searched in the literature, and simulations performed. The simulation results allowed confirming the hypothesis that weed control cost and grain price are good criteria to determine weed interference periods. WEEPPEL decreases with increasing crop grain prices, or decreasing weed control costs, or increasing crop potential yield, suggesting that under these conditions very early weed control is economically justifiable. This research points some limitations found in the scientific literature, and suggests alternatives for determination of WEEPPEL and other periods.

Recurrent evolution of heat-responsiveness in Brassicaceae COPIA elements

BackgroundThe mobilization of transposable elements (TEs) is suppressed by host genome defense mechanisms. Recent studies showed that the cis-regulatory region of Arabidopsis thaliana COPIA78/ONSEN retrotransposons contains heat-responsive elements (HREs), which cause their activation during heat stress. However, it remains unknown whether this is a common and potentially conserved trait and how it has evolved.ResultsWe show that ONSEN, COPIA37, TERESTRA, and ROMANIAT5 are the major families of heat-responsive TEs in A. lyrata and A. thaliana. Heat-responsiveness of COPIA families is correlated with the presence of putative high affinity heat shock factor binding HREs within their long terminal repeats in seven Brassicaceae species. The strong HRE of ONSEN is conserved over millions of years and has evolved by duplication of a proto-HRE sequence, which was already present early in the evolution of the Brassicaceae. However, HREs of most families are species-specific, and in Boechera stricta, the ONSEN HRE accumulated mutations and lost heat-responsiveness.ConclusionsGain of HREs does not always provide an ultimate selective advantage for TEs, but may increase the probability of their long-term survival during the co-evolution of hosts and genomic parasites.

Distribution and Cross-Resistance Patterns of ALS-Inhibiting Herbicide Resistance in Smallflower Umbrella Sedge (Cyperus difformis)

Abstract Basic factors contributing to the rapid evolution and broad distribution of acetolactate synthase (ALS)-inhibiting herbicide resistance in smallflower umbrella sedge L. have not yet been investigated. The objectives of this study were to examine patterns of cross-resistance to ALS herbicides and genetic diversity within and among smallflower umbrella sedge populations in California rice fields to provide insight into the processes contributing to resistance spread. Twelve different patterns of herbicide cross-resistance were found across the 56 populations sampled. The frequency of populations with at least one resistant individual in the North, Central and South Sacramento Valley, and the San Joaquin Valley were 76, 86, 67, and 50%, respectively. Analysis of the genetic diversity of 29 populations using 73 sequence-related amplified polymorphism molecular markers revealed little genetic diversity within populations, with estimates of Neis gene diversity index, h, ranging from 0 to 0.049, and Shannons information index (I) ranging from 0 to 0.079. Hierarchical analyses of molecular variance indicated that the majority of genetic variation was partitioned among populations, rather than within populations or among regional groups. No isolation by distance was evident. Unweighted pair group method with arithmetic averages analysis indicated that population clustering was not region specific. The results suggest that resistance to ALS-inhibiting herbicides in smallflower umbrella sedge populations from California rice fields appears to have evolved independently multiple times rather than spread from a single population where resistance originated. Consequently, prevention and management of smallflower umbrella sedge in California rice fields should emphasize in-field strategies that focus on decreasing the selection pressure caused by ALS-inhibiting herbicides. Nomenclature: Bensulfuron-methyl; bispyribac-sodium; halosulfuron-methyl; imazethapyr; penoxsulam; propoxycarbazone-sodium; smallflower umbrella sedge, Cyperus difformis L.; rice, Oryza sativa L.

Ecologically sustainable weed management: How do we get from proof‐of‐concept to adoption?

Weed management is a critically important activity on both agricultural and non-agricultural lands, but it is faced with a daunting set of challenges: environmental damage caused by control practices, weed resistance to herbicides, accelerated rates of weed dispersal through global trade, and greater weed impacts due to changes in climate and land use. Broad-scale use of new approaches is needed if weed management is to be successful in the coming era. We examine three approaches likely to prove useful for addressing current and future challenges from weeds: diversifying weed management strategies with multiple complementary tactics, developing crop genotypes for enhanced weed suppression, and tailoring management strategies to better accommodate variability in weed spatial distributions. In all three cases, proof-of-concept has long been demonstrated and considerable scientific innovations have been made, but uptake by farmers and land managers has been extremely limited. Impediments to employing these and other ecologically based approaches include inadequate or inappropriate government policy instruments, a lack of market mechanisms, and a paucity of social infrastructure with which to influence learning, decision-making, and actions by farmers and land managers. We offer examples of how these impediments are being addressed in different parts of the world, but note that there is no clear formula for determining which sets of policies, market mechanisms, and educational activities will be effective in various locations. Implementing new approaches for weed management will require multidisciplinary teams comprised of scientists, engineers, economists, sociologists, educators, farmers, land managers, industry personnel, policy makers, and others willing to focus on weeds within whole farming systems and land management units.