Ives Clayton Gomes dos Reis Goulart

Impacto da temperatura, irradiância e profundidade das sementes na emergência e germinação de Conyza bonariensis e Conyza canadensis resistentes ao glyphosate

Intense glyphosate use either in orchards or specially no-tilled glyphosate-resistant soybeans, has selected resistant biotypes of both Conyza bonariensis and C. canadensis. Studies of the species biology could provide insight for integrated weed management. A research program was designed to evaluate how seed germination of both species was affected by the following factors: biotype, substrate composition, soil depth, temperature and light. A factorial arrangement of the treatments was established for the first experiment, where factor A consisted of biotypes (two from each species); factor B was substrate composition (soil, sand, soil: sand); and factor C was substrate depths (0, 0.5, 1, 2, 5 cm). The second experiment included the first factor; plus factor B as temperature (constant 20, 25, or 30 oC, and alternating 20/30 oC), and factor C as light conditions (light, dark). In a third experiment, factors consisted of species and temperature (10, 15, 20, 25, 30 oC). Seedling emergence or seed germination were assessed at 12 days after treatments. All biotypes from both species had similar seedling emergence in relation to soil depth. Increasing soil depth reduced seedling emergence. Sandy substrate facilitated seed germination at 0.5 and 1.0 cm depth. The species are positive photoblastic. Optimum temperature for seed germination for both species was 20 oC, but C. canadensis germinates better at temperatures below the optimum and C. bonariensis germinates better at temperatures above the optimum.

Arroz-vermelho (Oryza sativa) resistente aos herbicidas imidazolinonas

O desenvolvimento de genotipos comerciais de arroz resistentes a herbicidas do grupo quimico das imidazolinonas proporcionou uma ferramenta eficaz para o controle seletivo do arroz-vermelho (Oryza sativa) em cultivo de arroz irrigado. Contudo, o uso continuo dessa tecnologia pode favorecer o desenvolvimento de populacoes de arroz-vermelho resistentes aos herbicidas utilizados para o seu controle. Objetivou-se com este trabalho avaliar a ocorrencia de populacoes de arroz-vermelho resistentes aos herbicidas imidazolinonas, por meio de curvas de dose-resposta, atraves do fator de resistencia (FR). Populacoes de arroz-vermelho nao controladas (escapes) advindas de lavouras de arroz cultivado no sistema Clearfield® no Estado do Rio Grande do Sul foram avaliadas em casa de vegetacao na sua sensibilidade ao herbicida Only (imazethapyr + imazapic - 75 + 25 g L-1). O resultado de resposta as doses do herbicida confirma a resistencia em 56% das populacoes de arroz-vermelho, as quais podem ser agrupadas em baixo (FR = 5,2) e alto (FR = 11,6) niveis de resistencia as imidazolinonas.

Controle de capim-annoni-2 (Eragrostis plana) com herbicidas pré-emergentes em associação com diferentes métodos de manejo do campo nativo

The weed South African lovegrass (Eragrostis plana) is one of the most important problems of rangelands and native pastures in southern Brazil. Several factors have limited its management in these areas. The aim of this study was to evaluate South African lovegrass control using pre-emergent herbicides safe to the native pasture by applying soil position selectivity. Two experiments were evaluated in this study. The first was conducted in a greenhouse, and South African lovegrass seeds were sown in plastic pots. The herbicides evaluated were alachlor, ametryne, ametryne + tebuthiuron, atrazine, clomazone, diuron, flumioxazin, imazaquin, mesotrione, metribuzin, oxadiazon, S-metolachlor, sulfentrazone, terbuthylazine and trifluralin. All products successfully controlled lovegrass. The second experiment was conducted on native pastures highly infested with South African lovegrass, arranged in a split-split-plot design. In the main plots, the following vegetation management methods were allocated before herbicide application: prescribed burning, and high and low cutting; in the split-plots, the herbicide doses: 75 and 100% of the label rate; and in the split-split-plots, the herbicide doses: atrazine, flumioxazin, mesotrione, S-metolachlor, sulfentrazone, trifluralin and the untreated-check control. None of the herbicides tested effectively controlled lovegrass under field conditions, likely due to the high density of South African lovegrass perennial plants. However, the herbicide effects were more pronounced when associated with prescribed burning and low cutting.

Distribution of Weedy Red Rice (Oryza sativa) Resistant to Imidazolinone Herbicides and its Relationship to Rice Cultivars and Wild Oryza Species

Abstract Several weedy red rice populations have evolved resistance to imidazolinone herbicides worldwide. The understanding of the factors related to the herbicide resistance in weedy red rice is important to prevent its occurrence in new areas where imidazolinone-resistant rice cultivars are being used, and to manage the new rice cultivars resistant to herbicides with modes of action other than the acetolactate synthase (ALS)-inhibitors that are being developed. The objectives of this study were to analyze the relationship of weedy red rice populations from southern Brazil with rice cultivars and wild Oryza species and to evaluate the occurrence of introgression from rice cultivars and seed migration as the origin of resistance to imidazolinone herbicides in weedy rice. The study was based on 27 weedy red rice populations, seven rice cultivars, and four wild Oryza species that were genotyped with 24 simple sequence repeats and three ALS-specific single-nucleotide polymorphism markers. A large proportion of the genetic variation of the weedy red rice populations was found within (74%) rather than among populations (26%). The weedy red rice populations were more closely related to the newer rice cultivars that are imidazolinone-resistant than to the older cultivars. The South American native Oryza glumaepatula and the other wild Oryza species—Oryza rufipogon, Oryza longistaminata, and Oryza glaberrima—clustered separately from weedy red rice populations, indicating a low likelihood of introgression among weedy red rice and these wild species. Seed migration was an important factor in the genetic structure of the evaluated weedy red rice populations, although gene flow by pollen from resistant cultivars was the principal reason for the spread of herbicide resistance. Nomenclature: Weedy red rice, Oryza sativa L. ORYSA; rice, Oryza sativa L. ORYSA; brownbeard rice, Oryza rufipogon Griffiths; longstamen rice, Oryza longistaminata A. Chev. & Roehr.; and African rice, Oryza glaberrima Steud.

Resistance to ACCase inhibitors in Eleusine indica from Brazil involves a target site mutation

Eleusine indica (goosegrass) is a diploid grass weed which has developed resistance to ACCase inhibitors during the last ten years due to the intensive and frequent use of sethoxydim to control grass weeds in soybean crops in Brazil. Plant dose-response assays confirmed the resistant behaviour of one biotype obtaining high resistance factor values: 143 (fenoxaprop), 126 (haloxyfop), 84 (sethoxydim) to 58 (fluazifop). ACCase in vitro assays indicated a target site resistance as the main cause of reduced susceptibility to ACCase inhibitors. PCR-generated fragments of the ACCase CT domain of the resistant and sensitive reference biotype were sequenced and compared. A point mutation was detected within the triplet of aspartate at the amino acid position 2078 (referred to EMBL accession no. AJ310767) and resulted in the triplet of glycine. These results constitute the first report on a target site mutation for a Brazilian herbicide resistant grass weed.

Reflectance indices as a diagnostic tool for weed control performed by multipurpose equipment in precision agriculture

Diversos equipamentos vem sendo desenvolvidos para utilizacoes especificas relacionadas a agricultura de precisao. No entanto, essa especificidade pode dificultar a implementacao da agricultura de precisao devido ao aumento da complexidade operacional e dos custos de producao. O uso de sensores de indices de vegetacao para o manejo de plantas daninhas em adicao a sua utilizacao mais comum - que e a fertilizacao de culturas - pode significar um uso multiplo desses sensores e resultar na maior otimizacao das ferramentas empregadas na agricultura de precisao. O objetivo deste trabalho foi avaliar a relacao de indices de reflectância das plantas daninhas obtidos com o sensor GreenseekerTM com parâmetros indicadores da competicao interespecifca, de forma a viabilizara adocao da agricultura de precisao para o controle de plantas daninhas. Foram realizados dois experimentos com as culturas de soja e milho, em que foi estabelecido um gradiente de infestacao de plantas daninhas atraves da utilizacao de herbicidas aplicados em pre e pos-emergencia. A quantificacao das plantas daninhas foi feita por meio do indice de vegetacao por diferenca normalizada (NDVI), e a relacao entre a reflectância no vermelho e no infravermelho proximo (Red/NIR) obtidos atraves do sensor GreenseekerTM, do controle visual, da massa seca da parte aerea e de fotografias digitais, que resultaram em informacoes sobre a proporcao de cobertura de area foliar das plantas daninhas e de palha. A cobertura vegetal obtida por fotografia digital foi altamente associada com o NDVI (r = 0,78) e Red/NIR (r = 0,66). A massa seca das plantas daninhas teve razoavel correlacao com o NDVI obtido em 1 m linear (r = 61). Os resultados indicaram que o sensor GreenseekerTM, originalmente utilizado para determinacao da fertilizacao em culturas, tambem pode ser empregado na obtencao dos indices de reflectância da vegetacao existente na entrelinha das culturas e utilizado para a tomada de decisao sobre a necessidade de controle de plantas daninhas.

Isolamento do gene ALS e investigação do mecanismo de resistência a herbicidas em Sagittaria montevidensis

California arrowhead (Sagittaria montevidensis Cham. & Schlecht) is an aquatic weed often found in rice paddy fields. Several biotypes of California arrowhead resistant to ALS-inhibiting herbicides were found in Brazil and in several rice fields worldwide. The objective of this study was to sequence the ALS gene of California arrowhead and to identify the occurrence of mutations related to target site insensitivity as the mechanism of herbicide resistance. The plant material consisted of seeds collected in rice paddy fields located in the state of Santa Catarina, Brazil. Nine pairs of primers were designed for the amplification of the domains C, A and D of the ALS gene. PCR reactions with four pairs of primers resulted in amplification of fragments with size close to expected, ranging from 360 to 393 nucleotides. These sequences showed high homology to the standard ALS gene Arabdopsis thaliana and rice having only three point mutations. One of these mutations was Pro 197 Phe that is related with herbicide resistance in several weeds. The sequences obtained indicated that the ALS gene evaluated was heterozygous. These results suggest the occurrence of insensitivity of the site of action as the mechanism of resistance to ALS-inhibitors herbicides in California arrowhead. The prevention and control of resistance to ALSinhibitors in California arrowhead should be based on the rotation of herbicides with different mechanisms of action.

Interações entre herbicidas e protetores para o controle de capim-annoni em pastagem natural

The botanical similarity of the invasive weed Eragrostis plana Nees (South African lovegrass) difficult its selective control in natural pastures. The aim of this study was to evaluate the effect of the association between herbicides and safeners on the control of E. plana and on the selectivity to the natural pastures. Two experiments were conducted at field conditions in area of natural grassland of the Biome Pampa where several herbicides were evaluated in pre and post-emergence. A third experiment was carried out in greenhouse evaluating the herbicides glufosinate-ammonium and imazethapyr and the species E. plana and Paspalum notatum. In both experiments, the herbicides were evaluated isolated and in association with the safeners anhydride naphtalic, dietholate and fluxofenim. The field experiments indicated that the evaluated safeners did not increase E. plana control and native grassland selectively. The greenhouse experiment indicated the occurrence of synergism on E. plana for the herbicide glufosinate-ammonium in mixture with the safeners anhydride naphtalic, dietholate and fluxofenim. The different results in the field and greenhouse experiments are related to the plant stage and density. The use of herbicides in association with safeners indicated a potentiality for selective control of E. plana when applied to plants in the early stages of development.