Marcelo Nicolai

Crescimento e competitividade de biótipos de capim-colchão resistente e suscetível aos herbicidas inibidores da acetil coenzima A carboxilase

Abstract€–€The€objective of this work was to compare the growth and the competitive ability of two crabgrass( Digitaria ciliaris ) biotypes, one resistant (R) and other susceptible (S) to the acetyl coenzyme A carboxylaseinhibiting herbicides. Biotypes growth was determined by collecting the plant dry mass at 14, 21, 25, 28, 34, 42, 49,57, 65, 72, 78, 86, 101, 111, and 118€days after emergence (DAE). Data of dry mass were adjusted to a logisticmodel, and were also used to calculate the absolute growth rate. Five experiments were installed to evaluate theintraspecific and interspecific competitive ability, using the substitutive method. The biotypes R and S werecompared between themselves and each one of them with the soybean crop seeded in the same day or sevendays after the seeding of the weeds. Plant proportions between species or biotypes used were: 5:0; 4:1; 3:2; 2:3;1:4, and 0:5. The biotypes presented similar dry mass accumulation, absolute growth rate and interspecificcompetition, and the reduction of soybean mass was similar in the presence of R and S crabgrass biotypes, whichsuggests that R and S crabgrass biotypes have the same ecological adaptability.Index term:

Resistance and differential susceptibility of Bidens pilosa and B. subalternans biotypes to ALS-inhibiting herbicides

The frequent application of herbicides in agricultural areas may select resistant biotypes in weed populations, whose biological characteristics influence the speed and patterns of resistance. This research aims to charactere, simultaneously, resistance patterns and differential susceptibility of Bidens pilosa and B. subalternans biotypes to ALS-inhibiting herbicides of the imidazolinone and sulfonylurea chemical groups. Six hairy beggarticks biotypes, four suspected resistant and two known susceptible, were treated with eight rates of chlorimuron-ethyl or imazethapyr, in greenhouse conditions. Percent control and percent fresh weight of the plants were evaluated at 28 days after the application. B. subalternans is less susceptible to ALS-inhibiting herbicides than B. pilosa; B. subalternans biotypes were more resistant than B. pilosa biotypes; there are B. pilosa and B. subalternans biotypes with cross resistance to the ALS-inhibiting herbicides of the sulfonylurea and imidazolinone groups; there are different patterns of cross resistance to the diverse groups of ALS-inhibiting herbicides.

Confirmation and mechanism of glyphosate resistance in tall windmill grass (Chloris elata) from Brazil.

BACKGROUND Overreliance on glyphosate as a single tool for weed management in agricultural systems in Brazil has selected glyphosate-resistant populations of tall windmill grass (Chloris elata Desv.). RESULTS Two C. elata populations, one glyphosate resistant (GR) and one glyphosate susceptible (GS), were studied in detail for a dose-response experiment and for resistance mechanism. The dose causing 50% reduction in dry weight was 620 g a.e. ha(-1) for GR and 114 g ha(-1) for GS, resulting in an R/S ratio of 5.4. GS had significantly higher maximum (14) C-glyphosate absorption into the treated leaf (51.3%) than GR (39.5%), a difference of 11.8% in maximum absorption. GR also retained more (14) C-glyphosate in the treated leaf (74%) than GS (51%), and GR translocated less glyphosate (27%) to other plant parts (stems, roots and root exudation) than GS (36%). There were no mutations at the Pro106 codon in the gene encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). There was no difference in EPSPS genomic copy number or EPSPS transcription between GS and GR populations. CONCLUSION Based on these data, reduced glyphosate absorption and increased glyphosate retention in the treated leaf contribute to glyphosate resistance in this C. elata population from Brazil.

Crescimento e desenvolvimento da planta daninha capim-camalote

Itchgrass (Rottboelia exaltata L.f.) is a weed that has presented fast dissemination in sugar-cane fields in Brazil, causing significant yield losses to the crop. Therefore, this research had the objective of evaluating the growth, vegetative development and reproductive capacity of the species, as a mechanism of improving the management to be adopted. The experiment was conducted in the greenhouse of ESALQ/USP, Piracicaba, State of Sao Paulo, Brazil, during the months of July to October 2004; when 14 periodic evaluations of growth were done, for determination of: fresh and dry weight (total, shoot and roots), leaf area and phenology. After flowering, the number of racemes of 16 plants, and the number of seeds of 100 racemes were evaluated. It was observed a fast initial growth of the plants, once the flowering occurred 49 days after seeding. About the end of the cycle, plants showed values near than 120 g, 25 g and 1600 cm² of total fresh weight, total dry weight and leaf area, respectively. On average, plants emitted a total of 163 racemes with 12 seeds each, that corresponds to more than 2,000 seeds per plant. These results showed the high growth capacity and reproductive hability of R. exaltata, explaining the reasons that make this weed a new potential problem for Brazilian agriculture.

Multiple Resistance to Glyphosate and Acetolactate Synthase Inhibitors in Palmer Amaranth (Amaranthus palmeri) Identified in Brazil

Palmer amaranth is native to the United States, but was discovered in 2015 in Brazil. Palmer amaranth populations in Brazil were very difficult to control using glyphosate, which resulted in many changes to standard weed management practices. A genotyping assay was used to confirm that the population detected in Mato Grosso State, Brazil, was correctly identified as Palmer amaranth and that it was not tall waterhemp. Greenhouse dose—response curves and shikimate accumulation assays showed that the Brazilian population was highly resistant to glyphosate, with an LD50 value (3,982 g glyphosate ha-1) more than twice the typical use rates and very little shikimate accumulation at 1 mM glyphosate concentrations in a leaf-disk assay. The Brazilian population was also resistant to sulfonylurea and imidazolinone acetolactate synthase (ALS) inhibitor herbicides. The resistance mechanisms in the Brazilian population were identified as increased EPSPS gene copy number for glyphosate resistance (between 50- and 179-fold relative EPSPS gene copy number increase) and two different alleles for target-site mutations in the ALS gene (W574L and S653N). These results confirm the introduction of Palmer amaranth to Brazil using a genetic marker for species identification, as well as resistance to glyphosate and ALS inhibitors. Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats; tall waterhemp, Amaranthus tuberculatus (Moq.) Sauer.

Crescimento inicial de Merremia cissoides, Neonotonia wightii e Stizolobium aterrimum

This work aimed to evaluate the initial growth of three species of weed considered as emerging problems for sugarcane crop: Neonotonia wightii, Stizolobium aterrimum, and Merremia cissoides. The experiment was arranged in a completely randomized design, with seven treatments and four repetitions for each species studied. Seven growth evaluations (treatments) were carried out every 15 days, totaling a 105 day-cycle, followed by the analysis of the variables, such as leaf area (Af) given in (cm2 per plant). The sampled material was dried in an oven, with the dry mass (g per plant) of the roots (Mr), the shoot (Ma) and total (Mt) being measured. The biomass accumulation observed shows the high ability of S. aterrimum to produce biomass. At the end of the experiment, stabilization of the dry mass of the shoot (Ma) was observed for the three species, followed by the variable total dry mass (Mt) also showing stabilization at the end of the experiment. S. aterrimum presented the highest initial growth rate and total dry mass accumulation, besides the highest leaf area (Af). N. wightii presented slow initial growth, while M. cissoides showed a significant accumulation of total dry mass (Mt), compared with the other species.

DETECTION OF GLYPHOSATE-RESISTANT PALMER AMARANTH (Amaranthus palmeri) IN AGRICULTURAL AREAS OF MATO GROSSO, BRAZIL

The recent introduction of Palmer amaranth (Amaranthus palmeri) in Brazilian agricultural areas may promote several changes on weed management, especially in no-till systems and in glyphosate-resistant crops, since glyphosate-resistant biotypes of A. palmerihave been frequently selected in other countries. Therefore, this research was developed in order to evaluate the glyphosate susceptibility of a Palmer amaranth biotype recently identified in the State of Mato Grosso, Brazil. For this purpose, glyphosate susceptibility of three Amaranthusbiotypes was compared: A.hybridus var. patulus, collected in the State of Rio Grande do Sul - Brazil; A.hybridus var. patulus, collected in the State of Sao Paulo - Brazil; and A.palmeri, collected in the State of Mato Grosso - Brazil. Dose-response curves were generated for all biotypes, considering eight rates of glyphosate and six replicates. All the experiments were repeated twice. Both A.hybridus biotypes were satisfactorily controlled by glyphosate, demanding rates equal to or lower than 541.15 g a.e. ha-1 for 80% control (LD80). The A.palmeri biotype was not controlled by glyphosate in any of the assessments and required rates greater than 4,500 g a.e. ha-1 to reach LD80, which are economically and environmentally unacceptable. Comparison of the Brazilian A.palmeri biotype to the A. hybridus biotypes, as well as, to the results available in scientific international literature, led to the conclusion that the Brazilian Palmer amaranth biotype is resistant to glyphosate.

Aplicação conjunta de herbicidas e inseticidas na cultura do milho

The selectivity of post-emergence applied herbicides in the corn crop (Zea mays L.) when mixed in tank with insecticides used to control Spodoptera frugiperda (J.E. Smith) was verified. The experiment was carried out in off-season maize, seeded in February 2004, using the hybrid AGN 2012, in conventional system. The experimental design was randomized blocks with split-plots scheme, on double check model, four replicates and 15 treatments. The treatments were constituted by the combination of three levels of the factor herbicide (g ha-1): mesotrione (120) + atrazine (1500) + Assist 0,5%, nicosulfuron (20) + atrazine (1500) and hand-weeded checks; with five levels of the factor insecticide: lambdacyhalothrin (10), chlorpyrifos CE (240), chlorpyrifos EC (225), lambdacyhalothrin + thiamethoxam (12,5 + 5,5) and checks without insecticide application. Moderate phytotoxic symptoms were observed to mesotrione treatments and severe symptoms were observed to nicosulfuron caused by the interaction of these herbicides with the insecticide chlorpyrifos (formulations CE and EC). No yield losses were recorded as due to phytotoxicity.

Frequency and Dispersal of Glyphosate-Resistant Sourgrass (Digitaria insularis) Populations across Brazilian Agricultural Production Areas

The rapid spread of glyphosate-resistant sourgrass populations generates concern in the agricultural production sector in Brazil. Nonetheless, there is not much information related to the frequency and dispersion of sourgrass throughout recent years. We investigated the frequency and dispersion of glyphosate-resistant sourgrass populations in Brazilian agricultural regions as part of a larger-scale weed resistance monitoring study. A discriminatory rate of 960 g ae ha−1 of glyphosate was used on plants at the 2- to 3-tiller stage, originating from 2,593 populations of sourgrass sampled in 329 counties in 14 Brazilian states between 2012 and 2015. The dispersion of sourgrass populations originated in western Paraná State, next to the Paraguay border, where the first resistance case was reported. Its dispersion to the central region of Brazil, mainly in soybean-producing areas, is most likely a consequence of agricultural equipment movement and wind-mediated dispersal. Glyphosate-resistant sourgrass populations were found in every geographical region across all Brazilian states tested. These data highlight the importance of an appropriate weed resistance monitoring program to track the evolution and dispersion of resistance to mitigate these issues by focusing efforts regionally and raising awareness among stakeholders in each region. Nomenclature: glyphosate, sourgrass, Digitaria insularis (L.) Mez ex Ekman, soybean, Glycine max (L.) Merr.

Atividade residual de seis herbicidas aplicados ao solo em época seca

Este trabalho foi desenvolvido em campo, com o objetivo de avaliar a atividade residual de herbicidas recomendados para a cultura da cana-de-acucar, quando aplicados ao solo na epoca seca. Os tratamentos foram organizados em esquema de parcelas subdivididas, em que, no âmbito das parcelas, foram aplicados seis herbicidas e, no âmbito das subparcelas, foram considerados tres periodos de permanencia dos produtos no solo (130 dias, 70 dias e testemunha, sem aplicacao). Os tratamentos herbicidas foram (g ha-1): amicarbazone a 1260; clomazone a 1250; hexazinone a 450; imazapic a 147; isoxaflutole a 187,5; e sulfentrazone a 900. Alem da infestacao natural de plantas daninhas, para avaliacao da atividade residual dos produtos, semeou-se pepino na area, considerado como bioindicador. A mesma molecula herbicida teve avaliacao diferenciada em razao da especie bioindicadora considerada. Os herbicidas amicarbazone, hexazinone, isoxaflutole e sulfentrazone tem propriedades positivas para aplicacao ao solo em epoca seca, tais como elevada solubilidade, baixo Kow e baixa fotodegradacao. A aplicacao de imazapic em pre-emergencia tem eficacia consistente em epoca seca, controlando adequadamente o pepino e a comunidade natural de plantas daninhas. O herbicida clomazone nao controlou adequadamente o pepino e a comunidade natural de plantas daninhas.