ABSTRACT Glyphosate is the herbicide most used worldwide. In cropping systems that rely on repeated applications of glyphosate or cultivate genetically modified soyabean crop, there are numerous cases of glyphosate resistant weeds, including Conyza bonariensis. Differences among competitive ability of Conyza spp. have been found. However, little information is available on the fitness costs related to glyphosate resistance in Conyza bonariensis. We evaluated growth, phenology, and seed viability of glyphosate-resistant (GR) and glyphosate-susceptible (GS) Conyza bonariensis from Brazil, in 2012 (fall/winter) and 2013 (spring/summer). When grown alone, in pots, C. bonariensis GR biotype developed more rapidly than the GS biotype, as evidenced by their earlier bolting, flowering, and seed set. In 2012, GR biotype showed 221.9 cm of plant height compared to 181.1 cm from GS, at the flowering time. In both years, the seed production per plant was superior for GR biotype, showing germination higher than 80% against 66.5% from the GS biotype. Thus, C. bonariensis GR biotype confirmed no fitness penalty also showing characteristics that allow us to infer in superior competitive with the absence of the herbicide. It is important to point out that the biotypes evaluated here have different genetic background and the differences between them may not be fully attributed to the resistance to glyphosate. However, the GR biotype can persist in the environment and outcompete with GS biotypes regardless of further glyphosate selection of pressure.

RESUMO O estabelecimento de culturas comerciais em sucessão a coberturas de inverno, com presença de densa camada de palha, proporciona significativa supressão de plantas daninhas. O objetivo deste trabalho foi avaliar o potencial supressor de coberturas de inverno sobre a incidência inicial de plantas daninhas na cultura do milho e seu efeito na produtividade da cultura semeada em sucessão. Um experimento foi conduzido no ano agrícola de 2012/2013, em área experimental da UFSM, Campus de Frederico Westphalen RS. Foram utilizadas quatro diferentes espécies de cobertura de inverno (aveia-preta, azevém, ervilhaca e nabo) semeadas em faixas, além da testemunha mantida em pousio. No pleno florescimento das coberturas foi realizada a quantificação da massa seca e a dessecação das mesmas. O milho foi semeado em sistema de plantio direto em sucessão às coberturas. Aos 15 dias após a emergência do milho foi avaliada a incidência e a massa seca de parte aérea das plantas daninhas presentes (0,25 m²). As principais espécies daninhas presentes na área foram: corriola (Ipomoea grandifolia), leiteiro (Euphorbia heterophylla), milhã (Digitaria sanguinalis), tiririca (Cyperus rotundus). De forma geral, a ervilhaca e o azevém foram as coberturas de inverno com maior capacidade supressora sobre as plantas daninhas avaliadas. O melhor desempenho produtivo do milho foi observado sobre a palhada de azévem, inferindo para uma relação de supressão de plantas daninhas e produtividade da cultura.

ABSTRACT The establishment of commercial crops in succession to winter cover crops that leaves a dense straw layer provides significantly suppression of weeds. The objective of this work was to evaluate the suppressive potential of winter cover crops on weed infestation in maize and its effect on the yield of the maize sown in succession. The experiment was conducted in the 2012/2013 crop season, in an area of the UFSM Campus Frederico Westphalen, State of Rio Grande do Sul. Four different species of cover crops (black oat, ryegrass, vetch and forage radish) were seeded and a fallow area was used as control. Evaluations to quantify the dry matter and chemical desiccation were performed at the full flowering period of the cover crops. Maize was sown in no-tillage system, in succession to the cover crops. The incidence and shoot dry matter of weeds (g 0.25 m-2) was evaluated 15 days after the maize emergence. The main weed species in the area were: morning-glory (Ipomoea grandifolia), wild poinsettia (Euphorbia heterophylla), large crabgrass (Digitaria sanguinalis) and purple nutsedge (Cyperus rotundus). In general, vetch and ryegrass were the winter cover crops that better suppressed the weeds evaluated. The best maize yield was found in the area previously covered with ryegrass, inferring a relation between the cover crop and suppression of weeds and crop yield.

Two experiments with 25 maize commercial hybrids were carried out in a direct sowing system in Southern Brazil in the harvests of 2009/2010 and 2010/2011. Quantitative descriptors were used with the objective of determining the genetic divergence and the relative contributions of traits among hybrids for extraction of inbred lines. This study was carried out in Oxisol soil using a randomized block design with four replicates. Data were subjected to combined analysis of variance, and based on the multivariate analyses, Tocher and average linkage (UPGMA) cluster analyses, based on generalized distance of Mahalanobis, to quantify divergence in addition to Singh criterion to validate trait with the most contribution. The multivariate methods were consistent with each other, and the weight of 100 grains was the trait that contributed most to the divergence and had similar behavior in grain yield between hybrids in both years. Furthermore, this descriptor representing significant genetic variability for crossings and lines extraction to hybridization between BM 3061, ATL 200 and P 30B39 Y.

O objetivo deste trabalho foi quantificar o teor de pigmentos fotossintéticos em biótipos de azevém (Lolium multiflorum) suscetíveis e resistentes ao glyphosate, por dois diferentes métodos, bem como, estabelecer uma correlação entre o índice de clorofila obtido pelo equipamento portátil e a metodologia clássica (clorofila extraível). Um experimento foi conduzido em casa de vegetação e laboratório da Universidade Federal de Santa Maria, Campus de Frederico Westphalen - RS - em esquema fatorial 2X4, em que o fator A equivaleu aos biótipos de azevém (resistente e suscetível a glyphosate) e o fator B a estádios de desenvolvimento das plantas (afilhamento, vegetativo I e II, e reprodutivo). O biótipo de azevém suscetível apresentou maiores teores de clorofila a, b, total e carotenoides, inferindo em um maior potencial competitivo frente ao biótipo resistente ao herbicida. A determinação do teor de clorofila pelo determinador portátil apresentou alta correlação com o método clássico de determinação de pigmentos fotossintéticos, podendo, assim, ser usado com precisão na avaliação deste, proporcionando economia de tempo bem como do uso de reagentes.

The aim of this study was to quantify the content of photosynthetic pigments in ryegrass (Lolium multiflorum) susceptible and resistant to glyphosate, by two different methods, as well as the correlation between chlorophyll content obtained by portable and classical methodology (chlorophyll extractable). An experiment was conducted in a greenhouse and laboratory of the Federal University of Santa Maria, Frederico Westphalen Campus - RS in a 2X4 factorial scheme, where factor A was equivalent to ryegrass (resistant and susceptible to glyphosate) and factor B to the developmental stages of plant (tillering, vegetative I and II and reproductive stage). The susceptible ryegrass biotype showed higher contents of chlorophyll a, b, and total carotenoids, inferring a superior competitive potential to the herbicide-resistant biotype. The determination of chlorophyll by portable determinato showed high correlation with the classical method of determination of photosynthetic pigments, and can thus be used to assess this accurately, saving time, as well as the use of reagents.

Além das avaliações entre genótipos, a utilização de técnicas multivariadas possibilita restringirem-se os erros, principalmente quanto à diversidade genética, podendo-se, assim, prever combinações com maior efeito heterótico, além da maior possibilidade de recuperação dos genótipos superiores. Objetivou-se, com este trabalho, avaliar a divergência genética entre 18 cultivares de soja, por meio de seis caracteres morfoagronômicos. Foi realizada a análise de trilha, para averiguar as contribuições direta e indireta desses caracteres sobre o rendimento de grãos. A distância generalizada de Mahalanobis fundamentou as técnicas de agrupamentos, tanto a de Tocher, bem como a do dendrograma por ligação simples. Observaram-se cinco grupos divergentes, sendo nove genótipos considerados similares entre si, enquanto os cultivares CEP 59, Netuno e Urano foram formadores de grupos isolados pelos dois métodos de agrupamento. Quanto à análise de trilha, observou-se que os caracteres indiretos pouco influenciaram o rendimento de grãos, tendo relação direta significativa com massa de 100 grãos, tendo-se destacado os cultivares Tertulha e CEP 53, com produtividade de grãos acima de 3,7 t ha-1.

In addition to the evaluations among genotypes, the use of multivariate techniques enables to restrict errors, mainly concerning genetic diversity, and therefore to predict combinations with greater heterotic effect, and the greater possibility of recovery of superior genotypes. The objective of this study was to evaluate the genetic divergence between 18 soybean cultivars based on six morphological characteristics. Path analysis was performed to verify the contribution of direct and indirect characters on grain yield. The Mahalanobis distance has founded techniques of both Tocher Method and dendrogram by Single Linkage. Five different groups were formed: with nine genotypes considered similar among them; while the cultivars CEP 59, Netuno and Urano formed groups isolated by the two grouping methods. The path analysis showed that the indirect characters had little influence on grain yield, with significant direct relationship with mass of 100 grain, and cultivars Tertulha and CEP 53 standing out with grain yields above 3.7 t.ha-1.