Hellen Martins da Silveira

Aspectos fisiológicos da mandioca após a aplicação dos herbicidas fluazifop-p-butil e fomesafen

Physiological responses of cassava to application of the herbicides fluazifop-p-butil and fomesafen Acredita-se que alguns herbicidas possam influenciar a eficiencia do uso da agua, pelo efeito negativo direto sobre fotossintese, transpiracao e condutância estomatica ou, indiretamente, pela reducao da taxa metabolica da planta. Diante disso, objetivou-se, neste trabalho, avaliar a influencia dos herbicidas fluazifop-p-butil e fomesafen, isolados e em mistura, sobre as caracteristic as associadas ao uso da agua, por cultivares de mandioca, visando a selecionar aqueles mais tolerantes aos referidos herbicidas. Realizou-se experimento, em casa de vegetacao no delineamento de blocos casualizados, com quatro repeticoes. Adotou-se arranjo fatorial em esquema 5x7, constituido pela combinacao de cinco cultivares de mandioca: Cacau-UFV, Platina, Coqueiro, Coimbra e IAC-12, com quatro doses da mistura comercial dos herbicidas fomesafen + fluazifop-p-butil (0,5; 0,75; 1,0 e 1,5 L ha -1 ), alem da dose comercial recomendada de cada principio ativo isolado e uma testemunha sem herbicida. As caracteristicas avaliadas foram: condutância estomatica (gs), taxa de transpiracao ( E) e eficiencia do uso da agua ( EUA). De maneira geral, a E, gs e EUA foram afetadas pela aplicacao da mistura dos herbicidas. Os cultivares de mandioca apresentam diferentes niveis de sensibi- lidade ao fluazifop-p-butil + fomesafen, sendo que o cultivar Platina e o mais tolerante a aplicacao da mistura. O fluazifop-p-butil mostrou-se seletivo para a cultura e o fomasafen causou efeitos negativos na fisiologia da mandioca. Palavras-chave: transpiracao, condutância estomatica, controle quimico, Manihot esculenta.

From tolerance to resistance: mechanisms governing the differential response to glyphosate in Chloris barbata

BACKGROUND Susceptibility and the mechanism (s) governing tolerance/resistance to glyphosate were characterized in two putative-glyphosate-resistant Chloris barbata populations (R1 and R2), collected in Persian lime orchards from Colima State, Mexico, comparing them with one non-treated population (referred to as S). RESULTS Glyphosate doses required to reduce fresh weight or cause mortality by 50% were 4.2-6.4 times higher in resistant populations than in the S population. The S population accumulated 4.3 and 5.2 times more shikimate than the R2 and R1 populations, respectively. There were no differences in 14 C-glyphosate uptake between R and S populations, but the R plants translocated at least 12% less herbicide to the rest of plant and roots 96 h after treatment. Insignificant amounts of glyphosate were metabolized to aminomethyl phosphonate and glyoxylate in both R and S plants. The 5-enolpyruvylshikimate-3-phosphate synthase gene of the R populations contained the Pro106-Ser mutation, giving them a resistance 12 (R2) and 14.7 (R1) times greater at target-site level compared with the S population. CONCLUSION The Pro106-Ser mutation governs the resistance to glyphosate of the R1 and R2 C barbata populations, but the impaired translocation could contribute to the resistance. These results confirm the first case of glyphosate resistance evolved in this species.

Características fisiológicas de cultivares de mandioca após aplicação do mesotrione

Neste trabalho, avaliou-se a taxa fotossintetica e a eficiencia do uso da agua em cultivares de mandioca (Coimbra, Platina, IAC-12, Coqueiro e Cacau-UFV), pulverizados com cinco doses do mesotrione (0, 72, 108, 144 e 216 g ha-1). Aos 45 dias apos aplicacao do herbicida, foram avaliados o CO2 consumido, o carbono interno, a taxa fotossintetica, a condutância estomatica de vapores de agua, a taxa de transpiracao, a temperatura da folha e a eficiencia do uso da agua. O cultivar Platina mostrou-se menos afetado pelo mesotrione. Apenas neste cultivar as doses aplicadas de 144 e 216 g ha-1 nao alteraram a taxa fotossintetica das plantas. A temperatura da folha dos cultivares de mandioca tambem nao foi alterada pelo herbicida; entretanto, observou-se reducao na eficiencia de uso da agua para o cultivar Coqueiro.

Stacked traits conferring multiple resistance to imazamox and glufosinate in soft wheat: Imazamox and glufosinate resistance in wheat

BACKGROUND Conventional crossing of soft wheat cultivars resistant to imazamox and glufosinate resulted in two (Rados and Helter) lines resistant to both herbicides. Stacked traits conferring this dual herbicide resistance in these lines, compared with a susceptible (S) cultivar, were characterized. RESULTS Rados and Helter lines were ∼ 18-fold more resistant (R) to glufosinate, and between 15.1 and 19.8-fold more resistant to imazamox than the S cultivar. Resistance to glufosinate and imazamox decreased up to 12% and 50%, respectively, when the herbicides were applied sequentially. The basal activities of the acetolactate and glutamine synthases were similar between R and S plants. Rados and Helter lines were 11.7- and 17.7-fold more resistant to imazamox than the S cultivar, due to the Ser653-Asn mutation in their imi-ALS genes. R lines, susceptible to glufosinate at the target site level, showed lower ammonia accumulation evidencing the activity of the phosphinothricin acetyl transferase. Absorption and translocation patterns for 14 C-imazamox and 14 C-glufosinate were similar between R and S cultivars and so do not contribute to resistance. CONCLUSION Stacked traits conferring dual herbicide resistance to the lines Rados and Helter come from the resistant parents. These R lines are potential tools for weed management in wheat production, mainly via herbicide rotation.

Mycorrhizal Association and Microbial Activity of Soil Cultivated with Cassava After Application of Mesotrione and Fluazifop-p-Butyl

Soil is a very heterogeneous environment that allows the establishment of wide range of microorganisms populations, whose balance is affected by biotic and abiotic factors. This study has aimed to assess the effect of doses of mesotrione and fluazifop-p-butyl herbicides and two assessment periods on microbial activity and biomass of soil cultivated with cassava Cacau-UFV cultivar, besides the root colonization by arbuscular mycorrhizal fungi. Two trials were conducted in a protected environment where was realized post-emergence application of mesotrione in the doses of 72, 108, 144 and 216 g ha-1 and fluazifop-p-butyl in the doses of 100, 150, 200 and 300 g ha-1, besides a control without application. Soil samples were collected for determination of soil respiratory rate (RR), microbial biomass carbon (MBC), metabolic quotient (qCO2), and colonization of roots by arbuscular mycorrhizal fungi at the 30 and 60 days after applications (DAA) of the herbicides. Fluazifop-p-butyl increased the RR, MBC and the percentage of cassava roots colonized by mycorrhizal fungi in the assessment performed at 60 DAA. The larger effects of mesotrione on soil microbial indicators were up to 30 DAA, being the changes minimized at 60 DAA. It is concluded that the herbicides alter the soil microbial indicators, with effects dependent of the product, of dose applied and also of the period of assessment.