Influence of temperature on the retention, absorption and translocation of fomesafen and imazamox in Euphorbia heterophylla.

Climate change will be an additional issue to the challenge to manage herbicide resistant weeds. This work investigated the impact of three temperature regimes (10/5, 20/15 and 30/25 °C) on the efficacy, foliar retention, absorption and translocation of fomesafen, protoporphyrinogen oxidase (PPO) inhibitor, and imazamox, acetolactate synthase (ALS) inhibitor, between two Euphorbia heterophylla populations, one susceptible (S) and one multiple PPO and ALS resistant (R). The R population went from 5 (fomesafen) and 12 (imazamox) times more resistant than the S population at 10/5 °C to more than 100 times to both herbicides at 20/15 and 30/25 °C. Leaf retention of fomesafen was not affected by temperature; however, imazamox retention was less at 10/5 and 20/15 °C than at 30/25 °C, and the R population always retained less imazamox than the S population. 14C-fomesafen absorption was similar between populations, but lower amounts were absorbed at 10/5 °C regardless of the evaluation time. Recovered 14C-imazamox rates decreased in both populations as the evaluation time increased, ranging from 82 to 92% at 6 h after treatment (HAT), and from 47 to 76% at 48 HAT, depending on the temperature regime. The 14C-imazamox losses were greater from 24 HAT in R plants grown at 30/25 °C and in all temperature regimes at 48 HAT. Although both populations translocated large amounts of imazamox, the S population distributed it in the rest of the plant (33%) and roots (15%), while the R population kept it mainly on the treated leaf (24%) or lost ~20% more herbicide than S population at 48 HAT, indicating the need for further studies on root exudation between these populations. Low temperatures reduced resistance levels to fomesafen and imazamox in E. heterophylla, suggesting that temperature influences the expression of the mechanisms that govern this multiple resistance.

Superação de dormência em sementes de três espécies de Ipomoea / Overcoming dormancy seed in three Ipomoea species

O conhecimento do método de superação de dormência mais adequado para cada espécie auxilia na identificação do tipo de dormência, bem como na definição de estratégias de manejo que permitam o controle mais eficaz. As espécies do gênero Ipomoea encontram-se amplamente distribuídas nos estados brasileiros, as mais comumente encontradas em lavouras de soja na região Sudoeste do Paraná são I. purpurea, I. indivisa e I. grandifolia. Assim, neste trabalho, o objetivo foi selecionar métodos eficazes de superação da dormência nas espécies Ipomoea indivisa, I. grandifolia e I. purpurea e determinar como eles influenciam na cinética da germinação das sementes dessas espécies. Os tratamentos utilizados foram água quente, escarificação mecânica, escarificação mecânica + resfriamento, escarificação química e testemunha. Na avaliação do efeito dos tratamentos, determinou-se a porcentagem de germinação, tempo médio, índice de velocidade e frequência relativa de germinação. A escarificação com ácido sulfúrico incrementou a germinação das sementes de I. indivisa e I. purpurea e o índice de velocidade de germinação àquelas de I. purpurea. O tratamento com água quente foi o mais eficiente em promover a germinação das sementes de I. grandifolia, e em reduzir o tempo médio de germinação das sementes de I. grandifolia e I. purpurea, de forma que, nos tratamentos de superação de dormência, há sincronização do processo de germinação.

The knowledge of the method of overcoming dormancy for each species helps in identification of dormancy type and to outline the most appropriate management strategies for effective control measures. The species of the genus Ipomoea are widely distributed in the Brazilian states, the most commonly found in soybean crops in the Southwest region of Paraná are I. purpurea, I. indivisa and I. grandifolia. In this research the aim was select methods of overcoming seed dormancy for species Ipomoea indivisa, I. grandifolia and I. purpurea, and determine how these methods influence the kinetic germination of these species. The treatments consisted of hot water, chiseling, chiseling plus cooling, chemical scarification and control. In evaluating the effect of the treatments were determined the germination percentage, mean germination time, germination speed index and relative frequency of germination. Scarification with sulfuric acid increased the germination of I. indivisa and I. purpurea seeds and the germination speed index of I. purpurea seeds. The hot water treatment was more effective in promoting germination of I. grandifolia seeds, and reduce the average time of germination of I. grandifolia and I. purpurea seeds, so that in treatments for overcoming dormancy there are synchronization of the germination process.