RESUMO

Herbicide resistant (HR) weeds are of major concern in modern agriculture. This situation is exacerbated by the massive adoption of herbicide-based technologies along with the overuse of a few active ingredients to control weeds over vast areas year after year. Also, many other anthropological, biological, and environmental factors have defined a higher rate of herbicide resistance evolution in numerous weed species around the world. This review focuses on two central points: 1) how these factors have affected the resistance evolution process; and 2) which cultural practices and new approaches would help to achieve an effective integrated weed management. We claim that global climate change is an unnoticed factor that may be acting on the selection of HR weeds, especially those evolving into non-target-site resistance mechanisms. And we present several new tools -such as Gene Drive and RNAi technologies- that may be adopted to cope with herbicide resistance spread, as well as discuss their potential application at field level. This is the first review that integrates agronomic and molecular knowledge of herbicide resistance. It covers not only the genetic basis of the most relevant resistance mechanisms but also the strengths and weaknesses of traditional and forthcoming agricultural practices.

Assuntos

RESUMO

Continuous use of glyphosate in citrus groves in the Gulf of Mexico region has selected for resistant Parthenium hysterophorus L. populations. In this study, the target-site and non-target-site resistance mechanisms were characterized in three putative glyphosate-resistant (GR) P. hysterophorus populations, collected in citrus groves from Acateno, Puebla (GR1 and GR2) and Martínez de la Torre, Veracruz (GR3), and compared with a susceptible population (GS). Based on plant mortality, the GR populations were 9.2-17.3 times more resistant to glyphosate than the GS population. The low shikimate accumulation in the GR population confirmed this resistance. Based on plant mortality and shikimate accumulation, the GR3 population showed intermediate resistance to glyphosate. The GR populations absorbed 15-28% less 14C-glyphosate than the GS population (78.7% absorbed from the applied) and retained 48.7-70.7% of 14C-glyphosate in the treated leaf, while the GS population translocated ~68% of absorbed herbicide to shoots and roots. The GR3 population showed the lowest translocation and absorption rates, but was found to be susceptible at the target site level. The 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene sequence of the GR1 and GR2 populations showed the Pro106-Ser mutation, conferring 19- and 25-times more resistance in comparison to the GS population, respectively. Reduced absorption and impaired translocation conferred glyphosate resistance on the GR3 population, and contributed partially to the resistance of the GR1 and GR2 populations. Additionally, the Pro-106-Ser mutation increased the glyphosate resistance of the last two P. hysterophorus populations.

Assuntos

RESUMO

The Chloris genus is a C4 photosynthetic species mainly distributed in tropical and subtropical regions. Populations of three Chloris species occurring in citrus orchards from central Cuba, under long history glyphosate-based weed management, were studied for glyphosate-resistant status by characterizing their herbicide resistance/tolerance mechanisms. Morphological and molecular analyses allowed these species to be identified as C. ciliata Sw., Chloris elata Desv., and Chloris barbata Sw. Based on the glyphosate rate that causes 50% mortality of the treated plants, glyphosate resistance (R) was confirmed only in C. elata, The R population was 6.1-fold more resistant compared to the susceptible (S) population. In addition, R plants of C. elata accumulated 4.6-fold less shikimate after glyphosate application than S plants. Meanwhile, populations of C. barbata and C. ciliata with or without glyphosate application histories showed similar LD50 values and shikimic acid accumulation rates, demonstrating that resistance to glyphosate have not evolved in these species. Plants of R and S populations of C. elata differed in 14C-glyphosate absorption and translocation. The R population exhibited 27.3-fold greater 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) activity than the S population due to a target site mutation corresponding to a Pro-106-Ser substitution found in the EPSPS gene. These reports show the innate tolerance to glyphosate of C. barbata and C. ciliata, and confirm the resistance of C. elata to this herbicide, showing that both non-target site and target-site mechanisms are involved in its resistance to glyphosate. This is the first case of herbicide resistance in Cuba.