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In Brazil, horseweed is one of the most important weeds because of the resistance to herbicides and high competitive for the crops. A large of losses were reported in major crops such as soybeans, wheat and corn, where the use a no-tillage system and the herbicide resistance promote better establishment. A correct understanding of the way temperature influences germination enables the prediction of the regions with the highest potential for colonization by this weed and thus facilitates its control. The objective of this study; therefore, was to discern the ways temperature affected the germination, viability and longevity of horseweed seeds. Testing was done at 10, 20 and 30°C, while evaluation occurred on days 0, 15, 30, 45 and 60. Seeds were packed in a nylon mesh bag (5x5cm), with 10g of upland soil (Yellow Red Argissolo, sandy loam texture), placed in transparent plastic boxes at 0 to 0.5cm soil depth, at the temperatures specified. Percentage of remaining seeds, first and second germination counts, abnormal seedlings, and dead, dormant, viable and non-viable seeds, were assessed. Horseweed seeds achieve secondary dormancy at 10, 20 and 30°C, while their quality and the longevity showed damage at 20 and 30°C temperatures. [ABSTRACT FROM AUTHOR]

Radish is an important weed that causes yield reduction in winter crops in southern Brazil. The control chemical of radish is an important and essential step to prevent damage on crops. However the intensive use of ALS-inhibitors herbicides favors the selection resistant biotypes. The selection can influence the adaptive traits of biotypes with physiological changes and growth variables and plant reproduction. The objective of the study was compare the fitness costs of susceptible and resistant radish biotypes to ALS-inhibitors herbicides. The experiment was conducted in greenhouse using completely randomized design with five replications. The treatments were arranged in factorial arrangement corresponding to susceptible and resistant biotypes (B1 and B4) and nine sampling times (14, 28, 42, 56, 70, 84, 98, 112 and 126 days after emergency), respectively. The variables evaluated were plant height, shoot dry matter, root dry matter, total dry matter, leaf area, growth rate, relative growth rate, leaf area ratio, number of siliques and seeds produced per plant. The results showed that the resistant biotype (B4) had no fitness costs when compared to the susceptible biotype (B1). [ABSTRACT FROM AUTHOR]

Cyperus difformis L. is a weed that occurs in flooded rice, which has presented difficulty in controlling due to the resistance to ALS inhibiting herbicides. The objectives of this research were to investigate kinetic characteristics of ALS enzyme from C. difformis biotypes and to determine the biochemical bases of resistance from the species to pyrazosulfuron-ethyl herbicide. For that, experiments were conducted at the BIOAGRO/UFV laboratory. The method used was based on the methodology used by CAREY et al. (1997) and adapted by VARGAS et al. (1999), with some modifications. It was evaluated substratum concentration (pyruvate) that provides initial velocity equal to half the speed reaction (KM) and maximum velocity of reaction (Vmáx), as well the activity of the ALS enzyme in the presence of the inhibitor (pyrazosulfuronethyl). According to the results, it is possible to observe that C. difformis resistance to pyrazosulfuron-ethyl is due to the insensibility of the ALS enzyme to the herbicide, however without penalty to KM and Vmáx kinetic parameters of the ALS enzyme. [ABSTRACT FROM AUTHOR]