High seed production and dispersal capacity and glyphosate resistance are among the main factors that have made hairy fleabane (Conyza bonariensis) one of the most important and dispersed weeds in the world. Herbicide-resistant weeds populations may have fitness cost due to molecular, physiological, and biochemical changes. This study aimed to evaluate the physiological quality of seeds of Conyza spp. and determine whether glyphosate resistance causes fitness costs for resistant biotypes. Seeds from six hairy fleabane biotypes, three glyphosate-resistant and three -sensitive, with a resistance factor average of 11.7 were studied. Among the studied biotypes, five were identified as C. bonariensis and one as C. blakei. Seed analyses were performed in a completely randomized design with ten replications of 100 seeds each (1,000 seeds per biotype). The analyzed seeds were originated from second-generation self-pollinating plants with known segregation rate. The mean results indicate that, in relation to sglyphosate-sensitive biotypes of C. bonariensis, seeds from -resistant biotypes showed a 16% reduction in vigor and 13% in germination, a 44% increase in the number of empty seeds and approximately five times more viable dormant seeds. The lower physiological quality of glyphosate-resistant hairy fleabane seeds regarding to -sensitive indicates that resistance affect the seed’s physiology and causes a fitness costs. It implies a reduction of invasive potential and persistence in the environment of resistant biotypes. Therefore, in the absence of glyphosate as a selective factor, the frequency of resistant biotypes tends to decrease and increase the predominancy of glyphosate-sensitivre biotypes. However, the highest number of viable dormant seeds of resistant biotypes supplies the soil seed bank. All biotypes of C. bonariensis showed higher physiological quality of seeds when compared to C. blakei, indicating that the first species is more adaptably evolved for survival in agricultural and disturbed areas.
Glyphosate-resistant hairy fleabane [Conyza bonariensis (L.) Cronq.] is one of the most important weeds in the world. Among the factors that make this weed species widely distributed in the most diverse environments is the high seed production capacity and dispersal. Hairy fleabane plants not controlled by herbicide application regrowth and overcome crop canopy, use environmental resources, interfere with crops, and complete their life cycle by producing thousands of seeds and replenishing the seed bank. Management strategies that reduce production and viability of hairy fleabane seeds can be adopted within the integrated management to reduce the seed bank and prevent further infestations. In this way, experiments were carried out in a greenhouse and laboratory of seed analysis to evaluate the effect of glyphosate (1,480 g a.e. ha-1) on the production and viability of glyphosate-resistant hairy fleabane seeds when applied at the vegetative and reproductive stages. Seed production was reduced by 68.4 and 100% when glyphosate was applied on hairy fleabane plants at the vegetative and early reproductive stages, respectively, regarding to the control. The viability of hairy fleabane seeds was not influenced by treatments at the evaluated stages. However, glyphosate treatment reduced the hairy fleabane seed production when applied at the vegetative stage . Hairy fleabane seed production is not feasible when glyphosate is applied at the early reproductive stage.
It is essential that tests for evaluating seed vigour be faster and increasingly efficient to enable precise differentiation among batches. In this way, it is possible to evaluate the quality of seeds based on the anaerobic metabolism of cells when exposed to environments lacking oxygen. Thus, the objective of this study was to establish methodology for evaluating the viability and vigour of 3 lots of cowpea (Amendoim cultivar) seeds using the ethanol test. The treatments were carried out in a completely randomized design with four replications. For the test, 25 seeds were stored in hermetically sealed PET (Polyethylene the Ethylene) bottles containing 40 ml of distilled water and subjected to 3 soaking times in distilled water (6, 24, and 48 h) at a controlled temperature of 40°C in a germinator. The amount of ethanol produced was quantified with the aid of an adapted breath analyser. The results are expressed as mg L-1; these data were then compared with data for the following: germination; the first germination count; the total length, root length and shoot length of the seedling; dry weight of the seedling; emergence in the field; emergence speed index; and electrical conductivity. The experimental design was completely randomised, and the data were subjected to analysis of variance and correlation analysis. The results were compared using the Tukey test at 5% probability. Measurement of ethanol after 6 or 48 h of soaking at 40°C was effective for determining the viability and vigour of cowpea seeds. As ethanol test results have high correlation with germination and vigour test results, this approach is a viable alternative for analysts and seed producers.
The incidence of volunteer Enlist TM soybean in the post-emergence of crops in succession, such as wheat, requires changes in chemical control. Thus, the objective of the work is to evaluate the efficiency of different post-emergence herbicides in the control of volunteer Enlist TM soybean and wild radish and their selectivity to wheat. For this, four experiments were conducted in 2017 and 2018 in field and greenhouse. The treatments tested were pyroxsulam, saflufenacil, pyroxsulam + saflufenacil, pyroxsulam + bentazon, pyroxsulam + metribuzin, saflufenacil + bentazon, and saflufenacil + metribuzin in 2017, and triclopyr, saflufenacil, MCPA, quinclorac, dicamba, pyroxsulam + metribuzin, metribuzin + metsulfuron, pyroxsulam + bentazon and bentazon + metsulfuron in 2018. The variables were the control of wild radish and volunteer Enlist TM soybean phytotoxicity to wheat crop, yield components, and yield total. The association of the herbicides pyroxsulam and saflufenacil is efficient in the management of volunteer soybean Enlist TM , showing selectivity to wheat. The isolated application of dicamba and the associations of pyroxsulam with metribuzin and metribuzin with metsulfuron represent alternatives for selective management of volunteer Enlist TM soybean in wheat, in addition to efficiently controlling wild radish in post-emergence.
Vigor tests are very important to obtain additional information to the standard germination test and can assist in decision-making. The aim of this work was to evaluate accelerated aging test methodologies for the determination of vigor in tobacco seeds. For the study, ten seed lots of tobacco were used. The initial quality of the tobacco seeds was determined through the germination test, first count of germination, germination speed index, seedling emergence at 7, 14 and 21 days after sowing, emergence speed index and the accelerated aging with water performed as proposed by the Association of Official Seed Analysts. After the determination of seed initial quality, the accelerated aging test was studied in the following methods: accelerated aging with water, saturated saline solution (40g NaCl 100mL-1 water) and unsaturated saline solution (11g NaCl 100mL-1 water), submitted to the temperatures of 45 and 41°C, for the exposure periods of 24, 48 and 72 hours. According to the results obtained, the accelerated aging test with water conducted under a temperature of 45°C combined with a 24-hour exposure period is shown as adequate for evaluating the vigor of tobacco seeds.
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