Abstract
ABSTRACT: 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.
Highlights
Weed management is one of the major challenges for agricultural sustainability (Bajwa et al, 2016)
Experiments were conducted with six selected biotypes originated from two regions with different edaphoclimatic conditions from the state of Rio Grande do Sul (RS), Brazil
The other biotypes evaluated in the present study showed no variation for glyphosate resistance or sensitivity in the evaluated generations (Table 2)
Summary
Weed management is one of the major challenges for agricultural sustainability (Bajwa et al, 2016). All biotypes of C. bonariensis showed higher physiological quality of seeds when compared to C. blakei, indicating that the first species is more High production and dispersion of Conyza spp. seeds have favored the selection and dissemination of glyphosate-resistant populations, being currently considered a cosmopolitan plant, i.e., they are present in most environments (Bajwa et al, 2016).
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