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.
Keywords:
herbicide resistance; integrated weed management; weed biology; soil seed bank; Conyza blakei
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Bars indicate the standard deviation of the mean. Different letters among biotypes indicate statistical difference by the Tukey’s test at p≤0.05. B01R, B11R, and B29R: glyphosate-resistant biotypes of Conyza sp. B17S, B20S, and B48S: glyphosate-sensitive biotypes of Conyza sp. F) The sum of two interfaces for each biotype indicate the total percentage of dormant seeds, and individual values indicate viable and not viable seeds. (A) First germination count (FGC - vigor) at 7 days after sowing (DAS); and (B) total germination, (C) abnormal seedlings, (D) dead seeds, (E) empty seeds, and (F) dormant seeds (viable and not viable by tetrazolium test) at 14 DAS.
Bars indicate the standard deviation of the mean. Different letters among biotypes (R and S) indicate statistical difference by the Tukey’s test at p≤0.05. B01R, B11R, and B29R: glyphosate-resistant biotypes of Conyza sp. B17S and B20S: glyphosate-sensitive biotypes of Conyza sp. F) The sum of two interfaces for each biotype indicate the total percentage of dormant seeds, and individual values indicate viable and not viable seeds. (A) First germination count (FGC - vigor) at 7 days after sowing (DAS); and (B) total germination, (C) abnormal seedlings, (D) dead seeds, (E) empty seeds, and (F) dormant seeds (viable and not viable by tetrazolium test) at 14 DAS. B48S was not considered.
