Glyphosate Resistance Affect the Physiological Quality of Conyza bonariensis seeds

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.

Taxonomic resolution of fleabane species (Conyza spp.) based on morphological and molecular markers and their dispersion across soybean-cropping macroregions and seasons in Brazil

“…sumatrensis by its leaves, stems, and involucres being glabrous or subglabrous (vs. moderately to largely pilose) (Figure 4). We did not find C. blakei and C. canadensis among the 314 plants from 20 accessions (fields) across Brazil, although they were reported in field crops in the country (Piasecki et al 2019;Vidal et al 2007). Conyza blakei differs from C. bonariensis and C. sumatrensis by its pinnatisect lower leaves (vs. linear or obovate) and narrow capitulescence (vs. moderately elongated) (Sancho 2014).…”

Stressful Conditions Affect Seed Quality in Glyphosate Resistant Conyza bonariensis (L.)

“…In addition, the GR 50 values of the S populations, regardless of the different geographic origins of each biotype, were similar. Piasecki et al [18] observed a similar phenomenon, with S populations of C. bonariensis collected in different regions of southern Brazil showing no differences in their GR 50 (also less than 100 g ae ha −1 ). The R biotypes, in turn, presented different GR 50 values, revealing different profiles of glyphosate resistance; however, the GR 80 values were below the field dose recommended by the manufacturer for this species (960 g ae ha −1 ), except for biotype R1 (GR 80 = 1.030 g ha −1 ).…”

“…At the vegetative level, there is no evidence for fitness cost in glyphosate-resistant Conyza species [5,26,28,37]; however, our results suggest that there may be a seed level fitness penalty in C. bonariensis. Piasecki et al [18] also observed a reduction in the vigor and germination rate in seeds of glyphosate-resistant Conyza species and, in turn, a significant increase in both empty and dormant seeds. In addition, glyphosate application at the vegetative and reproductive stages impairs the production and viability of glyphosate-resistant C. bonariensis seeds [29].…”

“…Great efforts have been made to characterize the factors involved in the glyphosate resistance, dispersal, and management of C. bonariensis, including growth analysis and bioecological aspects [10]. In considering its seed biology, there is abundant information regarding Conyza's seed germination growing degree days requirements for different sowing dates (autumn, winter, and spring) and agricultural environments [10], as well as its seed viability [11,15], emergence times over a growing season [16], seed longevity [17], and some aspects related to seed quality, such as factors related to seed production, dead seeds, empty seeds, and dormant seeds, among others parameters [18,19]. However, studies on how stress conditions (cold or heat) affect the seed quality of glyphosate-resistant C. bonariensis-which may contribute to its management by reducing seed persistence, reducing the soil seed bank, and consequently preventing the emergence of weeds at critical times [20]-are scarce.…”

Management of Glyphosate-Resistant Hairy Fleabane and Contribution of the Physiological Potential of Seeds to Resistance

“…In addition, the superior root length presented by the resistant biotype provides rapid growth of the roots, and can confer a competitive advantage in cases in which interactions below ground predominate (SEIBERT; PEARCE, 1993). However, in a similar study, Piasecki et al (2019) observed a reduction in the physiological quality of glyphosate-resistant C. bonariensis seeds, demonstrating a possible effect of the origin of the biotypes on the physiological capacity of the seeds.…”