Inheritance of Glyphosate Resistance in Hairy Fleabane (Conyza bonariensis) from California

Abstract

Inheritance of glyphosate resistance was investigated in hairy fleabane populations from California as part of providing the information needed to predict and manage resistance and to gain insight into resistance mechanism (or mechanisms) present in the populations. Three glyphosate-resistant individuals grown from seed collected from distinct sites near Fresno, CA, were crossed to individuals from the same susceptible population to create reciprocal F1populations. A single individual from each of the F1populations was used to create a backcross population with a susceptible maternal parent, and an F2population. Based on dose response analyses, reciprocal F1populations were not statistically different from each other, more similar to the resistant parent, and statistically different from the susceptible parent, consistent with nuclear control of the trait and dominance to incomplete dominance of resistance over susceptibility in all three crosses. Glyphosate resistance in two of the three crosses segregated in the backcross and the F2populations as a single-locus trait. In the remaining cross, the resistant parent had approximately half the resistance level as the other two resistant parents, and the segregation of glyphosate resistance in backcross and F2populations conformed to a two-locus model with resistance alleles acting additively and at least two copies of the allele required for expression of resistance. This two-locus model of the segregation of glyphosate resistance has not been reported previously. Variation in the pattern of inheritance and the level of resistance indicate that multiple resistance mechanisms may be present in hairy fleabane populations in California.

Differential Susceptibility of <i>Conyza bonariensis</i> Biotypes to Glyphosate and ALS-Inhibiting Herbicides in Argentina

“…Resistance factors for glyphosate were similar or lower (approximately 4 for both weed stages) relative to other studies in C. bonariensis which showed resistance factors about 7 and 9 [13] or ranged between 3 -9 [17]. In those studies, resistance has arisen in orchards or vineyards after multiple applications of glyphosate as the only herbicide.…”

“…and four modes of action C. bonariensis have been reported [12]. Resistance biotypes were identified in Europe [13]- [15], Brazil [16] and USA [17]. In Argentina, a better understanding of the differences in control between biotypes is essential for developing effective long-term management strategies.…”

Evolution and spread of glyphosate resistance in Conyza bonariensis in California and a comparison with closely related Conyza canadensis

“…However, the magnitude of the variation in response to glyphosate between repetitions also varied among populations under the 2x treatment, suggesting variation among populations in response to environmental conditions. A significant environmental effect on the expression of glyphosate resistance has been previously reported (Urbano et al ., ; Walker et al ., ; Okada & Jasieniuk, ) and appears to be a characteristic of the resistance trait in C. bonariensis (Moretti et al ., ). Phenotypically, plastic responses to varying environmental conditions may be followed by adaptive evolution (Schwander & Leimar, ) and could play a role in the evolution of glyphosate resistance in weeds.…”

Evolutionary and ecological insights from herbicide‐resistant weeds: what have we learned about plant adaptation, and what is left to uncover?

“…For example, researchers studying the resistance problem will examine the phenotype by diagnosing the scale and extent of resistance among natural populations (Menchari et al, 2006;Kuester et al, 2015;Okada et al, 2015;D elye et al, 2016;Hicks et al, 2018), and will often pair this with a marker-assisted assessment of genetic differentiation and diversity to examine the likelihood that resistance alleles may migrate between areas via gene flow (Menchari et al, 2007;Okada et al, 2013Okada et al, , 2015Kuester et al, 2015;D elye et al, 2016). Furthermore, and often within the same herbicide-resistant species, researchers will investigate the genetic control of resistance (D elye, 2005;Powles & Preston, 2006;D elye et al, 2013aOkada & Jasieniuk, 2014;Scarabel et al, 2015) whether it is controlled by a single locus or is polygenicand will similarly identify both the genetic and physiological mechanism(s) responsible for resistance (reviewed in D elye et al, 2013a). As an outcome of these highly interdisciplinary, synthetic studies, weed scientists have generated enviable models for studying the adaptive process.…”