Author ORCID Identifier:
Date of Graduation
7-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)
Degree Level
Graduate
Department
Crop, Soil & Environmental Sciences
Advisor/Mentor
Roma-Burgos, Nilda
Committee Member
Lewis, Jeffrey
Second Committee Member
Adams, Rich
Third Committee Member
Butts, Thomas
Fourth Committee Member
Srivastava, Vibha
Keywords
Abiotic stress; Herbicide resistance; Integrate weed management; Junglerice; Synthetic auxins; Weed Physiology
Abstract
Echinochloa colona (junglerice) is considered a highly competitive weed species primarily due to its rapid early growth. The utility of relatively new herbicides, such as florpyrauxifen-benzyl (FPB, Group 4), is at risk due to increasing weed resistance. FPB is an auxinic herbicide with the potential of controlling quinclorac-resistant (other auxinic, HRAC Group 4) junglerice. Several factors remain to be understood in the Echinochloa spp. resistance mechanisms to auxin herbicides, including the influence of abiotic stress on resistance evolution. Therefore, this project aimed to (1) evaluate growth and seed production of junglerice, after three and five generations of recurrent selection with sublethal doses of four commonly used rice herbicides with or without heat stress; (2) understand the competitiveness of hybrid and inbred rice with auxinic-resistant junglerice and (3) understand the effect of heat stress and recurrent selection of auxin herbicides (quinclorac and FPB) after six generations in junglerice; and understand the genetic mechanisms governing resistance to FPB and quinclorac in junglerice under the joint effect of heat stress and herbicide by RNA-seq and candidate gene validation by RT-qPCR. The joint effect of heat stress and sublethal herbicide doses reduced junglerice sensitivity to the four herbicides tested. The interspecific study showed that, regardless of the resistance trait, junglerice was more competitive than the rice cultivars evaluated. The FPB- and heat-acclimatized seed line (SL7) had a higher tolerance index (up to 1.9) than the original (SL1) to FPB. Without FPB and heat stress, SL7 did not show differentially expressed metabolic-based herbicide resistance genes compared to SL1; instead, SL7 showed exclusive upregulation of RNA-directed RNA polymerase activity and ethylene response transcription factor (AP2/ERF), suggesting a complex shift in gene regulation resulting in elevated tolerance to FPB. At 30°C, both SLs exhibited a classical metabolic-based detoxification model (upregulation of oxidoreductase-, conjugation-, and transport genes) in response to FPB. At 45°C, the common oxidoreductase network weakened among SLs after FPB treatment, but a FMO, a DIMBOA/BX8 type UGT, an ABCC transporter, and genes involved in protein folding and RNA splicing were upregulated in SL7. Heat stress led to high resistance to quinclorac in junglerice (SL6: survivors to 16-fold the commercial rate). The upregulated genes in SL6 were associated with photosynthesis, electron transport, and chlorophyll biosynthesis. Additionally, RNA modifications, protein modifications, and auxin response factors were exclusively upregulated in SL6. These findings indicate that: (1) heat stress and sublethal doses of auxinic herbicides reduced junglerice sensitivity to FPB andincreased seed production potential, (2) breeding and planting competitive rice varieties is an ecologically viable strategy to combat auxinic-herbicide-resistant junglerice, (3) resistance evolution to FPB under heat stress is not solely facilitated by classical detoxification pathways but by complex regulatory reprogramming, (4) heat-stress acclimation led to high resistance to quinclorac in junglerice, caused by active photosynthesis protection, potential epigenetic reprogramming and changes in hormone signaling not detected in SL1. These findings contribute to understanding the evolution of weed resistance to herbicides under climate change scenarios, with major implications for future weed management.
Citation
Velasquez Rodriguez, J. C. (2026). Resistance Evolution to Auxinic Herbicides Forpyrauxifen-benzyl and Quinclorac in Echinochloa colona Under Heat. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6374
