Date of Graduation

5-2023

Document Type

Thesis

Degree Name

Bachelor of Science in Biology

Degree Level

Undergraduate

Department

Crop, Soil and Environmental Sciences

Advisor/Mentor

Burgos, Nilda

Committee Member/Reader

Pinto, Ines

Committee Member/Second Reader

Zhuang, Xuan

Committee Member/Third Reader

Chapman, Kate M.

Abstract

The tolerance of mutagenized rice (Oryza sativa) lines to selector herbicides was investigated and the sequence of ALS gene was analyzed in plants that survived treatment with 4x the label rate of imazethapyr herbicide. This was done to determine if insensitivity to imazethapyr is due to mutation(s) in the herbicide binding site. Seedlots previously treated with ethyl-methyl sulfonate were planted in the field and 3-leaf seedlings were treated with various herbicides to screen for herbicide-tolerant mutants. Seeds from survivors composed the rice lines tested in the current research. Seeds were planted in the greenhouse and 3-leaf seedlings were treated with either 4x the recommended rate of imazethapyr, 4x mesotrione, 2x topramezone, 1x fluridone, 1x fluazifop, or 1x clethodim with their respective recommended adjuvants. Rice injury was assessed visually 14 days after treatment, leaf tissue samples were collected from survivors, and processed for sequencing of herbicide target genes. RNA was extracted from frozen plant tissues and converted to cDNA. PCR primers were designed to amplify the target genes for mesotrione (HPPD) and imazethapyr (ALS), respectively. The expected PCR product was isolated via gel electrophoresis, purified, and sent off for sequencing. Attempts to amplify HPPD failed; therefore, only ALS was sequenced. ALS sequence analysis revealed a mutation, Ser653Asn. This is one of the ALS point mutations that confer high resistance to imidazolinone (i.e. imazethapyr) and broad cross resistance to other ALS-inhibitor herbicide families including sulfonylurea8.

Keywords

ALS; acetolactate synthase; Oryza sativa; herbicide resistance

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