Date of Graduation

12-2020

Document Type

Thesis

Degree Name

Master of Science in Cell & Molecular Biology (MS)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Roma-Burgos, Nilda

Committee Member

Srivastava, Vibha

Second Committee Member

Thallapuranam, Suresh

Third Committee Member

Egan, Martin J.

Keywords

Amaranthus palmeri; Fomesafen; G399A; Herbicide resistance; PPO-mutations; Weed science; ΔG210

Abstract

Palmer amaranth (Amaranthus palmeri S. Wats.) is one of the most problematic agronomic weeds to control in fields across Arkansas. Thus far, this species has evolved resistance to several herbicides, including protoporphyrinogen IX oxidase (PPO) inhibitors. The majority of PPO-resistant Palmer amaranth populations harbor a target-site mutation (substitution or deletion of amino acids). The objective of this thesis was to identify the level of fomesafen resistance conferred by PPO2 mutations from Palmer amaranth. The experiments conducted aimed to (1) characterize the level of resistance conferred by the transgene Palmer amaranth ppo2 carrying ΔG210 mutation into the wild type rice (Oryza sativa cv. ‘Nipponbare’); and (2) study the resistance level of Palmer amaranth plants having a single mutation (ΔG210 or G399A) or a combination. For objective 1, ‘Nipponbare’ rice was transformed with Palmer amaranth ppo2 ΔG210 gene via particle bombardment. The presence of the transgene in T0 plants was confirmed, and seeds (T1) were harvested. After selection with foliar treatment of fomesafen (0.78 kg ai ha-1), T1 plants carrying the mutation and showing low injury were maintained to produce T2 seeds. Soil-based assay was conducted with T2 seeds and the survivors were cultured to produce T3 seeds. Seeds from each surviving plant were kept as a separate line. The insertion of Palmer amaranth ppo2 ΔG210 conferred resistance to fomesafen in rice. The data suggests that only homozygous transgenic plants had full resistance to fomesafen. For objective 2, one susceptible and six resistant accessions were used to conduct dose response assay with the PPO-herbicide, fomesafen, and to test cross resistance or multiple resistance. Selected survivors from these tests were genotyped for the two expected mutations. Homozygosity of ΔG210 was correlated with high fomesafen resistance. At higher fomesafen rates, survivors carrying ΔG210 in both alleles or accumulating ΔG210+G399A recovered better than heterozygous ΔG210 plants. Populations with higher frequency of individuals with these mutation profiles were also less sensitive to the other two PPO-herbicides tested, saflufenacil and trifludimoxazin.

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