Herbicide safeners: upregulating detoxification mechanisms for selective weed management in grain sorghum (Sorghum bicolor L. Moench)

Goodrich, Loren Victoria

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Description

Title

Herbicide safeners: upregulating detoxification mechanisms for selective weed management in grain sorghum (Sorghum bicolor L. Moench)

Author(s)

Goodrich, Loren Victoria

Issue Date

2017-04-27

Director of Research (if dissertation) or Advisor (if thesis)

Riechers, Dean E.

Committee Member(s)

• Huber, Steven C.
• Brown, Patrick J.
• Davis, Adam S.

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Herbicide safeners
• Grain sorghum
• Pyroxasulfone
• S-metolachlor
• Glutathione S-transferase
• Phi-class GSTs

Abstract

Grain sorghum (Sorghum bicolor L. Moench) is one of the world’s most important crops based on area sown and production. Sorghum utilizes C4 photosynthesis and is one of the most efficient crops for water usage and solar energy conversion. It is grown for human consumption, animal feed, and fuel worldwide. Originating in the northeast Sahel region of Africa, the wide range of sorghum cultivation can be attributed to its tolerance to both high heat and drought conditions. It is the third largest cereal grain grown in the United States with acreage in the U.S. increasing over 20% from 2014. Controlling weeds selectively is one of the most significant challenges when producing grain sorghum. Growers are restricted to preemergence (PRE) and post emergence (POST) herbicides that typically target broadleaf weeds, but options for controlling grasses are limited. Due to the high potential of gene flow from sorghum to wild and weedy relatives, the use of transgenes to confer herbicide selectivity in grain sorghum is limited. In order to achieve herbicide selectivity, seed-applied herbicide safeners are frequently used with herbicides that normally cause injury in unsafened grain sorghum. The use of herbicide safeners increases the range of herbicides that can be used in grain sorghum to achieve weed control. A current seed safener marketed for sorghum is fluxofenim (Concep® III; Syngenta Crop Protection, LLC.), which was first introduced in 1979. Fluxofenim is typically applied as a seed treatment to avoid safening weedy Sorghum relatives. Safeners confer protection to cereal crops by inducing herbicide detoxification and defense systems. This includes massive increases in the expression and activity of glutathione S-transferases (GSTs) and cytochrome P450s, although the precise molecular mechanism of action and signaling pathways remain unknown. Chapter 1 of this thesis includes a literature review of grain sorghum as a model crop, common PRE herbicides used in grain sorghum with a specific focus on very-long-chain fatty acid (VLCFA)-inhibiting herbicides, a section on the history and use of herbicide safeners in cereals, and safener-mediated herbicide metabolism in plants. Chapter 2 covers a genome-wide association study conducted to identify key molecular-genetic factors involved in the safener-induced detoxification pathway. Diverse sorghum inbred lines (761) were evaluated for their responses to seed-applied safener and PRE herbicide applications. Data analysis revealed that the molecular marker most significantly associated with safener-induced response was located on chromosome 9, where a single nucleotide polymorphism (SNP) was located within a phi-class SbGST gene and about 15 kb from a different phi-class SbGST. Transcript levels of these two candidate SbGSTs were quantified in etiolated shoot tissues using quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) and gene-specific primers designed from each SbGST coding region. Basal and safener-induced expression of these SbGSTs was examined in three sorghum genotypes at 4, 8, and 12 hrs after treatment (HAT) to quantify safener induction of these genes relative to three stably expressed reference genes: GTPB, SAND, and EIF4a. Results indicated expression of each SbGST gene increased within 12 hr following safener treatment but differed by specific gene and genotype, suggesting these SbGSTs play a functional role in the safening response from herbicides. Chapter 3 provides applied information on the use of fluxofenim as herbicide safener for hybrid grain sorghum when used with the PRE herbicide pyroxasulfone (Zidua®), a VLCFA inhibitor. A greenhouse study was first conducted to understand how pyroxasulfone affects grain sorghum emergence and seedling growth under controlled conditions, and to determine the efficacy of fluxofenim in protecting sorghum seedlings from pyroxasulfone. Using the data from the greenhouse, a field study was designed to evaluate the protective ability of seed-applied fluxofenim from pyroxasulfone at single and split application times. Weed control, crop injury, stand count, and yield data were assessed to compare the effects of pyroxasulfone to S-metolachlor (Dual Magnum®; a different VLCFA inhibitor) applied PRE in grain sorghum, with or without fluxofenim. Results indicated that pyroxasulfone provides greater weed control compared to S-metolachlor. However, as weed control increases, crop injury also increases regardless of safener. This finding demonstrates that a herbicide safener tailored towards enhancing the ability of grain sorghum to metabolize pyroxasulfone is needed for future use of this product under field conditions. Chapter 4 summarizes the discussion and conclusions from Chapters 2 and 3 and identifies current limitations and future research goals for utilizing seed-applied safeners in grain sorghum.

Graduation Semester

2017-05

Type of Resource

text

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Copyright 2017 Loren Goodrich

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