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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Publications at this Location » Publication #130994
Title: CROSS-RESISTANCE OF TWO SULFONYLUREA-RESISTANT SUNFLOWER SOURCES TO SELECTED ALS HERBICIDES

Author
item FABIE, A - COURBINES, FRANCE
item Miller, Jerry

Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: 1/17/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Acetolactate synthase (ALS) is the first enzyme in the biosynthetic pathway of the branched amino acids valine, leucine, and isoleucine. Four classes of herbicides inhibit this enzyme, with the inhibition causing the herbicidal action. These four classes are the imidazolinones (IMI), sulfonylureas (SU), triazolopyrimidines (TRI) and pyrimidinyl thiobenzoates (PYRI). The alteration of the ALS enzyme has been reported to be by point mutations in the coding sequence of the ALS gene. Point mutations result in varying degrees of herbicide binding affinity to the ALS enzyme, resulting indifferent degrees of enzyme inhibition or cross- resistance by the four classes of herbicides. The objective of this study was to determine the cross-resistance of the two sources of SU resistance found in sunflower, a USDA line and a Pioneer hybrid. The results of this study would indicate that the conserved region of the ALS gene involved in the USDA line and the Pioneer hybrid would be the AITGQVPRRMIGT region. The resistance of the USDA source is thought to be a substitution of proline to histidine, while the resistance of the Pioneer hybrid is thought to be a substitution of proline to isoleucine. Practical implications are that the USDA source would be more tolerant to the SU herbicide, Pinnacle, which would control four difficult broad-leaf weeds. However, the Pioneer hybrid would be more susceptible to the IMI class of herbicide, making it work better in rotations by producers using IMI- resistant crops.

Technical Abstract: Acetolactate synthase (ALS) is the first enzyme in the biosynthetic pathway of the branched amino acids valine, leucine, and isoleucine. Four classes of herbicides inhibit this enzyme, with the inhibition causing the herbicidal action. These four classes are the imidazolinones (IMI), sulfonylureas (SU), triazolopyrimidines (TRI) and pyrimidinyl thiobenzoates (PYRI). The alteration of the ALS enzyme has been reported to be by point mutations in the coding sequence of the ALS gene. Point mutations result in varying degrees of herbicide binding affinity to the ALS enzyme, resulting indifferent degrees of enzyme inhibition or cross- resistance by the four classes of herbicides. The objective of this study was to determine the cross-resistance of the two sources of SU resistance found in sunflower (Helianthus annuus L.), a USDA line and a Pioneer hybrid. The results of this study would indicate that the conserved region of the ALS gene involved in the USDA line and the Pioneer hybrid would be the AITGQVPRRMIGT region. The resistance of the USDA source is thought to be a substitution of proline to histidine, while the resistance of the Pioneer hybrid is thought to be a substitution of proline to isoleucine. Practical implications are that the USDA source would be more tolerant to the SU herbicide, Pinnacle, which would control four difficult broad-leaf weeds. However, the Pioneer hybrid would be more susceptible to the IMI class of herbicide, making it work better in rotations by producers using IMI-resistant crops.