Molecular characterisation of resistance to ALS-inhibiting herbicides in Hordeum leporinum biotypes.
BACKGROUND
The acetolactate synthase (ALS)-inhibiting herbicide sulfosulfuron is registered in Australia for the selective control of Hordeum leporinum Link. in wheat crops. This herbicide failed to control H. leporinum on two farms in Western Australia on its first use. This study aimed to determine the level of resistance of three H. leporinum biotypes, identify the biochemical and molecular basis and develop molecular markers for diagnostic analysis of the resistance.


RESULTS
Dose-response studies revealed very high level (>340-fold) resistance to the sulfonylurea herbicides sulfosulfuron and sulfometuron. In vitro ALS assays revealed that resistance was due to reduced sensitivity of the ALS enzyme to herbicide inhibition. This altered ALS sensitivity in the resistant biotypes was found to be due to a mutation in the ALS gene resulting in amino acid proline to serine substitution at position 197. In addition, two- to threefold higher ALS activities were consistently found in the resistant biotypes, compared with the known susceptible biotype. Two cleaved amplified polymorphic sequence (CAPS) markers were developed for diagnostic testing of the resistant populations.


CONCLUSIONS
This study established the first documented case of evolved ALS inhibitor resistance in H. leporinum and revealed that the molecular basis of resistance is due to a Pro to Ser mutation in the ALS gene.
Yu
Qin
Q
Western Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, Crawley, WA 6009, Australia. yuqin@plants.uwa.edu.au
Nelson
Jared K
JK
Zheng
Ming Q
MQ
Jackson
Michael
M
Powles
Stephen B
SB
D000095:Acetolactate Synthase / Q000037:antagonists & inhibitors / Q000235:genetics*; D001483:Base Sequence; D004305:Dose-Response Relationship, Drug; D053209:Herbicide Resistance; D006540:Herbicides / Q000008:administration & dosage / Q000494:pharmacology; D001467:Hordeum / Q000187:drug effects*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D011110:Polymorphism, Genetic; D011743:Pyrimidines / Q000008:administration & dosage / Q000494:pharmacology; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013449:Sulfonamides / Q000008:administration & dosage / Q000494:pharmacology; D013453:Sulfonylurea Compounds / Q000008:administration & dosage / Q000494:pharmacology
D006540:Herbicides; D011743:Pyrimidines; D013449:Sulfonamides; D013453:Sulfonylurea Compounds; D000095:Acetolactate Synthase; C439268:sulfosulfuron