Inheritance and molecular characterization of broad range tolerance to herbicides targeting acetohydroxyacid synthase in sunflower |
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Authors: | Email author" target="_blank">Carlos?A?SalaEmail author Mariano?Bulos |
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Institution: | (1) Biotechnology Department, NIDERA S.A, Ruta 8 km 376, Casilla de Correo 6, 2600 Venado Tuerto, Santa Fe, Argentina |
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Abstract: | Ahasl1 is a multilallelic locus where all the induced and natural mutations for herbicide tolerance were described thus far in sunflower
(Helianthus annuus L.). The allele Ahasl1-1 confers moderate tolerance to imidazolinone (IMI), Ahasl1-2, and Ahasl1-3 provides high levels of tolerance solely to sulfonylurea (SU) and IMI, respectively. An Argentinean wild sunflower population
showing plants with high level of tolerance to either an IMI and a SU herbicide was discovered and used to develop an inbred
line designated RW-B. The objectives of this work were to determine the relative level and pattern of cross-tolerance to different
AHAS-inhibiting herbicides, the mode of inheritance, and the molecular basis of herbicide tolerance in this line. Slight or
no symptoms observed after application of different herbicides indicated that RW-B possesses a completely new pattern of tolerance
to AHAS-inhibiting herbicides in sunflower. Biomass response to increasing doses of metsulfuron or imazapyr demonstrated a
higher level of tolerance in RW-B with respect to Ahasl1-1/Ahasl1-1 and Ahasl1-2/Ahasl1-2 lines. On the basis of genetic analyses and cosegregation test, it was concluded that tolerance to imazapyr in the original
population is inherited as a single, partially dominant nuclear gene and that this gene is controlling the tolerance to four
different AHAS-inhibiting herbicides. Pseudo-allelism test permitted us to conclude that the tolerant allele present in RW-B
is an allelic variant of Ahasl1-1 and was designated as Ahasl1-4. Nucleotide and deduced amino acid sequence indicated that the Ahasl1-4 allele sequence of RW-B has a leucine codon (TTG) at position 574 (relative to the Arabidopsis thaliana AHAS sequence), whereas the enzyme from susceptible lines has a tryptophan residue (TGG) at this position. The utilization
of this new allele in the framework of weed control and crop rotation is discussed. |
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