Weed management is one of the most important considerations impacting sorghum [Sorghum bicolor (L.) Moench] production in the United States today. The objectives of this study were to evaluate the level of resistance, type of inheritance, and causal mutation of wild sorghum accessions that are resistant to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides compared to susceptible grain sorghum seed parents. Acetyl-coenzyme A carboxylaseinhibiting herbicides used in this study were fluazifop-P and quizalofop-P from the aryloxyphenoxypropionate (APP) family and clethodim and sethoxydim from the cyclohexanedione (CHD) family. Dose-response studies indicated the level of resistance was very high for APP herbicides but low to nonexistent for CHD herbicides. Estimates of the resistance factors to APP herbicides based on herbicide rate required for 50% growth reduction (GR^Q) were 54 to 64 for homozygous plants and 9 to 19 for heterozygous plants. Resistance to CHD herbicides was very low with resistance factors ranging from one to about five. Genetic segregation studies indicated a single gene is the cause of resistance to APP herbicides, Polymerase chain reaction (PCR) amplicons from the carboxyl transferase (CT) domain of the chloroplast directed ACCase gene were sequenced and a single point mutation that results in a cysteine replacing tryptophan (conversion from tryptophan at amino acid position 2027 to cysteine [Trp-2027-Cys]) was discovered. Given the high level of herbicide resistance and simple inheritance, these sources of APP resistance may provide useful herbicide resistance traits for use in sorghum.
Sorghum [Sorghum bicolor (L.) Moench] germplasm lines designated KS201 through KS234 (Reg. No. GP‐684, PI 659520 to Reg. No. GP‐717, PI 659553) were developed and released by the Kansas Agricultural Experiment Station, Manhattan, KS in 2007. The donor of the herbicide resistance gene, Tailwind, was crossed to adapted‐seed and pollinator‐parent lines. The progenies were treated with the target herbicide, and resistant individuals were repeatedly backcrossed to the adapted parents. Backcrossing was performed until the undesirable wild characteristics from the donor parent were eliminated. Lines KS201 through KS218 are R lines and restore fertility in A1 cytoplasm system; lines KS219 through KS234 are B lines and do not restore fertility in A1 cytoplasm. All lines possess a unique genetic resistance to acetolactate synthase (ALS)–inhibitor herbicide families and are useful breeding materials for the development of commercial hybrids with ALS resistance. The lines are all of combine‐harvester height and reach 50% flowering 60 to 82 d after planting at Manhattan, KS. A majority of the lines are pigmented plant types and have variable grain color and seed sizes within the range common to existing public inbreds.
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