|dc.description.abstract||The evolution of herbicide-resistant weed species in cotton production has created a need for new herbicide technology tools. Herbicide technologies not classified as genetically modified by recombinant DNA can provide tools with less associated registration and development costs and regulatory and market barriers. Research herein aims to advance herbicide crop tolerance through improvement and genetic analysis of mutation derived herbicide tolerance in cotton. Germplasm exhibiting elevated tolerance to the imidazolinone class of herbicides has been previously identified after mutagenesis with ethyl methanesulfonate (EMS). However, the physiological basis, genetic behavior, and potential for herbicide tolerance improvement are not fully understood and studies were designed to elucidate these factors.
Three lines (EM4-3-1-1, EM4-3-1-2, and SCM3-4-3-1) show high levels of imazamox tolerance. Data indicate that yield for all EMS treated lines was equal to or greater than their respective non-EMS treated cultivar. EMS treatment had no adverse effects on other cotton fiber properties. In 2012, levels of imazamox herbicide injury were seen at 14 days after application (DAA) ranging from 25-34 per cent. A greater level of injury was observed in 2013 ranging from 30-37% 7 DAA, and from 60-68% 14 DAA. Injury was transient throughout both growing seasons. Acetolactate synthase (ALS) gene sequencing characterized a mutation at Ala122 that is classified as conferring tolerance to imidazolinone herbicides, but was inconsistent in lines evaluated. Sequencing also revealed lines that have a truncated form of the protein in this region that may inhibit imidazolinone binding to the ALS protein. Chi-square analysis indicated this trait behaves in a simple, dominant fashion. Data from parent-offspring regression analysis indicated moderate correlation between parents and F2 progeny (53%). Correlation is relatively high between F2 and F3 progeny (84%) and demonstrates a strong relationship between these generations. Gain from selection indicates a 13.6% improvement in herbicide tolerance, lending to low progress from selection. These studies have shown that non-transgenic breeding methods can confer and improve imidazolinone herbicide tolerance in cotton, though levels of imidazolinone herbicide injury remained commercially unacceptable.||