Selection of glyphosate-susceptible and –resistant plants in Echinochloa colona for the study of fitness costs associated with resistance

GOH, S.S.; VILA AIUB, MM; BUSI, R.; POWLES, SB

Conferencia; Global Herbicide Resistance Challenge Conference; 2013

Australian Herbicide Resistance Initiative

When assessing fitness costs associated with herbicide resistance, it is crucial to ensure that herbicide susceptible (S) and -resistant (R) individuals share a similar genetic background, except for the herbicide resistance alleles. Glyphosate resistance has evolved in Echinochloa colona populations from WA cropping systems and we intend to determine the existence of associated fitness costs. A plant cloning technique followed by phenotypic identification after glyphosate selection is the experimental approach that is being used to identify S and R plants within a segregating glyphosate resistant E. colona population. For selection of R plants, seeds were sown in trays and at the two- to three-leaf stage, seedlings were treated with 2,160 g ha-1 of glyphosate (Roundup 540 g a.i. L-1). Plant survival was recorded two weeks after glyphosate treatment and surviving plants (27 out of 100 plants; 27.0%) were classified as R plants. For selection of S plants, about 89 plants were cloned and numbered. When the clones achieved two- to three-leaf stage, they were sprayed with 300 g ha-1 of glyphosate (Roundup 540 g a.i. L-1). Twenty five seedlings did not survive the glyphosate treatment (25 out of 89, 28.1%) and were classified as S plants. All identified S and R plants were grown outdoors until reproduction. Enclosures were built to prevent pollen contamination from other sources. Further glyphosate resistance verification of homogeneous S and R individuals from within both sub-populations were conducted after selection with glyphosate field recommended rate (Roundup 540 g a.i. L-1). Subsequently, seeds from each S and R individuals were bulked and served as the plant materials for whole-plant-dose response studies at controlled environmental room and evaluation of fitness costs associated with glyphosate resistance in E. colona. This glyphosate-resistant E. colona was found to be 4.7-fold more resistant to glyphosate than the susceptible population. Based on biomass, the resistance index was 5.7. Besides, EPSPS gene sequencing was also studied and the mutations in the EPSPS gene known to confer glyphosate resistance in other species are not present in this glyphosate resistant E. colona population.