Published online by Cambridge University Press: 20 January 2017
Inheritance of glyphosate resistance was investigated in hairy fleabanepopulations from California as part of providing the information needed topredict and manage resistance and to gain insight into resistance mechanism(or mechanisms) present in the populations. Three glyphosate-resistantindividuals grown from seed collected from distinct sites near Fresno, CA,were crossed to individuals from the same susceptible population to createreciprocal F1 populations. A single individual from each of the F1 populations was used to create a backcross population witha susceptible maternal parent, and an F2 population. Based ondose response analyses, reciprocal F1 populations were notstatistically different from each other, more similar to the resistantparent, and statistically different from the susceptible parent, consistentwith nuclear control of the trait and dominance to incomplete dominance ofresistance over susceptibility in all three crosses. Glyphosate resistancein two of the three crosses segregated in the backcross and the F2 populations as a single-locus trait. In the remainingcross, the resistant parent had approximately half the resistance level asthe other two resistant parents, and the segregation of glyphosateresistance in backcross and F2 populations conformed to atwo-locus model with resistance alleles acting additively and at least twocopies of the allele required for expression of resistance. This two-locusmodel of the segregation of glyphosate resistance has not been reportedpreviously. Variation in the pattern of inheritance and the level ofresistance indicate that multiple resistance mechanisms may be present inhairy fleabane populations in California.
Current address: Department of Evolution and Ecology, University of California, Davis, One Shields Avenue, Davis, CA 95616.