Inbreeding coefficients of field populations ofKochia scopariausing chlorsulfuron resistance as a phenotypic marker

Inbreeding coefficients were determined for nine southeastern Idaho kochia populations using chlorsulfuron resistance as a phenotypic marker. Inbreeding coefficients in six of the populations approximated 0, indicating that these field populations were random mating. One population had an inbreeding coefficient of 0.32, indicating partial selfing. No susceptible genotypes were identified in one population, which suggested recent selection and skewed the inbreeding coefficient. One population had an inbreeding coefficient of −0.19, suggesting either heterozygote advantage or some recent selection in the population. Our results suggest that kochia populations generally approximate random mating. Therefore, unlinked alleles will be independently assorted in field populations of kochia.

Characterization of Chlorsulfuron Resistant and Susceptible Kochia (Kochia scoparia)

Kansas and North Dakota kochia populations identified as chlorsulfuron resistant (R) contained 20 and 30% susceptible (S) plants, respectively. Biotypes that were chlorsulfuron R or S were selected from each field R or S collection and selfed through three generations in the greenhouse. Chlorsulfuron at 7.6 and 17.8 g ai/ha suppressed shoot biomass of the Kansas and North Dakota R biotypes by 50%, respectively, which was a 30- and 105-fold greater dose than that required to reduce the respective S biotypes growth 50%. The R and S kochia biotypes are diploid with 2N = 18 chromosomes. Chlorsulfuron resistance is inherited in kochia as a dominant trait controlled by a single nuclear gene. Thus, the resistance trait can be spread by seed and pollen.

Sulfonylurea-Resistant Russian Thistle (Salsola iberica) Survey in Washington State

The repeated use of sulfonylurea (SU) herbicides to control broadleaf weeds in wheat fields and right-of-ways has selected for herbicide-resistant Russian thistle populations. A survey was conducted in 1991 and 1992 to ascertain the relative occurrence of SU-resistant Russian thistle in eastern Washington state. The 55 574 km2survey area was divided into 149 equal sample areas. All sample areas were surveyed for Russian thistle and seed was collected from plants in 86 sample areas. No Russian thistle was found in the center of the remaining 63 sample areas. Seeds were collected, by plant, from 30 plants at each site. Site samples were tested in the greenhouse for resistance or susceptibility to chlorsulfuron. Populations that were either homogeneous or heterogeneous for chlorsulfuron-resistance were found in 70% of the sample areas and all of the plants were susceptible in 30% of the sample areas.