Two DNA molecular marker techniques were used to evaluate genetic diversity in 58 accessions of jointed goatgrass and 6 accessions of the related wild species barb goatgrass. Random amplified polymorphic DNA (RAPD) assays were performed on 8 U.S. and 50 Eurasian jointed goatgrass accessions using 30 random decamer primers. The frequency of scorable polymorphic bands within jointed goatgrass was 6 out of 90 (6.7%). Cluster analysis of RAPD data showed small genetic distances (values of 0.005 or less) among jointed goatgrass accessions. To validate the effectiveness of RAPD techniques to detect genetic diversity in tetraploid Aegilops species, six accessions of barb goatgrass were assayed using a subset of 20 decamer primers (from the original 30). RAPD data for barb goatgrass were pooled with jointed goatgrass data from the same primers. A total of 63 scorable bands were generated, of which 27 (43%) were polymorphic between two or more accessions. RAPD analysis readily distinguished between the two species and detected much greater levels of genetic diversity within barb goatgrass than between the jointed goatgrass accessions. Amplified fragment length polymorphism (AFLP) assays were performed on a subset of the 58 jointed goatgrass accessions, 3 U.S. and 13 Eurasian. These accessions were selected to represent a range in geographic diversity within our collection. Ten primer combinations generated 560 scorable bands of which 28 (5%) were polymorphic. Cluster analysis of AFLP data showed a slightly smaller range in genetic distance (0.0002 to 0.0022) among accessions compared with RAPD results; however, AFLPs distinguished among all but 2 of the 16 accessions surveyed. Although AFLP produced more scorable bands than RAPD did, both methods revealed limited genetic diversity in jointed goatgrass.

Prescribed burning can control invasive annual grasses that threaten the biological and economic value of California grasslands. Susceptibility of grass seed to burning can depend on burn timing, exposure time, and type of exposure (direct flame heat or convective heat); thus, these factors can influence the success of a prescribed burning program. To further investigate these factors, laboratory simulations were conducted on barb goatgrass, medusahead, and ripgut brome at several stages of seed maturity, as determined by percent moisture of the inflorescences. Seeds were exposed either to direct flame using a Bunsen burner or to heated air in a muffle furnace. Flame treatments were conducted at one temperature (∼400 C) and several exposure times (0 to 14 s), depending on the species. Furnace treatments included four temperatures (150, 200, 250, and 300 C) and seven exposure times (0, 10, 20, 30, 40, 60, or 80 s). Seed germination was analyzed for each temperature series to determine the LD50 and LD90 in seconds of exposure time. Susceptibility to furnace treatments, which simulated heat exposure of seeds on the soil surface, was not statistically different within a range of seed moisture levels for all three species. The LD50 values at 250 C (typical soil temperature with grassland fire) ranged from 28 to 49 s, which far exceeds the time of exposure during a typical grassland fire. Susceptibility to flame showed a similar lack of change over maturation of medusahead and barb goatgrass seeds, with LD90 values ranging between 4.8 and 7.4 s for all seed moisture levels. In contrast, ripgut brome seeds exposed to flame showed increasing susceptibility with reduced seed moisture content. The LD90 values for exposure were less than one second for seed moisture levels at or below 10%, compared to 3.7 s for seeds at 55 to 60%. Although flame susceptibility increased for ripgut brome, seeds at all maturation stages were more sensitive than medusahead and barb goatgrass. Additionally, the LD90 values for all three species are attainable under field conditions. Thus, burn prescriptions for these three species are not constrained by maturation stage, but should occur prior to seed drop and when fuel loading is high. This will maximize exposure time of seeds to direct flame.