Evaluation location: , United States
In early spring of 2011, the BTx623HKZ_recombinant inbred mapping population including the two parents and 8 commercial checks were planted in replicated plots in three locations representing the US sorghum belt temperate region, USDA zones 4b to 6b between April 1 and 18 (differing due to latitudes of location and precipitation) to evaluate variation for early season field traits for cold tolerance based on field emergence and seedling vigor, biomass. The locations used for field testing were; Lubbock, Texas (33.6°N -101.88°W, 2381 ft. elevation), Manhattan, Kansas (39.21°N -96.51°W, 1053 ft. elevation) and Wall, South Dakota (43.99°N -102.24°W, 2208 ft. elevation). The mean ambient and soil temperatures for all three locations at the time of planting were: Lubbock, TX- 18.3; 17.7 °C; Manhattan, KS- 12.2; 14.4°C; Wall, SD- 12.6; 12.5°C. Each entry was planted in 10 m long plots with 100 cm spacing between plots and equal number of seeds were planted per plot. Field emergence was evaluated on a weekly basis and at 30 days after planting as % field emergence. Seedling vigor was rated on a 1-5 scale, with rating of 1 as robust vigor and 5 as poor vigor. Subsequently, five seedlings in the inner section of each plot were harvested for above ground biomass to determine dry weight.