Phenotypic data

The efficiency of genomic selection across successive years was evaluated using a doubled-haploid (DH) population derived from a single cross between two commonly grown hard red winter wheat (Triticum aestivum L.) cultivars, ‘Duster’ (Edwards et al. 2012) and ‘Billings’ (Hunger et al. 2014). In total, 282 DH lines were developed, and among which, 257 lines were evaluated for grain yield in 2014 and 2015 at the Agronomy Research Station in Stillwater, OK, USA (36.12 N, 97.09 W). Plot size was 1.5 m × 3 m, with a sowing density about 200 seeds per m², following a randomized complete block design. The soil type in Stillwater location was Kirkland silt loam or Norge loam (for details, see http://oaes.okstate.edu/frsu/agronomy-research-station/Stillwater_soilmap.pdf); in 2014, urea and diammonium phosphate (DAP) were applied (broadcast and incorporated) to achieve a final rate of 96 lb N/acre and 69 lb P/acre before planting. Similarly, in 2015, urea and DAP were applied to achieve a final rate of 91.5 lb N/acre and 57.5 lb P/acre. In both years, 239 out of the 257 lines were replicated twice, and the remaining 18 were screened for grain yield only once. When applicable, the mean of the two replications was taken to represent an individual line’s phenotype. Since the genotypes evaluated were identical for 2014 and 2015, the year effect was considered as environmental replications during data analysis. The 2014 trial was planted on 11 November 2013 and harvested on 20 June 2014. The 2015 trial was planted on 14 November 2014 and harvested on 14 June 2015. The total rainfall was 7.78 in. for the year 2014 growing season and 16.27 in. for year 2015. No trial received supplemental irrigation.

Days to heading (HD) were recorded for each DH line for both 2014 and 2015, as the variability of HD (measured as the duration from planting to heading) in wheat is an indicator of adaptability to its growing environment (Kiseleva et al. 2016). In addition, naturally occurring stripe rust (Puccinia striiformis) infection was observed in the 2015 trial. The infection type (severity) of stripe rust was recorded using the basic 0-to-9 scale described by Line et al. (1974), where 0 was completely resistant and 9 was completely susceptible; the incidence was rated by the modified Cobb USDA scale (Peterson et al. 1948); the severity of stripe rust was also recorded. Assessment of the rust infection was carried out on the 5th and 11th of May; at each time, the severity (RS₅, RS₁₁) and incidence (RI₅, RI₁₁) of the disease were recorded for each individual line.