Field Phenotyping

The population was phenotyped in 2018 and 2019 at Colby (Manhattan, KS, USA), and in 2020 at (Manhattan, KS, USA). In both locations and years, an augmented design was used to establish the trials. Plots were planted using a New Holland six-row wheat drill. Plot dimensions were 2.5 m long by 0.5 m wide and consisted of three rows with 18 cm row spacing. Starter fertilizer was applied with the seed at planting using granular 18-46-0 diammonium phosphate (DAP) at a rate of 168.1 kg/ha. Additional nitrogen was applied as a topdress in the spring using liquid 28-0-0 urea ammonium nitrate (UAN) at a rate of 67.3 kg/ha. A lateral irrigation system was used at Colby to ensure uniform germination and emergence as well as to provide additional water throughout the growing season in the irrigated treatment. Three hexaploid winter wheat lines well-adapted to Kansas environments (checks) and the hexaploid wheat parents were used as controls with at least three biological replications per block. In 2018 and 2019, two complete blocks were established and one block was irrigated (COI18 and COI19, respectively), whereas the other was rainfed/non-irrigated (CO18 and CO19, respectively), simulating optimal and farmer-field growth conditions. In 2020, only one block was grown under rainfed conditions (AS20).

The population was phenotyped for yield and yield components traits, BM traits, and Tg. Agrobase software (Mulitze, 1990) was used to adjust the grain yield (GY) (bushels per acre (BPA)], for spatial variability. The MARVIN seed imaging system [GTA Sensorik GmbH, Neubrandenburg, Germany) was used to assess the grain morphometric traits such as GN per sample, TGW, grain area (GA), GW, and grain length (GL) from the two technical replicates in 2018, and one measurement in 2019 and 2020. In 2019 and 2020, data were collected for the number of spikes per square foot (SPSF) from two random points within a plot. The 1 × 1 ft square frame was dropped over two rows at least one foot away from the plot edges to avoid the border effect. In 2019, only one row within a frame was cut above the ground level for BM determination, whereas in 2020, both rows were sampled. Biomass samples were collected in paper bags and dried for at least 3 weeks at 32°C (90°F) before processing. We collected data on aboveground dry BM measured as the total weight of the dry sample without the bag, the number of spikes per sample (SPB), the average spikelet number per spike (SNS) from 10 random spikes, and grain weight after threshing [grain sample weight (GSW)]. During threshing, we scored samples for the presence and absence of the Tg trait depending on the threshability. Harvest index (HI) was calculated as the percentage of GSW relative to BM.

In 2020, data for HD were collected from each plot when approximately 50% of the spikes had emerged from the flag leaves. The number of days to heading were calculated as the difference between the heading and planting dates. After all the plots had completed heading, PH, in centimeters was measured on the same day from two random but representative main tillers per plot for the whole field. PH was measured as the distance from the ground surface to the first spikelet of the spike.