This collection (datasets) comprises wheat flag leaf Tcrit (the critical temperature at which incipient damage to photosystem II occurs) of 54 wheat genotypes evaluated in 12 thermal environments  in grain growing regions in Australia between 2017-2019.

A total of 54 wheat genotypes were grown in eight field and four controlled environments over 3 years (2017–2019). Of these 54 genotypes, 20 were common to all environments. The eight field experiments were conducted in major wheat-growing regions of Australia (Dingwall, Victoria in 2017, Barraport West, Victoria in 2018, and Narrabri, New South Wales in 2019). The field trials were sown 1 month apart over 3 months in 2017 and 2018, and 2 months apart in 2019, with the initial sowing time being the optimum sowing time for each region. Later sowing exposed plants to higher temperatures at the critical reproductive and grain-filling stages of development. Across the different trials, plants received water from a combination of rainfall and irrigation of 152–185 mm in Dingwall, 217–235 mm in Barraport West, and 363–492 mm in Narrabri between sowing and anthesis. Twenty genotypes were evaluated during the 2017 and 2018 trials, and 24 genotypes in 2019. The experimental designs, crop husbandry and data collection methods were similar across all three field experiments, except for the differences mentioned above (i.e. number of sowings and genotypes). 

Geographic locations of the experimental sites are as follows:

Kerang, VIC (East=143.9212, and North=-35.7350);
Boort, VIC (East=143.7322, and North=-36.1175); 
Narrabri, NSW (East=149.7667, and North=-30.3167)

In addition to the field trials, a trial with 50 wheat genotypes (including 20 genotypes common to the field trials) was conducted in four high-precision Growth Capsules, with independent control of temperature, relative humidity and multispectral LED light. The Growth Capsules were managed by the Australian Plant Phenomics Facility (APPF) and Grain Phenomics Climate Facility at the Australian National University (ANU), Canberra (https://www. plantphenomics.org.au). Each Growth Capsule comprised two separate chambers 3.8 m wide × 1.1 m deep × 2.1 m high. The chambers were used to dynamically simulate four environments: two cool and two warm (approximately 5°C higher than the cool) wheat-growing seasons, based on the 15- min average temperature from the vegetative growth period to the end of anthesis (June–October) each year from 2013 to 2018 for the Narrabri site. Simulation of dawn, daylight and dusk timings also mimicked conditions in Narrabri. Lights were supplied by colour-adjustable LED modules that were kept thermally insu- lated from the plant growth area. The simulated environments will henceforth be identified as simulated cool season 1 (SIM-C1), simulated cool season 2 (SIM-C2), simulated warm season 1 (SIM- W1) and simulated warm season 2 (SIM-W2).

Flag leaves were harvested when at least 50% of the genotypes were at anthesis. In the field, leaves were harvested from plants from one of the inner three rows of five-row plots between 08:30 and 10:30 hours. In the chambers, flag leaves of main tillers at anthesis were harvested between 08:45 and 11:00 h. Immediately after harvesting a flag leaf, a section of approximately 3–4 cm was cut from the middle. The middle and upper sections of the leaves were kept in resealable bags and dark-adapted for between 1.5 and 6 h prior to estimating Tcrit (middle section). Fluorescence was measured by excitation using short flashes (10 μsec) of extremely weak blue light. Wheat Tcrit was determined from the temperature and fluorescence data. The breakpoint was taken as Tcrit, along with the estimate of its standard error. 

R software was used for statistical analysis.

For further enquiries please contact:
Onoriode Coast at ocoast@une.edu.au or 
Richard Trethowan at richard.trethowan@sydney.edu.au