Frost-after-spike-emergence (FASE) is a major production risk to global grain production. This study evaluated if wheat cultivars with varying susceptibility to FASE have different patterns of grain set and weight contributions under field frost conditions. Field plot trials were conducted in 2018 and 2019, with three wheat cultivars sown multiple times.

Primary tillers were assessed for floret sterility, individual grain set, individual grain weight and yield components. Natural frost events (screen air temperatures ≤ 2 °C) occurred on 22 and 33 occasions from July to October in 2018 and 2019, resulting in grain yields being reduced by up to 65% relative to the control (heated plots). Without frost, cultivars Cutlass and Scout (known to be less susceptible to frost) had higher grain number per spike, lower average grain weight, with proportionally more grains formed in distal florets.

In contrast, the more FASE susceptible cultivar, Wyalkatchem had lower grain number per spike, higher average grain weight, with proportionally more grains set in proximal florets and less in distal florets. With frost, Cutlass and Scout had a higher grain number per spike but lower individual grain weights compared to more FASE susceptible Wyalkatchem.

This study identified less susceptible wheat cultivars form more grains in distal florets, have higher grain number per spike with lower individual grain weights and high grain number per unit area and thus higher grain yield under FASE compared to a more susceptible cultivar. Further detailed studies into the physiological basis for grain yield under FASE conditions are needed to improve grain yield in frost prone growing regions.