Frost Injury in Wheat Ears After Ear Emergence

Abstract

The reaction of ears of wheat (Triticum aestivum L.) to frost after their emergence from the flag leaf sheath was studied for a number of cultivars under controlled conditions of radiative and convective energy exchange. Frost injury was measured in terms of the fertility of the ear, viz. number of grains set per spikelet. Despite being covered with frost crystals, the ear was unaffected by freezing temperature until a threshold level, below which there was a steep reduction in grain set, approximating 100% per 1°C. A threshold of about -4°C and T₅₀ of -4.7°C were observed for the hardiest cultivar, Florence. Crystallization can be initiated within a supercooled floret by spread of freezing from either the peduncle or the vegetative structures of the spikelet. Neither of these pathways was critical and it was concluded that any nucleation in the rachis was sufficient to result in the patterns of injury described. A mechanism of injury was discussed, based on the proposal that nodal regions within the rachis and rachilla provided a distributed system of bamers to the spread of crystallization. These could be effective in allowing supercooled reproductive organs to remain so and avoid lethal injury.