Variation in reproductive frost susceptibility of wheat cultivars is not associated with variation in glume and lemma thickness

The thickness of wheat (Triticum aestivum L.) glumes and lemmas (T-GL) influences their thermal insulation properties, which in turn, may influence reproductive frost susceptibility. The objectives of this study were to (i) determine the variability in T-GL in bread wheat cultivars, (ii) quantify the frost susceptibility of cultivars with different T-GL under field conditions and natural frosts, and (iii) find out, based on the estimation of the heat transfer through the glume + lemma, if differences in frost susceptibility are associated with differences in T-GL. T-GL was evaluated in 11 long-cycle and 11 short-cycle cultivars and frost susceptibility in five cultivars with contrasting T-GL was also determined. Additionally, the thermal properties of the glumes and lemmas were measured and the heat transfer through them was estimated. Significant and consistent differences in T-GL were measured among cultivars. It was estimated that as T-GL increased the inner side of the lemma would cool more slowly. However, differences in frost susceptibility of cultivars were not associated with variation in T-GL. The research also showed that frost susceptibility does differ among Argentine cultivars. Further work is needed to confirm and understand the physiological basis of the variation in frost susceptibility of wheat.