Heat priming effects on anthesis heat stress in wheat cultivars (Triticum aestivum L.) with contrasting tolerance to heat stress.

The incidence of heat episodes during the phase of reproductive development in crops is accountable for great yield losses worldwide. Plants subjected to stress events during vegetative stages (primed) are reported be more resistant to future stress exposure during the reproductive phases. We aimed to test if repeated early abiotic stresses could improve heat tolerance during anthesis in wheat cultivars. Two wheat cultivars (Triticum aestivum L.), 'Gladius' and 'Paragon', were subjected to a heat priming process consisting of two periods with heat at the developmental stages of three and five completely developed leaves, respectively. The primed and non-primed plants were later subjected to either a heat stress or non-heat stress (control) temperature for seven days during anthesis. Gas exchange and chlorophyll fluorescence were used to investigate the physiological performance of the plants. No difference in assimilation rate was observed between treatments for 'Gladius'. Measurements were not possible to obtain for heat stressed 'Paragon' plants due to premature senescence. We did not observe strong evidence to prove our hypothesis of early heat stress (priming) being accountable for improving heat tolerance. However, a significant difference between cultivars in response to heat stress was observed. The yield parameters of 'Gladius' primed plants did not differ from their respectively control treatment. A distinct result was observed for the heat sensitive cultivar 'Paragon', suggesting a cumulative deleterious effect caused by the repeated heat stress.