A robust field-based method to screen heat tolerance in wheat

Wheat is highly sensitive to heat shocks and their timing. Hence, field-based ranking for heat tolerance may be confounded by phenological variations at the time of heat events. A photoperiod-extension method (PEM) was developed, allowing screening of wheat genotypes at matched developmental stages despite phenological variations. Paired trials were conducted to compare PEM and conventional field screening. In the PEM, artificial lighting was installed at one end of each row, inducing a gradient of flowering times. Individual stems or plot quadrats of each genotype were tagged at flowering. Late-sown plants experienced significantly more heat and greater grain yield reductions than early sown plants. Strong correlations between trials experiencing a similar degree of heat were found both for individual grain weight (IGW) and total grain weight with the PEM, either with individual stem tagging or quadrat tagging. By contrast, correlations for IGW and yield in these environments were either poor or negative for conventional trials. With the PEM, strong genetic correlations were found between irrigated environments of similar heat stress, with respective r correlations ranged from 0.46 to 0.8 for IGW; and 0.54–0.75 for total grain weight. By contrast these correlations were substantially weaker for conventional yield plots (average r values ranged from 0.11 to 0.53 for IGW; and 0.05–0.36 for grain yield. The quadrat sampling appeared overall more suitable for high-throughput phenotyping. The method promises to improve the efficiency of heat tolerance field screening, particularly when comparing genotypes of different maturity types