Maximum lethal temperature for flowering and seed set in maize with contrasting male and female flower sensitivities

With a warming climate, heat events occur more frequently especially during flowering of many crops which increasingly threatens food security. The maximum temperature thresholds (TTmax) for different flowering processes and kernel formation, however, are not explicit in maize ( Zea mays L.). For this, a temperature-controlled experiment was conducted including two maize hybrids ZD958 and XY335 that were widely grown in China and six temperature levels (maximum/minimum temperature; 30/20, 32/22, 34/24, 36/26, 38/28 and 40/30 degrees C for 14 consecutive days bracketing the silking stage). Both tasseling and pollen shedding time were advanced with elevated temperature, but silking time was advanced from 30/20 to 36/26 degrees C and then delayed with further temperature increase, thus extending anthesis-silking interval (ASI). Silking rate was significantly reduced to 63% at 40/30 degrees C for ZD958 but maintained at 88%-95% for XY335 compared to that at 30/20 degrees C. Pollen shed weight and pollen viability decreased with elevated temperature with larger reductions in XY335 than in ZD958. Hence, ZD958 and XY335 are female and male flower sensitive hybrids, respectively. Silking rate, pollen shed number and ASI were the most important constraints to kernel formation under HT stress. TTmax for seed set of both hybrids were estimated to be similar to 38 degrees C, and different flowering processes have respective TTmax. These detailed information are important to uncover heat impacts on maize and increase simulation accuracy when modelling heat effects on maize yield. Besides, more attentions need to be directed at female flower sensitivity when breeding and/or selecting heat-tolerant maize hybrids.

Automated summary

With a warming climate, heat events have a significant impact on maize, highlighting the importance of studying the maximum temperature thresholds for flowering and kernel formation to improve simulation accuracy. Attention should be paid to female flower sensitivity when breeding and selecting heat-tolerant maize hybrids.