Heat stress on maize with contrasting genetic background: Differences in flowering and yield formation

High temperature is becoming a growing threat to global food security with warming climate. Maize grain yield greatly reduces when subjected to heat stress around flowering and early grain filling, but the responses of temperate (Te) and tropical (Tr) maize genotypes to heat stress are unclear. For this, 162 maize inbred lines including 40 Te, 45 Tr and 77 Te x Tr lines were grown at six sowing dates over four years of 2015 - 2018. Yield reduction was mainly a function of the reduced kernel number under heat stress around flowering and early grain filling period. Kernel number on average reduced by 73-98% under heat stress around flowering, with Tr inbred lines having significantly smaller reductions than Te and Te x Tr inbred lines. Kernel number reduction of Te, Tr, and Te x Tr varied largely in heat stress, indicating there are both heat sensitive and tolerant inbred lines in each group. Tasseling, pollen shedding, and silking time were all advanced by high temperature with a larger advance in pollen shedding than in silking, thus extending anthesis-silking interval. Tr inbred lines on average maintained a lower flowering - time plasticity than Te inbred lines, which partly explained the higher heat tolerance of Tr maize. Post-silking growth in a short period of approximately two weeks were most sensitive to high temperature in maize. Adjusting sowing date was a more effective strategy to reduce heat impacts around flowering than maize genotypes, but sowing date and genotype combined together alleviated ~80% of negative effects of heat stress on yield. Hence, selecting of and breeding for heat tolerant maize genotypes is becoming more urgent, and heat tolerant inbred lines used in this study can be potential germplasm resource. Heat tolerant genotype and proper sowing date should be combined with alternative strategies to cope with heat stress with warming climate.

Automated summary

High temperature poses a growing threat to global food security, particularly the yield of maize during flowering and early grain filling. There are both heat sensitive and tolerant inbred lines within temperate and tropical maize genotypes. Adjusting sowing date is an effective strategy to mitigate the negative effects of heat stress on yield.