2.1 Crop husbandry and experimental design
Field experiments were performed over four years of 2015-2018 at Lvfeng
Experimental Station of Chongqing Academy of Agricultural Sciences
(29.86°N, 106.0°E), southwest of China. The region’s climate was
classified as Cfa according to Köppen, with mild winter and fully humid,
hot, and rainy summer, with an average annual precipitation of 1000 –
1350 mm and an average annual temperature between 16 – 18 °C. The soil
of the region was red earth soil with 4.6 – 5.5 pH, 0.4 – 1.2%
organic matter, 0.05 – 0.06% total nitrogen, 0.01 – 0.02% total
phosphorus, and 1.2 – 1.8% total potassium at a depth of 0 – 20 cm.
The experimental design was a randomized complete block with three
replicates. Each block consisted of six rows, 5 m long, spaced 0.8 m
apart. There were 162 maize inbred lines used in each of four
experimental years, of which, 40 temperate (Te), 45 tropical (Tr), and
77 Te×Tr lines were included. Germplasms information was provided in the
Supplementary Table 1. All the inbred lines were sown at two sowing
dates in 2015 and 2016 (first sowing date, Mar. 21 in two years; second
sowing dates were Apr. 28 in 2015 and May. 24 in 2016) and one sowing
date in 2017 (Apr. 6) and 2018 (Apr.13). Plants that were sown at the
first sowing date in 2015 and 2016 were not or slightly subjected to
high temperature only during late growth period, that were regarded as
control. Plants sown at the second sowing date were subjected to high
temperature mainly during flowering that were regarded as high
temperature treatment at flowering (HDF). And, plants sown in 2017 and
2018 were exposed to high temperature during the early grain filling
period, being regarded as high temperature treatment during early grain
filling (HEGF). The temperature data during the entire growing period of
maize was shown in Supplementary Table 2.
At sowing, three seeds per hill were hand sown and thinned to one plant
at the 3-leaf stage. Crops were fertilized with 60 kg N
ha-1, 105 kg P2O5ha-1, and 120 kg K2O
ha-1 at sowing, and additional extra 70 kg N
ha-1 was applied at the 6- and 12-leaf stages,
respectively. Crop management consistent with local practices were
performed to control weeds, insects, and diseases during the entire
growing period.