Objectives We explored the alleviation effect of exogenous 6-benzylaminoadenine (6-BA) on the decline of photosynthetic performance and yield of wheat after low temperature (LT) stress at booting stage, and the appropriate spray concentration.

Methods A low temperature insensitive wheat variety ‘Yannong 19’ and a sensitive wheat variety ‘Wanmai 52’ were selected as the test materials in a pot experiment. The wheat pots were filled with the 0−20 cm layer soil, and then the potted plants were buried into soil during the wheat growing periods. At the boosting stage, wheat pots were dug out and subjected to low temperature stress in a growing chamber for one day. The designed low temperatures were −2°C, and 0°C during 18: 00−6: 00, and 5°C during 6: 00−18: 00. Then the wheat pots were moved back to the field and sprayed with 10, 20 and 30 mg/L 6-BA solution, and the same amount of distilled water as control, respectively. At the booting, grain filling and maturing stage of wheat, the flag leaf samples were collected for the measurements of SPAD, photosynthetic parameters and relative enzyme activities. Grain samples were collected since the 10th day of anthesis for the determination of grain filling rate, at maturing stage, yield and 1000-grain weight were investigated.

Results Compared with the control group, spraying 6-BA increased the SPAD value, net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r) and maximum photochemical efficiency (F_v/F_m) of flag leaves of wheat subjected to low temperature stress, and increased the RuBP carboxylase activity by 12.72%−53.64% and the PEP carboxylase activity by 6.40%−44.17%. Compared with the control, spraying 6-BA increased the average grain filling rate and 1000-grain weight of Yannong 19 by 1.12%−25.00% and 1.32%−20.84%, respectively, and increased the average grain filling rate and 1000-grain weight of Wanmai 52 by 2.75%−28.42% and 6.26%−27.67%, respectively. The recovery effect of exogenous 6-BA on the yield of sensitive wheat variety ‘Wanmai 52’ was superior to that on the low temperature insensitive wheat variety ‘Yannong 19’.

Conclusions Spraying 6-BA at booting stage can significantly improve the photosynthetic characteristics of wheat flag leaves after low temperature stress, speed up the grain filling rate and enhance the 1000-grain weight of wheat, thus reduce the yield loss caused by low temperature stress. In this experiment, 20 mg/L 6-BA solution shows the best mitigation effect on the effects of low temperature stress.