Abstract: Taking Yunyan 87 as experimental material, the growth of axillary buds, the total number of flowers, the seed yield and the number of single fruit grains were investigated after applying different concentrations and different types of exogenous plant growth regulators, to select a kind of plant growth regulator which can promote tobacco flower bud differentiation, increase the total number of flowering, and then improve the seed yield and the suitable application concentration. The results showed that the application of polyamine （Spd, Put, Spm, Cad）, vitamin E, 6-BA and so on could increase the number of tobacco flowering obviously. Among them, 10 mg/L Spd and 10 mg/L Put had the better effect, which increased by 44.21% and 37.65%, respectively. Put, Spm, Cad, vitamin E and so on could increase the yield of tobacco seed obviously. Among them, 30 mg/L Put and 30 mg/L Spm had the best effect, which increased by 136.47% and 81.18%,respectively compared with the control. Application of 30 mg/L Put and 200 mg/L 6-BA significantly increased the number of single fruit grains by 9.93% and 4.02%, respectively, and application of 50 mg/L Put and 100 mg/L Spd significantly increased the 1 000-grain weight of tobacco seeds, it increased by 9.52% and 9.90%,respectively. The application of GA₃ and NAA did not increase the number of flowers, seed yield and seed number per fruit.

Key words: exogenous plant growth regulator, tobacco, number of flowers, number of grains per fruit, seed yield