Abstract: 【Objective】 hybrids between indica and japonica rice can produce significant hybrid vigor or heterosis, application of which can improve yields and tolerance to the biotic and abiotic stresses of rice. One of the major factors limiting the application of heterosis in rice is the big difference of flowering time in a day between the two subspecies. Indica rice often blooms early, but japonica rice blooms later. The flowering asynchronism will reduce the yields of hybrid seeds, enhance the cost of hybrid seed production, and further constrain the application of heterosis between the two subspecies. Previous results show that spraying methyl jasmonate (MeJA) can effectively promote rice flowering in the day. But the sensitivity of flowering time of rice varieties to MeJA remains obscure. In this study, the differential responses of the floret opening to MeJA between indica and japonica rice were investigated, which will provide a theoretical basis for improving the yields of the inter-subspecies hybrid rice seed production and enhancing the possibility to utilize the heterosis between indica and japonica rice directly.【Method】 To investigate the dynamics of floret opening, six varieties of subsp. indica and japonica were respectively, planted in the experimental station of Rice Research Institute at Shenyang Agricultural University in 2012 and 2013. Three concentrations of MeJA, 0.04 mmol•L-1, 0.4 mmol•L-1, and 4 mmol•L-1, were sprayed on the panicle and top leaves of the rice plants at 17:00 last afternoon, 6:00 and 8:00 in the morning, respectively. Water, no addition of MeJA, was used as control (CK). The flowering-begin-time (FBT), the vigorous-flowering-time (VFT), the flowering-end-time (FET), the time from the beginning of flowering to vigorous flowering (BVT), the time from the beginning of vigorous flowering to flowering end (VET), the time from the beginning of flowering to end (BET) of indica and japonica rice were investigated after application of MeJAs at different times. Criteria for determining the flowering time were as follows: The time of the first flower opening, the time of the most flowers opening, and the time of all the flowers closed were used as the measurement of the FBT, the VFT, and the FET, respectively. The experiment was designed on the randomized block with three replications.【Result】 The concentration of MeJA could significantly promote the flowering time of indica rice compared to the no MeJA treatment (CK). There was no significant difference among the MeJA treatments. Flowering time in a day of japonica rice only responded to the high (4 mmol•L-1) and medium (0.4 mmol•L-1) concentrations of MeJA. There was a significant difference between high concentration and medium concentration of MeJA treatments. The concentration of MeJA had no significant effect on the BVT and VET of both indica rice and japonica rice in contrast to CK. However, the application of MeJA, no matter of the concentration, could obviously extend the BET in indica rice. The spraying time did not affect the flowering time of indica rice. In contrast to indica rice, spraying MeJA at different times of a day, such as 5:00 pm last afternoon, 6:00 am, and 8:00 am in the morning, had significant effects on the flowering time of japonica rice. The results also indicated that high concentration of MeJA could promote the flowering time of indica and japonica rice equally. But lower (0.04 mmol•L-1) and medium (0.4 mmol•L-1) concentrations of MeJA were more effective on accelerating flowering of japonica rice than that of indica rice.【Conclusion】The initial time of floret opening in all indica and japonica rice varieties tested was significantly promoted by applying 4 mmol•L-1 and 0.4 mmol•L-1 of MeJA. The flowering time in a day of six indica varieties, not all, was response to the low dosage of MeJA (0.04 mmol•L-1), suggesting that indica rice was more sensitive to the MeJA treatments compared to japonica rice. The varieties of indica rice responded to MeJA more quickly than japonica rice. Longer time was needed for varieties of japonica rice to flowering as the results of applying MeJA. Treatment with high concentration (4 mmol•L-1) of MeJA at 17:00 last afternoon was the best combination to promote flowering of japonica rice. The optimal combination to promote flowering of indica rice varied from cultivar to cultivar. The most economic and efficient combination was 0.04 mmol•L-1 MeJA sprayed in the morning.

Key words: methyl jasmonate , floret opening time , subsp. indica rice and japonica rice