Abstract: Population characteristics of super-high-yielding hybrid japonica rice (13.5 t ha^-1) were studied and its formation mechanism was explored using Yongyou 8 as material in Xinghua and Jiangyan. Results showed that population of 13.5 t ha^-1 had more spikelets per panicle and total spikelets than population of 12.0 t ha^-1. There was no significant difference in panicles, filled-grain percentage and 1000-grain weight between populations of 13.5 t ha^-1 and 12.0 t ha^-1. Population of 13.5 t ha^-1 exhibited fewer tillers at the early growth stage and achieved excepted number of stems and tillers at critical leaf-age for productive tillers, whose max number of stems and tillers was at jointing stage and was about 1.3 times of excepted number. Then, the number of population stems and tillers began to decrease stably, which achieved expected number again. At last, ratio of productive tillers to total tillers of 13.5 t ha^-1 population was more than 75%, which was higher than that of population of 12.0 t ha^-1.The leaf area index of 13.5 t ha^-1 population was lower than that of 12.0 t ha^-1 population at the early growth stage, and the max leaf area index was about 8.5 at booting, which decreased stably and was above 4.0 at maturity. The photosynthetic potential of population with 13.5 t ha^-1 was small at early stage and larger at middle and late stages, as compared with population with 12.0 t ha^-1. The total photosynthetic potential was above 6.75×10⁶ m² d ha^-1, of which most than 45.0% was from heading to maturity. The dry matter accumulation was smaller compared with population with 12.0 t ha^-1 before jointing, and the weight of it was above 60 kg ha^-1 at heading, which was significantly higher than that of population with 12.0 t ha^-1. The total weight of dry matter was above 23.25 t ha^-1, of which above 9.75 t ha^-1 was accumulated from heading to maturity. Formation mechanism of super-high yielding population (13.5 t ha^-1) was that: population quality was enhanced at critical leaf-age for productive tillers through cultivating strong seedlings, germinating low positiontillers and achieved expected number of stems and tillers in time, which formed the biological foundation for high quality population at middle stage; in order to form high photosynthetic efficiency of population structure with strong lodging-resistance and large population spikeletes at heading, suitable number of strong stems and large panicles was cultivated through establishing suitable dynamic and size of population; in order to enlarge sink-filling and keep strength of stems and sheaths, dry matter accumulation was enriched after heading through photosynthetic system smooth and steady fade away.

Key words: Hybrid Japonica rice, Super*high yielding, Characteristics of population, Formation mechanism