【Objective】 The aim of this study is to clarify the differences in yield, growth period and the allocation of temperature and light resources of different types of double-cropping late japonica rice in different ecological regions in the middle and lower reaches of the Yangtze River, so as to lay a theoretical basis for application of early indica and late japonica model in the rice growing area of the middle and lower reaches of the Yangtze River.【Method】 The experiment was conducted at Fuyang (30.13°N, 41.7 m above sea level) and Wenzhou (28.52°N, 83 m above sea level ), Zhejiang Province from 2018 to 2019. Rice cultivars were selected based on the large area of application, including inbred japonica (IJR) and indica/japonica hybrid rice (IJHR) with the high-yield indica rice (IR) as a control. The differences in yield, growth period and the allocation of temperature and light resources of IR, IJR and IJHR in the late growing season in different ecological regions were compared.【Result】 1) The dry matter, effective panicle number and sink of japonica rice declined at low latitude as compared to high latitude. As a result, the yield declined by 2.4%–19.1%, while the grain setting and 1000-grain weight remained stable or went up slightly. Meanwhile, the yield of IJHR was 8.8–10.3 t/hm2 in Fuyang and 8.0–10.2 t/hm2 in Wenzhou, being the highest in both sites. 2) The growth period of the tested cultivars at two latitudes differed. Compared with the high latitude, there was no significant difference in the vegetative stage at the low latitude, and the reproductive stage was slightly reduced (4.2%–27.3%), while the grain filling stage was significantly shortened, among which IR, IJR and IJHR shortened by 7.3%–11.9%, 20.8%–41.9%, 23.1%–35%, respectively. 3) The differences in the temperature and light allocation in different growth period mainly reflected in the grain filling stage. The average temperature during the grain filling stage at the low latitude was higher than that at the high latitude (IR, IJR and IJHR increased by 0.4–2.4 ℃, 2.3–3.5 ℃ and 2.5–2.8 ℃, respectively). The effective accumulated temperature at the two latitudes varied with cultivars, and IR had no significance, while IJR and IJHR declined by 24.7–126.4 ℃ and 25.7–107 ℃, respectively. 4) The analysis of PCA showed that latitude was the primary cause for the accumulation differences of temperature and light resources and the yield (PC1 and PC2, contribution of 49%), followed by the cultivars' temperature and light sensitivity (PC5, contribution of 18%) and the panicle and grain structure (PC3, contribution of 14%).【Conclusion】 Compared to the high latitude, the decrease of yield of japonica rice is mainly due to the shortened growth period especially the grain filling stage, decreased effective accumulative temperature and sink. IJHR is characterized by higher yield advantages, which may be due to its grain superiority. Therefore, japonicas with heavy or large panicles may have higher application potential in the middle and lower reaches of the Yangtze River.
