弱光胁迫已成为水稻生产中日趋严重的逆境，然而关于弱光胁迫对华东地区水稻产量和品质的研究报道仍较少；此外，也应探索合理的氮肥施用措施以减轻弱光胁迫对水稻产量和品质的负面效应。本研究旨在明确遮光（无遮光、花后遮光）和穗肥施用量（N_DP，降低穗肥用量；N_MP，正常穗肥用量；N_IP，增加穗肥用量）对水稻产量和品质相关性状的影响。与无遮光相比，遮光处理下水稻减产9.5%-14.8% (P<0.05)，主要是由于较低的结实率和粒重。无遮光处理下，N_MP和N_IP的产量显著高于(P<0.05)N_DP；遮光处理下，不同穗肥施用处理的产量则无显著差异。与N_MP和N_IP相比，N_DP在遮光处理的减产幅度小，这主要是由于其较高的结实率和粒重。与无遮光相比，遮光处理降低了花后叶片光合速率、成熟期干物质、抽穗至成熟期干物质积累量和成熟期茎鞘非结构性碳水化合物(NSC)的积累量。N_DP则提高了遮光处理下的收获指数和NSC运转效率。与无遮光相比，遮光处理降低了稻米糙米率、精米率、整精米率和直链淀粉含量，提高了垩白米率、垩白面积和垩白度以及蛋白质含量。无遮光处理下稻米加工品质以N_MP最优，遮光处理下则以N_DP最优。在无遮光和遮光处理下，N_DP的垩白米率、垩白面积和垩白度均低于N_MP和N_IP。遮光处理下，N_DP的直链淀粉含量和崩解值降低，蛋白质含量和消减值则提高，从而实现了与无遮光处理相近的食味值。本研究结果表明，花后遮光显著恶化水稻产量和稻米品质。遮光处理下，N_DP可促进NSC转运、提高收获指数以及库容充实效率，从而降低产量损失；此外，N_DP可维持遮光处理下稻米加工、外观和蒸煮食味品质。因此，适当降低穗肥施用可减轻弱光胁迫对水稻产量和品质的负面效应。

   Understanding the morphological and physiological traits associated with improved filling efficiency in large-panicle rice varieties is critical to devise strategies for breeding programs and cultivation management practices. Information on such traits, however, remains limited. Two large-panicle varieties with high filled-grain percentage (HF) and two check large-panicle varieties with low filled-grain percentage (LF) were field-grown in 2012 and 2013. The number of spikelets per panicle of HF and LF both exceeded 300, and the filled-grain percentage (%) of HF was approximately 90, while that of LF was approximately 75 over the two years. The results showed that when the values were averaged across two years, HF yielded 12.9 t ha^–1, while LF yielded 11.0 t ha^–1. HF had a greater leaf area duration, biomass accumulation and transport of carbohydrates stored in the culm to the grains from heading to maturity compared with LF. HF exhibited a higher leaf photosynthetic rate, more green leaves on the culm, and higher root activity during filling phase, especially during the middle and late filling phases, in relative to LF. The length of HF for upper three leaves was significantly higher than that of LF, while the angle of upper three leaves on the main culm was less in both years. Meanwhile, specific leaf weight of HF was significantly higher when compared with LF. In addition, the grain filling characteristics of HF and LF were investigated in our study. Our results suggested that a higher leaf photosynthetic rate and root activity during filling phase, greater biomass accumulation and assimilate transport after heading, and longer, thicker and more erect upper three leaves were important morphological and physiological traits of HF, and these traits could be considered as selection criterion to develop large-panicle varieties with high filled-grain percentage.

Late-maturity type of Yongyou japonica/indica hybrids series (LMYS) have shown great yield potential, and are being widely planted in the lower reaches of Yangtze River, China. Knowledge about suitable growing zone and evaluation of yield advantage is of practical importance for LMYS in this region. Fifteen LMYS, two high-yielding inbred japonica check varieties (CK-J) and two high-yielding hybrid indica check varieties (CK-I) were grown at Xinghua (119.57°E, 33.05°N) of Lixiahe region, Yangzhou (119.25°E, 32.30°N) of Yanjiang region, Changshu (120.46°E, 31.41°N) of Taihu Lake region, and Ningbo (121.31°E, 29.45°N) of Ningshao Plain in 2013 and 2014. The results showed that maturity dates of the 15 were later than the secure maturity date at Xinghua and 6, 14 and 15 LMYS were mature before the secure maturity date at Yangzhou, Changshu and Ningbo, respectively. One variety was identified as high-yielding variety among LMYS (HYYS) at Yangzhou, 8 HYYS in 2013 and 9 HYYS in 2014 at Changshu, 9 HYYS at Ningbo. HYYS here referred to the variety among LMYS that was mature before the secure maturity date and had at least 8% higher grain yield than both CK-J and CK-I at each experimental site. Grain yield of HYYS at each experimental site was about 12.0 t ha–1 or higher, and was significantly higher than CK varieties. High yield of HYYS was mainly attributed to larger sink size due to more spikelets per panicle. Plant height of HYYS was about 140 cm, and was significantly higher than check varieties. Significant positive correlations were recorded between duration from heading to maturity stage and grain yield, and also between whole growth periods and grain yield. HYYS had obvious advantage over check varieties in biomass accumulation and leaf area duration from heading to maturity stage. Comprehensive consideration about safe maturity and yield performance of LMYS at each experimental site, Taihu Lake region (representative site Changshu) and Ningshao Plain (representative site Ningbo) were thought suitable growing zones for LMYS in the lower reaches of Yangtze River. The main factors underlying high yield of HYYS were larger sink size, higher plant height, longer duration from heading to maturity stage and whole growth periods, and higher biomass accumulation and leaf area duration during grain filling stage.