Paclobutrazol (PBZ) is extensively used to modulate plant architecture in rice. However, its comprehensive effects on grain yield and aroma in aromatic rice have not been thoroughly investigated. This study used the local aromatic rice cultivars (Meixiangzhan 2 and Xiangyaxiangzhan) as experimental materials to evaluate the impacts of foliar-applied PBZ at three concentrations (0 (CK), 150 (T1), and 300 (T2) mg L⁻¹) on grain yield, photosynthetic characteristics, fragrance formation, and radiation use efficiency (RUE). Field experiments revealed that T1 significantly reduced the leaf area index (LAI) by 10.12% and intercepted photosynthetically active radiation (IPAR) by 10.74%, meanwhile significantly increasing SPAD values by 12.94% and net photosynthetic rate (Pn) by 9.95%, leading to improved RUE up to 25.21%. These changes contributed to a larger number of grains per panicle and increased 1000-grain weight, ultimately enhancing grain yield. In contrast, T2 resulted in a sharp reduction by 24.84% in IPAR and a significant decline in Pn by 10.07% during the late grain-filling stage, thus limiting the supply of photosynthetic assimilates, eventually reducing grain yield. PBZ application also significantly elevated 2-acetyl-1-pyrroline (2-AP) content by 28.74% under T1 and 17.51% under T2, compared to the control. The increase in 2-AP was mainly associated with elevated levels of key precursors, including proline, Δ1-pyrroline-5-carboxylic acid, and Δ1-pyrroline. In spite of differences in traits between cultivars, the traits responded to PBZ in the same pattern. These results indicate that foliar application of PBZ at 150 mg L⁻¹ can effectively improve both yield and aroma of aromatic rice, offering a promising cultivation strategy for high-quality aromatic rice production.

Ultrasonic treatment and optimal cultivation techniques are both conducive to the high yield of super rice in South China. Many previous studies have shown that the increase in intercepted photosynthetically active radiation (IPAR) and radiation use efficiency (RUE) is an important reason for high rice yield. Field experiments were conducted over two years to evaluate the effects of IPAR and RUE on the yield under different treatments (CK: conventional cultivation technique without ultrasonic treatment; T1: conventional cultivation technique with ultrasonic treatment; T2: super rice-specific cultivation technique without ultrasonic treatment and T3: super rice-specific cultivation technique with ultrasonic treatment), with two representative rice varieties, Wufengyou-615 (WFY) and Jingnongsimiao (JNSM) during the late seasons of rice cultivation in South China. The super rice-specific cultivation technique and the ultrasonic treatment could significantly increase the yield, which was significantly (p < 0.01) and positively correlated with panicle number, grain-filling rate, and aboveground total dry weight. The higher grain yield depended more highly on higher RUE in the mid-tillering stage and maturity stage. The results of multiple-regression models also showed that the contributions of IPAR and RUE to yield were significant (p < 0.01). Conclusively, IPAR and RUE contributed a lot to yield progress of super rice in both super rice-specific cultivation techniques with fewer times of topdressing and ultrasonic treatment in South China. It is worth further studying how to reasonably improve the RUE of high-RUE varieties through other means.

Double-cropping rice in South China continued to break through the total yield record, but the yield potential of single-cropping rice wasn’t realized. Radiation use efficiency (RUE) has been singled out as an important determinant of grain yield in cereal species. However, there is no information on whether this yield gaps involved differences to RUE in double-cropping rice. Field experiments were performed over two years to evaluate the effects of intercepted radiation (IP) and RUE, on the above-ground biomass production, crop growth rate (CGR), and harvest index (HI), in four representative rice varieties, i.e., Xiangyaxiangzhan (XYXZ), Meixiangzhan-2 (MXZ2), Nanjingxiangzhan (NJXZ), and Ruanhuayoujinsi (RHYJS) during the early seasons and late seasons of rice cultivation in South China. The results revealed that grain yield of early season was 8.2% higher than late season. The yield advantage in early season was primarily owing to higher spikelet per panicle and above-ground biomass resulting from a higher RUE. The spikelet per panicle in the early season were 6.5, 8.3, 6.9, and 8.5% higher in XYXZ, MXZ2, NJXZ, and RHYJS than late season. The higher grain yield in early season was more closely related to RUE in middle tillering stage (R²=0.34), panicle initiation (R²=0.16), maturation stage (R²=0.28), and intercepted photosynthetically active radiation (IPAR) in maturation stage (R²=0.28), while the grain yield in late season depended higher IPAR in middle tillering stage (R²=0.31) and IPAR in panicle initiation (R²=0.23). Conclusively, the results of this research show that higher RUE contribute to yield progress of early season rice, while the yield improvement of late season rice is attributed to higher radiation during early reproductive stage. To rationally allocate the RUE of the double-cropping rice with high RUE varieties or the adjustment of sowing period deserve the further studied.

This study explored the effects of the sowing stage and nitrogen application rate on the grain yield and its allocation of light-temperature resources over a 9-year experiment from 2011 to 2019. Measurement indicators include the effective accumulative temperature on different growth durations, leaf area index (LAI), above-ground biomass production, and harvest index (HI). Methods: A split-plot design was arranged in the treatment, with N supply as the main plot and the sowing stage as the subplot. The main plots consisted of two nitrogen treatments: low nitrogen (LN: 120 kg ha⁻¹) and high nitrogen (HN: 180 kg ha⁻¹). The subplots contained two sowing stages: the early sowing stage (ES) and the late sowing stage (LS). Results: Compared with LNLS, LNES, and HNLS from 2011 to 2019, HNES of HHZ increased the grain yield by 9.5%, 2.5%, and 5.3%, while the difference in grain yield in YY8 was higher than HHZ, especially under HNES. Compared with LNLS, LNES, and HNLS from 2011 to 2019, HNES of HHZ increased the panicle number by 6.0%, 5.9%, and 1.0%, and HNES of YY8 increased by 12.7%, 11.4%, and 3.8%. Compared with HNLS of HHZ, LNES, LNLS, and HNES decreased the spikelets per panicle by 2.3%, 2.9%, and 1.1%, and decreased by 3.5%, 1.9%, and 2.2% in YY8. The early sowing or increasing N supply significantly increased the dry matter accumulated, grain weight, LAI, and HI. The higher grain yield in LNES was more closely related to the average temperature and the number of spikelets per panicle. The grain yield in HNES was more dependent on the effective accumulative temperature. Conclusions: Sowing in mid-May and increasing the N application (180 kg ha⁻¹) are beneficial to the allocation of light temperature and the increase in yield. Therefore, this research provides a theoretical basis for improving rice yield and optimizing the utilization of light-temperature resources in the future.

Aromatic rice has gained significant attention due to its high economic and nutritional value. 2-Acetyl-1-pyrroline (2-AP), a key aroma compound in aromatic rice, plays a crucial role in elucidating the aroma characteristics of aromatic rice. However, there is no report on the effect of aromatic rice in rice–potato rotation on aroma characteristics. In order to study the influences of winter-planted potatoes on the yield, quality, and 2-AP biosynthesis of aromatic rice grains, the commonly cultivated aromatic rice variety Meixiangzhan-2 and the potato cultivar Huashu-5 were selected as experimental materials for a three-year consecutive field experiment with different tillage patterns consisting of rice–winter fallow as the control group (CK) and rice–potato rotation as the experimental group (RP). The results indicated that the RP treatment enhanced the soil nutrient content and decreased the bulk density. Compared with CK, RP treatment increased the effective panicle number by 10.88% and grain number per panicle by 8.82%, thereby increasing the yield by 11.99%. Meanwhile, RP treatment improved the brown rice rate by 2.61%, milled rice rate by 4.53%, head milled rice rate by 7.51%, and crude protein content by 6.98%. Regarding 2-AP biosynthesis in grains, in contrast to CK, the RP treatment raised the levels of related precursors (Δ1-pyrroline, Δ1-pyrrolidine-5-carboxylic acid, and proline increased by 8.95%, 18.14%, and 13.75%, respectively) and enzymes (proline dehydrogenase, ornithine transaminase, and diamine oxidase increased by 18.37%, 14.61%, and 11.36%, respectively) in its synthesis pathway, thereby facilitating the accumulation of 2-AP. Furthermore, we also observed a more stable yield and grain 2-AP content in aromatic rice under RP treatment. Overall, with regard to enhancing the aromatic rice yield and aroma, the rice–potato rotation system can be contemplated for vigorous promotion.