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Hill number per unit area and seedling number per hill are foundational agrotechnical factors shaping the growth and development of rice plants. This study aimed to determine the effects of decreasing the hill number per unit area combined with increasing the seedling number per hill on grain quality in hybrid rice. Field experiments were performed in Hengyang, Hunan Province, China, in 2022 and 2023 using the hybrid rice variety Huazheyou 261, as well as in Liuyang, Hunan Province, China, in 2023 using the hybrid rice varieties Yueyou 2646 and Zhenliangyouyuzhan. Treatments (combining hill number per unit area and seedling number per hill) encompassed a combination of 24 hills per m2 and one seedling per hill (H24S1) and a combination of 14 hills per m2 and three seedlings per hill (H14S3) in Hengyang, as well as a combination of 28 hills per m2 and two seedlings per hill (H28S2) and a combination of 14 hills per m2 and four seedlings per hill (H14S4) in Liuyang. There were no significant differences in the leaf area index at the heading stage, as well as no significant differences in canopy light transmittance during the grain-filling period between H24S1 and H14S3 in Hengyang, or between H28S2 and H14S4 in Liuyang. The differences in grain quality traits, including milling traits (brown, milled, and head rice rate), appearance traits (rice length, rice length-width ratio, chalky grain rate, and chalkiness degree), amylose and protein content, and pasting characteristics were also not significant between H24S1 and H14S3 in Hengyang, nor between H28S2 and H14S4 in Liuyang. This study indicates that the grain quality in hybrid rice is unaffected by decreasing the hill number per unit area integrated with increasing the seedling number per hill.

Improving grain quality is critical to the development of hybrid rice. In recent years, multiple hybrid rice cultivars with superior grain quality have been developed in China through dedicated breeding efforts. However, limited information is available on yield performance and yield formation characteristics of these high-quality hybrid rice cultivars. In this study, field experiments were conducted to compare yield attributes between a recently developed indica hybrid rice with superior grain quality (Jingliangyou 1468, JLY1468) and a relatively older indica hybrid rice cultivar with high yield potential (Liangyoupeijiu, LYPJ). Results showed that grain yield was 13–17% higher in JLY1468 than in LYPJ. The higher grain yield of JLY1468 than of LYPJ was mainly attributable to a higher spikelet filling percentage, which was closely related to a higher harvest index resulting from a higher crop growth rate during the post-heading period. The results of this study suggest that late-stage vigor may be a vital trait for the development of indica hybrid rice cultivars with both high quality and high yield.

The demand for and consumption of soft-textured, high-quality rice with low amylose content have substantially increased in China with improved economic and living standards. Shifting sowing date is a common strategy to optimize temperature conditions and improve rice quality. In this study, a high-quality rice cultivar with low amylose content (Jingliangyou 1468) was grown under four sowing dates (May 15th and 25th, and June 4th and 14th) in 2019 and 2020 to determine the effects of sowing date on palatability-related traits and evaluate relationships between palatability-related traits and daily mean temperature during the grain-filling period. Results showed that delaying sowing date decreased daily mean temperature during the grain-filling period and consequently increased amylose content and setback viscosity of milled rice flour, which in turn increased hardness and chewiness of cooked rice. The finding of this study suggests that the strategy of delayed sowing does not improve the palatability of high-quality rice in the context of consumers’ preference for soft-textured rice.

Field experiments were conducted to compare two hybrid rice cultivars—a recently released high-quality cultivar (Jingliangyou 1468, JLY1468) and a relatively older cultivar (Liangyoupeijiu, LYPJ). Results showed that hardness, springiness, cohesiveness, resilience, and chewiness of cooked milled rice were all lower in JLY1468 than in LYPJ, due to its lower amylose content and altered paste properties of milled rice flour. Active digestion duration of cooked milled rice was 26% shorter and the glucose production rate from starch digestion was 33% faster in JLY1468 compared with LYPJ. Texture and starch digestion properties of cooked milled rice as a factor of temperature during the grain-filling period were different between LYPJ and JLY1468 due to differing amylose contents and gel consistencies of milled rice flour in response to temperature. This study highlights that attention should be paid to potential health risks associated with the development of high-quality hybrid rice cultivars with soft texture.

Head milled rice is the main form of rice for sale and consumption. However, previous studies on the yield change due to the development of new cultivars in rice generally focus on grain yield but few on head milled rice yield. In this study, field experiments were conducted in two years (2019 and 2020) to compare head milled rice yield and associated traits (grain yield, milled recovery traits, and shape and chalkiness traits of rice grains) between two middle-season hybrid rice cultivars released 18 years apart, i.e., Jingliangyou 1468 (JLY1468), a recently-released cultivar with high eating quality, and Liangyoupeijiu (LYPJ), an old cultivar with high grain yield. JLY1468 had higher head milled rice yield than LYPJ by 30% in 2019 and by 33% in 2020. The higher head milled rice yield in JLY1468 than in LYPJ was attributable to improvements in both grain yield, and head milled rice rate (HMRR). The improvement in HMRR in JLY1468 compared to LYPJ was mainly attributable to a reduction in chalkiness degree, which was associated with a decrease in rice grain size. The results of this study provide evidence for the improvement in head milled rice yield in middle-season hybrid rice with the development of new cultivars in recent years.

Inbred rice has been grown more and more widely, while the planting area of hybrid rice has decreased by approximately 25% in China since 1995. This study aimed to assess the changes in grain yield and yield attributes due to cultivar development in indica (Oryza sativa ssp. indica) inbred rice in China. Field experiments were conducted in 2019 and 2020 to determine the performance of grain yield and yield attributes of an indica super inbred rice cultivar Jinnongsimiao (JNSM) released in 2010 by comparing it with an indica high-yielding inbred rice cultivar Guichao 2 (GC2) released in 1978 and an indica super hybrid rice cultivar Y-liangyou 900 (YLY900) released in 2016. Results showed that JNSM produced 18% higher grain yield than GC2 but 6% lower grain yield than YLY900. Compared with GC2, JNSM had higher spikelets per panicle, spikelet-filling percentage, and harvest index by 67%, 4%, and 11%, respectively. Compared with YLY900, JNSM had 14% lower grain weight and 19% lower biomass production during the pre-heading period. The difference in biomass production during the pre-heading period between JNSM and YLY900 was explained more by crop growth rate than growth duration. This study suggests that (1) the recently released indica super inbred rice cultivar JNSM outyields the old indica high-yielding inbred rice cultivar GC2 as a result of increasing panicle size, spikelet-filling percentage, and harvest index, and (2) further improvement in grain yield in indica inbred rice can be achieved by improving biomass production through promoting pre-heading crop growth.

Early vigor is important for crop establishment in rice. This study was conducted to determine the seed and seedling traits in relation to early vigor in rice. Laboratory tests and pot experiments were carried out in 2013 and 2014. Morphological and physiological traits of seeds and seedlings were compared between two contrasting rice cultivars, Yuxiangyouzhan with superior early vigor and Huanghuazhan with general early vigor. For seed traits, Yuxiangyouzhan had lower seed hull weight but higher seed amylose content, seed amylase activity, and plumule–radicle ratio than Huanghuazhan, and consequently, Yuxiangyouzhan had about 10% higher germination percentage and velocity and 37% longer plumule than Huanghuazhan. For seedling traits, leaf area, specific leaf weight, leaf chlorophyll and soluble protein contents, leaf net photosynthetic rate, and shoot–root ratio were higher in Yuxiangyouzhan than in Huanghuazhan, and as a result, seedling shoot biomass was 23–32% higher in Yuxiangyouzhan than in Huanghuazhan. These results indicate that Yuxiangyouzhan has both superior seed and seedling vigor. The former is attributed to the low mechanical strength of seed hull, high conversion efficiency of seed reserve, and high mobilization of seed reserve to plumule, while the latter is due to large leaf area, high leaf photosynthetic capacity, and high partitioning of dry matter to shoot. This study enriches the physiological understanding of superior early vigor in rice.

To compare N uptake and use efficiency of rice among different environments and quantify the contributions of indigenous soil and applied N to N uptake and use efficiency, field experiments were conducted in five sites in five provinces of China in 2012 and 2013. Four cultivars were grown under three N treatments in each site. Average total N uptake was 10–12 g m−2 in Huaiji, Binyang, and Haikou, 20 g m−2 in Changsha, and 23 g m−2 in Xingyi. Rice crops took up 54.6–61.7% of total plant N from soil in Huaiji, Binyang, and Haikou, 64.3% in Changsha, and 63.5% in Xingyi. Partial factor productivity of applied N and recovery efficiency of applied N in Changsha were higher than in Huaiji, Binyang, and Haikou, but were lower than in Xingyi. Physiological efficiency of soil N and fertilizer N were lower in Changsha than in Huaiji, Binyang, and Haikou, while the difference in them between Changsha and Xingyi were small or inconsistent. Average grain yields were 6.5–7.5 t ha−1 (medium yield) in Huaiji, Binyang, and Haikou, 9.0 t ha−1 (high yield) in Changsha, and 12.0 t ha−1 (super high yield) in Xingyi. Our results suggest that both indigenous soil and applied N were key factors for improving rice yield from medium to high level, while a further improvement to super high yield indigenous soil N was more important than fertilizer N, and a simultaneous increasing grain yield and N use efficiency can be achieved using SPAD-based practice in rice production.

The development of large-scale farming has encouraged the adoption of mechanical transplanting techniques for rice production. However, the increased farming operation times that often occur under large-scale farming conditions necessitate shortening the duration of rice growth, especially that of late-season rice; therefore, rice cultivars with short growth durations are popular under such conditions. A field experiment using two short-duration rice cultivars (SRCs), i.e., Jiuliangyou 3 and Shengyou 9520, and two long-duration rice cultivars (LRCs), i.e., Shengyou 957 and Tianyouhuazhan, was conducted in the late season in Yongan and Santang, Hunan Province, China in 2017 and 2018. The grain yield and yield attributes were compared between the SRCs and LRCs, showing that the SRCs, which exhibited an 11–12-day shorter growth period, revealed similar grain yield to the LRCs. The SRCs also exhibited a 10–31% higher spikelet filling rate and a 13% higher harvest index than the LRCs. Moreover, the biomass accumulation, crop growth rate, and apparent radiation use efficiency of the SRCs were significantly higher than those of the LRCs during the postheading phase. Our results indicate that the higher spikelet filling rate, the harvest index, and the apparent radiation use efficiency of the postheading period were the underlying factors for the SRCs’ grain yield.

Warm temperature during post-heading is generally hypothesized to be the critical factor limiting grain yield of early-rice in South China. However, there is no direct evidence to confirm this hypothesis in the field. This study was conducted to determine the temperature-related yield constraints of early-rice in South China. Field experiments were carried out in Huaiji (a location in South China) and Changsha (a location in the Yangtze River basin) in 2011-2013. In each year, two rice cultivars were grown in early-rice growing season in Huaiji and in single-rice growing season in Changsha. Huaiji had higher average daily maximum temperature during post-heading than Changsha. The higher temperature during post-heading induced early plant senescence (slower crop growth rate and shorter grain filling duration), but grain weight did not reduce because it was compensated for by increased translocation of pre-heading biomass. The higher temperature during post-heading also did not cause a reduction in grain filling percentage. Huaiji had lower temperature during pre-heading than Changsha, which to some extent resulted in slower crop growth rate and consequently lower biomass production and smaller sink size in Huaiji than in Changsha. As a result, grain yield was about 30% lower in Huaiji than in Changsha. Our results indicate that grain yield of early-rice in South China is limited not by warm temperature during post-heading but partially by cool temperature during pre-heading, and suggest that enhancing sink size and meanwhile maintaining good translocation of pre-heading biomass may be an effective way to achieve high yield for early-rice in South China.

Ensuring rice (Oryza sativa) self-sufficiency in China relies significantly on achieving high grain yields in hybrid rice production. This study conducted field experiments across two site-years, comparing grain yield per unit of land area, grain yield generated per seedling, and associated yield traits for a hybrid rice variety under two combinations of hill spacing and the number of seedlings per hill. The combinations included a hill spacing of 30 cm × 14 cm with one seedling per hill (H14S1) and a hill spacing of 30 cm × 24 cm with three seedlings per hill (H24S3). The results revealed that H14S1 consistently outperformed H24S3, demonstrating a 7%–16% increase in grain yield per unit of land area and an impressive 88%–104% higher grain yield generated per seedling. H14S1 exhibited 56%–77% more panicles formed per seedling and 10%–15% more spikelets per panicle compared to H24S3. H14S1 produced 78%–115% higher biomass at heading and maturity per seedling and 8%–25% higher biomass at heading and maturity per tiller than H24S3. This study underscores the importance of promoting the individual growth and development of seedlings as a crucial strategy for achieving higher grain yield in hybrid rice production. [ABSTRACT FROM AUTHOR]

Rice yield stability is a breeding goal, particularly for short-growth duration rice, but its underlying mechanisms remain unclear. In an attempt to identify the relationship between yield stability and source-sink characteristics in short-growth duration rice, a field experiment was conducted at three sites (Yueyang, Liuyang, and Hengyang) in 2021 and 2022. This study compared yield, yield components, source-sink characteristics, and their stability between two stable-yielding short-growth duration rice cultivars, Zhongzao 39 (Z-39) and Lingliangyou 268 (L-268), and two unstable-yielding short-growth duration rice cultivars, Zhongjiazao 17 (Z-17) and Zhuliangyou 819 (Z-819). The stability of agronomic parameters was represented by the coefficient of variation (CV). The respective CVs of yield in Z-17, Z-819, Z-39, and L268 were 10.2%, 10.1%, 4.5%, and 5.7% in 2021 and 19.7%, 15.0%, 5.4%, and 6.5% in 2022. The respective CVs of grain weight were 6.3%, 5.7%, 3.4%, and 4.5% in Z-17, Z-819, Z-39, and L-268 in 2021, and 8.1%, 6.3%, 1.5%, and 0.8% in 2022. The mean source capacity per spikelet and pre-heading non-structural carbohydrate reserves per spikelet (NSCpre) were 7%-43% and 7%-72% lower in Z-819 and Z-17 than in L-268 and Z-39 in 2021 and 2022. The mean quantum yield of photosystem II photochemistry of leaf, leaf area index, and specific leaf weight of L-268 and Z-39 were higher than those of Z-819 and Z-17 at the heading stage. This study suggests that high NSCpre, caused by great leaf traits before heading, increases source capacity per spikelet and its stability, thereby increasing the stability of grain weight and yield. Increasing NSCpre is critical for achieving grain weight and yield stability in short-growth duration rice. [ABSTRACT FROM AUTHOR]

We report the measurement of the terahertz (THz) spectra of 4-aminobenzoic acid by using Fourier transform infrared (FTIR) spectroscopy in the 1.5-19.5 THz. Low frequency intermolecular (or phonon) modes between 0.3 and 2.4 THz were also investigated via THz time-domain spectroscopy. Structure and vibrational frequencies of the sample were calculated through density functional theory(DFT). The calculated results are in agreement with the experimental data. Moreover, we have interpreted observed vibrational frequencies using DFT. Two intermolecular or phonon modes were identified at 1.54 and 2.19 THz. [ABSTRACT FROM AUTHOR]