Jiana Chen

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Identifying the key yield components influencing rice yield is crucial for developing high-yielding ultrashort- and short-duration cultivars, which could meet the demands of intensified cropping systems. This study used data collected over 6 years to compare grain yield and yield components between the ultrashort-duration (85–100 days) and short-duration (100–110 days) rice cultivars under mechanical transplanting conditions. Grain yield in the ultrashort-duration group ranged from 5.71 to 10.47 t ha⁻¹ (mean: 7.97 t ha⁻¹), while that in the short-duration group ranged from 6.00 to 11.84 t ha⁻¹ (mean: 7.67 t ha⁻¹), with no significant difference between the groups (p > 0.05). The ultrashort-duration group had 15.56% fewer spikelets per panicle but a 7.9% higher grain filling percentage than the short-duration group (p < 0.01). In terms of importance, grain weight was the most critical factor in the ultrashort-duration group (contributing 42.8% to yield), followed by the grain filling percentage (37.5%). Conversely, in the short-duration group, spikelets per panicle was the most important factor, contributing 43.1%, with grain weight accounting for 32.1%. In summary, the ultrashort-duration varieties should prioritize grain weight and the grain filling percentage, while the short-duration varieties should focus on spikelets per panicle and grain weight. Future research should integrate these insights into breeding programs to develop high-yielding short-duration cultivars for intensified cropping systems.

Grain filling is a critical determinant of yield and quality in rice. This study aims to clarify the association between grain photosynthesis and the filling rate of rice varieties with different grain weights, providing a theoretical foundation for optimizing grain-filling processes. Two rice varieties with similar growth duration but different grain weights were selected: a large-grain variety, Lingliangyou 268 (L268), and a small-grain variety, Ruiliangyou 1053 (R1053). Differences in grain filling, grain photosynthetic rate, and grain chlorophyll content were systematically examined during the filling stage. Results showed significant differences in grain-filling, grain photosynthetic rate, and grain chlorophyll content between large-grain and small-grain rice varieties. The grain photosynthetic rate of L268 was a significantly higher than R1053. L268 also exhibited significantly higher initial grain filling rate, maximum grain-filling rate, and mean grain filling rate compared to R1053. Throughout the grain filling period, L268 showed higher grain chlorophyll content (including chlorophyll a, chlorophyll b, and total chlorophyll) than R1053. The increase in chlorophyll content, particularly total chlorophyll, enhanced the grain photosynthetic rate during the early and middle stages of grain filling significantly. These findings suggested that rice varieties with higher grain weights exhibited stronger panicle photosynthetic capacity due to their higher chlorophyll content. The enhanced grain photosynthetic rate contributed to improved grain filling and increased grain weight.

The objective of this study was to explore the rumen fermentation characteristics, bacterial diversity, community composition, and metabolite profiles of rice straw from three distinct varieties. Straws from two hybrid rice varieties, Lingliangyou 268 (L268) and Yueyou 9113 (Y9113), and one inbred rice variety, Zhongzao 39 (Z39), were selected for a 72 h in vitro rumen fermentation test. The fermentation products were analyzed for rumen fermentation characteristics, bacterial community, and rumen metabolomics. The results showed that Y9113 had higher total gas and methane production, greater dry matter digestibility, and higher concentrations of ammonium nitrogen and volatile fatty acids compared to Z39 (p < 0.05). The variety of rice straw did not affect the richness or diversity of the rumen bacterial community (p > 0.05). However, the relative abundances of Verrucomicrobiota, Euryarchaeota, Elusimicrobiota, Probable genus 10, Lachnospiraceae AC2044 group, WCHB1-41, and VadinBE97 were higher in Z39 than in Y9113, while the opposite was observed for Saccharofermentans, UCG-010, and NK4A214 group (p < 0.05). Both principal coordinates analysis (PCoA) and partial least squares discrimination analysis (PLS-DA) revealed clear distinctions in the rumen bacterial communities between Y9113 and Z39. Metabolomic analysis identified eighteen differential metabolites among L268, Z39, and Y9113, with six showing strong correlations with the rumen microbiota. These findings suggest that the feed value of rice straw is influenced by the variety under the same cultivation conditions, due to nutritional disparities that subsequently affect the rumen microbial community and metabolite profiles. This study offers valuable data and insights for the strategic resource utilization of rice straw from different varieties in the livestock industry.

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.

Understanding the yield attributes of the popular rice (Oryza sativa L.) hybrids can provide useful information for developing new hybrid rice varieties. Field experiments were conducted at two subtropical sites (Hengyang and Xingyi) in two years (2021 and 2022) to compare grain yield and yield attributes of three currently popular hybrid rice varieties (Jingliangyouhuazhan, Jingliangyou 534, and Longliangyouhuazhan) with three representative super hybrid rice varieties (Y-liangyou 1, Y-liangyou 2, and Y-liangyou 900). No significant differences in grain yield were observed between the group of popular hybrids and the group of super hybrids at Hengyang and Xingyi in 2021 or at Xingyi in 2022, but at Hengyang in 2022, the group of popular hybrids produced a 15% higher grain yield. The grain yield at Hengyang in 2022 was lower than that at Hengyang and Xingyi in 2021 and at Xingyi in 2022. At Hengyang in 2022, the group of popular hybrids had 9–15% higher panicles per m², spikelet filling percentage, and harvest index but similar spikelets per panicle and total biomass production and 12% lower grain weight compared to the group of super hybrids. Correlation plot analysis showed that grain yield was significantly related to panicles per m² but not other yield attributes across six varieties at Hengyang in 2022. These results indicated that the currently popular hybrid rice varieties had higher yield performance than the representative super hybrid rice varieties under the condition of relatively lower productivity, and the key factor for this higher yield performance in the popular hybrids was the higher panicles per m². This finding highlights that more attention should focus on the yield performance under medium- and low-productivity conditions in hybrid rice breeding programs, and an effective breeding strategy is to select the varieties with high panicle numbers.