On-farm comparison in grain quality between main and ratoon crops of ratoon rice in Hubei Province, Central China.

BACKGROUND: While ratoon rice has been increasingly practiced by farmers recently in China, on-farm performance in grain quality of main and ratoon crops in the mechanized rice ratooning system is less studied and remains poorly understood. Therefore, a multi-location on-farm survey was conducted to collect rice grain samples from farmers' fields to determine grain quality of main and ratoon crops of ratoon rice at 12 locations across Hubei Province, central China, in 2016. RESULTS: On average, milled and head rice percentage in the ratoon crop was 70.2% and 65.7%, which was significantly higher than in the main crop, whereas chalky grain percentage and grain chalkiness in ratoon crop (10.1% and 2.8%, respectively) were significantly lower than those in the main crop (36.6% and 14.2%, respectively). The differences in these quality traits between the two crops were consistent at all locations. Averaged across 12 locations, scores of translucency and gel consistency were significantly lower but amylose content and alkali spreading value were significantly higher in the ratoon crop than in the main crop, with the difference between the two crops varying in gel consistency by location. CONCLUSION: Overall, grain quality, especially milling and appearance of the ratoon crop, was superior to the main crop in the mechanized rice ratooning system. As a result, this study emphasizes the potential role of the rice ratooning system in other regions with a similar biophysical background producing high-quality rice. © 2022 Society of Chemical Industry.

Appropriately Reduced Nitrogen and Increased Phosphorus in Ratooning Rice Increased the Yield and Reduced the Greenhouse Gas Emissions in Southeast China.

Reducing greenhouse gas emissions while improving productivity is the core of sustainable agriculture development. In recent years, rice ratooning has developed rapidly in China and other Asian countries, becoming an effective measure to increase rice production and reduce greenhouse gas emissions in these regions. However, the lower yield of ratooning rice caused by the application of a single nitrogen fertilizer in the ratooning season has become one of the main reasons limiting the further development of rice ratooning. The combined application of nitrogen and phosphorus plays a crucial role in increasing crop yield and reducing greenhouse gas emissions. The effects of combined nitrogen and phosphorus application on ratooning rice remain unclear. Therefore, this paper aimed to investigate the effect of combined nitrogen and phosphorus application on ratooning rice. Two hybrid rice varieties, 'Luyou 1831' and 'Yongyou 1540', were used as experimental materials. A control treatment of nitrogen-only fertilization (187.50 kg·ha-1 N) was set, and six treatments were established by reducing nitrogen fertilizer by 10% (N1) and 20% (N2), and applying three levels of phosphorus fertilizer: N1P1 (168.75 kg·ha-1 N; 13.50 kg·ha-1 P), N1P2 (168.75 kg·ha-1 N; 27.00 kg·ha-1 P), N1P3 (168.75 kg·ha-1 N; 40.50 kg·ha-1 P), N2P1 (150.00 kg·ha-1 N; 13.50 kg·ha-1 P), N2P2 (150.00 kg·ha-1 N; 27.00 kg·ha-1 P), and N2P3 (150.00 kg·ha-1 N; 40.50 kg·ha-1 P). The effects of reduced nitrogen and increased phosphorus treatments in ratooning rice on the yield, the greenhouse gas emissions, and the community structure of rhizosphere soil microbes were examined. The results showed that the yield of ratooning rice in different treatments followed the sequence N1P2 > N1P1 > N1P3 > N2P3 > N2P2 > N2P1 > N. Specifically, under the N1P2 treatment, the average two-year yields of 'Luyou 1831' and 'Yongyou 1540' reached 8520.55 kg·ha-1 and 9184.90 kg·ha-1, respectively, representing increases of 74.30% and 25.79% compared to the N treatment. Different nitrogen and phosphorus application combinations also reduced methane emissions during the ratooning season. Appropriately combined nitrogen and phosphorus application reduced the relative contribution of stochastic processes in microbial community assembly, broadened the niche breadth of microbial communities, enhanced the abundance of functional genes related to methane-oxidizing bacteria and soil ammonia-oxidizing bacteria in the rhizosphere, and decreased the abundance of functional genes related to methanogenic and denitrifying bacteria, thereby reducing greenhouse gas emissions in the ratooning season. The carbon footprint of ratooning rice for 'Luyou 1831' and 'Yongyou 1540' decreased by 25.82% and 38.99%, respectively, under the N1P2 treatment compared to the N treatment. This study offered a new fertilization pattern for the green sustainable development of rice ratooning.

Comparative Proteomic Analysis Provides New Insights into Improved Grain-filling in Ratoon Season Rice.

Grain-filling of rice spikelets (particularly for the later flowering inferior spikelets) is an important characteristic that affects both quality and yield. Rice ratooning technology is used to cultivate a second crop from dormant buds that sprout from stubble left after the first harvest. This study used two rice varieties, the conventional indica rice 'Jinhui 809' and the hybrid indica-japonica rice 'Yongyou 1540', to assess the impact of rice ratooning on grain-filling. The results indicated that the grain-filling process in inferior spikelets of ratoon season rice (ISR) showed significant improvement compared to inferior spikelets of main crop (late season) rice (ISL). This improvement was evident in the earlier onset of rapid grain-filling, higher seed-setting percentage, and improved grain quality. A label-free quantitative proteomic analysis using mass spectrometry identified 1724 proteins with significant abundance changes, shedding light on the molecular mechanisms behind the improved grain-filling in ISR. The functional analysis of these proteins indicated that ratooning stimulated the metabolic processes of sucrose-starch, trehalose, and hormones in rice inferior spikelets, leading to enhanced enzyme activities related to starch synthesis, elevated concentrations of trehalose-6-phosphate (T6P), indole-3-acetic acid (IAA) and zeatin riboside (ZR) during the active grain-filling phase. This research highlighted the importance of the GF14f protein as a key regulator in the grain-filling process of ISR. It revealed that GF14f transcriptional and protein levels declined more rapidly in ISR compared to ISL during grain-filling. Additionally, the GF14f-RNAi plants specific to the endosperm exhibited improved quality in inferior spikelets. These findings suggest that the enhancement of starch synthesis, increased levels of IAA, ZR, and T6P, along with the rapid decrease in GF14f protein, play a role in enhancing grain-filling in ratoon season rice.

Genetic Dissection of Rice Ratooning Ability Using an Introgression Line Population and Substitution Mapping of a Pleiotropic Quantitative Trait Locus qRA5.

Ratooning ability is a key factor that influences ratoon rice yield, in the area where light and temperature are not enough for second season rice. In the present study, an introgression line population derived from Minghui 63 as the recipient parent and 02428 as the donor parent was developed, and a high-density bin map containing 4568 bins was constructed. Nine ratooning-ability-related traits were measured, including maximum tiller number, panicle number, and grain yield per plant in the first season and ratoon season, as well as three secondary traits, maximum tiller number ratio, panicle number ratio, and grain yield ratio. A total of 22 main-effect QTLs were identified and explained for 3.26-18.63% of the phenotypic variations in the introgression line population. Three genomic regions, including 14.12-14.65 Mb on chromosome 5, 4.64-5.76 Mb on chromosome 8, and 10.64-15.52 Mb on chromosome 11, were identified to simultaneously control different ratooning-ability-related traits. Among them, qRA5 in the region of 14.12-14.65 Mb on chromosome 5 was validated for its pleiotropic effects on maximum tiller number and panicle number in the first season, as well as its maximum tiller number ratio, panicle number ratio, and grain yield ratio. Moreover, qRA5 was independent of genetic background and delimited into a 311.16 kb region by a substitution mapping approach. These results will help us better understand the genetic basis of rice ratooning ability and provide a valuable gene resource for breeding high-yield ratoon rice varieties.