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Peptide transport is important for plant tissues where rapid proteolysis occurs, especially during germination and senescence, to enhance redistribution of organic nitrogen (N). However, the biological role of peptide transporters is poorly investigated in rice. We characterized the function of the peptide transporter OsNPF8.1 of rice nitrate transporter 1/peptide transporter family (NPF). Ectopic expression of OsNPF8.1 in yeast revealed that OsNPF8.1 encoded a high-affinity di-/tri-peptide transporter, and the osnpf8.1 mutants had a lower uptake rate of the fluorescent-labelled dipeptide c in leaves of rice seedlings. Histochemical assays showed that OsNPF8.1 was highly expressed in mesophyll cells and vascular parenchyma cells, but not detected in root hairs and epidermises. Expression of OsNPF8.1 was induced by N deficiency, drought, NaCl and abscisic acid, and kept at a high level in senescing leaves. Under N deficiency conditions, compared with the wild type Zhonghua 11, the osnpf8.1 mutants grew slower at the seedling stage, and had lower grain yield and lower N content in the grains. In contrast, OsNPF8.1-over-expressing rice (OsNPF8.1-OE) grew faster at the seedling stage and had a higher grain yield. The osnpf8.1 seedlings were less tolerant to salt and drought stresses. These results suggested that stress-induced organic N transportation mediated by OsNPF8.1 might contribute to balance plant growth and tolerate to salt/drought stress and N-deficiency.

Soil and plant analyzer development (SPAD) value and leaf nitrogen concentration (LNC) based on dry weight are important indicators affecting rice yield and quality. However, there are few reports on the use of machine learning algorithms based on hyperspectral monitoring to synchronously predict SPAD value and LNC of indica rice. Meixiangzhan No. 2, a high-quality indica rice, was grown at different nitrogen rates. A hyperspectral device with an integrated handheld leaf clip-on leaf spectrometer and an internal quartz-halogen light source was conducted to monitor the spectral reflectance of leaves at different growth stages. Linear regression (LR), random forest (RF), support vector regression (SVR), and gradient boosting regression tree (GBRT) were employed to construct models. Results indicated that the sensitive bands for SPAD value and LNC were displayed to be at 350–730 nm and 486–727 nm, respectively. Normalized difference spectral indices NDSI (R497, R654) and NDSI (R729, R730) had the strongest correlation with leaf SPAD value (R = 0.97) and LNC (R = −0.90). Models constructed via RF and GBRT were markedly superior to those built via LR and SVR. For prediction of leaf SPAD value and LNC, the model constructed with the RF algorithm based on whole growth periods of spectral reflectance performed the best, with R2 values of 0.99 and 0.98 and NRMSE values of 2.99% and 4.61%. The R2 values of 0.98 and 0.83 and the NRMSE values of 4.88% and 12.16% for the validation of leaf SPAD value and LNC were obtained, respectively. Results indicate that there are significant spectral differences associated with SPAD value and LNC. The model built with RF had the highest accuracy and stability. Findings can provide a scientific basis for non-destructive real-time monitoring of leaf color and precise fertilization management of indica rice. [ABSTRACT FROM AUTHOR]

Background: Enhancing grain yield and nitrogen use efficiency (NUE) of rice is of great importance for sustainable agricultural development. Little effort has been made to increase grain yield and NUE of direct‐seeded rice under the double‐cropping system in South China. Field trials were conducted during 2018–2020 with four treatments, including nitrogen‐free, farmers' fertilization practice (FP), 'three controls' nutrient management (TC), and simplified and nitrogen‐reduced practice (SNRP). Results: Grain yield under SNRP averaged 6.46 t ha−1 during the three years and was 23.0% higher than that of FP but comparable to that of TC. Recovery efficiency (REN), agronomic efficiency (AEN), and partial factor productivity (PFPN) of nitrogen under SNRP increased by 12.0–22.7%, 159.3–295.0% and 94.6–112.5% respectively compared with FP. Harvest index and sink capacity increased by 7.3–10.8% and 14.9–21.3% respectively. Percentage of productive tillers (PPT) and biomass after heading increased by 24.0% and 104.5% respectively. Leaf nitrogen concentration at heading and nitrogen accumulation after heading increased by 16.3% and 842.0% respectively. Grain yield was positively correlated with PPT, sink capacity, harvest index, biomass and nitrogen accumulation after heading, REN, AEN, and PFPN. Conclusion: Grain yield and NUE under SNRP were superior to those under FP and comparable to those under TC. Increase in sink capacity, higher PPT, more biomass and nitrogen accumulation after heading, and greater harvest index were responsible for high grain yield and NUE in SNRP with reduced nitrogen fertilizer and labor input. SNRP is a feasible approach for direct‐seeded rice under a double‐cropping system in South China. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Rice–fish co-cultures have been practiced for over 2000 years, and they have tremendous potential in terms of increasing food security and economic benefits. However, little research has been conducted into achieving stable yields and high lodging resistance with regard to rice while simultaneously promoting the harmonious and healthy growth of fish in rice–fish co-culture paddy fields. We conducted a field study aimed at selecting suitable rice varieties for rice–fish co-culture systems (encompassing both ratoon and main crop). This selection process was grounded in an evaluation of lodging resistance and grain yield among 33 rice varieties used throughout the studied region. The results revealed a range of lodging indices of the main crop for the second internode, spanning from 62.43 to 138.75, and the annual grain yield (main crop and ratoon crop) ranged from 7.17 to 13.10 t ha−1 within rice–fish co-culture systems. We found that the use of rice–fish co-culture farming could improve the milling quality, nutrient quality, and appearance quality of rice, though the improvement gained through co-culturing varied across rice varieties. Moreover, the lodging index of the three basal internodes of rice plants was significantly and positively correlated with the plant height and the culm fresh weight, but it was negatively correlated with the bending strength of the rice basal internodes. Additionally, the 33 tested rice varieties were clustered in accordance with their lodging resistance (i.e., high resistance with lodging indices 62.43–75.42; medium resistance with lodging indices 80.57–104.62; and low resistance with lodging indices 113.02–138.75) according to the hierarchical cluster analysis. The 33 rice varieties were also clustered in accordance with the annual (main crop and ratoon crop) grain yield (i.e., high yield with 11.17–13.10 t ha−1; medium yield with 10.15–10.83 t ha−1; and low yield with 7.16–9.88 t ha−1). In all, 11 rice varieties were identified by a comprehensive evaluation as suitable varieties for grain production in the rice–fish co-culture system. These varieties displayed favorable traits, including a high annual rice yield, strong lodging resistance, and good grain quality. This is the first study to systematically evaluate rice varieties based on grain yield, lodging resistance, and grain quality in rice–fish co-culture systems. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is a principal macronutrient and plays a paramount role in mineral nutrition of rice plants. Mixed provision of ammonium- and nitrate-nitrogen (MPAN) at a moderate level could enhance N uptake and translocation and promote growth of rice, but current understanding of their molecular mechanisms is still insufficient. Two rice lines of W6827 and GH751, with contrasting ability of N uptake, were subjected to four levels of MPAN (NH 4 +/NO 3 − = 100:0, 75:25, 50:50, 25:75) in hydroponic experiments. In terms of plant height, growth rate and shoot biomass, growth of GH751 tended to increase firstly and then decrease with enhancement in NO 3 −-N ratio. It attained maximal level under 75:25 MPAN, with an 8.3% increase in shoot biomass. In general, W6827 was comparatively less responsive to MPAN. For GH751, the uptake rate of N, phosphor (P) and potassium (K) under 75:25 MPAN was enhanced by 21.1%, 20.8% and 16.1% in comparison with that of control (100:0 MPAN). Meanwhile, the translocation coefficient and content in shoots of N, P and K were all increased significantly. In contrast to transcriptomic profile under control, 288 differentially expressed genes (DEGs) were detected to be up-regulated and 179 DEGs down-regulated in transcription under 75:25 MPAN. Gene Ontology analysis revealed that some DEGs were up-regulated under 75:25 MPAN and they code for proteins mainly located in membrane and integral component of membrane and involved in metal ion binding, oxidoreductase activity and other biological processes. KEGG pathway enrichment analysis indicated that DEGs related to nitrogen metabolism, carbon fixation in photosynthetic organisms, photosynthesis, starch and sucrose metabolism, and zeatin biosynthesis were up- or down-regulated in transcription under 75:25 MPAN, and they are responsible for improved nutrient uptake and translocation and enhanced growth of seedlings. [ABSTRACT FROM AUTHOR]

Relative tillering rate (RTR) increases linearly as leaf nitrogen concentration (NLV) increases in rice (Oryza sativa L.) plants. Leaf area index (LAI) has a negative effect on the emergence and survival of tillers. The objectives of this paper were to quantify the interactive effect of NLV and LAI on tillering in irrigated rice. Field experiments were conducted at Philippine Rice Research Institute (PRRI) and International Rice Research Institute (IRRI), Philippines during the dry seasons of 1995 and 1998. Two indica cultivars, IR72 and IR68284H, were subjected to various nitrogen (N) treatments. Number of tillers (including main stems), leaf area, and tissue N concentration were measured. The NLV explained a large part of variation in number of tillers m-2 among treatments. However, the residual, defined as the difference between observed and estimated number of tillers m-2, was negatively correlated with LAI (P < 0.01). When LAI was considered in addition to NLV, the model explained the variation in number of tillers m-2 much better, and the correlation between the residual and LAI declined and became insignificant (P > 0.05). The critical NLV and critical LAI for tillering to stop were interrelated; higher NLV was needed to prevent tillers from dying when LAI was high, and vice versa. Use of stem or shoot N concentration instead of NLV gave similar results. Results suggest that LAI, in addition to NLV, should be considered in predicting tillers in rice crop. [ABSTRACT FROM AUTHOR]

• A total of 21 QTLs for nitrogen and phosphorus uptake-related traits distributed in 16 regions along 6 chromosomes were detected, with QTLs maximum explaining 8.19% of the phenotypic variation. • Two QTL clusters including AGB, TNC, TPC and GNC were detected in the region bin 140 and bin 146 on the chromosome 2, the distance between the two clusters was only 4.1 cM. • These genomic regions might be deployed for the simultaneous improving the use efficiency of nitrogen and phosphorus in rice breeding. To understand the genetic basis of nitrogen and phosphorus uptake in the cultivated rice, quantitative trait loci (QTL) analysis for 7 nitrogen and phosphorus uptake-related traits including above-ground biomass (AGB), leaf colour value (SPAD) in heading stage, grain nitrogen concentration (GNC), grain nitrogen content of the plant, total nitrogen content (TNC), grain phosphorus concentration, total phosphorus content (TPC) were conducted using SNP markers in a F2 population derived from a cross between GH128 and W6827. A total of 21 QTLs for nitrogen and phosphorus uptake-related traits distributed in 16 regions along 6 chromosomes were detected using a high density genetic map consisting of 1582 bin markers, with QTLs maximum explaining 8.19% of the phenotypic variation. Nine QTLs (42.9% of total QTLs) were detected on chromosome 2. Among them, two QTL clusters including AGB, TNC, TPC and GNC were also detected in the region bin 140 and bin 146 on the chromosome 2. The distance between the two clusters was only 4.1 cM. The presence of QTL clusters has important significance and could be useful in molecular marker assisted breeding. These genomic regions might be deployed for the simultaneous improving the use efficiency of nitrogen and phosphorus in rice breeding. [ABSTRACT FROM AUTHOR]

The increasing scarcity of irrigation water necessitates the development of water-saving technology in rice production. Our previous studies have shown that “safe” alternate wetting and drying irrigation (AWD15) can effectively save water, improve water productivity while maintain grain yield compared to continuous flooding (CF) and farmer's water management practice (FP) under a single fertilizer-N input. The objectives of this study are (1) to investigate the superiority of this novel water management practice compared with FP; and (2) to examine whether there is an interaction between water and N input and whether fertilizer-N input needs to be adjusted under AWD15. Two field experiments were conducted during the late cropping seasons of 2014 and 2015. A hybrid rice variety Tianyou3618 was grown under two water management (AWD15 and FP) and four fertilizer-N rates (0, 90, 180, 270 kg N ha −1 ). Grain yield, water productivity and nitrogen use efficiency were determined. Compared to that of FP, irrigation water input of AWD15 was reduced by 24.1% in 2014 and 71.4% in 2015. The number of irrigations decreased and water productivity increased significantly. No significant differences existed between AWD15 and FP in grain yield, biomass, leaf area index and nitrogen use efficiency. Nitrogen input level had significant effects on yield, biomass, harvest index and nitrogen use efficiency in both years. Grain yield increased with N rate and the optimal N rate was 180 kg N ha −1 . No significant interaction was found between water and nitrogen rate regarding biomass production and grain yield. Our results demonstrated that no change in N input is needed under AWD15 condition and AWD15 is advantageous over farmer's water management practice under all N levels investigated in South China. This is the first report on the performance of AWD15 under different fertilizer-N levels in South China. [ABSTRACT FROM AUTHOR]

Abstract: Variety and nitrogen (N) fertilizer input are the two main factors that influence the development of sheath blight (ShB) caused by Rhizoctonia solani in intensive and high-input rice (Oryza sativa L.) production systems. This study was conducted to determine the varietal difference in ShB development and its association with yield loss across N rates. Two indica inbred and two indica/indica F1 hybrid varieties were grown under 0 and 90kgNha−1 in 2003 wet season (WS) and under 0, 75, 145, and 215kgNha−1 in 2004 dry season (DS). Inoculation was done in 3.2m2 in each experiment unit to achieve uniform disease development. Disease intensity was quantified by measuring relative lesion height (RLH) and ShB index (ShBI) of inoculated 10 hills at flowering and 14 days after flowering. Plant traits, grain yield, temperature, and relative humidity inside the canopy were also measured. Consistent and significant varietal differences in ShB intensity were observed across N rates in both WS and DS. Among the four varieties, IR72 and IR75217H had higher RLH and ShBI than PSBRc52 and IR68284H at all N rates. Sheath blight index at 14 days after flowering had the closest correlation with yield loss from ShB. Varieties with taller stature, fewer tillers, and lower leaf N concentration such as IR68284H generally had lower RLH and ShBI, and consequently lower yield loss from the disease. Disease intensity and yield loss from ShB increased with increasing N rates, but the magnitude of yield loss varied among varieties. This suggests that fertilizer N should be managed more precisely and differently for varieties with different plant type in order to reduce the disease development and maximize grain yield in the irrigated rice systems. [Copyright &y& Elsevier]

Abstract: Rice in China receives high amounts of fertilizer nitrogen (N) that are often not used efficiently by the crop. A recently developed site-specific N management (SSNM) approach enables the application of fertilizer N to dynamically match the field- and season-specific needs of the rice crop for N. We used farmer participatory research for on-farm testing of N fertilization by standard and farmer-modified SSNM for irrigated rice. Our study was done in 14 villages in four provinces of China in 2003 and 2004. Twelve to 15 farmers were randomly selected in each study village in each year for a dialogue with the research team and for a rapid rural technology assessment (RRTA). Based on the information obtained from the RRTA, modified SSNM (MSSNM) schemes were developed through dialogue between a research team and farmers at a workshop in each village. Modification mainly involved decreasing the number of fertilizer-N topdressings and increasing the rate of basal N application. Among the 514 farmers surveyed during the workshops, 95% were willing to adopt SSNM and MSSNM technologies and 76% were willing to conduct SSNM or MSSNM experiments. More than two-thirds of the farmers preferred adopting MSSNM rather than the standard SSNM. Based on the farmers’ willingness, 144 farmers were selected to conduct an experiment to compare SSNM or MSSNM with the farmers’ fertilizer practices (FFP). The rate and distribution of fertilizer N during the growing season of MSSNM were in between those of SSNM and FFP. SSNM and MSSNM, compared with FFP, maintained rice yields with significantly less fertilizer N and no significant increase in total labour input. The reduction in fertilizer-N input averaged 48kg N/ha for SSNM and 23kg N/ha for MSSNM. The study suggests that there is potential for large-scale dissemination of SSNM technology in China. [Copyright &y& Elsevier]