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Many studies have been carried out on N sources effect on fragrant rice; however, their impact on rice grain quality is largely unclear. In this study, we evaluated the effects of different types of N sources on rice growth, yield, 2-acetyl-1-pyrroline (2AP), amylose and cooked rice elongation. Two indica rice cultivars, Basmati 385 (B385), Xiangyaxiangzhan (XYXZ) and two japonica cultivars, Yunjingyou (YJY), Daohuaxiang (DHX) were grown in experimental pots with six replications under four N sources: Potassium nitrate (KNO3), ammonium bicarbonate (NH4HCO3), urea (H2NCONH2) and sodium nitrate (NaNO3) in 2019 and 2020 early seasons. Our results showed that N dynamics regulated the number of panicles, 1000-grain weight, grain yield, 2-acetyl-1-pyrroline, amylose and cooked rice elongation across all the four treatments. The NH4HCO3 treatment significantly increased the number of panicles and grain yield across the four rice varieties compared with KNO3, H2NCONH2 and NaNO3 N sources in both 2019 and 2020 early season, The KNO3 treatment significantly showed higher 1000-grain weight in B-385, YJY, XYXZ and DHX compared to other N sources. Compared with other N sources treatment, the NH4HCO3 treatments significantly increased the 2AP contents in heading stage leaves, matured leaves and grains of B-385, YJY, XYXZ and DHX respectively. Cooked rice elongation percentage also showed significant difference in all treatments studied with KNO3 recorded the highest across the four varieties. Analysis of major enzymes and compounds such as P5C, P5CS, PDH, Pyrroline, proline and Methylglyoxal showed remarkable differences in each cultivar at heading and maturity stages with higher activity in NH4HCO3 and H2NCONH2 treatments. Similarly, in all treatments, we also observed significant increase in amylose content percentage, with NH4HCO3 having greater percentage of amylose.

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Rice (Oryza sativa L.) is a staple food for over half of the world's population. However, rice grain quality is one of the major problems facing rice breeders across the world. Cooked rice elongation, cooked rice expansion, and water absorption have been identified as some of the parameters used in gauging rice grain quality. Biomarkers such as proteins or metabolites can be used to differentiate among a pattern of variations among various samples (e.g., various locations within a plant, various germplasm accessions); consequently, they present a type of internal validation for a given biological state. In the present study, we investigated the putative metabolite biomarkers associated with the variation of cooked rice elongation for Hua Jing Xian 74 (receptor), Basmati 370 (donor), and five hybrid lines resulting from a cross of these parent lines. We also investigated their cooked rice expansion and water absorption properties. After carrying out cooked rice elongation studies, metabolomics studies, correlation analyses, V-plot analyses, and thorough searches in public metabolite databases (Metlin, Massbank and KEGG), and in-house secondary metabolite database, we identified a metabolite with molecular weight of 280.25 and retention time of 6.4 min as a putative biomarker associated with cooked rice elongation in the varieties investigated. We also discovered that changes in cooked rice elongation and changes in cooked rice expansion follow a similar pattern; however, it appears that cooked rice elongation and cooked rice expansion do not affect water absorption in these rice lines. Our findings may facilitate the improvement of the cooked rice elongation of hybrids resulting from the crosses of Basmati 370 and Hua Jing Xian 74. Our results also offer interesting insight into cooked rice elongation, cooked rice expansion, and water absorption.

Rice (Oryza sativa L.) is mainly grouped into indica and japonica varieties. The aim of this study was to investigate the effect of temperature on cooked rice elongation, cooked rice expansion, and rice fragrance. This study was conducted in three growth temperature chambers with indica cultivar Basmati 385 (B385) and japonica cultivar Yunjingyou (YJY). Grains of B385 grown in low-temperature regimes had the highest cooked rice elongation and expansion, whereas the grains of YJY grown in high-temperature regimes had the highest cooked rice elongation and expansion. Starch granules of B385 grown in low-temperature regimes were more compact and bigger, compared to grains grown in medium- and high-temperature regimes. Conversely, the starch granules of YJY grown in high-temperature regimes were more compact and bigger, compared to those grown in medium- and low-temperature regimes. Metabolomic analyses showed that temperature affected the rice metabolome and revealed that cyclohexanol could be responsible for the differences observed in cooked rice elongation and expansion percentage. However, in both B385 and YJY, grains from low-temperature regimes had the highest 2-AP content and the lowest expression levels of the badh2 gene. The findings of this study will be useful to rice breeders and producers.

The cooking and eating qualities of rice are some of the problems facing by rice producers and consumers around the world. In this study we investigated the cooking and eating qualities of Basmati 385 and Hua Jing Xian 74. Both are rice cultivars with different phenotypic traits.The results show that Basmati 385 increased by an average of 102.14% after cooking while Hua Jing Xian 74 increased by an average of 69.91% after cooking. Basmati 385 had a pasting temperature of 78°C, while Hua Jing Xian 74 had a pasting temperature of 84°C. However, Hua Jing Xian 74 had a final viscosity of 4,686 cP while Basmati 385 had a final viscosity of 3,514 cP. The amylose contents of the two cultivars were also different; Hua Jing Xian 74 had an amylose content of 19.4%, while that of Basmati 385 was 18%. We also discovered that the starch granule morphology of the two cultivars were remarkably different.The lower pasting temperature of Basmati 385 positively correlated with good cooking qualities of rice. However, Hua Jing Xian 74 appears to have relatively better eating qualities due to its higher viscosity and higher amylose content. It would be pertinent to do more research about hybrid lines resulting from a cross of Hua Jing Xian 74 and Basmati 385, to see if they possess the good cooking qualities of Basmati 385 and the good eating qualities of Hua Jing Xian 74.

Improving grain yield potential in rice is an important step toward addressing global food security challenges. The meta-QTL analysis offers stable and robust QTLs irrespective of the genetic background of mapping populations and phenotype environment and effectively narrows confidence intervals (CI) for candidate gene (CG) mining and marker-assisted selection improvement. To achieve these aims, a comprehensive bibliographic search for grain yield traits (spikelet fertility, number of grains per panicle, panicles number per plant, and 1000-grain weight) QTLs was conducted, and 462 QTLs were retrieved from 47 independent QTL research published between 2002 and 2022. QTL projection was performed using a reference map with a cumulative length of 2,945.67 cM, and MQTL analysis was conducted on 313 QTLs. Consequently, a total of 62 MQTLs were identified with reduced mean CI (up to 3.40 fold) compared to the mean CI of original QTLs. However, 10 of these MQTLs harbored at least six of the initial QTLs from diverse genetic backgrounds and environments and were considered the most stable and robust MQTLs. Also, MQTLs were compared with GWAS studies and resulted in the identification of 16 common significant loci modulating the evaluated traits. Gene annotation, gene ontology (GO) enrichment, and RNA-seq analyses of chromosome regions of the stable MQTLs detected 52 potential CGs including those that have been cloned in previous studies. These genes encode proteins known to be involved in regulating grain yield including cytochrome P450, zinc fingers, MADs-box, AP2/ERF domain, F-box, ubiquitin ligase domain protein, homeobox domain, DEAD-box ATP domain, and U-box domain. This study provides the framework for molecular dissection of grain yield in rice. Moreover, the MQTLs and CGs identified could be useful for fine mapping, gene cloning, and marker-assisted selection to improve rice productivity.