Fragrant Rice Varieties Research Articles

Effects of Selenium Foliar Spraying on Seedling Growth and Stem Sheath Hardness in Fragrant Rice

Previous studies have shown that selenium (Se) can influence rice growth and yield. However, the Se effect on rice lodging remains unknown. This study aimed to investigate the impact of different Se treatments on seedling growth and stem sheath hardness in fragrant rice. A hydroponic experiment was conducted using two fragrant rice varieties, Yuxiangyouzhan and Xiangyaxiangzhan, as experimental materials. Two forms of selenium fertilizers (amino acid-chelated selenium and sodium selenite) were used. There were five foliar spraying selenium fertilizer treatments (CK: no selenium fertilizer; T1: 4 μmol·L−1 amino acid-chelated selenium; T2: 8 μmol·L−1 amino acid-chelated selenium; T3: 4 μmol·L−1 sodium selenite; and T4: 8 μmol·L−1 sodium selenite), and the effects of the different selenium fertilizer treatments on seedling growth and stem sheath hardness in fragrant rice were studied. Significant Se treatment effects on root fresh weight, seedling dry weight, plant height, stem sheath length, number of leaves, chlorophyll content, stem sheath hardness, peroxidase activity in leaf and stem sheaths, and lignin content in the roots were detected. A significant Se treatment and variety interaction effect on the stem sheath hardness was observed. The different forms/levels of selenium fertilizer affected the seedling growth and the stem sheath hardness differed. The Se treatments improved seedling growth and significantly affected the dry weight, chlorophyll content, stem sheath hardness, and peroxidase activity in leaf and stem sheaths. Compared with the CK treatment, the Se treatments increased the total dry weight of seedlings in Xiangyaxiangzhan and Yuxiangyouzhan by the ranges of 25.43–52.77% and 18.97–30.09%, respectively. The T2–T4 treatments increased the stem sheath hardness values in Xiangyaxiangzhan and Yuxiangyouzhan by the ranges of 21.6–54.7% and 38.3–146.6%, respectively, as compared to the CK treatment. The Se treatments had a promoting effect on physiological indexes such as stem sheath length, lignin content in the stem sheath, and dry matter accumulation in different plant tissues, thereby increasing the total dry weight. The Se treatment had an inhibitory effect on chlorophyll b content and total chlorophyll content, whilst it increased the chlorophyll a content and chlorophyll a/b ratio, which in turn affected the photosynthesis of rice. Therefore, appropriate Se treatments (the application of 8 μmol·L−1 amino acid-chelated selenium, 4 μmol·L−1 sodium selenite, and 8 μmol·L−1 sodium selenite) could improve seedling growth and stem sheath hardness, which was related to the parameter changes, such as the dry weight, photosynthesis pigments, and peroxidase activity. These findings suggest that different Se fertilizers can positively regulate rice resistance to lodging and growth. This study can provide theoretical support for the application of selenium fertilizer.

Mechanism harvesting of main crops straw returning effects on ratooning fragrant rice yield and 2-accetyl-1-pyrroline and their drivers to soil microbial communities

Straw return to the field is an important measure for increasing soil fertility to increase production. Recent studies have shown that straw return to fields can increase rice yield, but the effect of straw return to fields on ratooning rice is limited. To address this problem, this paper investigated the effect of straw return on a ratooning rice system by harvesting at different heights during the first season.A two-year field experiment was conducted by using a fragrant rice variety (Meixiangzhan 2) as the material. Three experimental treatments including i) the CK treatment: manual harvesting and straw harvested at a height of 20 cm was not returned to the field; ii) the MT1 treatment: mechanical harvesting and straw was returned to the field at a harvest height of 10 cm; iii) the MT2 treatment: mechanical harvesting and straw at a harvest height of 20 cm was returned to the field. The investigated parameters in the rice cropping system in this study were the agronomic traits, yield formation, soil properties, and root soil microorganisms.We found that compared with those in the CK treatment, the yield and 2AP content in the MT treatment significantly increased, the yields of MT1 and MT2 increased by 18.17-32.64% and 12.19-20.42%, respectively. The contents of available potassium, available phosphorus, ammonium nitrogen and active organic carbon in the soil were significantly increased by straw return to the field. The soil capacity increased, and rice production increased. In addition, the straw returned to the field produced a large amount of cellulose and anaerobic environment, which provided an explanation for the increase in some anaerobic bacteria, such as pseudxanthomonas, Rhodobacteriaceae and desulphurides in the MT treatment group. Specifically, straw return provides a large amount of organic material for rice cultivation systems and improves soil fertility under the action of microorganisms to increase production.Overall, the interaction between straw return and harvest height had different effects on yield and 2AP content, and the MT2 treatment was the most beneficial for harvesting ratooning fragrant rice.

Analysis of Volatile Compounds' Changes in Rice Grain at Different Ripening Stages via HS-SPME-GC-MS.

Aroma is a crucial determinant of rice taste quality, with volatile organic compounds (VOCs) playing a key role in defining this characteristic. However, limited research has explored the dynamic changes in these aromatic substances during the ripening stages of rice grains. In this study, we analyzed VOCs in rice grains across four ripening stages post-flowering using headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). A total of 417 VOCs were identified, among which 65 were determined to be key aroma-active compounds based on relative odor activity value (rOAV) analysis. Most of these aroma-active compounds exhibited an accumulation pattern as the grains matured. Notably, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone and 2-Methyloxolan-3-one had the largest rOAV values. Additionally, (Z)-6-nonenal, (Z,Z)-3,6-nonadienal, 2-thiophenemethanethiol, 5-methyl-2-furanmethanethiol, 2,2,6-trimethyl-cyclohexanone, and 3-octen-2-one were identified as potential key markers for distinguishing rice-grain maturity stages. Moreover, 2-acetyl-1-pyrroline (2-AP), heptanal, and 1-nonanol were identified as marker metabolites differentiating aromatic from non-aromatic brown rice. These findings contribute to a deeper understanding of the dynamic variation and retention of aroma compounds during rice-grain ripening, and they offer valuable insights into the improvement of fragrant rice varieties.

Rapid identification of fragrant rice using starch flavor compound via NIR spectroscopy coupled with GC–MS and Badh2 genotyping

The identification of fragrant rice varieties using near-infrared reflectance spectroscopy (NIRS) models has attracted extensive attention from regulatory authorities worldwide. In this study, 138 fragrant and 54 nonfragrant rice varieties were planted in the same region and distinguished using sensory evaluation, gas chromatography–mass spectrometry analysis, and betaine aldehyde dehydrogenase 2 (Badh2) genotyping. Then, the 2-acetyl−1-pyrroline (2-AP) content was assessed based on partial least-squares discriminant (PLS-DA) models generated after 2nd individually or combined with SNV/MSC/smoothing preprocessing successfully classified fragrant rice both in the calibration and predictive sets. Moreover, design of experiments (DoE)-based preprocessing selection was employed as an effective strategy to optimize the calibration models compared with the one variable at a time (OVAT) method. Further, Badh2 genotype sample screening assisted with identifying authentic fragrant rice and guaranteed the NIRS model's prediction accuracy in identifying fragrant rice. In conclusion, the high throughput PLS-DA multivariate method coupled with NIRS data was applied to identify fragrant rice varieties in routine monitoring and was effective, accurate, and rapid.

Mangrove endophytic fungi: Biocontrol potential against Rhizoctonia solani and biofertilizers for fragrant rice cultivation

The mangrove ecosystem has emerged as a fascinating source for exploring novel bioresources which have multiple applications in modern agriculture. This study evaluates the potential applications of mangrove endophytic fungi (MEF), such as biocontrol agents against Rhizoctonia solani and as biofertilizers for improving the yield of fragrant rice variety Malaysian Rice Quality 76 (MRQ76). Through the antagonism assays, it is observed that among the 14 MEF studied, 4 fungal isolates (Colletotrichum sp. MEFN02, Aspergillus sp. MEFN06, Annulohypoxylon sp. MEFX02 and Aspergillus sp. MEFX10) exhibited promising antagonistic effect against the pathogen R. solani compared to the chemical fungicide (Benomyl). These isolates also revealed significant production of enzymes, phytochemicals, indoleacetic acid (40.96 mg/mL) and ammonia (32.54 mg/mL) and displayed tolerance to salt and temperature stress up to 2000 mM and >40 °C respectively. Furthermore, employing the germination and pathogenicity test, inoculation of these endophytes showed lower percentage of disease severity index (DSI%) against R. solani, ranging from (24 %–46 %) in MRQ76 rice seedlings. The in-vivo experiments of soil and seed inoculation methods conducted under greenhouse conditions revealed that these endophytes enhanced plant growth (8–15 % increase) and increased crop yield (≥50 %) in comparison to control treatments. The current findings provide valuable insights into eco-friendly, cost-effective and sustainable alternatives for addressing R. solani infection and improving the agronomic performance of the fragrant rice cultivar MRQ76, contributing to food security.

Application of Silicon Influencing Grain Yield and Some Grain Quality Features in Thai Fragrant Rice.

Silicon (Si) is a beneficial nutrient that has been shown to increase rice productivity and grain quality. Fragrant rice occupies the high end of the rice market with prices at twice to more than three times those of non-fragrant rice. Thus, this study evaluated the effects of increasing Si on the yield and quality of fragrant rice. Also measured were the content of proline and the expression of the genes associated with 2AP synthesis and Si transport. The fragrant rice varieties were found to differ markedly in the effect of Si on their quality, as measured by the grain 2AP concentration, while there were only slight differences in their yield response to Si. The varieties with low 2AP when the Si supply is limited are represented by either PTT1 or BNM4 with only slight increases in 2AP when Si was increased. Si affects the gene expression levels of the genes associated with 2AP synthesis, and the accumulation of 2AP in fragrant rice mainly occurred through the upregulation of Badh2, DAO, OAT, ProDH, and P5CS genes. The findings suggest that Si is a potential micronutrient that can be utilized for improving 2AP and grain yield in further aromatic rice breeding programs.

Regulation of 2-Acetyl-1-pyrroline Content in Fragrant Rice under Different Temperatures at the Grain-Filling Stage.

2-Acetyl-1-pyrroline (2-AP) is a key volatile organic compound in fragrant rice aroma. However, the effects of temperature on 2-AP biosynthesis in fragrant rice and its regulation mechanism have been rarely reported. In the present study, three fragrant rice varieties were used as plant materials, and four temperature treatments during the grain-filling stage, i.e., (T1) 22/17 °C, (T2) 27/22 °C, (T3) 32/27 °C, and (T4) 37/32 °C, were adopted. The results showed that grain contents of 2-AP, proline, and γ-aminobutyric acid (GABA) significantly (P < 0.05) increased with decreased temperature, while the lowest and highest 2-AP contents were recorded in the T4 and T1 treatments, respectively. Higher pyrroline-5-carboxylic acid (P5C) content was recorded in low-temperature treatments (T1 and T2) than in high-temperature treatments (T3 and T4). The transcript levels of genes BADH2, PRODH, and OAT significantly (P < 0.05) decreased with decreased temperature. Lower transcript levels of genes P5CR, P5CS2, DAO2, DAO4, and DAO5 were recorded in low-temperature treatments (T1 and T2) than in high-temperature treatments (T3 and T4). In conclusion, low temperature increased 2-AP content and high temperature decreased 2-AP content in fragrant rice. We deduced that temperature regulated 2-AP biosynthesis through the metabolism of proline and GABA.

L-Glutamate Seed Priming Enhances 2-Acetyl-1-pyrroline Formation in Fragrant Rice Seedlings in Response to Arsenite Stress.

2-Acetyl-1-pyrroline (2-AP) is a fragrance compound and flavor in fragrant rice whose precursors are generally glutamate (Glu) and proline (Pro). Our previous study revealed that exogenous Glu enhanced the arsenic (As) tolerance in fragrant rice by improving the ascorbic acid-glutathione cycle and the Pro content in roots. However, less is known about how Glu is involved in 2-AP biosynthesis in fragrant rice under As stress. Herein, a hydroponic experiment of L-Glu seed priming with 0, 100, and 500 μM l-glutamic acid solutions was conducted with two fragrant rice varieties. After that, the 10-day-old seedlings were cultured under 0 and 100 μM arsenite stress for 10 d. Results showed that the 2-AP and Pro contents were increased by 18-30% and 21-78% under As100 μM-Glu100 μM treatment in comparison to the control As100 μM to Glu0 μM, while the activities of pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (ProDH) were increased by 19-46% and 3-19%, respectively. Furthermore, the 2-AP, Pro contents, and P5CS activity were correlated positively. Correspondingly, a significant abundance of differential expressed metabolites (18) and differential expressed genes (26) was observed in amino acid metabolism and glutathione metabolism pathways. In addition, several essential genes were verified and grouped into the pathways of glutathione metabolism, proline, and arginine metabolism with antioxidant defense system to comodulate 2-AP biosynthesis and stress detoxification. Therefore, the Glu seed priming treatment had a positive impact on the 2-AP biosynthesis of fragrant rice under 100 μM arsenite toxicity.

Effects of Different Tillage and Fertilization Methods on the Yield and Nitrogen Leaching of Fragrant Rice

Conservation tillage and deep-side fertilization both hold the potential to reduce nitrogen leaching and improve grain yield and nitrogen use efficiency in fragrant rice cultivation practices. However, the combined impact of different tillage practices with deep-side fertilization on nitrogen leaching remains uncertain. Therefore, this study conducted on-site experiments for four rice-growing seasons in both early and late seasons in 2018 and 2019 using the fragrant rice varieties “Meixiangzhan 2” (MX) and “Xiangyaxiangzhan” (XY). The four experimental treatments included the following: conventional tillage with regular fertilization (T1), conventional tillage with simultaneous deep fertilization (T2), reduced tillage with simultaneous deep fertilization (T3), and no-tillage with simultaneous deep fertilization (T4). Our results indicate that the T4 treatment exhibited higher nitrogen leaching rates and potential nitrogen losses throughout the entire rice growth cycle, with a 4.51% increase in total mineral nitrogen leaching (TMNL) and a 1.86% increase in potential nitrogen leaching compared to T1 treatment. In contrast, the T2 treatment demonstrated the lowest nitrogen leaching rate, resulting in a 6.01% reduction in TMNL and a 9.57% decrease in potential nitrogen leaching compared to T1, demonstrating the most optimal performance. It is important to note that a reduction in nitrogen leaching does not directly translate into an increase in rice yield. Our study involved the cultivation of two fragrant rice varieties, ‘Meixiangzhan2’ (MX) and ‘Xiangyaxiangzhan’ (XY), and the results revealed some interesting insights. For MX, the T1 treatment resulted in lower daily grain outputs compared to the other treatments, with disparities ranging from 5.35% to 9.94%. Similarly, for XY, the T1 treatment yielded significantly lower daily grain outputs compared to the other treatments, with discrepancies ranging from 6.26% to 10.81% during the late season of 2019. Therefore, this study suggests that conventional tillage combined with deep fertilizer application can be considered as an effective agricultural strategy to reduce nitrogen leaching and enhance fragrant rice yields.

Discussion on the Differences in Aroma Components in Different Fragrant Rice Varieties during Storage.

Rice (Oryza sativa L.) is an important food crop in Taiwan, among which fragrant rice is highly regarded for its special aroma when cooked. During the storage of fragrant rice, the aroma components will change, which will affect the aroma quality of fragrant rice. Therefore, headspace solid-phase microextraction (HS-SPME) was used in this study, combined with gas chromatography and gas chromatography-mass spectrometry, to analyze the difference in the aroma components of Taikeng No. 4 (TK4), Tainung No. 71 (TN71), Kaohsiung No. 147 (KH147), and Taichung No. 194 (TC194) fragrant rice. A total of 28 aroma components were identified in the four varieties of fragrant rice, and the main components were all Nonanal. Among them, TK4 contains a very high content of hydrocarbons, including Tridecane and Dodecane; TN71, KH147, and TC194 contain mainly aldehydes such as Nonanal and Hexanal. During different storage times, the contents of alcohols, monoterpenes, aromatic aldehydes, and furans increased with storage time, while the content of aliphatic aldehydes decreased with storage time. After storage, the fragrant rice samples showed a tendency for the total volatile component content to decrease, with the most pronounced reduction observed in Nonanal content.

Bridging the Gap Between Consumer Preferences and the Development of Fragrant Rice Varieties in Malaysia

Bridging the Gap Between Consumer Preferences and the Development of Fragrant Rice Varieties in Malaysia

Integrative Effect of Reduced Tillage and Shading Enhanced Yield and Grain Quality of Fragrant Rice

The major challenge in fragrant rice production is to improve both yield and grain quality in fragrant rice. Reducing tillage has been singled out as an effective impact to improve grain yield. However, information on the improvement of grain yield and grain quality and their relationship is sparse. This study aimed to assess the influence of different tillage methods on rice growth during the booting stage under shading conditions. The experiments were conducted with rotary tillage and no-shading (RTNS), rotary tillage and shading (RTS), reduced tillage and no-shading (LTNS), reduced tillage and shading (LTS), no-tillage and no-shading (NTNS) and no-tillage and shading (NTS), using two fragrant rice varieties, Meixiangzhan 2 (MXZ2) and Xiangyaxiangzhan (XYXZ). Grain yield, grain quality, Malondialdehyde (MDA) content and antioxidant activities were all investigated. Our results showed that grain yield of reduced tillage and no-tillage were 27.9% and 27.0% higher than rotary tillage, respectively. In addition, with shading applied, grain yield significantly decreased. Moreover, with the application of a shading treatment, the brown rice rate, chalkiness degree and chalk grain rate decreased, while the milled rice rate, amylose content and protein content increased. The results of this study revealed that shading improves the grain quality of fragrant rice but has a negative impact on its yield while reducing tillage effectively makes up for the yield loss resulting from shading and improves rice quality.

Genotypic Variation in Thai Fragrant Rice in Response to Manganese Application and Its Effects on 2-Acetyl-1-Pyrroline Content, Productivity and Gene Expression

The fragrance in rice plays a significant role in consumer decisions and is influenced by many environmental factors, e.g., water and fertilizer application during cultivation and post-harvest management. Manganese (Mn) is an essential micronutrient for plant growth and development, and its effects on the fragrance and yield of fragrant rice varieties have not been well-studied. The aim of this research was to determine the effects of Mn application rates on the 2-acetyl-1-pyrroline (2AP) content, yield and gene expression of Thai fragrant varieties. Three rice varieties, i.e., BNM4, KDML105 and KH-CMU, were grown in pots with varying concentrations of MnSO4—150, 200 and 250 mg kg−1 soil—and compared with a control with no Mn application (Mn0). At maturity, the grain yield was evaluated, and the 2AP was analyzed with GC-MS as the grain aroma content. Taken together, the results suggest that Mn application during cultivation tends to increase the 2AP content of fragrant rice and its productivity and tends to affect gene expression. However, it is important to conduct further studies to evaluate the responses for more fragrant rice varieties and additional gene expression, including the determination of key intermediate compounds along the 2AP biosynthesis pathway to confirm the effect of Mn application on fragrant rice. This information could be useful in assisting plant breeders and physiologists in their efforts to improve the crop productivity and grain quality of fragrant rice varieties.

Pyramiding Rice Blast Resistance Gene Pi2 and Fragrance Gene badh2

Rice is a major food crop across the globe, but the frequent occurrence of rice blast in recent years has seriously affected the yield of rice. In addition, fragrance rice is becoming increasingly popular among consumers. In this study, the fragrant rice variety Wenxiang-1 was used as the donor of the fragrance gene badh2, and the rice variety R1179 was used as the donor of rice blast resistance gene Pi2. Plants that were homozygous for both Pi2 and badh2 were selected using marker-assisted selection (MAS) applied to the Wenxiang-1/R1179 F2 segregation population with the functional markers Pi2-1 and Badh2-1 as well as whole-genome-SNP-genotyping technology. Finally, “elite” rice varieties R365 and R403 that had both high levels of rice blast resistance (level 3 and 4) and fragrance (0.650 and 0.511 mg/kg) were bred. Genetic composition analysis indicated that 40.67% of the whole genome of R365 was inherited from Wenxiang-1, while 59.33% was inherited from R1179. Similarly, 46.26% of the whole genome of R403 was inherited from Wenxiang-1, while 53.74% was inherited from R1179. These new hybrid lines with R365 and R403 as the male parents also exhibit high yield per hectare, especially C815S/R365 and Yu03S/R403 F1, with yields per hectare of 9.93 ± 0.15 and 9.6 ± 0.17 tons. These plants also possess high levels of rice blast resistance (level 3 and 4) and fragrance (0.563 and 0.618 mg/kg).

Novel Deletion in Exon 7 of Betaine Aldehyde Dehydrogenase 2 (BADH2)

The fragrance of rice is one of the premium characteristics that breeders want to include in rice varieties due to the higher market value. Nucleotide deletions in exons 2 (7 bp) and 7 (8 bp) of Betaine Aldehyde Dehydrogenase 2 (BADH2) are associated with fragrance in rice. In this study, a new 13 bp deletion in exon 7 of the BADH2 gene was discovered in the Nang Thom Cho Dao (NTCD) variety, and the mutation has been closely related to the genetic background of indica subspecies through the Bayesian phylogenetic approach and haplotype network analysis of the 3 000 Rice Genomes Project. In addition, a set of functional markers (EX07-13F, EX07-13RN, and EX07-13RM) identified the 13 bp deletion only within NTCD (no amplified band) compared with both non-aromatic and other aromatic rice varieties (110 bp band). The deletion of 13 bases instead of 8 bases in exon 7 of BADH2 caused a premature stop codon, which down-regulated the expression of the BADH2 transcript while associated with up-regulation of OsP5CS and the high amount of 2-acetyl-1-pyrroline. It is potential to use the deletion in exon 7 of the BADH2 gene as a novel marker for adulteration and breeding of fragrant rice varieties, particularly for NTCD.

Transcriptional cascades in the regulation of 2-AP biosynthesis under Zn supply in fragrant rice.

Transcription factors (TFs) regulate gene expression to control certain genetic programs, such as growth and development, phytohormone regulation, and environmental stresses. 2-acetyl-1-pyrroline (2-AP) is the key element involved in aroma biosynthesis pathway, and the application of micronutrients can increase the 2-AP levels. However, little is known about the micronutrient-induced TFs involved in 2-AP biosynthesis. Here, we identify a number of TF families in two fragrant rice varieties, "Meixiangzhan-2" (M) and "Xiangyaxiangzhan" (X), in response to Zinc (Zn) application through transcriptomic analysis. A total of ~678 TFs were identified and grouped into 26 TF families, each of which was found to be involved in numerous signaling pathways. The WRKY TF family was found to be the most abundant, followed by bHLH and MYB. Furthermore, members of the WRKY, bHLH, MYB, ERF, HSF, MADS-box, NFY, and AP2 TF families were significantly upregulated and may be involved in the transcriptional regulation of aroma biosynthesis. In brief, this study enhances our understanding of the molecular mechanism of 2-AP biosynthesis and highlights the key TFs potentially involved in the production of aroma in fragrant rice.

Epoxiconazole Improved Photosynthesis, Yield Formation, Grain Quality and 2-Acetyl-1-Pyrroline Biosynthesis of Fragrant Rice

Epoxiconazole is a triazole compound. However, the effects of epoxiconazole on crop productivity and quality were rarely reported. In this study, we investigated the effects of epoxiconazole application on yield formation, grain quality attributes, and 2-acetyl-1-pyrroline (2-AP) content in fragrant rice. A three-year field experiment was carried out with a fragrant rice variety, Meixiangzhan 2. At the heading stage, 0, 0.02, 0.04, 0.08, 0.16 and 0.32g/L epoxiconazole solutions were foliar applied to fragrant rice plants, respectively. The results showed that epoxiconazole application significantly increased grain yield, seed-setting rate and 1000-grain weight. Chlorophyll content and net photosynthetic rate of fragrant rice during the grain-filling stage significantly increased due to epoxiconazole application. Foliar application of epoxiconazole at 0.08g/L increased grain protein content and decreased both chalky rice rate and chalkiness area ratio of fragrant rice. Epoxiconazole also substantially increased grain 2-AP content by inducing the regulation in contents of related synthetic precursors, including proline, pyrroline-5- carboxylic acid, Δ1-pyrroline and methylglyoxal. Overall, foliar application of epoxiconazole could be used for the improvement in grain yield, grain quality and 2-AP content in fragrant rice production when applied concentration at 0.08–0.32g/L. Our findings provided the new roles of epoxiconazole in crop production.

ZnO nanoparticle-based seed priming modulates early growth and enhances physio-biochemical and metabolic profiles of fragrant rice against cadmium toxicity

BackgroundCadmium (Cd) is amongst the most toxic heavy metals that severely affects crop growth, whereas application of nanoparticles (NPs) to negate the toxic effects of heavy metals could be an effective management approach. In the present study, the seeds of two fragrant rice varieties i.e., Yuxiangyouzhan and Xiangyaxiangzhan under normal and Cd stress conditions i.e., 0 and 100 mg L− 1 applied with four levels of ZnO NPs i.e., 0, 25, 50, and 100 mg L− 1.ResultsSeed priming with ZnO NPs had no significant effect on the seed germination (p > 0.05) however, it substantially improved the seedling growth and other related physiological attributes under the Cd stress. The mean fresh weight of the shoot, and whole seedling was increased by 16.92–27.88% and by 16.92–27.88% after ZnO NPs application. The root fresh weight, root-shoot length was also substantially improved under ZnO NPs treatment. Moreover, application of ZnO NPs induced modulations in physiological and biochemical attributes e.g., the superoxide dismutase (SOD) activity in root and shoot, the peroxidase (POD) activity and metallothionein contents in root were increased under low levels of ZnO NPs. The α-amylase and total amylase activity were improved by ZnO NPs application under Cd Stress. Besides, modulation in Zn concentration and ZnO NPs uptake in the seedling were detected. The metabolomic analysis indicated that various pathways such as alanine, aspartate and glutamate metabolism, phenylpropanoid biosynthesis, and taurine and hypotaurine metabolism were possibly important for rice response to ZnO NPs and Cd.ConclusionOverall, application of ZnO NPs substantially improved the early growth and related physio-biochemical attributes in rice. Our findings provide new insights regarding the effects of ZnO NPs on seed germination, and early growth of rice, and its potential applications in developing crop resilience against Cd contaminated soils.

Effects of Light Quality Treatments during the Grain Filling Period on Yield, Quality, and Fragrance in Fragrant Rice

The effect of the light quality on 2-acetyl-1-pyrroline (2AP) during the grain filling period in fragrant rice has rarely been investigated. A pot experiment was carried out with two fragrant rice varieties, Xiangyaxiangzhan and Yuxiangyouzhan, grown under three light treatments, 100% red light (L1), 100% blue light (L2), and compound light (L3), during the grain filling period, and natural light was taken as the control (CK). The yield, quality, and fragrance were investigated. The results showed that light quality treatments significantly decreased the 2AP content in mature grains by 16.67–32.82% but improved the grain yield by 2.70–21.41% compared to CK. The regulation effects of light quality treatments on grain yield and 2AP are linked to yield-related traits, biomass accumulation, antioxidant physiology, and 2AP formation-related physiology. Additionally, light quality treatments decreased the chalky rice percentage and chalkiness, and increased the length-to-width ratio. Overall, light quality treatments during the grain filling period had a positive effect on the grain yield but not on fragrance in fragrant rice.

Light quality during booting stage modulates fragrance, grain yield and quality in fragrant rice

ABSTRACT 2-acetyl-1-pyrroline (2AP) is recognized as the key aromatic compound in fragrant rice, however, the effect of light quality on rice aroma is not fully understood. In this study, two fragrant rice varieties (Xiangyaxiangzhan and Yuxiangyouzhan) were grown under four light quality treatments (CK: natural light, L1: red light, L2: blue light and L3: combined light). Results depicted that L1, L2 and L3 treatments enhanced the grain yield by 14.24–35.36%, compared to CK whilst L2 and L3 treatments reduced the 2AP content in grains by 17.18–28.68%. Moreover, L1, L2 and L3 treatments enhanced the grain yield owing to improved filled grain percentage and regulation in antioxidant enzyme activities. On the other hand, L2 and L3 reduced the 2AP content in grains by decreasing pyrroline-5-carboxylic acid content and modulating proline and γ-aminobutyric acid content. Overall, this study revealed that light quality substantially affects the grain yield and quality characters of fragrant rice.