Effect of different shading materials on grain yield and quality of rice

Impacts of future climate change on rice yield based on crop model simulation-A meta-analysis

Rice is one of the world's major food crops. Changes in major climatic factors such as temperature, rainfall, solar radiation and carbon dioxide (CO2) concentration have an important impact on rice growth and yield. However, many of the current studies that predict the impact of future climate change on rice yield are affected by uncertainties such as climate models, climate scenarios, model parameters and structure, and showing great differences. This study was based on the assessment results of the impact of climate change on rice in the future of 111 published literature, and comprehensively analyzed the impact and uncertainty of climate change on rice yield. This study utilized local polynomial (Loess) regression analysis to investigate the impact of changes in mean temperature, minimum temperature, maximum temperature, solar radiation, and precipitation on relative rice yield variations within a complete dataset. A linear mixed-effects model was used to quantitatively analyze the relationships between the restricted datasets. The qualitative analysis based on the entire dataset revealed that rice yields decreased with increasing average temperature. The precipitation changed between 0 and 25 %, it was conducive to the stable production of rice, and when the precipitation changed >25 %, it would cause rice yield reduction. The change of solar radiation was less than -1.15 %, the rice yield increases with the increase of solar radiation, and when the change of solar radiation exceeds -1.15 %, the rice yield decreases. Elevated CO2 concentrations and management practices could mitigate the negative effects of climate change. The results of a quantitative analysis utilizing the mixed effects model revealed that average temperature, precipitation, CO2 concentration, and adaptation methods all had a substantial impact on rice production, and elevated CO2 concentrations and management practices could exert positive influences on rice production. For every 1 °C and 1 % increase in average temperature and precipitation, rice yield decreased by 3.85 % and 0.56 %, respectively. For every 100 ppm increase in CO2 concentration, rice yield increased by 7.1 %. The variation of rice yield under different climate models, study sites and climate scenarios had significant variability. Elevated CO2 concentrations and management practices could compensate for the negative effects of climate change, benefiting rice production. This study comprehensively collected and analyzed a wide range of literature and research, which provides an in-depth understanding of the impacts of climate change on rice production and informs future research and policy development.

Profiling and Improvement of Grain Quality Traits for Consumer Preferable Basmati Rice in the United States

Basmati rice is a premium aromatic rice that consumers choose primarily because of its distinct aroma and excellent grain quality. The grain quality of Basmati rice (GQBR) reflects the perspectives of producers, processors, sellers, and consumers related to the production, processing, marketing, and consumption of Basmati rice. Consumers, an invaluable part of the production demand and value chain of the Basmati rice industry, have the freedom to choose from different types of aromatic rice. Consumers expect their preferred Basmati rice to possess all superior rice grain qualities, including the physical, biochemical, and physiological properties. Gene functional analysis explained that a 10-base pair deletion in the promoter region of the OsSPL16 gene causes the slender grains in Basmati rice, whereas an 8-base-pair deletion in exon 7 of the OsBadh2 gene (located in the fgr region on rice chromosome 8) results in the distinct aroma. Furthermore, a combination of the genetic characteristics of the gw8 and gs3 genes has led to the creation of a long-grain Basmati-type rice cultivar. It has also been demonstrated that agricultural, genetic, and environmental conditions significantly influence GQBR. Hence, research on improving GQBR requires a multidimensional approach and sophisticated elements due to the complexity of its nature and preference diversity. This review covers the basic definitions of grain quality traits, consumer preference criteria, influencing factors, and strategies for producing superior-quality Basmati rice in the United States. This knowledge will be useful in improving the grain quality of Basmati and Basmati-type rice, as well as developing appropriate breeding programs that will meet the preferences of different countries and cultures.

Combining modeling and experimental approaches for developing rice-oil palm agroforestry systems

Monoculture systems in South East Asia are facing challenges due to climate change-induced extreme weather conditions, leading to significant annual production losses in rice and oil palm. To ensure the stability of these crops, innovative strategies like resilient agroforestry systems need to be explored. Converting oil palm (Elaeis guineensis) monocultures to rice (Oryza sativa)-based intercropping systems shows promise, but achieving optimal yields requires adjusting palm density and identifying rice varieties adapted to changes in light quantity and diurnal fluctuation. This paper proposes a methodology that combines a model of light interception with indoor experiments to assess the feasibility of rice-oil palm agroforestry systems. Using a functional-structural plant model of oil palm, the planting design was optimized to maximize transmitted light for rice. Simulation results estimated the potential impact on oil palm carbon assimilation and transpiration. In growth chambers, simulated light conditions were replicated with adjustments to intensity and daily fluctuation. Three light treatments independently evaluated the effects of light intensity and fluctuation on different rice accessions. The simulation study revealed intercropping designs that significantly increased light transmission for rice cultivation with minimal decrease in oil palm densities compared with conventional designs. The results estimated a loss in oil palm productivity of less than 10%, attributed to improved carbon assimilation and water use efficiency. Changes in rice plant architecture were primarily influenced by light quantity, while variations in yield components were attributed to light fluctuations. Different rice accessions exhibited diverse responses to light fluctuations, indicating the potential for selecting genotypes suitable for agroforestry systems.

A non-traditional Agrophotovoltaic installation and its impact on cereal crops: A case of the BRRI-33 rice variety in Bangladesh

Traditional Agrophotovoltaic (APV) installation (i.e., basic row layout with minimum or no usage of the space underneath the solar PV panels) is responsible for a vast amount of agricultural land waste as no regular crops are grown under the shade of APV. Bangladesh is no exception to this trend. A primary in-person survey of about 50 solar irrigation pumps (SIPs), i.e., APVs, in Bangladesh, shows that on average, 13.77 decimal or 7,200 sq.ft. of land is used for each APV system installation. If 10,000 SIPs are installed by 2027 in Bangladesh, as targeted by the government through Infrastructure Development Company Limited (IDCOL) by employing the same procedure, the land wastage would be 1,652 acres. Notably, this is a critical issue for a country like Bangladesh with a scarcity of agricultural lands. According to World Bank data, agricultural land in Bangladesh was about 80% in 1989 and reduced to 76% in 2020 due to population growth and urbanization. Therefore, to reduce agricultural land waste a non-traditional APV installation procedure, along with its shading impact on the BRRI-33 rice variety (a major crop in Bangladesh), has been investigated in this study. The results show that discontinuous sunlight has an insignificant impact on BRRI-33 rice production, and APV might be installed in the cultivating area for irrigation purposes. This non-traditional APV installation has a statistically insignificant impact on rice yield. For instance, the 100 grains' yield variation was between 1.45 and 4.82%, which is insignificant. Additionally, the APV shade does not negatively impact soil p^H level, and shadow helps keep the soil temperature low and ensures less irrigation. Hence, the proposed non-traditional APV installation could achieve sustainable agriculture and energy development through efficient land use at least in the case of the BRRI-33 rice variety.

Light intensity-mediated auxin homeostasis in spikelets links carbohydrate metabolism enzymes with grain filling rate in rice

Low light (LL) stress during the grain-filling stage acutely impairs the quality and quantity of starch accumulation in rice grains. Here, we observed that LL-induced poor starch biosynthesis is modulated by auxin homeostasis, which regulates the activities of major carbohydrate metabolism enzymes such as starch synthase (SS) and ADP-glucose pyrophosphorylase (AGPase) in rice. Further, during the grain-filling period under LL, the starch/sucrose ratio increased in leaves but significantly decreased in the developing spikelets. This suggests poor sucrose biosynthesis in leaves and starch in the grains of the rice under LL. A lower grain starch was found to be correlated with the depleted AGPase and SS activities in the developing rice grains under LL. Further, under LL, the endogenous auxin (IAA) level in the spikelets was found to be synchronized with the expression of a heteromeric G protein gene, RGB1. Interestingly, under LL, the expression of OsYUC11 was significantly downregulated, which subsequently resulted in reduced IAA in the developing rice spikelets, followed by poor activation of grain-filling enzymes. This resulted in lowered grain starch accumulation, grain weight, panicle number, spikelet fertility, and eventually grain yield, which was notably higher in the LL-susceptible (GR4, IR8) than in the LL-tolerant (Purnendu, Swarnaprabha) rice genotypes. Therefore, we hypothesize that depletion in auxin biosynthesis under LL stress is associated with the downregulation of RBG1, which discourages the expression and activities of grain-filling enzymes, resulting in lower starch production, panicle formation, and grain yield in rice.

RGA1 alleviates low-light-repressed pollen tube elongation by improving the metabolism and allocation of sugars and energy

Low-light stress compromises photosynthetic and energy efficiency and leads to spikelet sterility; however, the effect of low-light stress on pollen tube elongation in the pistil remains poorly understood. The gene RGA1, which encodes a Gα-subunit of the heterotrimeric G-protein, enhanced low-light tolerance at anthesis by preventing the cessation of pollen tube elongation in the pistil of rice plants. In this process, marked increases in the activities of acid invertase (INV), sucrose synthase (SUS) and mitochondrial respiratory electron transport chain complexes, as well as the relative expression levels of SUTs (sucrose transporter), SWEETs (sugars will eventually be exported transporters), SUSs, INVs, CINs (cell-wall INV 1), SnRK1A (sucrose-nonfermenting 1-related kinase 1) and SnRK1B, were observed in OE-1 plants. Accordingly, notable increases in contents of ATP and ATPase were presented in OE-1 plants under low-light conditions, while they were decreased in d1 plants. Importantly, INV and ATPase activators (sucrose and Na₂ SO₃ , respectively) increased spikelet fertility by improving the energy status in the pistil under low-light conditions, and the ATPase inhibitor Na₂ VO₄ induced spikelet sterility and decreased ATPase activity. These results suggest that RGA1 could alleviate the low-light stress-induced impairment of pollen tube elongation to increase spikelet fertility by promoting sucrose unloading in the pistil and improving the metabolism and allocation of energy.

Agronomic evaluation of shade tolerance of 16 spring Camelina sativa (L.) Crantz genotypes under different artificial shade levels using a modified membership function

Camelina [Camelina sativa (L.) Crantz] is currently gaining considerable attention as a potential oilseed feedstock for biofuel, oil and feed source, and bioproducts. Studies have shown the potential of using camelina in an intercropping system. However, there are no camelina genotypes evaluated or bred for shade tolerance. The objective of this study was to evaluate and determine the shade tolerance of sixteen spring camelina genotypes (growth stage: BBCH 103; the plants with 4-5 leaves) for intercropping systems. In this study, we simulated three different shade levels, including low (LST), medium (MST), and high shade treatments (HST; 15, 25, and 50% reduction of natural light intensity, respectively), and evaluated the photosynthetic and physiological parameters, seed production, and seed quality. The mean chlorophyll pigments, including the total chlorophyll and chlorophyll a and b across the 16 genotypes increased as shade level increased, while the chlorophyll fluorescence parameter F_v/F_m, chlorophyll a/b, leaf area, the number of silicles and branches plant^-1 decreased as shade level increased. The first day of anthesis and days of flowering duration of camelina treated with shade were significantly delayed and shortened, respectively, as shade increased. The shortened lifecycle and altered flowering phenology decreased camelina seed yield. Additionally, the shade under MST and HST reduced the seed oil content and unsaturated fatty acids, but not saturated fatty acids. The dendrograms constructed using the comprehensive tolerance membership values revealed that CamK9, CamC4, and 'SO-40' were the relatively shade-tolerant genotypes among the 16 camelina genotypes. These camelina genotypes can grow under the shade level up to a 25% reduction in natural light intensity producing a similar seed yield and seed oil quality, indicating the potential to intercrop with maize or other small grain crops. The present study provided the baseline information on the response of camelina genotypes to different shade levels, which would help in selecting or breeding shade-tolerant genotypes.

PHYTOCHROME-INTERACTING FACTORS: a promising tool to improve crop productivity

Light is a key determinant for plant growth, development, and ultimately yield. Phytochromes, red/far-red photoreceptors, play an important role in plant architecture, stress tolerance, and productivity. In the model plant Arabidopsis, it has been shown that PHYTOCHROME-INTERACTING FACTORS (PIFs; bHLH transcription factors) act as central hubs in the integration of external stimuli to regulate plant development. Recent studies have unveiled the importance of PIFs in crops. They are involved in the modulation of plant architecture and productivity through the regulation of cell division and elongation in response to different environmental cues. These studies show that different PIFs have overlapping but also distinct functions in the regulation of plant growth. Therefore, understanding the molecular mechanisms by which PIFs regulate plant development is crucial to improve crop productivity under both optimal and adverse environmental conditions. In this review, we discuss current knowledge of PIFs acting as integrators of light and other signals in different crops, with particular focus on the role of PIFs in responding to different environmental conditions and how this can be used to improve crop productivity.

Auxin-Glucose Conjugation Protects the Rice (Oryza sativa L.) Seedlings Against Hydroxyurea-Induced Phytotoxicity by Activating UDP-Glucosyltransferase Enzyme

Hydroxyurea (HU) is the replication stress known to carry out cell cycle arrest by inhibiting ribonucleotide reductase (RNR) enzyme upon generating excess hydrogen peroxide (H2O2) in plants. Phytohormones undergo synergistic and antagonistic interactions with reactive oxygen species (ROS) and redox signaling to protect plants against biotic and abiotic stress. Therefore, in this study, we investigated the protective role of Indole-3-acetic acid (IAA) in mitigating HU-induced toxicity in rice seedlings. The results showed that IAA augmentation improved the growth of the seedlings and biomass production by maintaining photosynthesis metabolism under HU stress. This was associated with reduced H2O2 and malondialdehyde (MDA) contents and improved antioxidant enzyme [superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and peroxidase (POD)] activity that was significantly affected under HU stress. Furthermore, we showed that the HU stress-induced DNA damage leads to the activation of uridine 5'-diphosphate-glucosyltransferase (UGT), which mediates auxin homeostasis by catalyzing IAA-glucose conjugation in rice. This IAA-glucose conjugation upregulates the RNR, transcription factor 2 (E2F2), cyclin-dependent kinase (CDK), and cyclin (CYC) genes that are vital for DNA replication and cell division. As a result, perturbed IAA homeostasis significantly enhanced the key phytohormones, such as abscisic acid (ABA), salicylic acid (SA), cytokinin (CTK), and gibberellic acid (GA), that alter plant architecture by improving growth and development. Collectively, our results contribute to a better understanding of the physiological and molecular mechanisms underpinning improved growth following the HU + IAA combination, activated by phytohormone and ROS crosstalk upon hormone conjugation via UGT.

Low Light/Darkness as Stressors of Multifactor-Induced Senescence in Rice Plants

Leaf senescence, as an integral part of the final development stage for plants, primarily remobilizes nutrients from the sources to the sinks in response to different stressors. The premature senescence of leaves is a critical challenge that causes significant economic losses in terms of crop yields. Although low light causes losses of up to 50% and affects rice yield and quality, its regulatory mechanisms remain poorly elucidated. Darkness-mediated premature leaf senescence is a well-studied stressor. It initiates the expression of senescence-associated genes (SAGs), which have been implicated in chlorophyll breakdown and degradation. The molecular and biochemical regulatory mechanisms of premature leaf senescence show significant levels of redundant biomass in complex pathways. Thus, clarifying the regulatory mechanisms of low-light/dark-induced senescence may be conducive to developing strategies for rice crop improvement. This review describes the recent molecular regulatory mechanisms associated with low-light response and dark-induced senescence (DIS), and their effects on plastid signaling and photosynthesis-mediated processes, chloroplast and protein degradation, as well as hormonal and transcriptional regulation in rice.

The impact of global dimming on crop yields is determined by the source-sink imbalance of carbon during grain filling

Global dimming reduces incident global radiation but increases the fraction of diffuse radiation, and thus affects crop yields; however, the underlying mechanisms of such an effect have not been revealed. We hypothesized that crop source-sink imbalance of either carbon (C) or nitrogen (N) during grain filling is a key factor underlying the effect of global dimming on yields. We presented a practical framework to assess both C and N source-sink relationships, using data of biomass and N accumulation from periodical sampling conducted in field experiments for wheat and rice from 2013 to 2016. We found a fertilization effect of the increased diffuse radiation fraction under global dimming, which alleviated the negative impact of decreased global radiation on source supply and sink growth, but the source supply and sink growth were still decreased by dimming, for both C and N. In wheat, the C source supply decreased more than the C sink demand, and as a result, crops remobilized more pre-heading C reserves, in response to dimming. However, these responses were converse in rice, which presumably stemmed from the more increment in radiation use efficiency and the more limited sink size in rice than wheat. The global dimming affected source supply and sink growth of C more significantly than that of N. Therefore, yields in both crops were dependent more on the source-sink imbalance of C than that of N during grain filling. Our revealed source-sink relationships, and their differences and similarities between wheat and rice, provide a basis for designing strategies to alleviate the impact of global dimming on crop productivity.

Nitrogen Use Efficiency Phenotype and Associated Genes: Roles of Germination, Flowering, Root/Shoot Length and Biomass

Crop improvement for Nitrogen Use Efficiency (NUE) requires a well-defined phenotype and genotype, especially for different N-forms. As N-supply enhances growth, we comprehensively evaluated 25 commonly measured phenotypic parameters for N response using 4 N treatments in six indica rice genotypes. For this, 32 replicate potted plants were grown in the green-house on nutrient-depleted sand. They were fertilized to saturation with media containing either nitrate or urea as the sole N source at normal (15 mM N) or low level (1.5 mM N). The variation in N-response among genotypes differed by N form/dose and increased developmentally from vegetative to reproductive parameters. This indicates survival adaptation by reinforcing variation in every generation. Principal component analysis segregated vegetative parameters from reproduction and germination. Analysis of variance revealed that relative to low level, normal N facilitated germination, flowering and vegetative growth but limited yield and NUE. Network analysis for the most connected parameters, their correlation with yield and NUE, ranking by Feature selection and validation by Partial least square discriminant analysis enabled shortlisting of eight parameters for NUE phenotype. It constitutes germination and flowering, shoot/root length and biomass parameters, six of which were common to nitrate and urea. Field-validation confirmed the NUE differences between two genotypes chosen phenotypically. The correspondence between multiple approaches in shortlisting parameters for NUE makes it a novel and robust phenotyping methodology of relevance to other plants, nutrients or other complex traits. Thirty-Four N-responsive genes associated with the phenotype have also been identified for genotypic characterization of NUE.