Tropical Rice Research Articles

Morphological and Physiological Responses of Two Tropical Rice (Oryza sativa) Varieties to High-Temperature Stress

Morphological and Physiological Responses of Two Tropical Rice (Oryza sativa) Varieties to High-Temperature Stress

Rational Nitrogen Reduction Helps Mitigate the Nitrogen Pollution Risk While Ensuring Rice Growth in a Tropical Rice–Crayfish Coculture System

The incorporation of aquaculture feed within a rice–crayfish coculture system significantly enhances nitrogen cycling, thereby diminishing the reliance on chemical fertilizers. However, this benefit is often overlooked in practice, and farmers continue to use large quantities of chemical fertilizers to maximize production, resulting in excessive soil fertility and water nitrogen pollution. Thus, avoiding nitrogen pollution in rice–crayfish coculture systems has become a pressing issue. In this study, we conducted a two-year experiment with two rice cultivars, and a 33.3% reduction in nitrogen fertilizer in a rice–crayfish coculture system (RC), to systematically analyze the overall nitrogen balance, rice nitrogen nutrition, and soil fertility, as compared with a rice monoculture system (RM). Our findings revealed the following: (1) Under the 33.3% reduction in nitrogen fertilizer, the nitrogen surplus in the rice–crayfish coculture system was comparable to that in the rice monoculture, and was controlled at an environmental safety level. (2) Nitrogen utilization efficiency and the accumulation of nitrogen in the rice–crayfish coculture were comparable to those in the rice monoculture. The nitrogen cycle in this system was able to provide the nitrogen required for rice growth after nitrogen fertilizer reduction. (3) The rice–crayfish coculture significantly improved the overall soil fertility and the effectiveness of soil nitrogen nutrition. Furthermore, cutting off the application of nitrogen fertilizer after the mid-tillering stage effectively controlled the total nitrogen content in soil after rice maturity. In conclusion, reducing nitrogen fertilizer in a rice–crayfish coculture system is feasible and beneficial. It ensures rice production, reduces the risk of excessive nitrogen surplus and surface pollution, and promotes a greener, more environmentally friendly paddy field ecosystem.

What are we saving? The amphibians and reptiles of the rice paddies in the Balasore District, Odisha, India

Agriculture is widely recognized as one of the major conservation threats to herpetofaunal species. Any conservationactions, particularly those aimed at herpetofauna beyond the network of protected areas, require baseline dataon existing species diversity in an area. Unfortunately, most biodiversity studies are focused on producing inventoriesof animals in a small number of protected areas. To accrue truly meaningful benefits, conservation needs to focus onhuman-dominated landscapes beyond protected areas, such as agricultural lands. Scientific documentation of farmlandherpetofauna is entirely lacking, which could lead to a lack of management and effective inclusion of herpetofaunain conservation. I assessed the species of amphibians and reptiles in tropical rice paddies near the Kuldiha WildlifeSanctuary in Balasore District, Odisha, India. Based on ecological sampling and community interviews, combined withliterature reviews and field guides, I report a total of 55 species including 16 species of amphibians in five families and39 species of reptiles in 15 families.

Quantifying Climate Influence on Net Ecosystem Exchange in Lowland Tropical Rice: A Five-Year Eddy Covariance Study

Quantifying Climate Influence on Net Ecosystem Exchange in Lowland Tropical Rice: A Five-Year Eddy Covariance Study

Adjustments of flower opening time and duration in tropical rice (Oryza sativa ssp. indica) landraces in response to heat stress

AbstractBased on our primary database of the flower opening time (FOT) and flower exposure duration (FED) of 1114 rice (Oryza sativa ssp. indica) landraces, we examined the influences of growing season, sunrise time as well as day maximum and minimum temperatures on the anthesis behaviour of indica rice landraces of South and Southeast Asia, flowering in summer and winter in 3 consecutive years (2020–2022). We also compared the FOT and FED on sunny and cloudy days of a small set of landraces, and also during summer and winter. Our data show that rice florets tend to open later in the morning and lengthen the sunrise‐to‐anthesis duration (SAD) on hotter sunny days during tropical summer than during winter and on cloudy days. These findings contradict the widely held conjecture, based on studies conducted at colder latitudes, that rice flowers open earlier in the morning to avoid heat stress. We propose that indica rice landraces are sufficiently adapted to tropical summer because they were selected and bred over millennia to withstand heat stress during tropical summer, so their FOT and SAD are weakly influenced by high day temperatures. However, the significant reduction in FED of these landraces, whose flowers open later in mid‐day, seems to be an adaptive mechanism to avoid longer exposure to rising air temperature approaching day maximum temperature.

Long-Term Effect of Rice and Non-rice Ecology on Pools of Carbon in Surface and Deep Soil in Farmer’s Field

The greatest terrestrial sink of carbon (C) is soil. In addition to improving soil quality, carbon absorption in soil helps reduce atmospheric CO2 loading. Not only the surface soil, but also the deep sub-soil act as a storehouse of C. Besides, the study of C dynamics in tropical rice soil is important in countries like India where rice is the predominant crop and soil C sequestration is at risk due to high temperatures. In this context, this study tried to understand the C dynamics in surface as well as deep soil under rice and non-rice ecology. Representative soil samples were collected from five sites of rice-rice (rice ecology) and vegetable-vegetable (non-rice ecology) cropping systems from three depths viz., 0-20 cm, 100-120 and 120-140 cm from long-term farmer’s field of Nadia district of West Bengal belonging to Alfisols to compare C dynamics of surface and deep soils as well as rice and non-rice ecology. Results indicated that surface soils exhibited higher amount of total C, total organic C and inorganic C in comparison to deep soil irrespective of crop ecologies. The rice ecology showed higher total C and total organic C in comparison to non-rice soil. As per water solubility, water-soluble (room temperature) C and hot water-soluble C which were highest in surface soil compared to deep soil as the former usually receives maximum amount of fresh C input compared to deep soil. Irrespective of crop ecology, water-soluble C (WSC), hot water-soluble C (HWC), recalcitrant C (RC) were highest in surface soil compared to deep soils. Again, irrespective of soil depth, WSC and RC were highest in rice ecology and lowest in non-rice ecology. But, HWC content was highest in non-rice ecology and lowest in rice ecology. Irrespective of crop ecology, per cent contribution of labile pool of C (WSC+ HWC) and that of RC pool towards TOC was the highest and the lowest respectively. However, irrespective of soil depth, per cent contribution of labile pool of C and that of recalcitrant pool of C towards TOC was highest and lowest in soils under non-rice ecology and rice ecology respectively. Thus, this study conclusively indicated the potential of subsoil layer to act as a C sink in comparison to surface soil. The rice soil also has been identified as a niche for soil C sequestration.

Recognition of multi-season rice in a complex tropical agronomy zone using time-series SAR data: a case study of Hainan, China

ABSTRACT Rice plays a significant role in regional food supply and international food trading, especially for Asian countries. However, accurate mapping of tropical rice cultivationis a challenging task due to the flexible planting calendar and the complicated topography. With the all-day and all-weather imaging ability, Synthetic Aperture Radar (SAR) provides an encouraging resolution for this task. In this research, we presented a case study in Hainan, China that identify the cultivation patterns of rice. As the only tropical province in China, Hainan has abundant crop resources and diverse rice cultivation practices. First, our previously proposedrice mapping method based on time-series Sentinel-1 data and U-Net modelwas applied to Hainan to generate the candidate rice fields in 2019. Then, a start of season (SOS) detection strategy was proposed to discriminate rice cultivation patterns. The accuracy of the annual rice map and the multi-season discrimination results were validated in pixel level and parcel level, respectively. The annual rice map achieved an overall accuracy of 95.03%. Besides, for 313 out of 360 rice parcels, the cultivation patterns were correctly identified. These results proved the effectiveness of phenology information of time-series SAR, and the proposed scheme will be easily extended to complex tropical agronomy zones.

Long-term impact of legume-inclusive diversification and nutrient management practices on phosphorus dynamics in alkaline Fluvisol

An insight into the dynamics of soil phosphorus (P) pools with long-term cropping/management practices would help in designing efficient and sustainable management module(s). The study aimed to investigate the long-term impact of diversified rice-based rotations and variable nutrient management practices on the dynamic composition of P pools and their influence on systems’ base-crop productivity in an alkaline soil of Indo-Gangetic plain (Fluvisol). Treatments consisted of four rotations [rice–wheat (R–W), rice–wheat–mungbean (R–W–Mb), rice–wheat–rice–chickpea (R–W–R–C), rice–chickpea (R–C)] each with three nutrient treatments [control (CT), integrated nutrient management (INM), sole-chemical fertilizers (CF)]. Notably, R–C exhibited higher levels of bioavailable-P (soluble-P, Ca2-P, labile-Po), particularly in subsurface soil depth (0.2–0.4 m) compared to other rotations. Likewise, the inclusion of chickpea every alternate year (R–W–R–C) resulted in higher Ca2-P (40%), labile-Pi (15%), labile-Po (11%), and moderately labile Po (8%) compared to R–W rotation demonstrating an increased significance of chickpea in maintaining a favorable soil P regime in alkaline soil. Both R–C and R–W–R–C reduced the surface-to-subsurface depth ratio (SSBR) of soluble-P and Ca2-P while increasing the ratio for microbial biomass P. Even with a suboptimal fertilizer-P rate, INM significantly increased soluble-P (4–33%), labile-Po (13–17%), microbial biomass P (10–26%), moderately labile-Po (4–17%) compared to CF and exhibited higher SSBR values. Correlation analysis demonstrated the substantial influence of very-labile carbon, microbial and phosphatase activities on P availability. The treatment-induced changes in labile-P pools significantly influenced rice (base-crop) yields. In conclusion, chickpea-inclusive diversification and INM could be a sustainable approach to enhance P bioavailability and crop productivity in tropical rice soils.

Influence of herbicide on rhizospheric microbial communities and soil properties in irrigated tropical rice field

Microbial diversity is an essential biological indicator of soil health as well as crop productivity and helps in maintaining the ecosystem dynamics. In land management, Nature based Solutions (NbS) are not mainstream management, however, for sustaining the balanced ecosystem, integrity in the structural and functional diversity of microbes via NbS is imperative. Direct seeded rice (DSR) cultivation is a promising technique for efficient rice production, but weed infestation can lead to yield loss, requiring extensive herbicide use like pendimethalin (PND) and pretilachlor (PRT). The results revealed that with a reduction in PND and PRT residues (0.93–0.01 µg g−1 soil), values of soil microbial biomass C (132.3–112.6 mg kg−1 soil) and MBN (12.6–8.5 mg kg−1 soil), and enzyme activities increased. Negative correlations were observed between herbicide residues and microbial parameters. In control soils, higher population sizes of archaea, bacteria, and fungi were obtained compared to herbicide-treated soils. High-throughput amplicon sequencing (16S rRNA, ITS genes) detected dominant archaea, atronorbrum_4312, MethanothrixX_B, and Methanosarcina_2619 in herbicide treated whereas Nitrosocosmicus, Methanoregula, in control. Bacillus, Methyloceanibacter, Azospira, and Nitrospira bacterial genera were present in both groups. Control soil showed the dominance of Humicola, Nigrospora, and Paramyrothecium fungi, while treated one exhibited Mariannaea, Ceratobasidium, Funneliformis (PND), Aspergillus, Pseudorhypophila, and Lecythophora (PRT). Overall, herbicides had a detrimental impact on microbial dynamics, and their residues correlated negatively with soil variables and microbial diversity. The research outcomes revealed the dramatic variations in microbial communities under the influence of herbicides. This will further aid in a better understanding of the development of NbS solutions for effectively managing herbicide application in direct-seeded rice for enhancing soil health and ecosystem services while supporting sustained productivity.

Unravelling spatial drivers of topsoil total carbon variability in tropical paddy soils of Sri Lanka

This study aimed to map and identify the spatial drivers of total carbon (TC) concentration in topsoil (0–15 cm) across paddy-growing regions in tropical climates using Sri Lanka as a case study. For model calibration, a total of 888 sampling locations were sampled using the conditioned Latin Hypercube sampling approach with a sample density of one sample per 11 km2. Additionally, 99 sampling sites were selected using a design-based (probabilistic) stratified random strategy for independent evaluation of the developed models. Two distinct spatial random forest (RF) models were developed using a variety of environmental covariates: Model 1: using all environmental covariates without variable selection; Model 2: only incorporated covariates selected based on the forward selection process. Evaluation of model quality using fully independent validation sites revealed that both Model 1 and Model 2 performed similarly. Based on the spatial estimates of Model 1 across the paddy-growing regions of Sri Lanka, the predicted TC concentration varied from 0.89% to 13.15%. The highest predicted TC concentration range was in the Wet zone (2.06% to 13.15%), followed by the Intermediate zone (1.18% to 7.23%), and the lowest was reported in the Dry zone (0.86% to 4.30%). In the spatial estimates of Model 2, the predicted values varied between 0.86% and 13.29% and were similar to Model 1. The highest predicted TC concentration range was in the Wet zone (2.09% to 13.29%), followed by the Intermediate zone (1.08% to 6.99%), and the lowest was reported in the Dry zone (0.86% to 4.30%) following the similar pattern to Model 1. In fact, this clearly showed the importance of mean annual rainfall on the dynamics of TC in tropical rice production systems. Furthermore, the variable importance plot of the RF models revealed that out of all considered environmental covariates, the mean annual rainfall was identified as being the most important variable in the developed spatial prediction function. Moreover, we deployed an area of applicability (AOA) calculation to quantify and identify regions where prediction is less reliable and quantified the prediction uncertainty using a bootstrapping approach. Additionally, we assessed the influence of increasing the number of calibration sites on model prediction quality and reliability using user defined sequence of calibration sites. Independent evaluations of each model indicated that model performance quality indices were improved up to n = 400 and thereafter stagnated. For AOA results, an improvement in model reliability is observed for Wet and Intermediate zones when models are developed using 400 calibration sites. Derived estimates of TC can be used for regional-scale planning to enhance the soil carbon and provide a baseline for designing a future land-based carbon accounting system for Sri Lanka.

Evaluating greenhouse gas mitigation through alternate wetting and drying irrigation in Colombian rice production

Rice demand in Latin America is increasing rapidly, but few studies have identified management practices to reduce water demand and soil greenhouse gas (GHG) emissions for irrigated rice systems in this region. Therefore, we tested the hypothesis that alternate wetting and drying (AWD) irrigation could maintain crop yields while mitigating global warming potential (GWP) compared to a conventional system with recommended irrigation and nutrient management practices for tropical rice in Colombia. Over four consecutive growing seasons, we monitored CH4 and N2O emissions, grain yield, and water consumption for two AWD treatments (AWD5 cm and AWD10 cm - where water drained to depths of 5 and 10 cm below the soil surface, respectively) and a control, in which the field was drained multiple times during fertilizer applications and then continuously flooded until harvest. The control had the highest water use across all rice seasons, with values ranging from 9260 to 16559 m3 ha−1 harvest−1. Implementation of AWD reduced cumulative water use by 19–56%, especially in dry seasons. Both AWD treatments significantly reduced cumulative CH4 emissions by 72–100%, which is consistent with previous research. A new finding is that AWD also decreased N2O emissions by 12–70%, which was attributed to management of soil moisture during fertilizer application events. In total, AWD reduced GWP by 25–73% compared to the control, with minimal impacts on crop productivity. Rice yields ranged from 5.2 to 8.2 Mg ha−1, with no significant difference among treatments in three of four seasons. This study shows that AWD saves irrigation water while greatly reducing GWP with little agronomic penalty, suggesting this technology could be a promising strategy for GHG mitigation in tropical rice in Colombia. Because there are important barriers to AWD adoption, future work should explore challenges at the farm-level as well as changes in policy, irrigation infrastructure, and institutional arrangements to understand the potential for broader implementation.

Assessment of the Suitability of Extractants for Predicting Plant Available Arsenic in Some Tropical Rice Growing Inceptisols of Eastern India

ABSTRACT The complex behavior of arsenic (As) in soil in conjunction to crop mediated transfer through the food chain necessitates a thorough evaluation of its phyto-availability. In this pretext, the present experiment has been conducted to determine the best chemical extractant for plant available As under the As-prone, rice-dominant agro-ecosystems of Gangetic West Bengal, India. Based on the tube-well arsenic data (JPOA, UNICEF), surface soil samples from high, medium, low and uncontaminated As sites have been collected. A pot study with rice cv. IR-36, exposed to varying levels of As (0, 0.1, 0.2, 0.3 and 0.4 mg L−1) was conducted. Ten chemical extractants were used in this study. The As extraction pattern followed the pattern of (HCl+H2SO4)>; (NH4-oxalate+Ascorbic acid)>; (Malic+Citric)> NaOH> KH2PO4> NaHCO3>; (H2O2+HNO3)> NH4F> NH4Cl> NH4OAc. On the 85th day after sowing, the rice plants were harvested keeping in mind that the maximum uptakes of heavy metals like As occurs during the peak vegetative growth (panicle initiation) stage. The soil As correlated with rice dry matter As accumulation as: NH4-oxalate+ascorbic acid (r = 0.729**)> NH4Cl (r = 0.698**)> H2O2+HNO3 (r = 0.697**)> NH4F (r = 0.693**)>Malic+Citric (r = 0.666**)> KH2PO4 (r = 0.615**)> HCl+H2SO4 (r = 0.608**)> NaOH (r = 0.589**)> NaHCO3 (r = 0.571**)> NH4OAc (r = 0.533*). Statistical analyses through correlation sum and stepwise multiple regression modeling revealed that NH4-oxalate+ascorbic acid had the best relationship with all other extractants, As fractions and soil physicochemical characters and therefore emerged as the best suited extractant of As for the wide-scale experimental locations under rice cultivation system.

Deciphering insights into rhizospheric microbial community and soil parameters under the influence of herbicides in zero-tillage tropical rice-agroecosystem

Extensive use of chemicals like herbicides in rice and other fields to manage weeds is expected to have a lasting influence on the soil environment. Considering this rationale, we aimed to decipher the effects of herbicides, Pendimethalin and Pretilachlor, applied at 0.5 and 0.6 kg ha−1, respectively on the rhizosphere microbial community and soil characteristics in the tropical rice field, managed under zero tillage cultivation. The quantity of herbicide residues declined gradually since application up to 60 days thereafter it reached the non-detectable level. Most of the soil variables viz., microbial biomass, soil enzymes etc., exhibited slight reduction in the treated soils compared to the control. A gradual decline was observed in Mineral-N, MBC, MBN and enzyme activities. Quantitative polymerase chain reaction results showed maximal microbial abundance of bacteria, fungi and archaea at mid-flowering stage of rice crop. The 16 rRNA and ITS region targeted amplicons high throughput sequencing microbial metagenomic approach revealed total of 94, 1353, and 510 species for archaea, bacteria and fungi, respectively. The metabarcoding of core microbiota revealed that the archaea comprised of Nitrososphaera, Nitrosocosmicus, and Methanosarcina. In the bacterial core microbiome, Neobacillus, Nitrospira, Thaurea, and Microvigra were found as the predominant taxa. Fusarium, Clonostachys, Nigrospora, Mortierella, Chaetomium, etc., were found in core fungal microbiome. Overall, the study exhibited that the recommended dose of herbicides found to be detrimental to the microbial dynamics, though a negative relation between residues and soil variables was observed that might alter the microbial diversity. The outcomes offer a comprehensive understanding of how herbicides affect the microbial community in zero tillage rice soil, thus has a critical imputation for eco-friendly and sustainable rice agriculture. Further, the long-term studies will be helpful in elucidating the role of identified microbial groups in sustaining the soil fertility and crop productivity.

Occurrence and ecological risks of flonicamid and its metabolites in multiple substrates from intensive rice–vegetable rotations in tropical China

Rice–vegetable rotations are dominant in (sub)-tropical agriculture worldwide. However, fate and risks of the insecticide flonicamid (FLO) and its main degradates (collectively called FLOMs) in multiple substrates from those cropping systems remain largely unknown. In this study, we characterized residual concentrations, driving factors, transport, and potential ecological risks of FLOMs in different substrates in 28 tropical rice–vegetable rotations. Concentrations (median) of FLOMs were 0.013–3.03 (0.42) ng g−1 in plants, 0.012–1.92 (0.23) ng g−1 in soil, 0.029–0.63 (0.126) μg L−1 in water, and 0.002–0.398 (0.055) ng g−1 in sediments. Flonicamid and its metabolite N-(4-trifluoromethylnicotinoyl) glycine were the dominant species in the four substrates (84.1 % to 88.5 %). Plants had the highest levels of FLOMs, with the highest bioconcentration factor in peppers. According to boosted regression trees coupled with a partial least squares structural equation model, levels and composition of FLOMs showed high spatiotemporal and crop-related patterns in different substrates, with patterns highly codetermined by agricultural practices (e.g., crop type and FLO/neonicotinoid/pyrethroid applications), substrate parameters (e.g., pH, organic matter or total organic carbon), and climate features (e.g., wet/dry seasons). Moreover, a fugacity method indicated differences in transport and partitioning patterns in different substrates during rice and vegetable planting periods. Integrated substrate risk assessment of FLOMs contamination was conducted based on species-sensitive distributions and substrate weight index. Although overall risks of FLOM contamination in tropical rice–vegetable rotations were negligible to low, the highest risks were in soils, vegetable planting periods, and a central intensively planted area.

Molecular markers to discriminate between aromatic and non-aromatic tropical rice cultivars

Molecular markers to discriminate between aromatic and non-aromatic tropical rice cultivars

Pest categorisation of Nilaparvata lugens

The EFSA Panel on Plant Health performed a pest categorisation of Nilaparvata lugens (Hemiptera: Delphacidae), the brown planthopper, for the European Union. N. lugens is widespread in Asia where it is native; it also occurs in Oceania where it is naturalised. N. lugens is not known to be present in the EU and is not listed in Annex II of Commission Implementing Regulation (EU) 2019/2072. It is a monophagous species and a major pest of rice (Oryza sativa). High populations of planthoppers cause leaves to initially turn orange yellow before becoming brown and dry and this is a condition called 'hopperburn' that kills the plant. N. lugens can also transmit plant viruses. It can complete 12 generations per year in tropical areas, where it resides year-round. N. lugens can undertake long-distance migration of up to 500 km from tropical areas to form transient populations in sub-tropical and temperate areas but due to low temperatures and absence of rice plants during the winter it does not establish in such areas. Entry to the EU via migration is unlikely given the distance from tropical rice growing areas. A possible but unlikely potential pathway is the import of infested rice seedlings, although we have no evidence that such trade exists. In the EU, rice is mainly planted from seed; when transplanted, it is sourced locally. N. lugens is very unlikely to survive year-round in the EU due to unsuitable climate and lack of hosts during the winter. Consequently, the pest is very unlikely to become established in the EU territory. Nevertheless, there are measures available to further reduce the likelihood of entry, establishment and spread of N. lugens within the EU. N. lugens does not satisfy the criteria that are within the remit of EFSA to assess for it to be regarded as a potential Union quarantine pest.

The Relationship between Cadmium-Related Gene Sequence Variations in Rice and Cadmium Accumulation

Cadmium (Cd) pollution and uptake into the grains of developing rice plants represent a major threat to human health. Studies of specific genes can offer new insights into the functional roles of particular genes, highlighting candidate alleles that can be leveraged as DNA markers. Accordingly, the identification of novel Cd-related traits and sequence variants can provide new molecular markers for Cd resistance in rice. In the present study, a genetic diversity analysis was carried out on 85 rice varieties exhibiting varied Cd accumulation, and 436 single polymorphic sites (SNP) corresponding to 43 haplotypes were detected across 12 Cd-associated genes (CAL1, OsCADT1, Oscd1, OsHMA4, OsHMA9, OsNRAMP1, OsNRAMP2, OsNRAMP5, OsHMA2, OsHSMA3, OsPCR1, and OsABCG43). By utilizing the information of the SNPs, 85 rice varieties was classified the into 2 clusters with different source categories and Cd contents. Among the variants, 45 sites in 5 genes were significantly associated with the Cd content in rice grains, of which 8 alleles in OsPCR1, CAL1, and Oscd1 were negatively correlated with Cd accumulation. The results of haplotype aggregation analysis for OsPCR1, Oscd1, and CAL1 showed that 85 rice varieties were divided into 5 clusters. Interestingly, most of the varieties in Cluster A belonged to tropical type, which contained the aggregation of three favorable alleles, whereas the temperate varieties constituted the majority of Cluster B lacking favorable alleles. This observation suggests that the allelic combination found in tropical rice varieties may hold promise for reducing Cd accumulation levels in rice grains. The Cd-associated alleles identified in the present study can not only be used to check the Cd tolerance of rice varieties, but also serve as functional molecular markers to differentiate the source of the rice varieties, which provides a better understanding of the relationship between the sequence variation in Cd-related genes and Cd accumulation in rice.

High ultraviolet-B sensitivity due to lower CPD photolyase activity is needed for biotic stress response to the rice blast fungus, Magnaporthe oryzae

Sensitivity to ultraviolet-B (UVB, 280–315 nm) radiation varies widely among rice (Oryza sativa) cultivars due to differences in the activity of cyclobutane pyrimidines dimer (CPD) photolyase. Interestingly, cultivars with high UVB sensitivity and low CPD photolyase activity have been domesticated in tropical areas with high UVB radiation. Here, we investigated how differences in CPD photolyase activity affect plant resistance to the rice blast fungus, Magnaporthe oryzae, which is one of the other major stresses. We used Asian and African rice cultivars and transgenic lines with different CPD photolyase activities to evaluate the interaction effects of CPD photolyase activity on resistance to M. oryzae. In UVB-resistant rice plants overexpressing CPD photolyase, 12 h of low-dose UVB (0.4 W m−2) pretreatment enhanced sensitivity to M. oryzae. In contrast, UVB-sensitive rice (transgenic rice with antisense CPD photolyase, A-S; and rice cultivars with low CPD photolyase activity) showed resistance to M. oryzae. Several defense-related genes were upregulated in UVB-sensitive rice compared to UVB-resistant rice. UVB-pretreated A-S plants showed decreased multicellular infection and robust accumulation of reactive oxygen species. High UVB-induced CPD accumulation promoted defense responses and cross-protection mechanisms against rice blast disease. This may indicate a trade-off between high UVB sensitivity and biotic stress tolerance in tropical rice cultivars.Graphical

Effects of levels of tropical rice husk-derived biochar in diet-based high rice straw on in vitro methane production and rumen fermentation

Effects of levels of tropical rice husk-derived biochar in diet-based high rice straw on in vitro methane production and rumen fermentation

A trait-based perspective toward the mechanistic understanding of benthic macroinvertebrate assemblage in a tropical rice field

A trait-based perspective toward the mechanistic understanding of benthic macroinvertebrate assemblage in a tropical rice field