Response Of Rice Cultivars Research Articles

Control of Echinochloa spp. and Leptochloa fascicularis with the novel dihydroorotate dehydrogenase inhibitor herbicide tetflupyrolimet in California water-seeded rice

Abstract The spread of herbicide-resistant weeds is considered a major problem for rice production in California, and there is a need for new herbicides. Tetflupyrolimet is a new herbicide with a novel dihydroorotate dehydrogenase–inhibiting site of action that has strong activity on grasses. Three field studies were conducted at the California Rice Experiment Station in Biggs, CA, in 2022 and 2023 to (1) determine control of watergrass species and bearded sprangletop with tetflupyrolimet, (2) characterize the effects of tetflupyrolimet combined with other herbicides on weed control and rice, and (3) determine the response of rice cultivars to tetflupyrolimet. In the first study, tetflupyrolimet was applied at preemergence (PRE) or at the 1- to 2-leaf stage of rice (POST) at 0.1, 0.125, or 0.15 kg ai ha−1 followed by carfentrazone. Tetflupyrolimet provided ≥99% control of watergrass species and 100% bearded sprangletop control regardless of the rate or application timing, while showing no crop injury symptoms or yield reduction. In the second study, tetflupyrolimet was applied PRE or POST at 0.1 or 0.15 kg ai ha−1 followed by herbicides labeled for use in California rice production. Tetflupyrolimet provided ≥98% control of watergrass species, which was better than the grower standard treatment, and ≥97% control of bearded sprangletop. In the third study, tetflupyrolimet was applied PRE or POST at 0.125, 0.15, 0.25, or 0.3 kg ai ha−1 followed by carfentrazone. The six California rice cultivars evaluated, ‘M-105’, ‘M-206’, ‘M-209’, ‘M-211’, ‘L-208’, and ‘CM-203’, did not show any trend of crop injury caused by tetflupyrolimet. Overall, tetflupyrolimet provided a high level of control of watergrass species and bearded sprangletop without causing visual rice injury or yield reductions, regardless of rice cultivar, when applied alone or in combination with commonly used sedge and broadleaf herbicides in California water-seeded rice.

Response of Rice Cultivars to Elevated Air Temperature and Soil Amendments: Implications towards Climate Change Adaptations and Mitigating Global Warming Potentials

Response of Rice Cultivars to Elevated Air Temperature and Soil Amendments: Implications towards Climate Change Adaptations and Mitigating Global Warming Potentials

Responses of rice cultivars with different cold tolerance to chilling in booting and flowering stages: An experiment in Northeast China

AbstractClimate change has led to an increasing trend in the intensity of global extreme weather events, including chilling. Breeding cultivars with high cold tolerance could be an important pathway to mitigate the negative effects of climate change. For rice, few studies have been focusing on the responses of different cold‐tolerance cultivars on chilling stress. In this study, we selected four japonica rice cultivars and conducted a chilling treatment experiment (with three chilling temperatures and three chilling durations) at the booting and flowering stages in 2020 and 2021 in Northeast China. The results showed that chilling treatment at the booting stage affected the biomass allocation and yield traits more than the chilling treatment at the flowering stage did. Overall, the chilling treatment affected the cold‐sensitive cultivars more than the cold‐tolerant cultivars. Among all the study yield traits, chilling treatment affected spikelet fertility the most, followed by the number of grains per panicle. For every 10°C day increase in CDD at the booting (flowering) stage, the grain yield per plant and spikelet fertility decreased by 4.8–12.8% and 3.6–10.8% (2.1–5.3% and 2.2–4.9%), respectively. Even with the intense chilling treatment, the cold‐tolerant cultivars had relatively high number of effective spikes per plant, grain weight, and stable spikelet fertility, hence they maintained relatively high grain yield. Therefore, it is important to factor in the cold tolerance of the cultivars when assessing the chilling effects on biomass allocation and yield traits for rice. In order to combat the negative effects of extremely low temperature at the reproductive stage on rice grain yield, the future breeding technology could focus on improving the spikelet fertility, grain filling size, and number of spikes per plant.

Transcriptome and Physio-Biochemical Profiling Reveals Differential Responses of Rice Cultivars at Reproductive-Stage Drought Stress.

Drought stress severely affects the growth and development of rice, especially at the reproductive stage, which results in disturbed metabolic processes, reduced seed-set/grain filling, deteriorated grain quality, declined productivity, and lower yield. Despite the recent advances in understanding the responses of rice to drought stress, there is a need to comprehensively integrate the morpho-physio-biochemical studies with the molecular responses/differential expression of genes and decipher the underlying pathways that regulate the adaptability of rice at various drought-sensitive growth stages. Our comparative analysis of immature panicle from a drought-tolerant (Nagina 22) and a drought-sensitive (IR 64) rice cultivar grown under control (well-watered) and water-deficit/drought stress (treatment, imposed at the reproductive stage) conditions unraveled some novel stress-responsive genes/pathways responsible for reproductive-stage drought stress tolerance. The results revealed a more important role of upregulated (6706) genes in the panicle of N 22 at reproductive-stage drought stress compared to that (5590) in IR 64. Functional enrichment and MapMan analyses revealed that majority of the DEGs were associated with the phytohormone, redox signalling/homeostasis, secondary metabolite, and transcription factor-mediated mitigation of the adverse effects of drought stress in N 22. The upregulated expression of the genes associated with starch/sucrose metabolism, secondary metabolites synthesis, transcription factors, glutathione, linoleic acid, and phenylalanine metabolism in N 22 was significantly more than that in the panicle of IR 64. Compared to IR 64, 2743 genes were upregulated in N 22 under control conditions, which further increased (4666) under drought stress in panicle of the tolerant cultivar. Interestingly, we observed 6706 genes to be upregulated in the panicle of N 22 over IR 64 under drought and 5814 genes get downregulated in the panicle of N 22 over IR 64 under the stress. In addition, RT-qPCR analysis confirmed differential expression patterns of the DEGs. These genes/pathways associated with the reproductive-stage drought tolerance might provide an important source of molecular markers for genetic manipulation of rice for enhanced drought tolerance.

Effect of Iron Nutrition on Growth and Productivity of Aerobic Rice (Oryza sativa)

A field experiment was conducted during kharif seasons (June–October) of 2012 and 2013 at College Farm, College of Agriculture, Professor Jayashankar Telangana State Agricultural University, Hyderabad, Telengana, India to evaluate the response of rice cultivars and iron nutrition on growth and yield of aerobic rice. Experiment comprising of three rice cultivars (Tellahamsa, MTU 1010 and KRH 2) and twelve sources and modes of iron nutrition i.e. control (no iron), basal application of iron sulphate @ 25 kg ha-1, basal application of Iron chelate @ 25 kg ha-1, 3 foliar sprays of 2% iron sulphate @ 7 days interval, 3 foliar sprays of 2% iron sulphate @ 10 days interval and 3 foliar sprays of 2% iron sulphate @ 15 days interval. Next 3 treatments were three foliar sprays of 2% iron sulphate in conjunction with basal application of iron sulphate @ 25 kg ha-1. Subsequent treatments were three foliar sprays of 2% iron sulphate with basal combination of iron chelate @ 25 kg ha-1. Results indicated that among rice cultivars KRH 2 gave significantly better agronomic performance with respect to growth parameters and yield. Iron nutrition treatments significantly affected the plant height, tillers, dry matter accumulation and yield of aerobic rice. Basal application of iron chelate @ 25 kg ha-1 with 3 foliar sprays of iron sulphate at 7 days interval produced tallest plants, maximum number of tillers, accumulated highest dry matter and produced maximum yield during both the years.

Different responses of rice cultivars to salt stress and the underlying mechanisms

<p id="C3">The objective of this study is to elucidate the responses of physiological traits and yield with different salt stress to salt-tolerant and salt-susceptible rice cultivars. Five salt-tolerant rice cultivars and two salt-susceptible rice cultivars were grown in pots with five different salt concentration levels including 0, 1, 2, 2.5, and 3 g kg^-1 of per pot for two years. Results showed that the yields of salt-tolerant cultivars were less reduced than that of salt-susceptible cultivars, and salt-tolerant cultivars was able to tolerate higher salt concentration of 2.5 g kg^-1. Salt-tolerant varieties produced higher grain yield mainly due to the greater total spikelets per area and higher filled grain percentage under salt stress. Salt-tolerant rice cultivars also had higher activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), higher contents of osmotic substances such as fructose, trehalose, and sorbitol, and higher K⁺/Na⁺ ratio from mid-tillering to heading. The crop growth rate from tillering to jointing and from heading to maturity, and photosynthetic rate at heading stage were higher in salt-tolerant cultivars than in salt-susceptible cultivars. The above results revealed that the differences in grain yields between salt-tolerant and salt-susceptible rice varieties were mainly due to the performances of physiological traits at mid-tillering, panicle initiation, and heading stages. These growth stages were the key stages that determined the number of panicles, spikelets per panicle, and the percentage of filled grains. The better physiological traits in the salt-tolerant rice varieties during key stages were the basis for higher grain yield. The results of this study could be helpful for the physiological researches and the breeding of salt-tolerant rice.

Florpyrauxifen-Benzyl Selectivity to Rice

Florpyrauxifen-benzyl (FPB) is a new class of auxinic herbicide developed for selective weed control in rice. This study aimed to evaluate the effect of environmental conditions, P450 inhibitors, rice cultivar response, and gene expression on FPB selectivity in rice. Field experiments established in a randomized block design showed that rice plant injury due to two FPB rates (30 and 60 g ai ha−1) was affected by planting time and rice stage at herbicide application. The injury was higher at the earliest planting season and more in younger plants (V2) than larger (V6 and R0). However, no yield reduction was detected. Under greenhouse conditions, two dose-response experiments in a randomized block design showed that spraying malathion (1 kg ha−1) before FPB application did not reduce herbicide selectivity. The addition of two P450 inhibitors (dietholate and piperonyl butoxide, 10 g a.i. seed-kg−1 and 4.2 kg ai ha−1, respectively) decreased the doses to cause 50% of plant injury (ED50) and growth reduction (GR50). However, it seems not to compromise crop selectivity. BRS Pampeira cultivar showed lower ED50 and GR50 than IRGA 424 RI. A growth chamber experiment was conducted in a completely randomized design to evaluate the gene expression of rice plants sprayed with FPB (30 and 60 g ai ha−1). Results showed downregulation of OsWAKL21.2, an esterase probably related to bio-activation of FPB-ester. However, no effect was detected on CYP71A21 monooxygenase and OsGSTL transferase, enzymes probably related to FPB degradation. Further research should focus on understanding FBP bio-activation as the selective mechanism.

Response of rice (Oryza sativa L.) cultivars to elevated ozone stress.

The plant response to elevated ozone stress reveals inter-species and intra-species disparity. Ozone-induced crop yield loss is predicted to increase in the future, posing a threat to the world economy. This study aims to evaluate the cultivar specific variation in rice exposed to elevated ozone. Fifteen short-duration rice cultivars were exposed to 50 ppb ozone for 30 days at reproductive stage. The physiological, biochemical, growth and yield traits of all test cultivars were significantly affected in response to elevated ozone. On an average, ozone stress decreased the tiller number by 22.52%, number of effective tillers by 30.43%, 1000 grain weight by 0.62% and straw weight by 23.83% over control. Spikelet sterility increased by 19.26% and linear multiregression 3D model significantly fits the spikelet sterility and photosynthetic traits with the R2 of 0.74 under elevated ozone. Principal Component Analysis with total variance of 57.5% categorized 15 rice cultivars into four major groups, i.e., ozone sensitive (MDU6, TRY(R)2 and ASD16), moderately ozone sensitive (ASD18, ADT43, and MDU5), moderately ozone tolerant (ADT37, ADT(R)45, TPS5, Anna(R)4, PMK(R)3, and ADT(R)48), and ozone tolerant (CO51, CO47, and ADT36). This study indicates that the different responses of rice cultivars to elevated ozone stress through a change in plant physiology, biochemical, growth, and yield traits and the results directed to provide scientific information on plant adaptations to ozone stress and helps in efforts to search ozone tolerant gene for plant breeding.

Comparative response of rice cultivars to elevated air temperature in Bhabar region of Indian Himalaya: status on yield attributes

Increasing atmospheric temperature is the consequence of global warming, which is expected to influence crop growth and development, resulting in declining productivity in the tropical agriculture system. The selection of temperature tolerant crop cultivars with higher productivity to meet the future demand of the world expanding human population requires a thorough understanding of crop growth feedback to increasing temperature. Therefore, a field experiment was conducted during the Kharif season of 2012 and 2013 to understand the response of yield and yield-related traits of eleven rice cultivars to elevated temperature grown inside field mounted temperature gradient tunnel (TGT) in the Bhabar region of the Indian Himalayas. The elevated temperature significantly impacted growth and yield and yield-related traits, especially tillers, panicles, filled and chaffy grains, grain, and 1000 grain weight, yield, and harvest index of all the cultivars during both years. The cultivars, i.e., IET 21404 and IET 21577, were reported to produced more tillers in 2012, whereas IET 21411 and KRH 2 had a maximum 2013. Likewise, maximum panicles were reported in IET 21404 and IET 21577 in 2012, while IET 21411, IET 21582, and KRH 2 in 2013 under elevated temperature. The highest grain filling under high temperature in 2012 was found in IET 21577, then IET 21404; however, IET 21411 and IET 21405 were the highest filled grains in 2013. Consequently, the cultivars IET 21577 and IET 21404 were reported as more tolerant towards yielding higher grain weight and Harvest Index. This study offers an opportunity to screen temperature tolerant cultivars with increased productivity for fulfilling the demand of rice-dependent regions in future changing climatic conditions.

Photosynthesis and morphological responses of rice cultivars to seedling stage soil N stress

Continuous cultivation of dry seeded rice in addition to adverse environmental factors make the rice soils deficient of nitrogen more than any other essential nutrient. The study was conducted under greenhouse conditions in pots by varying soil N during seedling growth. Six cultivars with diverse genetic background, CL152, R4100412, Antonio, Bowman, Nipponbare, and Rex, were seeded in 6 × 12 inch PVC pots filled with 3:1 (sand: soil) as the rooting medium. All plants were irrigated with full-strength Hoagland nutrient solution, delivered three times for 28 days after sowing. Then, half the plants in each cultivar were supplied with 100% of control nutrient solution minus N for another 4 weeks. Agronomic, physiological and root parameters measurements recorded at optimum interval. Cumulative indices were calculated by summing each response index value as a ratio of treatment by control values. Cultivars were classified based on total cumulative N stress response index (TCNSRI), the sum of all the traits measured, into different groups based on mean and standard error. The reductions in most of the measured traits were less in CL152 and R4100412 than other rice cultivars to soil N stress. Based on total cumulative N stress response indices, the cultivars were classified. The cultivar R41004122 was identified as tolerant, CL152 as intermediate, and Antonio, Bowman, Nipponbare and Rex were sensitive to soil N stress. The identified soil N stress tolerant and intermediately tolerant cultivars will be useful to breeders to develop new genotypes and farmers to select cultivars best suited for dry seeded rice.

Rice cultivar response to sublethal concentrations of glyphosate and paraquat late in the season

AbstractDifferential tolerance may be observed among rice cultivars with desiccant exposure events during rice reproduction and ripening. Five field studies were established at the Mississippi State University Delta Research and Extension Center in Stoneville, MS, to determine the effects of exposure to sublethal concentrations of common desiccants across multiple rice cultivars. Rice cultivars in the study were ‘CLXL745’, ‘XL753’, ‘CL163’, ‘Rex’, and ‘Jupiter’. Desiccant treatments included no desiccant, paraquat, or glyphosate and were applied at the 50% heading growth stage respective to cultivar. Differential injury estimates among cultivars and desiccant treatments was observed when glyphosate or paraquat was applied at 50% heading. Injury from glyphosate at 50% heading was nondetectable across all cultivars. However, injury following paraquat applications was &gt;7% across all rating intervals and cultivars. Hybrid cultivars exhibited less injury with paraquat applications than the inbred cultivars in the study. Rice following exposure to glyphosate or paraquat at 50% heading growth stage produced rough rice grain yield decreases ranging from 0% to 20% and 9% to 21%, respectively. Rough rice grain yield decreases were observed across all cultivars following paraquat exposure, and all inbred cultivars following glyphosate exposure. Across desiccant treatment, head rice yield was reduced in three of five cultivars in the study. When pooled across cultivar, paraquat applications cause a head rice yield reduction of 10%, whereas rice yield following glyphosate application remained &gt;95%. Although differential tolerance among cultivars to paraquat or glyphosate exposure was observed, impacts on grain quality coupled with yield reductions suggests extreme rice sensitivity to exposure to sublethal concentrations of these desiccants at the 50% heading growth stage.

Effect of phosphorus on iron toxicity: photosynthetic and antioxidant responses of rice cultivars

Iron (Fe) toxicity is a problem that affects many rice areas in lowland environments. The aim of this study was to investigate, through photosynthetic and antioxidant responses, the effect of phosphorus (P) nutrition as a mitigator of iron (Fe) toxicity in rice cultivars. The experimental design used was in randomized blocks, with four replications Three rice cultivars (Br/Irga 409, Irga 424, and Irga 425) were exposed to two concentrations of Fe (2 and 200 mg L-1) combined with two concentrations of P (2.5 and 15 mg L-1) in a nutrient solution, for 60 days. The results show that the excess of Fe reduced the root dry matter of all cultivars, but only the cultivar Br/Irga 409 showed a decrease in the shoot dry matter. The antioxidant enzymatic activity was not efficient to attenuate the toxicity by Fe due to the higher lipid peroxidation and decrease in the net CO2 assimilation rate. The cultivar Irga 425 showed greater tolerance to conditions of toxicity by Fe when associated with the increase in P availability, with high photosynthetic responses and enzymatic activity (superoxide dismutase). The cultivar Br/Irga 409 showed greater sensitivity to toxicity by Fe compared to other cultivars.

Physiological and Biochemical Response of Rice Cultivars (Oryza Sativa L.) To Elevated Ozone

ABSTRACT A study was carried out to evaluate the effect of elevated tropospheric ozone concentration on 15 rice cultivars. The cultivars were exposed to a weighted average ozone concentration of 51 ppb ±10% (10:00–17:00 h) for 30 days on its reproductive stage. On an average, elevated ozone significantly affects photosynthetic rate (−19.23%), stomatal conductance (−21.35%) and the contents of chlorophyll (−27.19%), malondialdehyde (+121.43%), proline (+98.38%), and ascorbic acid (−20.99%) over the control. Linear multiregression 3D model significantly fits the leaf traits related to leaf injury percentage which in turn affects all photosynthetic traits. The maximum R2 = 0.85*** was observed between photosynthetic rate, chlorophyll content, and leaf injury percentage. Rice cultivars exhibited significant interspecies variation in physiological and biochemical traits under elevated ozone. Among the tested rice cultivars, the multivariate analysis confirmed the Rice CO51, Anna(R)4, CO47, PMK(R)3, and Rice TPS5 were ozone tolerant. For the first time in South India, the study on response of rice cultivars to elevated ozone was done, which might support the rice breeders for selecting suitable donor parents for future climate change scenarios.

Characterization of rice cultivar response to florpyrauxifen-benzyl

AbstractMany factors such as environment, herbicide rate, growth stage at application, and days between sequential applications can influence the response of a crop to herbicides. Florpyrauxifen-benzyl is a new broad-spectrum, POST herbicide that was commercialized for use in U.S. rice production in 2018. Field experiments were conducted in 2018 at the Pine Tree Research Station (PTRS) near Colt, AR, and the Rice Research and Extension Center (RREC), near Stuttgart, AR, to evaluate crop injury and yield response of three rice cultivars to sequential applications of florpyrauxifen-benzyl. Greenhouse and growth chamber experiments were conducted at the Altheimer Laboratory in Fayetteville, AR, to evaluate cultivar responses when florpyrauxifen-benzyl was applied at 30 or 60 g ae ha−1 to rice exposed to different temperature regimes or at various growth stages. Three rice cultivars were used in all experiments: long-grain variety ‘CL111’, medium-grain variety ‘CL272’, and long-grain hybrid cultivar ‘CLXL745’. CL111 exhibited sufficient tolerance to florpyrauxifen-benzyl with only 10% visible injury and no effect on yield. CL272 showed 15% injury 3 wk after the second application in the field experiment when applications were made 14 d apart. Additionally, 12% injury was observed in greenhouse studies when florpyrauxifen-benzyl was applied at 30 g ae ha−1, averaged over various growth stages at application. Florpyrauxifen-benzyl did not reduce the yield of CL272 in field experiments, indicating that CL272 can recover from florpyrauxifen-benzyl injury. As much as 64% injury was observed for CLXL745 at 3 wk after application (WAA) when sequential herbicide applications were made 4 d apart. High levels of injury occurred in the growth chamber and greenhouse studies for this cultivar as well. Sequential applications of florpyrauxifen-benzyl reduced yields of CLXL745 in nearly all treatments. Data from these experiments suggest that CL272 and CLXL745 are sensitive to sequential applications of florpyrauxifen-benzyl. Growers must follow the prescribed guidelines for using florpyrauxifen-benzyl in these cultivars and others like it.

Simulation of the impacts of climate change on phenology, growth, and yield of various rice genotypes in humid sub-tropical environments using AquaCrop-Rice.

In the light of continuing anthropogenic climate change, it is important to gain a deep understanding of rice genotypic behavior under climate change. Most efforts on modeling rice performance under climate change focused on studying some aspects of climate change only such as CO2 concentration ([CO2]) or temperature. A comprehensive study on the role of genotypic variability in rice under diverse [CO2] × temperature × rainfall × representative concentration pathway (RCP) × environment is rare. The objective of the present study was to use AquaCrop-Rice model to study the impact of climate change on different rice cultivars in northern Iran. Three common improved and local rice cultivars were chosen, and their growth and yield behavior were simulated under three environments, three RCPs (2.6, 4.5 and 8.5), four temperature (+ 1 °C, + 2 °C, + 3 °C, + 4 °C), and two rainfall (± 20%) scenarios under two future timeframes (2020-2051 and 2052-2083). Results indicated different responses of rice cultivars under climate change. In general, improved cultivars acted better than the local cultivar although interaction with environment was also observed. Increase in [CO2] and temperature most often favored rice yield. However, RCP8.5 along with temperature scenario + 1 °C resulted in the highest aboveground biomass and yield. Rainfall variation was not of considerable importance. Phenology (flowering and physiological maturity) was accelerated especially by temperature. The length of the vegetative phase was more influenced by temperature than the length of the generative phase. Our simulations also indicated a potential for adaptation of improved cultivars under increasing [CO2] through their reduced stomatal conductance.

Effect of Root Colonization by Arbuscular Mycorrhizal Fungi on Growth, Productivity and Blast Resistance in Rice

BackgroundArbuscular mycorrhizal (AM) fungi form symbiotic associations with roots in most land plants. AM symbiosis provides benefits to host plants by improving nutrition and fitness. AM symbiosis has also been associated with increased resistance to pathogen infection in several plant species. In rice, the effects of AM symbiosis is less studied, probably because rice is mostly cultivated in wetland areas, and plants in such ecosystems have traditionally been considered as non-mycorrhizal. In this study, we investigated the effect of AM inoculation on performance of elite rice cultivars (Oryza sativa, japonica subspecies) under greenhouse and field conditions, focusing on growth, resistance to the rice blast fungus Magnaporthe oryzae and productivity.ResultsThe response to inoculation with either Funneliformis mosseae or Rhizophagus irregularis was evaluated in a panel of 12 rice cultivars. Root colonization was confirmed in all rice varieties. Under controlled greenhouse conditions, R. irregularis showed higher levels of root colonization than F. mosseae. Compared to non-inoculated plants, the AM-inoculated plants had higher Pi content in leaves. Varietal differences were observed in the growth response of rice cultivars to inoculation with an AM fungus, which were also dependent on the identity of the fungus. Thus, positive, negligible, and negative responses to AM inoculation were observed among rice varieties. Inoculation with F. mosseae or R. irregularis also conferred protection to the rice blast fungus, but the level of mycorrhiza-induced blast resistance varied among host genotypes. Rice seedlings (Loto and Gines varieties) were pre-inoculated with R. irregularis, transplanted into flooded fields, and grown until maturity. A significant increase in grain yield was observed in mycorrhizal plants compared with non-mycorrhizal plants, which was related to an increase in the number of panicles.ConclusionResults here presented support that rice plants benefit from the AM symbiosis while illustrating the potential of using AM fungi to improve productivity and blast resistance in cultivated rice. Differences observed in the mycorrhizal responsiveness among the different rice cultivars in terms of growth promotion and blast resistance indicate that evaluation of benefits received by the AM symbiosis needs to be carefully evaluated on a case-by-case basis for efficient exploitation of AM fungi in rice cultivation.

Rice Cultivar Response to Florpyrauxifen-Benzyl When Applied with Imazethapyr and a Cytochrome P450 Inhibitor

Understanding cultivar responses to a new herbicide is crucial to determining appropriate herbicide use and management practices. Florpyrauxifen-benzyl is a new rice herbicide developed to control troublesome weeds in rice production. Little research has been conducted to characterize rice cultivar responses to florpyrauxifen-benzyl, and thus, a field experiment was conducted at the Pine Tree Research Station (PTRS) in 2017 and 2018 and at the Rice Research and Extension Center (RREC) in 2018 to determine rice cultivar tolerance to florpyrauxifen-benzyl as influenced by herbicide rate, the addition of imazethapyr, and rice growth stage. Another experiment was conducted in 2018 at PTRS and RREC to assess crop response when florpyrauxifen-benzyl at different rates is applied with and without malathion, a known cytochrome P450 inhibitor. Three cultivars were evaluated in both experiments: a long-grain variety “CL111,” a medium-grain variety “CL272,” and a long-grain hybrid “CLXL745.” Injury in the first experiment was higher when florpyrauxifen-benzyl was applied at 60 g ae ha−1 than at the labeled rate of 30 g ha−1, with the most injury being 10% when averaged over growth stage at the time of application. Generally, applications made at the 3-leaf growth stage resulted in the most injury; however, this injury was at most 14%. Additionally, there was no reduction in grain yield for any cultivar, indicating florpyrauxifen-benzyl can be used safely in conjunction with imazethapyr in imidazolinone-resistant rice. In the second experiment, there was no more than 10% injury and no reduction in grain yield, with the addition of malathion not causing an increase in rice injury. Results from these experiments indicate florpyrauxifen-benzyl can be mixed with imazethapyr and the addition of malathion will not lead to increased risk for injury to rice.

Response of Rice Cultivars to Nitrogen Levels under Aerobic and Transplanted Conditions

An experiment on response of rice to nitrogen under aerobic and transplanted conditions was conducted in split-split -plot design with two methods of rice cultivation, seven rice varieties and five nitrogen levels. The grain yield was significantly higher in transplanted rice compared to aerobic rice. Significantly higher grain yield was observed with MTU 1001 and MTU 1010 as compared to IR 64, Tella hamsa and Rajendra and the grain yield in the former two varieities was comaparable with Naveen and Erramallelu. Increase in grain yield with every 100 kg of N ha-1 from 100 kg to 300 kg ha-1 was significant. Significant interaction effect on grain yield was observed due to method of crop establishment, varieties and nitrogen levels. Aerobic rice received 627 mm of irrigation water as compared to 1228 mm in transplanted rice and the mean water productivity was higher under aerobic rice (0.49 kg grain m-3) as compared to transplanted rice (0.31 kg grain m-3).

The potential role of sucrose transport gene expression in the photosynthetic and yield response of rice cultivars to future CO2 concentration.

The metabolic basis for observed differences in the yield response of rice to projected carbon dioxide concentrations (CO2) is unclear. In this study, three rice cultivars, differing in their yield response to elevated CO2, were grown under ambient and elevated CO2 conditions, using the free‐air CO2 enrichment technology. Flag leaves of rice were used to determine (1) if manipulative increases in sink strength decreased the soluble sucrose concentration for the ‘weak’ responders and (2), whether the genetic expression of sucrose transporters OsSUT1 and OsSUT2 was associated with an accumulation of soluble sugars and the maintenance of photosynthetic capacity. For the cultivars that showed a weak response to additional CO2, photosynthetic capacity declined under elevated CO2 and was associated with an accumulation of soluble sugars. For these cultivars, increasing sink relative to source strength did not increase photosynthesis and no change in OsSUT1 or OsSUT2 expression was observed. In contrast, the ‘strong’ response cultivar did not show an increase in soluble sugars or a decline in photosynthesis but demonstrated significant increases in OsSUT1 and OsSUT2 expression at elevated CO2. Overall, these data suggest that the expression of the sucrose transport genes OsSUT1 and OsSUT2 may be associated with the maintenance of photosynthetic capacity of the flag leaf during grain fill; and, potentially, greater yield response of rice as atmospheric CO2 increases.

Metabolic responses of rice cultivars with different tolerance to combined drought and heat stress under field conditions.

BackgroundRice is susceptible to both drought and heat stress, in particular during flowering and grain filling, when both grain yield and quality may be severely compromised. However, under field conditions, these 2 stresses rarely occur separately. Under well-watered conditions, plants avoid heat stress by transpirational cooling, while this is not possible under drought conditions. Although investigating combined drought and heat stress is clearly more agronomically relevant than analyzing the effects of the single stresses, only a few studies of this stress combination, in particular under field conditions, have been published.ResultsThree rice cultivars differing in drought and heat tolerance were grown in the field under control and drought conditions in 3 consecutive years. Drought was applied either during flowering or during early grain filling and resulted in simultaneous heat stress, leading to reduced grain yield and quality. Analysis by gas chromatography−mass spectrometry showed distinct metabolic profiles for the 3 investigated organs (flag leaves, flowering spikelets, developing seeds). The metabolic stress responses of the plants also strongly differed between cultivars and organs. Correlation analysis identified potential metabolic markers for grain yield and quality under combined drought and heat stress from both stress-regulated metabolites and from metabolites with constitutive differences between the cultivars.ConclusionsGas chromatography−mass spectrometry resolved metabolic responses to combined drought and heat stress in different organs of field-grown rice. The metabolite profiles can be used to identify potential marker metabolites for yield stability and grain quality that are expected to improve breeding efforts towards developing rice cultivars that are resilient to climate change.