Imidazolinone-resistant Rice Research Articles

Cytochrome P450 CYP81A104 in Eleusine indica confers resistance to multiherbicide with different modes of action.

Developing herbicide-resistant (HR) crop cultivars is an efficient way to control weeds and minimize crop yield losses. However, widespread and long-term herbicide application has led to the evolution of resistant weeds. Here, we established a resistant (R) E. indica population, collected from imidazolinone-resistant rice cultivar fields. The R population evolved 4.5-fold resistance to imazamox. Acetolactate synthase (ALS) gene sequencing and ALS activity assays excluded the effect of target-site resistance in this population. P450 inhibitor malathion pretreatment significantly reversed resistance to imazamox. RNA sequencing showed that a P450 gene CYP81A104 was expressed higher in R versus susceptible (S) plants. Arabidopsis overexpressing CYP81A104 showed resistance to ALS inhibitors (imazamox, tribenuron-methyl, penoxsulam and flucarbazone-sodium), PSII inhibitor (bentazone), hydroxyphenyl pyruvate dioxygenase inhibitor (mesotrione) and auxin mimics (MCPA), which was generally consistent with the results presented in the R population. This study confirmed that the CYP81A104 gene endowed resistance to multiherbicides with different modes-of-action. Our findings provide an insight into the molecular characteristics of resistance and contribute to formulating an appropriate strategy for weed management in HR crops. © 2024 Society of Chemical Industry.

Gene flow and spontaneous mutations are responsible for imidazolinone herbicide-resistant weedy rice (Oryza sativa L.)

For more than two decades, weedy rice (Oryza sativa L.) has been controlled in rice fields by using imidazolinone (IMI) herbicide-resistant rice technology (Clearfield®). Outcrossing in weedy rice populations and spontaneous mutations are potential problems with herbicide-resistant crop management technologies, such as the IMI-resistant rice. The aim of this study was to characterize the mechanism of IMI herbicide resistance in weedy rice through dose-response bioassay study and evaluating amino acid substitutions in acetolactate synthase (ALS) protein. A total of 118 suspected IMI-resistant weedy rice samples, which survived in the field after an IMI herbicide application, were collected at harvest time from Türkiye in 2020 and 2021. Single-dose imazamox application experiment revealed that 38 plants survived herbicide treatment. The imazamox resistance of the surviving plants was confirmed by dose-response experiment. ALS gene region underwent a sanger DNA partial sequencing. No substitution was found in 10 samples, however, amino acid substitutions were found in 26 samples with S563N, one sample with S653T, and one sample with E630D. The S653N point is the same substitution point that serves as the origin of resistance for the Clearfield® rice varieties that are commonly cultivated in the region. It has been hypothesized that the gene flow from IMI-resistant rice may be the cause of resistance in the IMI resistant weedy rice samples with S653N. The other substitution, S653T, were considered spontaneous mutation to IMI resistance. Interestingly, the S653T mutation was detected for the first time in weedy rice. The mechanism of resistance of 10 resistant weedy rice was not confirmed in this study, however, it may be a non-target resistance or another mutation point in target site, but evidently, they did not acquire resistance by gene flow from IMI-resistant rice. It has been concluded that the effectiveness of IMI-resistant rice technology in controlling weedy rice has drastically decreased due to possible gene flow, spontaneous mutation and non-target resistance. In addition to cultural controls like clean seed, clean machinery and crop rotation, other herbicide-tolerant rice systems such as Provisia® and Roxy-RPS® rice are needed to create a diverse weedy rice management ensemble available for rice production and move towards sustainable rice farming.

Quizalofop-resistant rice response to quizalofop when exposed to low rates of glyphosate and imazethapyr

AbstractInjury to quizalofop-resistant rice was reported in some fields following postemergence applications of quizalofop. Glyphosate-resistant (GR) corn, cotton, and soybean, and imidazolinone-resistant rice are grown near quizalofop-resistant rice. Herbicide drift from glyphosate and imazethapyr and the resulting crop injury and potential yield loss is a cause of concern for producers. Field experiments conducted near Colt, and Keiser, AR, in 2021 evaluated whether low rates of glyphosate or imazethapyr interact with sequential quizalofop applications to exacerbate injury to quizalofop-resistant rice compared to quizalofop applications alone. Herbicide treatments consisted of a low rate of glyphosate (90 g ae ha−1) or imazethapyr (10.7 g ai ha−1) applied 10, 7, 4, and 0 d before the 2-leaf growth stage of rice, and glyphosate or imazethapyr, at the same rate and timings, followed by quizalofop at 120 g ai ha−1 applied to 2-leaf rice. All plots treated with quizalofop received a subsequent application of the same herbicide and rate at the 5-leaf rice stage. At 28 d after final treatment (DAFT), glyphosate followed by quizalofop the same day to 2-leaf rice caused 77% injury compared with 58% when glyphosate was applied alone, regardless of location. Glyphosate followed by quizalofop the same day reduced rough rice grain yield by 67% compared with 33% when glyphosate was applied alone to 2-leaf rice at the Colt location. Application of imazethapyr followed by quizalofop the same day to 2-leaf rice caused more injury (63% and 19% injury at the Colt and Keiser locations, respectively) than imazethapyr alone (42% and 7% injury at the Colt and Keiser locations, respectively) at 35 DAFT. Overall, glyphosate and imazethapyr followed by quizalofop applications worsened injury compared to glyphosate, imazethapyr, and quizalofop applications alone. As the interval between exposure to a low rate of glyphosate or imazethapyr and quizalofop decreases, the detrimental effect of herbicide on rice likewise increases.

Benzobicyclon for weedy rice control in quizalofop- and imidazolinone-resistant rice systems

AbstractGowan Company recently registered benzobicyclon, a WSSA Group 27 herbicide, as a postflood option in rice. It is the first 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide commercially available in mid-southern U.S. rice production. In 2018 and 2019, field experiments were conducted across multiple sites in Arkansas to determine if the addition of benzobicyclon to quizalofop- or imidazolinone-resistant rice herbicide programs would improve weedy rice control. Across site-years, one application of quizalofop, either at the 1- or 3-leaf rice stage, followed by benzobicyclon applied postflood, provided comparable weedy rice control to two sequential applications of quizalofop, which is a standard herbicide program in quizalofop-resistant rice. Additionally, treatments containing quizalofop or quizalofop followed by benzobicyclon injured rice ≤5% at 28 d after the postflood application. Across site-years, at 28 d after the postflood application of benzobicyclon, all treatments containing a full-season herbicide program followed by benzobicyclon postflood provided comparable or improved weedy rice control when compared to two sequential early postemergence applications of imazethapyr. In both experiments, rice treated with benzobicyclon yielded comparably or better than treatments containing the standard herbicide program for each system. Findings from this research suggest that the use of benzobicyclon in quizalofop- and imidazolinone-resistant rice systems could be an additional and viable weedy rice control option for rice producers.

The Practice of Imidazolinone-Resistant Rice Production in the Irrigated Rice Fields of Kg Sungai Leman

Rice is an important crop and a staple food in Malaysia. Herbicides are used extensively to control weeds, which represent a major constraint to yield production. Although the introduction of Imidazolinone-resistant Rice with its management system (IRPS) has greatly improved both yields and weed control, the system is designed to be used for only a short term before transitioning to local varieties. Thus, a survey was conducted among 115 farmers to obtain information on their general knowledge on weed control and IRPS. The results showed that the majority of the farmers use herbicides to control all types of weed presented, with a small minority still using manual control. The majority of farmers using IRPS were applying the herbicide imidazolinone when soil condition were right, and only once per season, which is the recommendation. Most of the farmers still utilized imidazolinone to control weedy rice but would not use it on other weeds. However, many of the farmers perceived imidazolinone as becoming more ineffective and expensive and were willing to change to other herbicides if there was a viable alternative. Although herbicide is the main method employed in controlling weeds when using IRPS, farmers still regard imidazolinone as an ineffective herbicide. The reason IRPS is still in use is due to the high yields provided. This study shows a better understanding of knowledge on weeds and IRPS among farmers. Nonetheless, the IRPS will become a redundant system due to the ineffectiveness of imidazolinone and a new system should be introduced to replace it.

Response of acetyl-CoA carboxylase-resistant rice cultivars and advanced lines to florpyrauxifen-benzyl

AbstractFlorpyrauxifen-benzyl and quizalofop were available for POST applications in 2018; however, little is known about the response of acetyl-CoA carboxylase (ACCase)–resistant rice cultivars and advanced lines to POST herbicides. A field study was conducted in 2017 and 2018 at Stoneville, MS, to characterize the response of ACCase-resistant rice cultivars and advanced lines to POST applications of florpyrauxifen-benzyl. The imidazolinone-resistant (IR) rice cultivars ‘CL163’ and ‘CLXL 745’, and ACCase-resistant rice cultivars ‘PVL01’, ‘PVL013’, ‘PVL024-B’, ‘PVL038’, ‘PVL080’, and ‘PVL081’were treated with florpyrauxifen-benzyl at 0 (nontreated control for each cultivar) and 58 g ai ha–1 at the four-leaf to one-tiller (LPOST) growth stage. At 14 d after treatment (DAT), PVL01 was injured 5% to 6% greater than CLXL 745, PVL013, and PVL081; however, injury was ≤10% at that evaluation for all cultivars. Similarly, injury was ≤13% for all cultivars 28 DAT. Mature heights were reduced for all cultivars except PVL013 and PVL081. Rough rice yield was ≥100% of the control for all cultivars except PVL081, PVL013, and CL163. Results suggest that florpyrauxifen-benzyl can safely be applied POST to rice cultivars grown in Mississippi as well as ACCase-resistant cultivars that are currently under development.

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.

Influence of a thiamethoxam seed treatment on acetolactate synthase–inhibiting herbicide–induced injury to inbred and hybrid imidazolinone-resistant rice

AbstractThe increased use of insecticide seed treatments in rice has raised many questions about the potential benefits of these products. In 2014 and 2015, a field experiment was conducted near Stuttgart and Lonoke, AR, to evaluate whether an insecticide seed treatment could possibly lessen injury from acetolactate synthase (ALS)–inhibiting herbicides in imidazolinone-resistant (IR) rice. Two IR cultivars were tested (a hybrid, ‘CLXL745’, and an inbred, ‘CL152’), with and without an insecticide seed treatment (thiamethoxam). Four different herbicide combinations were evaluated: a nontreated control, two applications of bispyribac-sodium (hereafter bispyribac), two applications of imazethapyr, and two applications of imazethapyr plus bispyribac. The first herbicide application was to two- to three-leaf rice, and the second immediately prior to flooding (one- to two-tiller). At both 2 and 4 wk after final treatment (WAFT), the sequential applications of imazethapyr or bispyribac plus imazethapyr were more injurious to CLXL745 than CL152. This increased injury led to decreased groundcover 3 WAFT. Rice treated with thiamethoxam was less injured than nontreated rice and had improved groundcover and greater canopy heights. Even with up to 32% injury, the rice plants recovered by the end of the growing season, and yields within a cultivar were similar with and without a thiamethoxam seed treatment across all herbicide treatments. Based on these results, thiamethoxam can partially protect rice from injury caused by ALS-inhibiting herbicides as well as increase groundcover and canopy height; that is, the injury to rice never negatively affected yield.

Characterization of Acetolactate Synthase (ALS)-Inhibitor Resistance in Pennsylvania smartweed (Persicaria pensylvanica)

AbstractPennsylvania smartweed [Persicaria pensylvanica(L.) M. Gómez] is a common weed of rice (Oryza sativaL.) in the midsouthern United States and has recently become a concern for farmers because of reduced tillage systems. Acetolactate synthase (ALS) inhibitors have been extensively used for controlling smartweeds in imidazolinone-resistant and conventional rice. In the present study, we confirmed resistance to commonly used ALS inhibitors in rice and characterized the underlying resistance mechanism in aP. pensylvanicabiotype from southeast Missouri. A dose–response experiment was conducted in the greenhouse using bensulfuron-methyl, imazethapyr, and bispyribac-sodium to determine the resistance index (resistance/susceptibility [R/S]) based on GR50estimates. The target-siteALSgene was amplified from R and S plants, and sequences were analyzed for mutations known to confer ALS-inhibitor resistance. TheP. pensylvanicabiotype in question was found to be resistant to bensulfuron-methyl (R/S=2,330), imazethapyr (R/S=12), and bispyribac-sodium (R/S=6). Sequencing of theALSgene from R plants revealed two previously known mutations (Pro-197-Ser, Ala-122-Ser) conferring resistance to sulfonylureas and imidazolinones. This is the first report of ALS-inhibitor resistance inP. pensylvanica.

Evolutionary and social consequences of introgression of nontransgenic herbicide resistance from rice to weedy rice in Brazil.

Several studies have expressed concerns about the effects of gene flow from transgenic herbicide‐resistant crops to their wild relatives, but no major problems have been observed. This review describes a case study in which what has been feared in transgenics regarding gene flow has actually changed biodiversity and people's lives. Nontransgenic imidazolinone‐resistant rice (IMI‐rice) cultivars increased the rice grain yield by 50% in southern Brazil. This increase was beneficial for life quality of the farmers and also improved the regional economy. However, weedy rice resistant to imidazolinone herbicides started to evolve three years after the first use of IMI‐rice cultivars. Population genetic studies indicate that the herbicide‐resistant weedy rice was mainly originated from gene flow from resistant cultivars and distributed by seed migration. The problems related with herbicide‐resistant weedy rice increased the production costs of rice that forced farmers to sell or rent their land. Gene flow from cultivated rice to weedy rice has proven to be a large agricultural, economic, and social constraint in the use of herbicide‐resistant technologies in rice. This problem must be taken into account for the development of new transgenic or nontransgenic rice technologies.

Imazethapyr Co-Application Interactions in Imidazolinone-Resistant Rice

A study was conducted to evaluate interactions of imazethapyr co-application with propanil, thiobencarb, or a prepackaged mixture of propanil plus thiobencarb. At 7, 14, 21, and 49 d after treatment (DAT), synergism occurred for red rice treated with imazethapyr at 70 g ai ha−1mixed with propanil plus thiobencarb at 1,680 and 3,360 g ai ha−1. A synergistic response was also observed with imazethapyr at 70 g ha−1mixed with propanil at 1,680 g ha−1; however, all other co-applications evaluated resulted in a neutral response with no antagonism observed. At 7 DAT, antagonism was observed for barnyardgrass when treated with imazethapyr at 70 g ha−1mixed with propanil plus thiobencarb at 1,680 g ha−1, propanil at 840 g ha−1, or thiobencarb at 840 and 1,680 g ha−1; however, a synergistic response occurred for barnyardgrass control at 14, 21, and 49 DAT with imazethapyr at 70 g ha−1mixed with propanil plus thiobencarb at 3,360 g ha−1. The synergistic response observed for red rice and barnyardgrass control with a mixture of imazethapyr plus propanil plus thiobencarb can benefit producers by increasing control of red rice and barnyardgrass, and this mixture contains three herbicides with three different modes of action, which can be part of an overall resistance-management strategy in imidazolinone-resistant (IR) rice.

Distribution and analysis of the mechanisms of resistance of barnyardgrass (Echinochloa crus-galli) to imidazolinone and quinclorac herbicides

SUMMARYThe lack of control of barnyardgrass in flooded rice cultivated with imidazolinone-resistant rice cultivars is challenging the utilization of this system, which is continuously expanding for new rice areas worldwide. The objectives of the present study were to evaluate the frequency, distribution and mechanisms of imidazolinone resistance in barnyardgrass to establish the best practices to control and prevent this problem. The distribution of resistance was evaluated in 624 populations collected in Southern Brazil. The frequency of imidazolinone-herbicide resistance was 0·81, broadly distributed in all sampled regions. Resistance to quinclorac was also found in 0·19 of the populations, but all of the evaluated populations were susceptible to cyhalofop-butyl. Further studies were conducted in six populations. The enhanced metabolism was assessed with the metabolic inhibitors that reversed the resistance to quinclorac from 0·54 to 1·00 in two populations and the resistance to imazethapyr from 0·15 to 0·41 in three populations. The acetolactase synthase (ALS) enzyme activity also indicated the occurrence of altered target site resistance in two populations caused by the ALS gene mutations Trp574Leu and Ser653Asn, which is a novel finding in this species. The herbicide resistance in barnyardgrass in Southern Brazil presented a complex basis of resistance because it is associated with resistance to multiple herbicides due to multiple mechanisms and with multiple mutations of the ALS gene. This indicates that it is necessary to adopt specific measures to prevent and control the evolution of multiple herbicide resistance in this species.

Distribution of Weedy Red Rice (Oryza sativa) Resistant to Imidazolinone Herbicides and its Relationship to Rice Cultivars and WildOryzaSpecies

Several weedy red rice populations have evolved resistance to imidazolinone herbicides worldwide. The understanding of the factors related to the herbicide resistance in weedy red rice is important to prevent its occurrence in new areas where imidazolinone-resistant rice cultivars are being used, and to manage the new rice cultivars resistant to herbicides with modes of action other than the acetolactate synthase (ALS)-inhibitors that are being developed. The objectives of this study were to analyze the relationship of weedy red rice populations from southern Brazil with rice cultivars and wildOryzaspecies and to evaluate the occurrence of introgression from rice cultivars and seed migration as the origin of resistance to imidazolinone herbicides in weedy rice. The study was based on 27 weedy red rice populations, seven rice cultivars, and four wildOryzaspecies that were genotyped with 24 simple sequence repeats and threeALS-specific single-nucleotide polymorphism markers. A large proportion of the genetic variation of the weedy red rice populations was found within (74%) rather than among populations (26%). The weedy red rice populations were more closely related to the newer rice cultivars that are imidazolinone-resistant than to the older cultivars. The South American nativeOryza glumaepatulaand the other wildOryzaspecies—Oryza rufipogon, Oryza longistaminata, andOryza glaberrima—clustered separately from weedy red rice populations, indicating a low likelihood of introgression among weedy red rice and these wild species. Seed migration was an important factor in the genetic structure of the evaluated weedy red rice populations, although gene flow by pollen from resistant cultivars was the principal reason for the spread of herbicide resistance.

One-step, codominant detection of imidazolinone resistance mutations in weedy rice (Oryza sativa L.)

article i nfo Background: Weedy rice (Oryza sativa L.) is a noxious form of cultivated rice (O. sativa L.) associated with intensive rice production and dry seeding. A cost-efficient strategy to control this weed is the Clearfield rice production system, which combines imidazolinone herbicides with mutant imidazolinone-resistant rice varieties.However,imidazolinone resistance mutationscan beintrogressed inweedy rice populations bynatural outcrossing, reducing the life span of the Clearfield technology. Timely and accurate detection of imidazolinone resistance mutations in weedy rice may contribute to avoiding the multiplication and dispersion of resistant weeds and to protect the Clearfield system. Thus, highly sensitive and specific methods with high throughput and low cost are needed. KBioscience's Allele Specific PCR (KASP) is a codominant, competitive allele-specific PCR-based genotyping method. KASP enables both alleles to be detected in a single reaction in a closed-tube format. The aim of this work is to assess the suitability and validity of the KASP method for detection in weedy rice of the three imidazolinone resistance mutations reported to date in rice. Results: Validation wascarriedoutbydetermining the analyticalperformance of thenew method andcomparing it with conventional allele-specific PCR, when genotyping sets of cultivated and weedy rice samples. The conventional technique had a specificity of 0.97 and a sensibility of 0.95, whereas for the KASP method, both parameters were 1.00. Conclusions: The new method has equal accuracy while being more informative and saving time and resources compared with conventional methods, which make it suitable for monitoring imidazolinone-resistant weedy rice in Clearfield rice fields.

Weed Management Practices and Needs in Arkansas and Mississippi Rice

Crop consultants in Arkansas and Mississippi were sent a direct-mail survey in fall of 2011 with questions concerning weed management in rice. The goal of the survey was to document the extent of imidazoline-resistant rice hectares, the herbicides most commonly recommended in rice, the weeds perceived to be most troublesome in rice including those resistant to herbicides, and suggested areas of research and educational focus that would improve weed management in rice. When appropriate, results from this survey were compared to a similar survey conducted in 2006. Completed rice surveys were returned by 43 consultants, accounting for 179,500 ha of scouted rice or 38% of the rice hectarage in Arkansas and Mississippi. Imidazolinone-resistant rice was grown on 64% of the hectares, and this technology was used continually for the past 5 yr on 11% of the rice hectares. Of the area planted to imidazolinone-resistant rice, 42% of this hectarage was treated solely with an acetolactate synthase (ALS)-inhibiting herbicide. Consultants listed improved control options for barnyardgrass and Palmer amaranth as the most important research and educational need in rice. The top five weeds in order of importance were (1) barnyardgrass, (2) sprangletops, (3) red rice, (4) northern jointvetch, and (5) Palmer amaranth. From a predetermined list of research and educational topics, consultants gave the highest ratings of importance to (1) control of herbicide-resistant weeds, (2) strategies to reduce the occurrence and spread of herbicide-resistant weeds, and (3) development of new economical herbicide-resistant rice varieties which was comparable to economical weed control options. Findings from this survey point to the overuse of imidazolinone-resistant rice and a lack of preemptive resistance management strategies such as crop rotation and use of multiple effective herbicide modes of action by some growers, which has likely contributed to selection for the ALS-resistant barnyardgrass and rice flatsedge recently confirmed in Arkansas and Mississippi rice.

Red rice (Oryza sativa) cross-resistance to imidazolinone herbicides used in resistant rice cultivars grown in northern Greece

A putative resistant red rice (Oryza sativa) accession, an imidazolinone-resistant rice cultivar (Clearfield), a susceptible red rice accession and a susceptible rice cultivar were evaluated for cross-resistance to imazamox and imazethapyr in a whole-plant response experiment and seed bioassay. Additionally, a 210-bp fragment of the ALS gene was sequenced to identify mutations responsible for resistance. Also, a 574bp of the ALS gene was sequenced and PCR for detection of the ‘Clearfield allele’ was conducted by the Andalusian Institute of Agricultural Research and Training (IFAPA, Spain). In the whole-plant response experiment, the putative resistant red rice was >23 and >21 times more resistant to imazamox and imazethapyr than the susceptible accession, respectively, whereas the respective resistance factor values based on seed bioassay were 86.4 and 141.7. Also, the respective resistance factor values for the Clearfield rice cultivar were similar with those calculated for putative resistant red rice. Additionally, the sequence of the 210bp ALS gene fragment from the putative resistant red rice and Clearfield rice cultivar revealed the same amino acid substitution of Ser653Asn in both alleles (homozygous). Furthermore, the sequence of a 574bp ALS gene fragment and the PCR for detection of the ‘Clearfield allele’ confirmed that the putative resistant red rice is homozygous mutant for the Ser653Asn mutation and provided additional evidence that its genetic background matches that of Clearfield rice. These findings indicate clearly that the insufficient control of the putative resistant red rice with imazamox was due to target-site resistance and particularly due to a point mutation at the Ser653 codon, which is positively identified as having been derived from the Clearfield rice cultivar.

Identification of origin and analysis of population structure of field-selected imidazolinone-herbicide resistant red rice (Oryza sativa)

Several red rice biotypes have evolved resistance to imidazolinone herbicides. The origin of resistance has been attributed to gene flow from the herbicide-resistant rice cultivars, but independent evolution of spontaneous mutation can also contribute to the herbicide resistance. The objective of this study was to quantify the occurrence of gene flow and independent selection as the mechanisms of origin of imidazolinone-resistance in red rice to correctly define the management practices for red rice control. Three single nucleotide polymorphism markers were used to identify acetolactate synthase (ALS) gene mutations, and four simple sequence repeat markers were used to identify hybrids of imidazolinone-resistant rice cultivars and red rice. In addition, genetic diversity and population structure analyses were performed. Artificial hybrids were used as controls. Gene flow was the main origin of imidazolinone herbicide resistance, but independent selection occurred in 1.1 % of the evaluated red rice plants. Two red rice plants that independently evolved herbicide resistance had the ALS gene mutation, Gly654Glu. Population structure analysis also indicated intense gene flow from rice cultivars to red rice, but some populations maintained a high genetic identity based on a small amount of gene introgression from the rice cultivars. These results indicate the importance of adopting controls of red rice escapees to avoid gene flow from the imidazolinone-resistant rice, and the necessity of biotechnological approaches to mitigating gene flow in the development of new herbicide-resistant rice cultivars.

A strategy to provide long‐term control of weedy rice while mitigating herbicide resistance transgene flow, and its potential use for other crops with related weeds

Transgenic herbicide-resistant rice is needed to control weeds that have evolved herbicide resistance, as well as for the weedy (feral, red) rice problem, which has been exacerbated by shifting to direct seeding throughout the world-firstly in Europe and the Americas, and now in Asia, as well as in parts of Africa. Transplanting had been the major method of weedy rice control. Experience with imidazolinone-resistant rice shows that gene flow to weedy rice is rapid, negating the utility of the technology. Transgenic technologies are available that can contain herbicide resistance within the crop (cleistogamy, male sterility, targeting to chloroplast genome, etc.), but such technologies are leaky. Mitigation technologies tandemly couple (genetically link) the gene of choice (herbicide resistance) with mitigation genes that are neutral or good for the crop, but render hybrids with weedy rice and their offspring unfit to compete. Mitigation genes confer traits such as non-shattering, dwarfism, no secondary dormancy and herbicide sensitivity. It is proposed to use glyphosate and glufosinate resistances separately as genes of choice, and glufosinate, glyphosate and bentazone susceptibilities as mitigating genes, with a six-season rotation where each stage kills transgenic crop volunteers and transgenic crop x weed hybrids from the previous season.

Herbicide Options for Rice Cutgrass (Leersia oryzoides) Control

Rice cutgrass is encroaching into rice fields from ditch banks and canals, especially into continuous rice fields where tillage is limited in the Mississippi Delta region of Arkansas. Experiments were conducted to evaluate the effectiveness of various herbicides applied alone on rice cutgrass and to determine if the effectiveness of bispyribac on rice cutgrass is influenced by number of applications, adjuvant type, and adjuvant rate. Glyphosate, glufosinate, and clethodim were the most effective herbicides when applied alone; however, none of these are labeled for over-the-top application in rice. Of those herbicides that can be applied over the top of rice, imazethapyr and bispyribac were the most effective, providing 52 to 62% rice cutgrass control, albeit imazethapyr can be used only in imidazolinone-resistant rice. The addition of an adjuvant to bispyribac improved rice cutgrass control, and sequential bispyribac applications were generally superior to a single application. Methylated seed oil/organosilicone/urea ammonium nitrate adjuvant increased rice cutgrass control with bispyribac, especially when bispyribac was applied as a single application. A single application of imazethapyr, bispyribac, halosulfuron, penoxsulam, clomazone, thiobencarb, cyhalofop, propanil, quinclorac, and fenoxaprop provided less-than-acceptable control, which partially explains the difficulty that growers are experiencing in controlling rice cutgrass, especially in continuous rice production.

Red Rice (Oryza sativa) Status after 5 Years of Imidazolinone-Resistant Rice Technology in Arkansas

Certified Crop Advisors of Arkansas and members of the Arkansas Crop Consultants Association were surveyed in fall 2006 through direct mail to assess the current situation of the red rice problem and early impact of imidazolinone-resistant (IMR) rice technology on red rice infestation. The information generated represented 40% (226,800 ha) of rice production areas in Arkansas. Barnyardgrass and red rice were the most problematic weeds, with 62% of fields infested with red rice. The estimated economic loss due to red rice averaged $274/ha. Red rice infestation was prevented mostly by crop rotation (96%) and use of certified seed (86%). Of the red rice–infested fields, 38% had light infestation and 26% had severe red rice problems before adopting IMR rice. Thirty-seven percent of infested fields had been planted with IMR rice once and 43% at least twice. Approximately 85% of the consultants reported > 90% red rice control when using IMR rice. The majority (92%) of IMR rice growers rotate to other crops, mostly soybean. Unsuitable field condition was the main reason for growing only rice. After 3 seasons, the consultants perceived that red rice infestation level declined by 77% on average. The herbicide-resistance gene had escaped to red rice in some fields, and 90% of growers are exerting effort to mitigate outcrossing.Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, red rice, Oryza sativa L. ORYSA, rice, Oryza sativa L, soybean, Glycine max (L.) Merr