Diversity of weedy red rice (Oryza sativa L.) in Arkansas,U.S.A. in relation to weed management

Weedy rice, specifically red rice (Oryza sativa L.), is a major weed in rice which causes up to 80% yield loss and reduction of grain quality. Red rice accessions from Arkansas, U.S.A., were characterized to classify red rice accessions into certain phenotypic groups relevant to weedy rice management. The red rice accessions were 70% strawhull, 22% blackhull, 7% brownhull and <1% goldhull. Generally, blackhull red rice was the tallest (139 cm) and strawhull the shortest (133 cm) among all accessions. Blackhull red rice had more tillers (102/plant), smaller flag leaves (13 cm wide, 34 cm long), and flowered later (1225 heat units) than strawhull red rice which had 85 tillers/plant, 15 cm-wide and 34 cm-long flag leaves, and flowered after accumulating 1195 heat units. Morphological differences between accessions within each hull type were highly significant, showing great diversity within a hull color group as indicated by large ranges in traits. For example, blackhulls were 75–190 cm tall with 18–69 cm long flag leaves, 21–188 tillers and produced 40–949 g seed. Strawhulls were 46–189 cm tall with 18–66 cm flag leaf length, 16–172 tillers and produced 100–608 g seed. Some traits, such as seed production, differed widely between accessions within each hull color group such that the average seed production/accession for blackhull did not differ from that of strawhull weedy rice (196 vs. 192 g/plant). The onset of flowering among all accessions ranged from 56 to 126 d after planting. Red rice accessions formed six phenotypic clusters generally segregated by plant size or flowering time. Each morphotype would have different competitive abilities; thus, weedy rice management could be geared toward plant types. Highly competitive plant types would require intensive control measures to minimize yield losses and reduce the soil seed bank. Flowering dates impact stewardship strategies for herbicide-resistant or any genetically modified rice.     

Polymorphisms in the ALS gene of weedy rice (Oryza sativa L.) accessions with differential tolerance to imazethapyr

Herbicide-resistant Clearfield™ rice technology allows the use of ALS inhibitors to control weedy rice. Weedy rice plants have differential tolerance to imazethapyr, perhaps due to ALS polymorphisms. We aimed to assess ALS polymorphisms in weedy rice accessions from Arkansas, USA, with differential tolerance to imazethapyr in seedling growth bioassays. Six base changes were identified in the ALS of 14 weedy rice accessions. Three of these nucleotide changes resulted in amino acid substitutions — Pro⁹³Thr, Glu⁶³⁰Asp, and Val⁶⁶⁹Met — in four accessions: Ark-4, Ark-9, Poi-1 and Poi-6. The GR₅₀ values and inhibition of root and shoot growth (%) of these accessions differed. The Glu⁶³⁰Asp substitution occurs in the herbicide binding domain B and Val⁶⁶⁹Met occurs at the C-terminal tail where the co-factor binds. Variability in weedy rice ALS exists, but polymorphism patterns did not relate to tolerance levels. The observed mutations presented the possibility that sustained selection pressure will eventually lead to selection of a herbicide-tolerant individual that will be the progenitor of a resistant population. Concomitantly, pollen-mediated gene flow from Clearfield™ rice to weedy rice will lead to the evolution of ALS-resistant weedy rice populations.     

Seed physicochemical characteristics of field-grown US weedy red rice (Oryza sativa) biotypes: Contrasts with commercial cultivars

Red rice in the US is an aggressive weed that reduces the yield of rice and contaminates its grain. It is the same species as rice, which provides an opportunity for intercrossing. This genetic similarity complicates the management of red rice in fields and rice mills, but also indicates a potential for its use in rice breeding or niche markets. Physicochemical and cooking quality characteristics, which are important components of consumer desirability for rice, are virtually unknown for red rice. Thus, a survey of red rice accessions and rice × red rice crosses was conducted to characterize these traits. Grain amylose levels of most indigenous red rice accessions were similar to those of high amylose indica cultivars from Asia. Amylose levels in crosses were highly variable, ranging as low as those in medium-grain commercial rice to as high as those in long-grains. Alkali spreading value was generally greater in awned than in awnless red rice accessions and the aroma chemical, 2-acetyl-1-pyrroline, was detected in two red rice crosses. The generally high seed amylose levels in red rice indicate that its cooking quality would not be suitable for most common uses of US rice, but may be acceptable for niche uses.     

Plant characteristics associated with weed competitiveness of rice under upland and lowland conditions in West Africa

Weeds are a major constraint to rice (Oryza spp.) production in West Africa. Superior weed competitive rice genotypes may reduce weed pressure and improve rice productivity. Two upland and two lowland experiments were conducted in southern Benin to examine genotypic variations in weed-suppressive ability and grain yield under weedy conditions, and to identify plant characteristics that could be used as selection criteria for improved weed competitiveness. A total of 19 genotypes, including Oryza sativa and Oryza glaberrima genotypes and interspecific hybrids developed from crossing O. sativa and O. glaberrima, were grown under weed-free and weedy conditions in an upland with supplemental irrigation and in a flooded lowland. In weedy plots, hand weeding was done once or not at all. Mean relative yield loss across all genotypes due to weed competition ranged from almost 0% to 61%. Large genotypic variations in weed biomass and grain yield under weedy conditions were found. Visual growth vigor at 42 and 63 days after sowing (DAS) under weed-free conditions significantly correlated with weed biomass at maturity in both upland and lowland experiments (R² = 0.26–0.48). Where weed pressure was low to moderate, with mean relative yield loss less than 23%, the multiple regression models using grain yield and plant height at maturity or only grain yield measured under weed-free conditions as independent variables could explain 66–88% of the genotypic variation in grain yield under weedy conditions. At higher weed pressure (mean relative yield loss: 61%), as observed in one of the upland experiments, biomass accumulation of rice at 42 days after sowing was associated with higher grain yield under weedy conditions. Biomass accumulation also significantly correlated with visual growth vigor at the same sampling dates. Therefore, we conclude that grain yield, plant height at maturity and visual growth vigor at 42–63 DAS under weed-free conditions appear to be useful selection criteria for developing superior weed competitive rice genotypes.     

Total phenolics,flavonoids, antioxidant capacity in rice grain and their relations to grain color,size and weight

Total phenolics, flavonoid contents and antioxidant capacity from a wide collection of rice germplasm were measured, and their relations to grain color, grain size and 100-grain weight were investigated. Highly significant genotypic differences were observed in total phenolics, flavonoid contents and 2,2-azino-bis-(3-ehylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation antioxidant capacity. They displayed an increasing order in the white rice, red rice and black rice, yet several white rice had higher phenolics and flavonoids contents than the red rice. Significant positive pair-wise correlations were found among the phenolics, flavonoid contents and antioxidant capacity, and the coefficient between the phenolic contents and antioxidant capacity was extremely high (r = 0.96). Among all rice accessions, the grain color parameters had negative correlations with the phenolics, flavonoid contents and antioxidant capacity (p < 0.001). The negative correlation between a* and antioxidant capacity, and the positive correlation between H° and antioxidant capacity were consistent within the respective white rice and red rice groups. Flavonoid contents had positive correlation with grain length and length to width ratio, and had negative correlation with the 100-grain weight among all rice accessions. It was also found that 100-grain weight still had negative correlations with phenolics, flavonoid contents and antioxidant capacity within the white rice genotypes. These relationships may serve as indexes to indirectly select breeding lines high in the phenolics, flavonoids and antioxidant capacity. Principal component analysis including the information for phenolics, flavonoids, antioxidant capacity, grain color parameters, grain size and 100-grain weight extracted five principal components that explained 83.7% of the total variances. The results of this study may provide new opportunities for rice breeders and eventually commercial rice growers to promote the production of rice with enhanced nutritional quality.     

广东雷州杂草稻黑壳基因Bh4和红皮基因Rc的基因型鉴定

为测定雷州杂草稻的黑色颖壳基因Bh4和红色果皮基因Rc的基因型,本研究对雷州10个杂草稻群体的100个单株的种子的颖壳和果皮颜色进行表型观察,同时通过PCR扩增及序列分析对Bh4和Rc的基因型进行鉴定。结果表明,雷州杂草稻中黑色颖壳和黄色颖壳的种子几乎各占一半,果皮颜色则以红色为主,有少量白色和浅红色果皮的种子。雷州杂草稻的Bh4和Rc的基因型与表型鉴定结果一致。57份黑色颖壳杂草稻的Bh4基因型为39个野生型和18个杂合型,25份黄色颖壳和18份黄色带黑斑颖壳杂草稻的Bh4基因型均为缺失22 bp的突变型;90份红色果皮杂草稻的Rc基因型为73个野生型和17个杂合型,4份白色和6份浅红色果皮杂草稻的Rc基因型均为缺失14 bp的突变型。本研究为分析雷州杂草稻的Bh4和Rc基因的来源提供了分子基础。     

江淮流域杂草稻叶绿体DNA的籼粳分化

 为了探明江淮流域杂草稻的细胞质来源,根据水稻叶绿体DNA ORF100（Open Reading Frame 100）序列在籼粳间存在69 bp差异的特征,设计了InDel标记cpDNA69。利用该标记对2个分别以籼稻和粳稻为母本的F2群体、22份栽培稻（Oryza sativa L.）、3份普通野生稻（O. rufipogon Griff.）进行了分析验证。PCR结果可以获得缺失和非缺失两种带型,缺失带型与以籼稻为母本的F2群体、10份籼稻材料完全对应;非缺失带型与以粳稻为母本的F2群体、11份粳稻材料完全对应,3份广西普通野生稻为非缺失带型,属粳型,1份以粳稻为母本的籼粳杂交材料为粳型。因此,cpDNA69可以用作叶绿体籼粳鉴定标记。利用该标记对22份杂草稻的叶绿体DNA鉴定的结果表明,7份早年发现的杂草稻,即江苏省连云港穭稻和安徽省怀远、来安、全椒、肥东的塘稻的叶绿体DNA为非缺失带型,属粳型,而近年来在江苏省扬中、高邮、灌云、洪泽、盐都、兴化、如皋等地直播稻田发现的15份红米杂草稻的叶绿体DNA为缺失带型,属籼型。这为进一步研究江淮流域杂草稻的来源提供了依据。     

广东雷州杂草稻sh4和qSH1基因的功能SNP位点序列分析

sh4和qSH1基因是水稻的主效落粒基因,本研究旨在测定雷州杂草稻的sh4和qSH1的基因型,为雷州杂草稻的落粒机制研究提供分子基础。本研究从雷州10个杂草稻群体采集了100个单株及10份栽培稻种子,观测其颖壳颜色、果皮颜色和芒及落粒率,并对sh4和qSH1的功能SNP位点进行PCR扩增及序列分析。结果表明,57份杂草稻的sh4功能SNP位点为野生落粒型（G）,15份为杂合型G/T,28份为突变难落粒型（T）。其中,G型和G/T型的72份杂草稻的落粒率都极高（95%~100%）,而28份T型杂草稻中,19份为中度落粒（30%~75%）,5份杂草稻的落粒率很高（>95%）,4份杂草稻的落粒率小于30%。100份杂草稻和10份栽培稻的qSH1功能SNP位点均为G。结合落粒表型及基因型,推测sh4是调控雷州杂草稻落粒性的一个主要基因。     

丹东杂草稻种子的耐冻能力和低温发芽特性研究

为了解丹东杂草稻种子冬季在野外能存活的原因,将丹东杂草稻和对照品种越光的干种子在水中浸不同时间,后在-20℃下处理7 d,在25℃下发芽。对照品种越光在浸种1 h后冷冻处理,其种子的发芽率从98％降为4％,浸种时间延长到1.5 h已不能成苗,而丹东杂草稻种子在1 h浸种处理后,其发芽基本不受影响,甚至在3 h浸种处理后成苗率仍达2.3％。在不同低温下发芽试验中发现丹东杂草稻在11℃能发芽,杂草稻的发芽临界温度要比对照越光低。讨论了杂草稻种子抗冻的潜在价值。      

Genetic Diversity and Relationship of Weedy Rice in Taizhou City, Jiangsu Province, China

Microsatellite markers and morphological charactedstics were used to explore the genetic diversity and possible origin of weedy dce in Taizhou City, Jiangsu Province, China. Fifty-two weedy rice (Oryza sativa L.) accessions were compared with two wild rice, four hybdd rice and five cultivars using 22 simple sequence repeat (SSR) primer pairs. A total of 107 fragments were amplified, averaging 5.6 alleles per primer pair. The polymorphic index content (PIC) values ranged from 0.3077 to 0.7951, averaging at 0.5870. The average genetic distance of all samples ranged from 0.02 to 0.46 with an average of 0.262. The genetic distance among Taizhou weedy rice ranged from 0.03 to 0.44 with an average of 0.224. Cluster analysis showed that all the weedy rice accessions from Taizhou City were indica, and could be subdivided into different genotypes. The majority (86%) of weedy rice was most closely related to hybrid rice. The Taizhou weedy dce accessions were morphologically similar, but still could be delineated into indica or japonica group by some morphological traits. it is suggested that the levels of genetic and morphological diversities of weedy rice in Taizhou City are low and these weedy rice plants originated from the segregating progenies of hybrid rice that had naturally introgressed with cultivated rice.     

Effects of winter flooding on weedy rice (Oryza sativa L.)

Weedy rice (Oryza sativa L.), characterised by competitiveness, seed longevity, and dormancy is a troublesome weed to rice fields. Furthermore, its close botanical affinity to cultivated rice makes its control particularly difficult. However, winter flooding of rice fields can be an efficient technique to control weedy rice infestation by promoting weed seed decay, animal predation, or germination.     

Effect of rice establishment methods on weedy rice (Oryza sativa L.) infestation and grain yield of cultivated rice (O. sativa L.) in Sri Lanka

Weedy rice is a great threat to rice production in Sri Lanka. Selective herbicides to manage weedy rice in conventional rice cultivars are not available in Sri Lanka. In the absence of appropriate chemical control measures, cultural approaches may help to achieve effective control of weedy rice. A study was conducted in two consecutive seasons in farmers' fields at three sites (Atalla, Samanthurai, and Girithale villages) in Sri Lanka to evaluate the effect of different establishment methods (farmers' practice, random broadcast, row seeding, seedling broadcast, and transplanted rice) on weedy rice infestation and rice yield. The farmers' practice had a higher number of weedy rice panicles (60–80 m⁻²) than the random broadcast (39–48 panicles m⁻²), seedling broadcast (3–15 panicles m⁻²), and transplanted rice (1.3–3.0 panicles m⁻²) methods. The use of clean rice seeds in the random broadcast method reduced weedy rice seed production by 29–41% compared with the farmers' practice (0.6–2.0 t ha⁻¹). Compared with the farmers' practice, the seedling broadcast method reduced weedy rice seed production by 71–87% and transplanted rice by 95–98%; and increased rice yield by 27–49% (7.5–9.1 t ha⁻¹). At all three sites, the farmers' practice resulted in the lowest grain yield (5.1–6.7 t ha⁻¹). Compared with the farmers' practice, the random broadcast and row seeding methods increased rice yield by up to 21% and 31%, respectively. The findings suggest that the use of clean rice seeds, the use of a row-seeded crop, and the adoption of different rice planting methods may help to suppress the spread of weedy rice.     

Weed pressure level and the correlation between weed competitiveness and rice yield without weed competition: An analysis of empirical data

Improving rice (Oryza spp.) competitiveness against weeds would provide a low-cost and safe tool for an integrated weed management strategy. This paper addresses the underlying causes of tradeoff between yield without weed competition and weed competitiveness. Rice yield or weed biomass under weedy conditions are used as indicators of weed competitiveness. For this analysis, a common database was compiled from the results of 45 concurrent field trials comparing the performance of four to 64 genotypes in weed-free and weedy conditions in Asia, West Africa, North America and Latin America. Cyperus spp., Echinochloa spp. and Eleusine indica were the most frequent dominant weed species, being found in 9, 20 and 7 trials, respectively. Mean relative yield reduction [(yield under weed-free conditions − yield under weedy conditions)/yield under weed-free conditions] across genotypes tested for each trial was defined as weed pressure level. Mean yield without weed competition across genotypes ranged from 1.8 to 11.6 t ha⁻¹ with mean relative yield reduction from almost 0 to 91%. Correlations for rice yield between weed-free and weedy conditions were generally positive, and significant in 27 trials. The correlations were related to weed pressure level and dominant weed species, but not to ecosystem (upland or lowland) or yield level under weed-free conditions. Relative yield reduction had a more pronounced effect than dominant weed species. Correlation decreased as weed pressure level increased, and became negative when relative yield reduction exceeded 80%, suggesting that different morpho-physiological mechanisms are responsible for high yields under weed-free conditions or severe weed competition. Correlations between rice yield under weed-free conditions and weed biomass varied, giving 17 and 19 for positive and negative ones, respectively. These correlations were related neither to weed pressure level, ecosystem and yield level under weed-free conditions, nor to dominant weed species. These results indicate that correlations between rice yields under weed-free and weedy conditions can be strongly affected by weed pressure level, and, unless severe weed competition occurs, there appears to be no tradeoff between them. Association of morpho-physiological mechanisms with weed competitiveness under conditions differing in weed pressure levels and dominant weed species deserves further investigation.     

Diversity of Sodium Transporter HKT1;5 in Genus Oryza

Asian cultivated rice shows allelic variation in sodium transporter, OsHKT1;5, correlating with shoot sodium exclusion (salinity tolerance). These changes map to intra/extracellularly-oriented loops that occur between four transmembrane-P loop-transmembrane (MPM) motifs in OsHKT1;5. HKT1;5 sequences from more recently evolved Oryza species (O. sativa/O. officinalis complex species) contain two expansions that involve two intracellularly oriented loops/helical regions between MPM domains, potentially governing transport characteristics, while more ancestral HKT1;5 sequences have shorter intracellular loops. We compared homology models for homoeologous OcHKT1;5-K and OcHKT1;5-L from halophytic O. coarctata to identify complementary amino acid residues in OcHKT1;5-L that potentially enhance affinity for Na⁺. Using haplotyping, we showed that Asian cultivated rice accessions only have a fraction of HKT1;5 diversity available in progenitor wild rice species (O. nivara and O. rufipogon). Progenitor HKT1;5 haplotypes can thus be used as novel potential donors for enhancing cultivated rice salinity tolerance. Within Asian rice accessions, 10 non-synonymous HKT1;5 haplotypic groups occur. More HKT1;5 haplotypic diversities occur in cultivated indica gene pool compared to japonica. Predominant Haplotypes 2 and 10 occur in mutually exclusive japonica and indica groups, corresponding to haplotypes in O. sativa salt-sensitive and salt-tolerant landraces, respectively. This distinct haplotype partitioning may have originated in separate ancestral gene pools of indica and japonica, or from different haplotypes selected during domestication. Predominance of specific HKT1;5 haplotypes within the 3 000 rice dataset may relate to eco-physiological fitness in specific geo-climatic and/or edaphic contexts.     

江苏省杂草稻的传播与籼粳分化研究

21世纪初,杂草稻仅在江苏省局部区域发生,目前已扩大到全省,并对粳稻的高产和稳产造成严重威胁。为了掌握其快速发生机制,便于杂草稻的防除工作,需要进一步明确江苏省13市杂草稻是独立发生还是相互传播,以及江苏省杂草稻籼粳地理分布。采集了江苏省13个市58个样地的58个种群,总计205份的杂草稻样品。所有样品在南京农业大学江浦农场田间种植,并测量了38个形态学性状和6个程氏指数鉴别性状。欧氏距离聚类分析,表明江苏省13个市的杂草稻是相互混杂的。籼粳地理分布表明,江苏省杂草稻主要以籼型和偏籼型为主,籼型和偏籼型杂草稻在全部58个样点中都有分布,分别占样品总量的54.15%和42.40%;偏粳型和粳型仅分布于6个样点(淮安、苏州、盐城与扬州),分别占样品总量的2.93%和0.48%。此外,对比江苏省杂草稻的籼粳地理分布与江苏省地方品种的籼粳地理分布,未显示对应关系。籼粳比例和地理分布揭示了江苏省杂草稻主要为籼型,其中极少数为粳型杂草稻,粳型杂草稻的比例与杂草稻和栽培稻之间的自然基因漂移比例相近。     

Control of winter cereals in the spring with glyphosate

Poor survival of winter cereals due to winter conditions in Ontario can necessitate destruction of the stand in the spring to allow the subsequent seeding of an alternative crop. Winter cereals were seeded in the autumn of 2004 and 2005 at the Huron Research Station and at the University of Guelph Ridgetown Campus in Ontario to evaluate two formulations of glyphosate [potassium (K) vs diammonium (DA) salt] at different doses (225, 450, 675, 900, or 1350 g a.e. ha⁻¹) for the burn-off of soft white winter wheat (SWW), soft red winter wheat (SRW), hard red winter wheat (HRW) and autumn rye (AR) in either late April or early May. There was no difference between the glyphosate formulations for the control of winter cereals at 1, 2, 3, and 4 weeks after treatment (WAT). There was generally improved control with glyphosate applications made in early May compared to late April however results were not always statistically significant. Generally, control of winter cereals increased as the glyphosate dose was increased from 225 to 1350 g a.e. ha⁻¹. The minimum dose of glyphosate required for providing 90% or greater control of SWW, SRW, HRW, and AR was 675 g a.e. ha⁻¹ at 4 WAT. Glyphosate applied at 675 g a.e. ha⁻¹ caused a 98, 97, 98, and 99% reduction in shoot dry weight of SWW, SRW, HRW, and AR, respectively. Based on this study glyphosate (K or DA) applied in late April or early May can be used at doses as low as 675 g a.e. ha⁻¹ to adequately control SWW, SRW, HRW, and AR in the spring.     

利用SRAP分子标记分析47份杂草稻样品遗传多样性

 利用SRAP分子标记分析了采集于杂草稻多发地区的47份样本的遗传多样性,旨在从基因的开放式阅读框区域（ORFs）深入研究杂草稻的遗传背景,为进一步揭示其来源提供依据。结果表明,参试的我国杂草稻材料在110对引物组合中共扩增出845种类型的谱带,多态性谱带590种,多态率为6982%,平均每对引物可以检测到54条多态性谱带。说明SRAP分子标记对于杂草稻基因组开放式阅读框区域序列的多态性具有很高的检测效率,适用于遗传多样性研究。我国杂草稻材料Shannon Weaver多样性指数（I）为063,且南北方杂草稻多样性指数（I）相当,分别为063和062。聚类分析结果表明,南方收集的杂草稻与北方收集杂草稻群体间遗传分化较大,遗传差异明显。程氏指数判定结果也表明杂草稻呈南籼北粳的分布状态。     

Clearfield® rice: Its development,success, and key challenges on a global perspective

Weedy rice (Oryza sativa) is a close relative of domesticated rice and a noxious weed prevalent in rice fields in world regions where rice is grown. Weedy rice management has remained challenging to farmers, mainly due to the weed's physiological and morphological resemblance to rice cultivars. The introduction of Clearfield^® rice provides an alternative solution and an additional tool for integrated weed management. Clearfield^® rice-based programs result in the cleanest rice fields in the southern U.S. However, persistent application of the imidazolinone herbicides (imazethapyr, imazamox, and imazapic) in Clearfield^® rice raises concerns about the possible evolution of resistance to ALS-inhibitor herbicides in weedy rice and the transfer of resistance trait. The risk of resistant weedy rice evolution is much higher in Asia, Latin America, and other tropical regions where there is no winterkill and rice is planted at least twice each year. Herbicide carryover to rotational crops is also a concern. We summarized the progress of commercialization of Clearfield^® rice in 15 countries across the continents of America, Asia and Europe. In some countries, imidazolinone-resistant weedy rice outcrosses have been found abundant, thereby negating the utility of Clearfield^® technology. The persistence of imidazolinone herbicide residues in the soil is a concern in regions where multiple crops are planted in a year, or the following year. These challenges should be anticipated by countries that are considering adopting Clearfield^® rice technology. Issues associated with gene escape, resistance evolution in weedy rice, and herbicide carryover to rotational crops remain to be resolved. Research to achieve sustainable solutions for weedy rice management, must be continued and intense educational programs for growers must be sustained.     

Effect of Pretilachlor on Weedy Rice and Other Weeds in Wet-Seeded Rice Cultivation in South Vietnam

Abstract

Wet-seeded rice is a common method of sowing in Vietnam. Weeds, including weedy rice, however, are a major problem in this establishment method. A study was conducted in a farmer’s field to evaluate the effect of pretilachlor dose (0, 300, 600, and 900 g ai ha^–1) on the management of weedy rice and other weeds in wet-seeded rice cultivation in the spring-summer, summer-autumn, and winter-spring seasons of 2012-13. The herbicide was applied 1 day after sowing. Weeds belonging to the grass, broadleaf, and sedge groups were effectively controlled by the lowest herbicide dose (300 g ha^–1). Overall, weed control did not increase with increases in herbicide dose after 300 g ha^–1, suggesting the optimum dose for pretilachlor in wet-seeded systems. The application of pretilachlor at 300 g ha^–1 significantly reduced the number of weedy rice panicles (20 – 69%) and weedy rice biomass (15 – 26%). The highest pretilachlor dose (i.e., 900 g ha^–1), however, was better than the lower doses in reducing the number of weedy rice panicles (47 – 80%) and weedy rice biomass (41 – 54%). The non-treated plots produced a rice grain yield of 210, 2000, and 1850 kg ha^–1 in the spring-summer, summer-autumn, and winter-spring seasons, respectively. Compared with the non-treated plots, the lowest dose of pretilachlor improved grain yield. However, maximum yield was obtained by applying the highest dose of pretilachlor; 2690, 4490, and 5150 kg ha^–1 in the spring-summer, summer-autumn, and winter-spring seasons, respectively. The results of our study suggest that a broad spectrum of weed flora can be easily managed by a lower dosage of pretilachlor in wet-seeded rice; however, the herbicide dose needs to be increased to 900 g ha^–1 in order to decrease the weedy rice problem.     

Detecting ALS and ACCase herbicide tolerant accession of Echinochloa oryzoides (Ard.) Fritsch. in rice (Oryza sativa L.) fields

Inconsistent control of Echinochloa oryzoides has been reported repeatedly by farmers in the major rice growing area of Turkey. Greenhouse studies confirmed the existence of cross and multiple herbicide tolerance of E. oryzoides accessions including acetolactate synthase (penoxsulam, bispyribac-sodium) and acetyl CoA carboxylase (cyhalofob-butyl) inhibiting herbicides. Comparison of 95% lower confidence intervals of ED₉₀ derived from log-logistic dose–response curves, and twice the recommended field rates of the herbicides showed some, but not distinct separation of susceptible and tolerant accessions. We used a novel method to separate heterogeneous data without a priori knowledge of grouping into more than one group. On the basis of the distribution of ED₉₀ it was possible to identify two distinct groups of the 172 accessions tested, 78% were not controlled by ALS inhibitors (penoxsulam, and bispyribac-sodium) at recommended field rates; and 38% were not controlled by the ACCase Inhibitor (cyhalofob-butyl) at twice the field rates. The effective response level of ED₉₀ resulted in 64 and 14 tolerant accessions to ALS and ACCase, respectively. Fourteen accessions showed multiple resistances to ALS and ACCase Inhibitors.Some of the accessions were strongly tolerant to both herbicide modes of action and had 100% survival even at 6 times the recommended rates. Most of these tolerant accessions were from Marmara region, predominantly in Edirne and Balıkesir, which are the regions without any crop rotation.