Root exudation of prometryn and its metabolites from Chinese celery (Apium graveolens)

Root exudates from Chinese celery (Apium graveolens) and Chinese cabbage (pak choi, Brassica chinensis) plants treated by prometryn, an herbicide, were qualitatively and quantitatively investigated and compared under hydroponic cultivation. Prometryn and its metabolites released into the nutrient solution were analyzed by ultra-performance liquid chromatograph coupled with orbitrap mass spectrometer to investigate whether this xylem-mobile herbicide is exuded from the roots. The results showed that celery and pak choi had different root exudation profiles. Celery metabolized prometryn to prometryn sulfoxide and released both compounds from the roots. In contrast, pak choi barely metabolized or actively released prometryn from the roots. The concentration of prometryn sulfoxide released from celery after 96 hr was 21 µg/L, which was nearly one-third that of released prometryn. Our results indicate that the root exudation and translocation of xylem-mobile herbicides could be significant in plants and are highly species dependent compared with phloem-mobile herbicides.     

Susceptibility of European bread and durum wheat cultivars to Tilletia indica

Representative European wheat cultivars were tested under quarantine containment for their susceptibility to Tilletia indica, the cause of Karnal bunt of wheat. Fifteen winter and 15 spring wheat ( Triticum aestivum ) and 11 durum wheat ( Triticum durum ) cultivars were inoculated by boot injection just prior to ear emergence to test their physiological susceptibility. Selected cultivars were then re-tested by spray inoculation after ear emergence to determine their morphological susceptibility, which is a better predictor of field susceptibility. At maturity, the ears and seeds were assessed for incidence and severity of disease. For the physiological susceptibility tests, 13/15 winter wheat cultivars were infected and the percentage of infected seeds ranged from 1 to 32%. For spring cultivars, 13/15 cultivars were infected and the percentage of infected seeds ranged from 1 to 48%. For the durum cultivars, 9/11 were infected and the percentage of infected seeds ranged from 2 to 95%. Across all cultivars, 35/41 were infected. Based on historical Karnal bunt susceptibility categories using coefficients of infection, one cultivar was classed as highly susceptible, three as susceptible, 11 as moderately susceptible, 20 as resistant and only six as highly resistant. The spray-inoculation morphological susceptibility tests broadly confirmed the physiological susceptibility results, although lower levels of infection were observed. Overall, the range of susceptibility was similar to that found in cultivars grown in Karnal bunt affected countries. The results demonstrate that European wheat cultivars are susceptible to T. indica and thus could potentially support the establishment of T. indica if introduced into Europe.     

Dynamic root exudation of phenolic allelochemicals from Johnson grass (Sorghum halepense)

The phenolic allelochemicals from the root exudates of Johnson grass (Sorghum halepense) were collected at different developmental stages and analyzed using high performance liquid chromatography‐ultraviolet/photo‐diode array. The results revealed that three simple phenolic components, p‐hydroxybenzoic acid, p‐hydroxybenzaldehyde and ethyl p‐hydroxybenzoate, along with two flavonoids, diosmetin (3′,5,7‐trihydroxy‐4′‐methoxyflavone) and tricin (5,7,4′‐trihydroxy‐3′,5′‐dimethoxyflavone), were found in the root exudates of Johnson grass. However, the major phenolic compounds varied and the quality of each compound was dynamic at different developmental stages: the only phenolic compound that was detected in the seedling stage was p‐hydroxybenzoic acid; three simple phenolic allelochemicals, p‐hydroxybenzoic acid, p‐hydroxybenzaldehyde and ethyl p‐hydroxybenzoate, were found in the jointing stage; and five compounds, including the two flavonoids, tricin and diosmetin, appeared in the reproductive stage along with the other three simple phenolic allelochemicals. The highest diversity in phenolic constituents was in the reproductive stage, with five allelochemicals. Only p‐hydroxybenzoic acid was found in the whole life cycle of Johnson grass, with a range of 2.9 nmol to 6.8 nmol per plant per day. p‐Hydroxybenzaldehyde had the highest quality among all the compounds, with the highest releasing rate of 26.8 nmol per plant per day. The lowest‐content compounds were the two flavonoids, with the highest quality of 1.8 nmol per plant per day. The results suggest that the temporal dynamic of phenolic allelochemicals in the root exudates of Johnson grass corresponds with the dynamic of development.     

Resistance to diclofop-methyl in two Lolium spp. populations from Italy: studies on the mechanism of resistance

The mechanisms of herbicide resistance were investigated in two diclofop-methyl-resistant Lolium spp. populations from central Italy, Roma '94 and Tuscania '97. These two populations were compared with two susceptible Italian populations (Vetralla '94, Tarquinia '97) and a resistant and a susceptible population from Australia, SLR31 and VLR1. The activity of acetyl Co-A carboxylase (ACCase) extracted from susceptible (S) or resistant (R) individuals from the Italian populations was inhibited by both aryloxyphenoxypropanoate (diclofop acid and fluazifop acid) and cyclohexanedione (sethoxydim) herbicides. Diclofop-methyl was rapidly de-esterified to diclofop acid at a similar rate in both R and S populations. In all populations, diclofop acid was subsequently degraded to other metabolites. The rate of degradation of diclofop acid was not significantly faster in R than in S populations; however, diclofop acid was degraded more completely in Roma '94 and Tuscania '97 compared with the S populations. Application of the mixed-function oxidase inhibitor 1-aminobenzotriazole (ABT) significantly enhanced diclofop-methyl toxicity towards both R populations, but not in S populations. However, enhanced herbicide metabolism does not completely account for the measured resistance level. A mechanism other than an altered ACCase and enhanced herbicide metabolism appears to be responsible for resistance to diclofop-methyl in Roma '94 and Tuscania '97.     

Growth and yield responses of Italian ryegrass (Lolium multiflorum) to diclofop-methyl and ozone

We evaluated the combined effects of diclofop‐methyl herbicide application and the air pollutant ozone (O₃) on diclofop‐methyl‐resistant and ‐susceptible biotypes of Italian ryegrass (Lolium multiflorum). We conducted two experiments, one with a long vegetative growth period and the other with a short vegetative growth in late spring with seed production in summer. As expected, because of its phytotoxicity, the herbicide alone reduced total vegetative biomass, leaf area, tiller number and seed production at most sampling periods in susceptible plants for both experiments. However, it had variable effects on resistant plants, including a positive effect on seed production. Ozone alone delayed vegetative biomass accumulation and reduced leaf area and seed biomass in both experiments. However, the effects of O₃ on some parameters were altered by herbicide rate and/or biotype. Especially notable was a greater reduction in seed biomass because of O₃ in resistant than in susceptible plants with no herbicide. If these apparent differential responses to herbicide and O₃ stress of susceptible and resistant plants are confirmed and persist over time, evolutionary tradeoffs may occur. For example, the frequency of resistant plants in a population may be altered in response to interactions between herbicides and other anthropogenic stresses.     

Low diversity and fast evolution in the population of Puccinia triticina causing durum wheat leaf rust in France from 1999 to 2009, as revealed by an adapted differential set

No internationally agreed differential set is available for characterization of virulences in populations of Puccinia triticina causing wheat leaf rust on durum wheat. In a first step, 73 potentially differential host genotypes were tested with 96 durum leaf rust isolates collected in France. A differential set, adapted to the local epidemiological context and useful for comparison with international studies was selected, including French commercial cultivars, Thatcher lines with Lr genes, and international cultivars. In the second step, a sample of 310 isolates collected in France from 1999 to 2009 was characterized on this set. Diversity was very low, as only five pathotypes were distinguished. Genotyping of a subset of 76 isolates according to 20 SSR markers confirmed this low diversity, with 73 isolates belonging to a single dominant genotype. Population was strongly shaped by cultivars, and the findings explain the successive breakdown of resistance sources deployed in French durum wheat cultivars. The gene Lr14a, suggested to be an efficient source of resistance in several European and American countries, was overcome by pathotypes frequent in France since 2000. Postulation of resistance genes in the commercial cultivars led to a proposed simplified version of the differential set. This study, providing new information about leaf rust resistance genes present in the French durum wheat germplasm, highlights the need to diversify sources of resistance to P. triticina in this germplasm. The results are also discussed in terms of relatedness and intercontinental migration of P. triticina on durum wheat.     

Non‐target‐site mechanism of glyphosate resistance in Italian ryegrass (Lolium multiflorum)

In Shizuoka Prefecture, Japan, glyphosate‐resistant Lolium multiflorum is a serious problem on the levees of rice paddies and in wheat fields. The mechanism of resistance of this biotype was analyzed. Based on LD₅₀, the resistant population was 2.8–5.0 times more resistant to glyphosate than the susceptible population. The 5‐enolpyruvyl‐shikimate‐3‐phosphate synthase (EPSPS) gene sequence of the resistant biotype did not show a non‐synonymous substitution at Pro106, and amplification of the gene was not observed in the resistant biotype. The metabolism and translocation of glyphosate were examined 4 days after application through the direct detection of glyphosate and its metabolite aminomethylphosphonic acid (AMPA) using liquid chromatograph‐tandem mass spectrometer (LC‐MS/MS). AMPA was not detected in either biotype in glyphosate‐treated leaves or the other plant parts. The respective absorption rates of the susceptible and resistant biotypes were 37.90 ± 3.63% and 41.09 ± 3.36%, respectively, which were not significantly different. The resistant biotype retained more glyphosate in a glyphosate‐treated leaf (91.36 ± 1.56% of absorbed glyphosate) and less in the untreated parts of shoots (5.90 ± 1.17%) and roots (2.76 ± 0.44%) compared with the susceptible biotype, 79.58 ± 3.73%, 15.77 ± 3.06% and 4.65 ± 0.89%, respectively. The results indicate that the resistance mechanism is neither the acquisition of a metabolic system nor limiting the absorption of glyphosate but limited translocation of the herbicide in the resistant biotype of L. multiflorum in Shizuoka Prefecture.     

Uptake, translocation and metabolism of the herbicide florasulam in wheat and broadleaf weeds

Florasulam is a triazolopyrimidine sulfonanilide post-emergence broadleaf herbicide for use in wheat (Triticum aestivum L.). The selectivity of florasulam to wheat has been determined to be related primarily to a differential rate of metabolism between wheat with a half-life of 2.4 h and broadleaf weeds with half-lives ranging from 19 to >48 h. To a lesser extent, selectivity, at least for the broadleaf weed cleavers (Galium aparine L.), involves uptake differences. Rate of metabolism data were generated using greenhouse-grown plants injected with radiolabelled florasulam and subsequent extraction and processing by high-performance liquid chromatography (HPLC). Structures of metabolites were determined by isolation for nuclear magnetic resonance and liquid chromatography/mass spectrometry. Wheat plants metabolised florasulam by hydroxylation of the aniline ring para to the nitrogen, followed by conjugation to glucose. Metabolism by broadleaf weeds was so slow that isolation of metabolite was not possible, but comparison of HPLC data suggested hydroxylation as the major pathway.     

Uptake and fate of triticonazole applied as seed treatment to spring wheat (Triticum aestivum L.)

Following seed treatment of wheat (Triticum aestivum L.) with ¹⁴C-labelled triticonazole at a dose of 1·8 g kg^-1 seed, the uptake of radioactivity by shoots and roots was investigated from the two- to three-leaf stage up to the beginning of the booting phase, 80 days after sowing. Triticonazole equivalents taken up by wheat plants reached 5·7% and 14·6% of the applied dose in the shoots and the roots, respectively. Between the two- to three-leaf stage and the beginning of the booting phase, the concentration of triticonazole equivalents in the shoots decreased from 2·5 to 0·15 μg g^-1 fresh weight. This was attributed to uptake of triticonazole by roots not keeping pace with shoot growth and increased retention in the roots of triticonazole taken up. The main factor limiting the uptake of triticonazole by the roots may be the rapid growth of the uptake-active apical root parts out of the dressing zone which had formed in the soil. Distribution of triticonazole equivalents taken up by the main shoot showed a decreasing concentration gradient from the oldest to the youngest leaf. An increase in the seed treatment dose was investigated as a way to increase the concentration of triticonazole in the shoots, but its influence remained limited. © 1998 SCI     

砜吡草唑与氟噻草胺协同作用防治多花黑麦草及其对小麦的安全性

多花黑麦草是近来危害严重,抗药性发生普遍的一种恶性杂草,对我国小麦安全生产造成了严重威胁。为筛选对多花黑麦草有效的防除药剂,本文采用盆栽法进行了除草剂室内配方配比筛选试验,并对筛选的配方进行了室内安全性评价。结果表明,麦田常用茎叶处理除草剂精噁唑禾草灵、炔草酯、甲基二磺隆、啶磺草胺、氟唑磺隆对多花黑麦草防除效果均不理想,多花黑麦草对其均产生了不同程度的抗性。而土壤处理除草剂中砜吡草唑和氟噻草胺对多花黑麦草防除效果较好。进一步通过室内配方配比筛选试验,得出砜吡草唑和氟噻草胺1∶1.2混合对多花黑麦草的ED₅₀为3.46 g/hm~2,共毒系数(CTC)为137.40,表明二者1∶1.2混配对多花黑麦草防除有增效作用。安全性试验表明,砜吡草唑和氟噻草胺1∶1.2混配下对小麦的ED₁₀为381.98 g/hm~2,对多花黑麦草和小麦的选择性指数为56.93,表明砜吡草唑和氟噻草胺混配选择性最高,能有效防除多花黑麦草且对小麦安全。     

Reduced translocation is involved in resistance to glyphosate and paraquat in Conyza bonariensis and Conyza canadensis from California

Resistance to glyphosate and paraquat has evolved in some populations of Conyza spp. from California, USA. This study evaluated whether herbicide absorption and translocation were involved in the mechanism of resistance to both herbicides. Three lines of each species were used: glyphosate‐paraquat‐susceptible (GPS), glyphosate‐resistant (GR) and glyphosate‐paraquat‐resistant (GPR). Radiolabelled herbicide was applied to a fully expanded leaf, and absorption and movement out of the treated leaf were monitored for up to 24 h for paraquat and 72 h for glyphosate. Plants treated with paraquat were incubated in darkness for the first 16 h and then subjected to light conditions. More glyphosate was absorbed in C. bonariensis (52.9–58.3%) compared with C. canadensis (28.5–37.6%), but no differences in absorption were observed among lines within a species. However, in both species, the GR and GPR lines translocated less glyphosate out of the treated leaf when compared with their respective GPS lines. Paraquat absorption was similar among lines and across species (71.3–77.6%). Only a fraction of paraquat was translocated in the GPR lines (3% or less) when compared with their respective GPS or GR lines (20% or more) in both species. Taken together, these results indicate that reduced translocation is involved in the mechanism of resistance to glyphosate and paraquat in C. bonariensis and C. canadensis.     

氟噻草胺与氟唑磺隆混配协同作用及在小麦田杂草防治中的应用

本文通过室内生物测定研究了氟噻草胺与氟唑磺隆对小麦及多花黑麦草的活性,田间试验测定了二者混配对阔叶杂草的防效及对小麦分蘖数的影响。室内水培法测定结果表明,氟噻草胺、氟唑磺隆对多花黑麦草有效抑制中剂量(ED50)分别为0.37mg/L和105.91mg/L,氟噻草胺与氟唑磺隆混配比例为8∶2、12∶2、16∶2、20∶2时,共毒系数(CTC)分别为94.3、239.7、198.1、156.5,表明氟噻草胺与氟唑磺隆混用具有相加或增效作用,其中以12∶2、16∶2比例混配对多花黑麦草防治增效最为显著。盆栽试验结果表明,苗前以12∶2和16∶2比例土壤封闭喷施对小麦与多花黑麦草的选择性指数为1.51和1.43;苗后3d及苗后15d茎叶喷施对多花黑麦草与小麦选择性较差,选择性指数低于1。田间测定结果表明,氟噻草胺与氟唑磺隆混配对阔叶杂草荠菜、播娘蒿、婆婆纳防效优于氟噻草胺单独使用,混配条件下株防效为85.45%~100%,鲜重防效为89.57%~100%,对小麦分蘖数无显著影响。     

Uptake and translocation of carpropamid in rice (Oryza sativa L)

Translocation of the antiblast compound, carpropamid, was investigated in rice using [¹⁴C]carpropamid. When applied to the seed, carpropamid was not only readily absorbed but was translocated to different parts of the seedlings emerging from treated seeds. A substantial portion of fungicide appeared to be exuded onto the leaf surface. In 21‐day‐old plants grown from [¹⁴C]carpropamid‐treated seeds, 27.2% of the radioactivity isolated from leaves was present on the surface of lamina. This exuded fraction is probably responsible for its action as a fungal anti‐penetrant compound. Following 30‐min root dipping of 14‐day‐old seedlings, carpropamid was rapidly absorbed and translocated throughout the seedling. Its intra‐laminar distribution was uniform as determined by autoradiography. Only a small fraction (<2%) of fungicide applied to the foliage was translocated beyond the site of application within the treated leaf. Translocation was primarily apoplastic. Approximately 54% of the radioactivity recovered from leaves was in the form of carpropamid. At least seven radiolabelled metabolic products were observed by TLC. Only 8.3% of radioactivity applied through the seeds could be recovered from 21‐day‐old seedlings. © 2001 Society of Chemical Industry     

An aspartate to glycine change in the carboxyl transferase domain of acetyl CoA carboxylase and non‐target‐site mechanism(s) confer resistance to ACCase inhibitor herbicides in a Lolium multiflorum population

BACKGROUND: The increasing use of ACCase‐inhibiting herbicides has resulted in evolved resistance in key grass weeds infesting cereal cropping systems worldwide. Here, a thorough and systematic approach is proposed to elucidate the basis of resistance to three ACCase herbicides in a Lolium multiflorum Lam. (Italian rye grass) population from the United Kingdom (UK24). RESULTS: Resistance to sethoxydim and pinoxaden was always associated with a dominant D2078G (Alopecurus myosuroides Huds. equivalent) target‐site mutation in UK24. Conversely, whole‐plant herbicide assays on predetermined ACCase genotypes showed very high levels of resistance to diclofop‐methyl for all three wild DD2078 and mutant DG2078 and GG2078 ACCase genotypes from the mixed resistant population UK24. This indicates the presence of other diclofop‐methyl‐specific resistance mechanism(s) yet to be determined in this population. The D2078G mutation could be detected using an unambiguous DNA‐based dCAPS procedure that proved very transferable to A. myosuroides, Avena fatua L., Setaria viridis (L.) Beauv. and Phalaris minor Retz. CONCLUSION: This study provides further understanding of the molecular basis of resistance to ACCase inhibitor herbicides in a Lolium population and a widely applicable PCR‐based method for monitoring the D2078G target‐site resistance mutation in five major grass weed species. Copyright © 2010 Society of Chemical Industry     

Influence of after-ripening environments on the germination characteristics and seed fate of Italian ryegrass (Lolium multiflorum)

Italian ryegrass ( Lolium multiflorum Lam.) is an exotic winter annual weed that recently has seriously infested wheat fields in central Japan. To understand the influence of tillage systems on the germination ecology and seedbank dynamics of naturalized Italian ryegrass, we compared the fate of the seeds that were after-ripened in the soil with that of the seeds on the soil surface, and then examined the germination characteristics of the seeds retrieved from both treatments by germination tests in both a light/dark (12 h photoperiod) condition and in constant darkness. The seedling emergence was greater initially for the seeds after-ripened on the soil surface than for the seeds in the soil. The component of emergent seeds after-ripened on the soil surface increased as time passed during the summer, whereas that of emergent seeds in the soil scarcely increased. This contrasting emergence was, in part, attributable to the ability of the seeds to germinate at higher temperatures in the light/dark condition than in constant darkness. These results suggest that untilled systems, which leave many seeds on the soil surface, might promote the rapid depletion of Italian ryegrass seeds through germination before wheat sowing in early winter. In contrast, seed burial by tillage might inhibit the germination of the seeds and form a large transient seed bank available to germinate during the wheat-growing season.