Conyza sumatrensis: A new weed species resistant to glyphosate in the Americas

Recent reports of weed‐control failures after the use of glyphosate led to suspicion about the selection of resistant biotypes of Conyza at locations in west and north Paraná, Brazil. Plants were collected, identified as Conyza sumatrensis and subsequently evaluated for possible resistance to glyphosate in four stages of weed development. The experiments were carried out in a greenhouse by combining biotypes, stages of development and a range of glyphosate doses. All the suspected biotypes were collected from locations in Cascavel, Toledo, Assis Chateaubriand, Tupãssi and Campo Mourão with a history of glyphosate use in burndown and in glyphosate‐resistant soybean for at least the four previous years and were compared to a susceptible biotype (São Jorge do Ivaí) with no previous history of herbicide use. The doses of glyphosate ranged from 0 to 5760 g ae ha^?1. The biotypes were considered as resistant if two combined criteria were present (resistance factor > 1 and the rate required to achieve 80% control is >720 g ha^?1). The results provided evidence that there is a marked difference in the level of control of older plants and also confirmed the presence of some resistant biotypes. For applications at the first stage of development, two biotypes that were resistant to glyphosate were identified (Cascavel‐1 and Tupãssi‐6). For applications in the second stage of development, beyond the biotypes that were found in the first stage, three other biotypes were considered as resistant: Toledo‐5, Assis Chateaubriand‐7 and Floresta‐10. However, for applications at the third and fourth stages, all the biotypes were considered as resistant.     

Oriënteerend onderzoek omtrent physiologiese specialisatie van Puccinia triticina Eriks. In Nederland

Summary Physiologic specialization inP. triticina, the organe leaf rust of wheat, was discovered byMains andJackson (8, 9, 10), who, in the United States, found 12 physiologic forms.Scheibe (11), in Germany, found form 11 and three new forms: 13, 14 and 15. The present author found forms 11, 14 and 15 to occur among five isolations ofP. triticina from different regions of the Netherlands (cp. table I on p. 7). The wheat-varieties, usually grown in Holland, were all found to be equally susceptible to all three forms of the rust. Foreign varieties, however, exist which are highly resistant to the three froms, so that improvement of the dutch wheat-varieties can be accomplished by crossing with such resistant varieties. (vroeger: Wageningen, Holland; thans: Buitenzorg, Java)     

Negative cross-resistance to bentazone and pyridate in atrazine-resistant Amaranthus cruentus and Amaranthus hybridus biotypes

Plants of Amaranthus cruentus and Amaranthus hybridus resistant to atrazine and cyanazine were found in maize fields in north-eastern Spain. Both resistant foiotypes survived doses of 5 kg ha^?1 of atrazine and 2–4 kg ha^?1 of cyanazine but were controlled by lower doses of bentazone and pyridate than were susceptible biotypes. Such a negative cross-resistance was not found for chloroacetamides and MCPA. Chlorophyll fluorescence studies revealed that atrazine, bentazone, cyanazine and pyridate (10 mg litre^?1) caused inhibition of photosynlhetic electron transport in susceptible leaves, while in resistant plants, atrazine and cyanazine had no effect. Conversely, bentazone and pyridate inhibited photosynthesis to a greater extent in resistant than in susceptible biotypes. Isolated chloroplast membranes from resistant biotypes showed resistance factors of 366 and 501 to atrazine and 39 and 60 to cyanazine for A. hybridus and A. cruentus, respectively. Bentazone and pyridate were found to be more effective in chloropiasts of the resistant biotypes than those of the susceptible plants. It is suggested that enhanced susceptibility to bentazone and pyridate in triazine-resistant A. cruentus and A. hybridus biotypes may be associated with the alteration of the D-I polypeptide subunit of photosystem II, as found in triazine-resistant plants.     

The effect of fungicides on fungal antagonists of onion white rot and selection of dicarboximide-resistant biotypes

The sensitivity of four fungal antagonists (Chaetomium globosum, Trichoderma harzianum, T. viride, Trichoderma sp.) to six fungicides was evaluated. The fungi were insensitive to captan, mancozeb and thiram but were sensitive to benomyl (EC₅₀ < 0 3/μg/ml) and the two dicarboximides iprodione and procymidone (EC₅₀ < 3 3/μg/ml). Conidia and mycelia of the four fungi were exposed to a series of ultraviolet irradiations in order to select biotypes resistant to benomyl and iprodione. Resistance to benomyl was not induced but a number of biotypes of each fungus were isolated from irradiated cultures that showed resistance to iprodione (EC₅₀ values of up to 56·4, 177·8, 171·5 and 216·4/μg/ml for Chaetomium globosum, Trichoderma harzianum, T. viride and Trichoderma sp., respectively). With three exceptions, all selected biotypes retained their fungicide-resistance after being extensively cultured on fungicide-free medium. In general, growth of the fungicide resistant biotypes on MEA plates and in MYE liquid medium was equal to that of the corresponding wild-type strains. One resistant biotype of Trichoderma sp. (C62UV3) grew significantly (P < 0·05) better both on solid and in liquid medium. This resistant biotype was also observed to have greatly enhanced conidial production on agar plates. All fungicide resistant-biotypes retained the ability to antagonize the pathogen Sclerotium cepivorum in dual culture and, in two instances (A53UV1, A53UV5), exhibited greater antagonism as evidenced by the production of larger inhibition zones. Similarly, with two exceptions, the resistant biotypes retained the ability to control onion white rot disease caused by S. cepivorum in the glasshouse. In particular, two fungicide-resistant biotypes (Trichoderma sp. C62UV3 and Chaetomium globosum A53UV1) reduced white rot of onion more effectively than did their respective wild-type parents.     

抗稻瘿蚊品种多抗1的抗性遗传分析及抗性基因定位

稻瘿蚊是亚洲稻区主要害虫,采用抗虫品种进行防治是最理想的方法。1993～1995年,广东省农科院与国际水稻研究所有关专家紧密合作,对能抗华南4个稻瘿蚊生物型的品种多抗1作进一步抗性遗传分析,确认多抗1对中国稻瘿蚊生物型1和4的抗性受显性单基因控制,这个基因暂定名为GM—6(t)。以多抗1×丰银占1组合的F3代160个家系作基因标记,据DNA库分离个体分析(BSA)原理,用随机扩增多态性DNA(RAPD)标记物OPM6(1.4kb),首次成功地标记了这个抗性基因。随后多态性扩增产物经~(32)p标记,用作探针,检测另一个参考作图群体IR64×Azucena,将这个抗性基因定位在水稻第4条染色体上,位于RG214和RG163两个DNA限制性片段长度多态性(RFLP)标记之间。应用这些分子标记辅助选择有可能不必通过稻瘿蚊的直接筛选,快速准确地选育抗稻瘿蚊品种或进行抗性基因累加。     

Resistance to paraquat in Mazus pumilus

Mazus pumilus is an annual self‐pollinating weed that is commonly found in arable land, vegetable gardens and roadsides. This weed harbours insects and pathogens that attack vegetables. The mechanism of resistance to paraquat of M. pumilus found in Ohita, Japan, was studied. Whole plant bioassays revealed that the resistant (R) biotypes were four to six times less susceptible than controls. Chlorophyll destruction of leaf discs by paraquat treatment in R biotypes was 4–20 times lower than those of susceptible (S) biotypes. Ferric reducing antioxidant power (FRAP) values in R biotypes were higher than those of S biotypes before and after paraquat treatments. The activity of superoxide dismutase (SOD) was also higher in R biotypes than those of S biotypes before and after treatment with paraquat, but the activities of ascorbate peroxidase (APX) and catalase (CAT) were not different between R and S biotypes. Change of ascorbate (AsA) contents before and after paraquat treatment was equivalent in both biotypes. These results indicate that the increased SOD activity and antioxidant capacity in R biotypes contribute to the resistance to paraquat of M. pumilus.     

水稻品种对稻褐飞虱抗性的研究

水稻品种对褐飞虱的不同生物型反应是不相同的。试验结果证实:(1)褐飞虱若虫在敏感性品种上的生存率显著地高于抗性品种。在TN_1上,无论那种生物型的生存率均很高;而栖息在Mudgo的褐飞虱若虫,其生存率以生物型2的最高,而生物型1与生物型3的均很低,栖息在ASD_7的若虫,以生物型3的生存率最高。(2)褐飞虱在敏感品种上的后代群体密度显著地比抗性品种的大。生活在敏感品种的若虫,发育进度较抗性品种的快,并且身体较重。(3)在敏感品种取食的飞虱,其分泌的蜜露量较抗性品种的多,生物型2取食Mudgo的和生物型3取食ASD_7的均分泌较多的蜜露。上述结果说明了水稻品种抗褐飞虱的机制属抗生性范畴。     

Sulfonylurea-resistant biotypes of Monochoria vaginalis generate higher ultraweak photon emissions than the susceptible ones

All living organisms spontaneously generate ultraweak photon emissions, which originate from biochemical reactions in cells. Current research uses the ultraweak photon emission from organisms as a novel indicator in nondestructive analyses of an organisms living state. This study indicates that ultraweak photon emissions from Monochoria vaginalis are different between resistant biotypes (R) to sulfonylurea (SU) and susceptible biotypes (S). In SU-R biotypes, distinct increases in photon emissions were observed, but there was little increase in SU-S biotypes. In addition, photon emissions from the resistant biotypes of M. vaginalis were suppressed by treatment with P450 inhibitors. This suggests that cytochrome P450 monooxygenase, which plays a crucial role in the metabolic detoxification of SUs, could be associated with the generation of ultraweak photon emissions. Ultraweak photon emissions have a potential use in a novel diagnosis system as an indicator in a nondestructive testing of weeds resistant to SUs.     

Variations in the resistance of Stellaria media to mecoprop due to biotype, application method and 1-aminobenzotriazole

An investigation was made into the resistance of some biotypes of Stellaria media to mecoprop. Comparison of the sensitivity of five biotypes to foliar applications of mecoprop salt confirmed the presence of resistant and sensitive types and one of intermediate sensitivity. Applications of mecoprop through the roots of plants growing in nutrient culture were also more active on biotypes sensitive to foliar mecoprop, although the differences were less marked than they were with foliar treatments. Thus, possible differ ences in retention, uptake and translocation do not seem to be important causes of resistance. Consequently, it appears that resistance is associated with detoxification of mecoprop at the site of action. In two further experiments the cytochrome P450 mixed function oxidase inhibitor, 1-aminobenzotdazole, had only a small effect on the susceptibility of resistant S. media plants to mecoprop. The importance of these data in the elucidation of the mechanism of resistance is discussed.     

Molecular basis of resistance to acetolactate synthase-inhibiting herbicides in Sisymbrium orientale and Brassica tournefortii

Three Australian Sisymbrium orientale and one Brassica tournefortii biotypes are resistant to acetolactate synthase (ALS)-inhibiting herbicides due to their possession of an ALS enzyme with decreased sensitivity to these herbicides. Enzyme kinetic studies revealed no interbiotypic differences within species in K_m (pyruvate) (the substrate concentration at which the reaction rate is half maximal) but a greater V_max (the rate when the enzyme is fully saturated with substrate) for two of the resistant S orientale biotypes over susceptible levels. F₁ hybrids from reciprocal crosses between resistant and susceptible biotypes of S orientale showed an intermediate response to chlorsulfuron compared to the parental plants. ALS herbicide resistance in S orientale segregated in a 3:1 (resistant:susceptible) ratio in F₂ plants with a single rate of chlorsulfuron, indicating that resistance is inherited as a single, incompletely dominant nuclear gene. Two regions of the ALS structural gene known to vary in ALS-resistant biotypes were amplified and sequenced. Resistant S orientale biotypes NS01 and SS03 contained a single nucleotide substitution in Domain B, predicting a Trp (in susceptible) to Leu (in resistant) amino acid change. Two adjacent nucleotide substitutions (CC T to AT T) predicting a Pro (in susceptible) to Ile (in resistant) change in the primary amino acid sequence were identified in Domain A of resistant S orientale biotype SS01. Likewise, a single nucleotide substitution at the same site in the resistant B tournefortii biotype predicts a Pro (in susceptible) to Ala (in resistant) substitution. No other interbiotypic nucleotide differences predicted amino acid changes in the sequenced regions, suggesting that the amino acid substitutions reported above are responsible for resistance to ALS-inhibiting herbicides in the respective biotypes. © 1999 Society of Chemical Industry     

An association between triazine resistance and powdery mildew resistance in Epilobium ciliatum and Senecio vulgaris

The response of four naturally occurring biotypes of Epilobium ciliatum and four sources of Senecio vulgaris to the herbicide atrazine were compared with their susceptibility to the powdery mildews Sphaerotheca epilobii and Erysiphe cichoracearum. Biotypes that were resistant to atrazine were also resistant to mildew. Mechanisms that might explain the association between atrazine resistance and mildew resistance are discussed, along with possible implications of these findings for farmland ecology and for the production of herbicide- and mildew-resistant crop plants.     

Seed germination behavior of glyphosate‐resistant and susceptible Italian ryegrass (Lolium multiflorum Lam.)

Ryegrass (Lolium multiflorum Lam.) is one of the most difficult annual weeds to control in cultivation systems worldwide, especially in temperate regions. The widespread use of herbicides in the past two decades has selected resistant biotypes of ryegrass in crops in Southern Brazil. Ryegrass seeds are dormant when disseminated and germination can be staggered over time (crop‐growing season). Knowledge of the germination behavior of seeds from herbicide‐resistant plants has been little studied, but it would be very useful in integrated weed management. Thus, this study aimed to characterize the dynamics of the soil seed bank of two biotypes of L. multiflorum, one glyphosate‐resistant and the other glyphosate‐susceptible, under a no‐tillage system. The treatments were arranged in a bifactorial scheme, using seeds from biotypes (glyphosate‐resistant and glyphosate‐susceptible) with monthly periods of removal from field (one to 12 months). Seeds of each biotype were placed on the soil surface and covered with soil and straw to simulate no‐till conditions. The percentage of germinated, dormant, and dead seeds was evaluated every 30 days. The ryegrass seed bank of glyphosate‐susceptible and glyphosate‐resistant biotypes was reduced to 11 and 15% of dormant seeds, respectively, at the end of 12 months. However, there was no variation in germination, dormancy, and seed mortality between susceptible and glyphosate‐resistant ryegrass. Seeds of glyphosate‐resistant biotype and susceptible showed germination behavior with similar dynamics in the soil over a period of 12 months.     

Mechanisms of resistance to simazine in Sonchus oleraceus

Sonchus oleraceus biotypes resistant to simazine were identified by chlorophyll fluorescence analysis of intact leaves. The mechanisms of resistance were determined on the basis of cpDNA and glutathione S‐transferase (GST) activity analyses. The results of the cpDNA analysis showed that most of the resistant biotypes had a Ser 264 Gly mutation in the psbA gene, which is responsible for an amino acid substitution in the D‐1 protein sequence. The cpDNA fragments were amplified by polymerase chain reaction and digested with restriction enzyme MaeI. Two restriction bands of 338 and 75 bp were recorded in biotypes with the target mutation, while three bands (218, 120 and 75 bp) were present in biotypes without this mutation. A second mechanism of resistance in this species was through the detoxification of simazine by conjugation with glutathione. In resistant biotypes without the above‐mentioned mutation, the average level of GST (simazine) activity in leaves was 4.5‐fold greater than in the resistant biotypes with the target mutation and 8.3‐fold greater than in the susceptible biotypes. Resistance as a result of the target mutation was more common than that achieved through detoxification by glutathione conjugation of simazine.     

Mechanism of resistance to bensulfuron-methyl in Alisma plantago-aquatica biotypes from Portuguese rice paddy fields

Two Alisma plantago‐aquatica biotypes resistant to bensulfuron‐methyl were detected in rice paddy fields in Portugal’s Mondego (biotype T) and Tagus and Sorraia (biotype Q) River valleys. The fields had been treated with bensulfuron‐methyl‐based herbicide mixtures for 4–6 years. In order to characterize the resistant (R) biotypes, dose–response experiments, absorption and translocation assays, metabolism studies and acetolactate synthase (ALS) activity assays were performed. There were marked differences between R and susceptible (S) biotypes, with a resistance index (ED₅₀R/S) of 500 and 6.25 for biotypes Q and T respectively. Cross‐resistance to azimsulfuron, cinosulfuron and ethoxysulfuron, but not to metsulfuron‐methyl, imazethapyr, bentazone, propanil and MCPA was demonstrated. No differences in the absorption and translocation of ¹⁴C‐bensulfuron‐methyl were found between the biotypes studied. Maximum absorption attained 1.12, 2.02 and 2.56 nmol g⁻¹ dry weight after 96 h incubation with herbicide, for S, Q and T biotypes respectively. Most of the radioactivity taken up by the roots was translocated to shoots. Bensulfuron‐methyl metabolism in shoots was similar in all biotypes. The R biotypes displayed a higher level of ALS activity than the S biotype, both in the presence and absence of herbicide and the resistance indices (IC₅₀R/S) were 20 197 and 10 for biotypes Q and T respectively. These data confirm for the first time that resistance to bensulfuron‐methyl in A. plantago‐aquatica is target‐site‐based. In practice, to control target site R biotypes, it would be preferable to use mixtures of ALS inhibitors with herbicides with other modes of action.     

Assessment of two biotypes of Solanum ptycanthum that differ in resistance levels to imazamox

Glasshouse and laboratory experiments were conducted on acetolactate synthase (ALS) homozygous resistant Solanum ptycanthum biotypes from Illinois (IL‐R) and Indiana (IN‐R), and homozygous susceptible biotypes from Illinois (IL‐S) and Indiana (IN‐S). Genetic similarity of biotypes was assessed by random amplified polymorphic DNA (RAPD) markers, which determined that the Illinois biotypes are more similar to each other than to the IN‐R biotype. ALS enzyme activity from the IL‐R and IN‐R biotypes had I₅₀ values of 362 and 352 μM imazamox respectively. Dose–response experiments using three‐ to four‐leaf‐stage plants of the IL‐R and IN‐R biotypes had GR₅₀ values of 242 and 69 g ae ha⁻¹ imazamox respectively. Whole‐plant and ALS enzyme results are different than previously reported values in the literature, which was attributed in the current study to the original IN‐R population having individuals that were segregating for ALS resistance. Metabolism studies showed no difference in percentage [¹⁴C]imazamox remaining between the IL‐R and IN‐R biotypes up to 72 h after treatment. The IL‐S biotype metabolised [¹⁴C]imazamox approximately two times faster than the IL‐R and IN‐R biotypes and this trait was heritable. Response of F₃ plants containing homozygous ALS‐resistant alleles from the IL‐R biotype in a genetic background of 50% Illinois and 50% Indiana biotypes suggests that genetic factors other than an altered target site or metabolism may also contribute to the magnitude of resistance at the whole‐plant level in resistant biotypes.     

Resistance of dicot weeds to acetolactate synthase (ALS)-inhibiting herbicides in Australia

A biotype of Sonchus oleraceus L. and two bio types of Sisymbrium orientate Torn., SSO 3 and NSO 1, are the first dicot weeds in Australia to develop resistance to ALS-inhibiting herbicides. The resistant biotypes had been exposed to va rying periods of selection with sulfonylurea her bicides. All three biotypes are resistant to a range of sulfonylurea and imidazolinone herbicides. The S. orientale biotypes are also resistant to the triazolopyrimidine herbicide, flumetsulam. LD₅₀ ratios of resistant Sonchus oleraceus for sulfony lurea and imidazolinone herbicides are greater than 64-fold and 4.5-fold, respectively. GR₅₀ ratios are greater than 9 for sulfonylureas and 7.4 for imazapyr. The LD₅₀ ratios for both S. orien tale biotypes for chlorsulfuron, sulfometuron methyl, metsulfuron-methyl, flumetsulam and imazethapyr are greater than 110-, 15-, 7-, 24- and 29-fold, respectively. All resistant biotypes are susceptible to MCPA, diuron and diflufenican, herbicides which do not inhibit ALS.     

Comparaison de la germination et de la croissance de biotypes sensibles et résistants aux triazines chez quatre espèces de mauvaises herbes

Comparison of germination and growth of biotypes sensitive and resistant to triazines in four weed species. By observing germination under various conditions and plant development in non-competitive conditions, a comparison was made between sensitive and resistant biotypes of four species in which resistant populations have been discovered: Chenopodium album, Amaranthus retroflexus. Solanum nigrum and Polygonum lapathifolium. In spite of différent levels of significance, results indicate that the sensitive plants develop better. However, these findings may be modified according to the growth conditions. Moreover, high variance values in the characteristics measured reflect considerable heterogeneity at least in the sensitive lots. Nevertheless, seed from resistant plants of P. lapathifolium and, to a lesser extent, of Amaranthus, germinate more readily at low temperatures. In the light of these findings the authors discuss the possible advantages conferred on different lots by these characteristics, stressing the need to consider each species separately and to take into account the nature of the genotypes being compared. From such findings, while the exact factor determining resistance is not known, it is difficult to deduce a lower level of adaptability in resistant, as opposed to sensitive individuals, based on their place of origin and in the absence of herbicide treatments.     

Atrazine metabolism in resistant and susceptible biotypes of Chenopodium album L., Chenopodium strictum Roth., and Amaranthus powellii S. Wats.

The metabolism of atrazine was studied in resistant and susceptible biotypes of Chenopodium album L., Chenopodium strictum Roth., and Amaranthus powellii S. Wats. Both biotypes metabolized atrazine by N-dealkylation, hydroxy lation at the 2-position and conjugation. In addition, binding of mono-N-dealkylated atrazine with plant constituents to form nonextractable (bound) residues was also observed. Although parent atrazine levels were similar in the shoots and roots of both biotypes of the three weed species, the resistant biotype in each case contained a higher level of polar conjugates and bound residues in the plant tissues. In contrast, presence of a phytotoxic metabolite, namely 2-chloro-4-amino-6-isopropylamino-s-triazine, was only observed in the susceptible biotype of the three weed species.     

多抗性晚籼浙丽1号(6202)对几种主要病虫的抗性

作者等自1973年开始进行抗病虫水稻品种的研究工作,现已育成抗主要病虫害:褐飞虱、自背飞虱、黑尾叶蝉和稻瘟病的晚籼浙丽1号(6202)。组合为广塘矮/Mudgo//竹科2号。本文还就耕作制度尤其抗虫品种以及褐飞虱“生物型”与稻飞虱种群动态的关系进行了讨论,并查明当地褐飞虱田间优势种群目前尚属生物型1。     

Resistance of Amaranthus hybridus to atrazine

Resistance of weeds to triazine herbicides has been recorded in many countries. The extent of the problem in South Africa is uncertain. In a pilot study, the atrazine resistance of Amaranthus hybridus L. (smooth pigweed) was investigated. Suspected resistant (R) and susceptible (S) biotypes were treated with commercially formulated atrazine. After post-and pre-emergence applications under tunnel conditions, it was found that the suspected R biotype plants were not affected at herbicide dosages of belween 1.25 and 25.0 kg a.i. ha^-1, i.e. up to 20 times gieater than the lowest recommended dosage. However, the S biotype plants were killed by the lowest dosage. In the fieid, mortalities in the R biolype were not observed after post-emergence applications of 1.25-10.00 kg a.i. ha^-1. In contrast, all S biotype plants were killed. In tunnel experiments, the R biotype was also found to be resistant to cyanazine and cyanazine+atrazine, while slight tolerance to linuron was observed. All these treatments resulted in 100% mortality of the S biotype. Although S biotype seeds oi A. hybridus were found to germinate slightly sooner under controlled conditions than R biotype seeds, preliminary results suggest that there are no major differences. Indications are that, although the growth of the S biotype may be greater than that of the R biotype, the competitive effect of the two biotypes on crop seedlings may well be similar.