Inheritance of resistance to fenoxaprop‐p‐ethyl in sprangletop (Leptochloa chinensis L. Nees)

Sprangletop (Leptochloa chinensis L. Nees) is a serious grass weed in direct‐seeded rice cropping systems in Thailand. One population of sprangletop, BLC1, was found to be resistant to fenoxaprop‐p‐ethyl at 62‐fold the concentration of a susceptible biotype, SLC1. This study elucidated the inheritance of resistance to fenoxaprop‐p‐ethyl in this sprangletop BLC1 genotype. The reaction to the herbicide at 0.12–2.4 mg ai L^?1 was determined in the seedlings of self‐pollinated resistant BLC1, susceptible SLC1 and SLC1 that had been allowed to cross‐pollinate with BLC1. At 0.24 mg ai L^?1, all the seedlings of SLC1 were killed, while 99% of BLC1 survived, along with 5% of the cross‐pollinated SLC1 seedlings, which were considered to be putative F₁ hybrids. The root and shoot lengths of the F₁ hybrids in 0.24 mg ai L^?1 of fenoxaprop‐p‐ethyl, relative to those in the absence of the herbicide, were close to or the same as the resistant parent, indicating that the resistance is a nearly complete to complete dominant trait. One‐hundred‐and‐forty‐one of the F₂‐derived F₃ families were classified by their response to the herbicide at 0.24 and 0.48 mg ai L^?1 into 39 homozygous susceptible : 72 segregating : 30 homozygous resistant, fitted with a 1:2:1 ratio at χ² = 1.21 and P = 0.56, indicating that the resistance to fenoxaprop‐p‐ethyl in the sprangletop BLC1 genotype is controlled by a single gene.     

Attempts to transfer paraquat resistance from barley grass (Hordeum glaucum Steud.) to barley and wheat

A paraquat-resistant biotype of barley grass (Hordeum glaucum Steud.) was hybridized with barley and wheat in an attempt to transfer paraquat resistance to these crops. Although hybridizations with barley did not result in the production of a plant, cytological evidence of chromosome elimination of one parent, presumably of H. glaucum, was obtained from squash preparations of young F₁ embryos. Hybridizations of wheat with both diploid and tetraploid H. glaucum resulted in the production of wheat haploids. These results indicate that it may not be possible to transfer paraquat resistance to barley and wheat using conventional hybridization techniques.     

Control by glyphosate and its alternatives of glyphosate‐susceptible and glyphosate‐resistant Echinochloa colona in the fallow phase of crop rotations in subtropical Australia

Echinochloa colona is the most common grass weed of summer fallows in the grain‐cropping systems of the subtropical region of Australia. Glyphosate is the most commonly used herbicide for summer grass control in fallows in this region. The world's first population of glyphosate‐resistant E. colona was confirmed in Australia in 2007 and, since then, >70 populations have been confirmed to be resistant in the subtropical region. The efficacy of alternative herbicides on glyphosate‐susceptible populations was evaluated in three field experiments and on both glyphosate‐susceptible and glyphosate‐resistant populations in two pot experiments. The treatments were knockdown and pre‐emergence herbicides that were applied as a single application (alone or in a mixture) or as part of a sequential application to weeds at different growth stages. Glyphosate at 720 g ai ha^?1 provided good control of small glyphosate‐susceptible plants (pre‐ to early tillering), but was not always effective on larger susceptible plants. Paraquat was effective and the most reliable when applied at 500 g ai ha^?1 on small plants, irrespective of the glyphosate resistance status. The sequential application of glyphosate followed by paraquat provided 96–100% control across all experiments, irrespective of the growth stage, and the addition of metolachlor and metolachlor + atrazine to glyphosate or paraquat significantly reduced subsequent emergence. Herbicide treatments have been identified that provide excellent control of small E. colona plants, irrespective of their glyphosate resistance status. These tactics of knockdown herbicides, sequential applications and pre‐emergence herbicides should be incorporated into an integrated weed management strategy in order to greatly improve E. colona control, reduce seed production by the sprayed survivors and to minimize the risk of the further development of glyphosate resistance.     

Identification of a constitutive 45 kDa soluble protein associated with resistance to downy mildew in muskmelon (Cucumis melo L.), line PI 124111 F

Analysis by sodium dodecylsulphate-polyacrylamide gel electrophoresis of the soluble proteins extracted from muskmelon (Cucumis melo L.), inbred line PI 124111F (PI) with resistance to Pseudoperonospora cubensis (Berk, et Curt.) Rost, and two susceptible cvs, Hemed and AnanasYokneam revealed the presence of a unique 45 kDa protein (P45) in the resistant but not in the susceptible plants. Subcellular fractionation indicated that P45 is a cytoplasmic soluble protein. It was detected in leaves and cotyledons but not in stems or roots. F₁ hybrid plants (Hemed × PI) that displayed only a partial resistance against P. cubensis expressed P45 at an intermediate level, whereas plants of the inbred generations F₅, F₇ and F₁₀ that displayed a high degree of resistance, expressed P45 at a level similar to the parental PI. Back-cross progeny plants [(Hemed × PI) × Hemed] segregate 1:2:1 partially resistant: susceptible: highly susceptible to the disease. The partially resistant plants showed an intermediate level of P45 (similar to F₁) whereas the highly susceptible plants had no P45, thus indicating cosegregation of P45 with resistance. The resistance of PI to P. cubensis was found to decrease at a colonization temperature of 12 °C. ³⁵S-methionine in vivo protein labelling revealed a reduction in the intensity of the P45 band in plants incubated for 11 h at 12 °C. The application of P45 in breeding programs of muskmelon for downy mildew resistance and its possible involvement in resistance to P. cubensis are discussed.     

Inheritance of sulfonylurea resistance in Monochoria vaginalis

The inheritance of sulfonylurea (SU) resistance in Monochoria vaginalis was investigated based on the bensulfuron‐methyl response phenotypes of F₁ plants between SU‐resistant (R) and ‐susceptible (S) and segregation analysis in F₂ progenies. Differences of SU resistance between SU‐R biotypes and F₁ plants at the recommended field dose were also investigated by comparing shoot dry weight. All F₁ plants survived the treatment with 25 g a.i. ha^?1 bensulfuron‐methyl, one‐third of the recommended field dose, and showed similar responses to SU‐R plants. Conversely, all F₁ plants died or showed extreme necrosis at 225 g a.i. ha^?1, three times the recommended field dose, as SU‐S plants. F₂ plants were classified as either R or S phenotype. Segregation for resistance to bensulfuron‐methyl in F₂ families did not differ from the expected 3:1 (R:S) ratio at 25 g a.i. ha^?1. At 225 g a.i. ha^?1, the F₂ families segregated in a 1:3 (R:S) ratio. These results suggest that SU resistance in M. vaginalis is controlled by a single nuclear allele with resistance being dominant at low dose and susceptibility dominant at high dose. Moreover, F₁ plants died or were extremely injured after application of bensulfuron‐methyl at the recommended field dose, although SU‐R biotypes grew normally.     

Appearance of a biotype of the weed, Hordeum glaucum Steud., resistant to the herbicide paraquat

A biotype of the grass weed Hordeum glaucum Steud, infesting a site at Willaura, Victoria, Australia has resistance to paraquat. Application of the recommended rate of paraquat does not cause death of the resistant biotype at any stage of growth. The LD₅₀ for the resistant biotype is 6.4 kg active ingredient ha^?1 which is 250 times greater than for the normal susceptible biotype (25 g active ingredient ha^?1). Growth of the resistant biotype is checked by paraquat with a clear dosage response evident. The paraquat resistant biotype is also resistant to diquat but is normally affected by herbicides with different modes of action. In addition to continued foliage growth of the resistant plants after paraquat application, seeds of these plants can germinate and seedlings elongate in the dark whereas seeds of susceptible plants germinate but there is no further growth. This suggests that studies of the mechanism(s) conferring resistance will have to consider both the effect of paraquat on the chloroplast and a non-photosynthetic effect on cell growth. Un biotype de la mauvaise herbe Hordeum glaucum Steud, résistant à l'herbicide paraquat Un biotype de la graminée Hordeum glaucum Steud. à Willaura, Victoria, Australie, s'est montré résistant au paraquat. L'application de la dose préconisée de paraquat ne provoque pas la mort de ce biotype, quel qu'en soit le stade végétal. La LD₅₀ pour le biotype résistant est 6,4 kg matière active ha^?1, c'est-à-dire 250 fois plus grande que pour le biotype normal sensible (25 g matière active ha^?1). Le paraquat provoque chez le biotype résistant une inhibition de croissance qui se rapporte à la dose. Le biotype résistant au paraquat l'est également au diquat mais réagit normalement envers les herbicides à mode d'action différente. Non seulement la croissance foliaire continue normalement après une application de paraquat chez les plantes résistantes, mais les graines sont capables de germer et les jeunes plants de s'allonger à l'obscurité, tandis que les graines de plantes sensibles germent à l'obscurité mais ne croissent pas. II semble donc que les études des mécanismes qui produisent la résistance devront examiner l'influence du paraquat sur le chloroplaste ainsi qu'un effet nonphotosynthétique sur la croissance cellulaire. Ueber das Auftreten eines gegen Paraquat resistenten Biotyps von Hordeum glaucum Steud. Bei Willaura, Victoria (Australien) tritt ein gegen Paraquat resistenter Biotyp von Hordeum glaucum Steud. auf. Die Application der normalerweise empfohlenen Dosierung Paraquat tötet den resistenten Biotyp in keinem Wachstumsstadium ab. Die Ld₅₀ für den resistenten Typ beträgt 6,4 kg ai ha^?1; dies ist 250 mal mehr als beim normal sensiblen Typ (25 g ai ha^?1). Das Wachstum des resistenten Biotyps wird durch steigende Dosen von Paraquat beeinträchtigt. Der gegen Paraquat resistente Typ ist auch gegen Diquat unempfindlich, weist aber gegenüber Herbiziden mil anderen Wirkungsmechanismen die normale Empfindlichkeit auf. Resistente Pflanzen zeigen nach Paraquatbehandlung ein weitergehendes Blattwachstum. Ihre Samen keimen und die Sämlinge entwickeln sich im Dunkeln weiter, während die Samen sensibler Pflanzen zwar keimen, sich aber nicht weiterentwickeln. Diese Beobachtungen weisen darauf hin, dass bei Forschungen zur Aufklärung der Resistenzmechanismen, sowohl die Wirkung von Paraquat auf die Chloroplasten als auch einen nicht photosynthetiseh wirksamen Effekt auf das Zellwachstum berücksichtigen müssen.     

Structural and physiological studies of paraquat-resistant Conyza

Structural and physiological studies were conducted with a population of Conyza bonariensis (L.) Cronq. that segregates into paraquat-resistant and -susceptible biotypes. Leaf disks from resistant seedlings, when incubated on 10 μM paraquat for 24 hr, exhibited little difference from the control disks incubated on H₂O as measured by conductivity change, malondialdehyde formation, or plastid ultrastructure. Leaf disks from the susceptible seedlings incubated on 10^?5M paraquat for 24 hr were uniformly bleached, had elevated malondialdehyde content, and leaked more electrolytes than control disks. Plastids of the susceptible biotype incubated on 10^?5M paraquat for 24 hr were swollen organelles with gross rearrangements of the lamella system. Most of the chloroplasts from the central area of the leaf disk of the resistant biotype incubated on a paraquat solution were structurally normal. Swollen plastids and plastids with twisted lamellae were also noted, although much less frequently. Plastids from the edges of the leaf disks of paraquat-resistant clones were structurally similar to those found throughout the leaf disks in susceptible seedlings. When the size of the leaf disk was increased, paraquat-resistant clones exhibited more “resistance” toward paraquat compared to similar-sized leaf disks of the susceptible seedlings. These data are consistent with the hypothesis that the paraquat-resistant seedlings have an altered uptake and/or compartmentalization of paraquat. Superoxide dismutase isozymes, which were previously considered to be related to paraquat resistance in Conyza, did not correlate with the segregation of paraquat resistance in this population.     

Genetic control of sorghum resistance to leaf anthracnose

A study was carried out to investigate the inheritance of resistance to anthracnose, caused by Colletotrichum sublineolum, in sorghum. Crosses between resistant and susceptible parents and backcrosses between F₁ plants and the susceptible parents were carried out under field conditions. The F₁ generations and the segregant populations were evaluated under artificial inoculation conditions in the greenhouse. In the F₁ generation of all crosses with the respective isolates, all of the plants presented a resistance reaction except for the F₁ plants resulting from the BR009 × SC283 cross. In the F₂ generation, the frequencies of resistant and susceptible plants conformed to the hypothesis that one gene with two alleles controls host resistance, except in one cross. Out of the eight backcrosses, six presented segregation that corresponded to the hypothesis formulated. For most crosses, resistance was dominant, and the proportions of resistant and susceptible plants in the segregant populations conformed to the frequencies expected under the hypothesis of gene‐for‐gene resistance and dominant gene action.     

Inheritance of resistance to a new non‐steroidal ecdysone agonist,fufenozide, in the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND: The diamondback moth (DBM), Plutella xylostella (L.), is a cosmopolitan pest of cruciferous crops. Fufenozide, a novel non‐steroidal ecdysone agonist, exhibits good efficacy and plays an increasingly important role in the control of Lepidopterous pests in China. A laboratory strain of DBM was selected for resistance to fufenozide, and the genetic basis of resistance was studied. RESULTS: The resistant strain, selected under laboratory conditions, exhibited a higher level of resistance to fufenozide (302.8‐fold based on LC₅₀s) than the laboratory susceptible strain. Mortality data from the testing of F₁ progeny of reciprocal crosses of resistant and susceptible DBM indicated that resistance was autosomal and incompletely recessive with a degree of dominance of ?0.664. Chi‐square analysis from responses of a backcross of crossed F₁ progeny and the resistant strain and F₂ progeny were highly significant, suggesting that the resistance was probably controlled by more than one gene. The estimated realised heritability (h²) of fufenozide resistance was 0.08, indicating that diamondback moth may have a lower chance of developing resistance to fufenozide than other kinds of insecticide. CONCLUSION: The resistance of DBM to fufenozide might be autosomal and incompletely recessive, and the resistance is probably controlled by more than one gene. These results provide the basic information for pest management programmes. Copyright © 2009 Society of Chemical Industry     

Genetics of resistance to Phytophthora capsici in the Mexican pepper‘Line 291

In order to establish a genetic model of the resistance to Phytophthora cupsici in Capsicum annuum genotype‘Line 29′, three experiments were conducted which included, as well as‘Line 29′, the susceptible genotype‘Morron INIA 224’and several of its F₁, F₂, F₃ and backcrosses. Plants with 4–6 leaves were inoculated by irrigating the culture substrate with a zoospore suspension of isolate B 1. The F² test was applied to the segregating generations to test whether there were one, two, three or four genes involved in the resistance. Additivity and equal weight of all the genes in the final effect were assumed. The hypothesis that best explained the results obtained was the one that assumed three genes in‘Line 29′; at least four alleles had to be present in any genotype for it to behave as resistant. The possible influence of isolate aggressiveness and inoculation method on the results is discussed.     

Characterisation of spinosad resistance in the housefly Musca domestica (Diptera: Muscidae)

BACKGROUND: Spinosad, a relatively new, effective and safe pesticide, has been widely used in pest control over the last 10 years. However, different levels of resistance to this insecticide have developed in some insects worldwide. RESULTS: After continuous selection for 27 generations, a strain (SpRR) of the housefly developed 247‐fold resistance to spinosad compared with the laboratory susceptible strain (CSS). The estimated realised heritability (h²) of spinosad resistance was 0.14. There was no significant difference in the LD₅₀ values and slopes between reciprocal progenies F₁ and F₁′, and values of 0.33 (F₁) and 0.30 (F₁′) were obtained for the degree of dominance. Chi‐square analysis from responses of self‐bred (F₂) and backcrosses (BC₁ and BC₂) were highly significant, suggesting that the resistance was probably controlled by more than one gene. Synergists piperonyl butoxide (PBO), diethyl maleate (DEM) and S,S,S‐tributyl phosphorotrithioate (DEF) affected the toxicity of spinosad at a low level, and demonstrated that metabolic‐mediated detoxification was not an important factor in conferring resistance to spinosad in the SpRR strain. CONCLUSION: It was concluded that spinosad resistance in the housefly was autosomal and incompletely dominant, and the resistance was probably controlled by more than one gene. These results provide the basic information for designing successful management programmes for the control of houseflies. Copyright © 2011 Society of Chemical Industry     

Resistance to quinclorac and ALS-inhibitor herbicides in Galium spurium is conferred by two distinct genes

Classical Mendelian experiments were conducted to determine the genetics and inheritance of quinclorac and acetolactate synthase (ALS)‐inhibitor resistance in a biotype of Galium spurium. Plants were screened with the formulated product of either quinclorac or the ALS‐inhibitor, thifensulfuron, at the field dose of 125 or 6 g active ingredient (a.i.) ha^?1 respectively. Segregation in the F₂ generation indicated that quinclorac resistance was a single, recessive nuclear trait, based on a 1 : 3 segregation ratio [resistant : susceptible (R : S)]. Resistance to ALS inhibitors was due to a single, dominant nuclear trait, segregating in the F₂ generation in a 3 : 1 ratio (R : S). The genetic models were confirmed by herbicide screens of F₁ and backcrosses between the F₁ and the S parent. F₂ plants that survived quinclorac treatment set seed and the resulting F₃ progeny were screened with either herbicide. Quinclorac‐treated F₃ plants segregated in a 1 : 0 ratio (R : S), hence F₂ progenitors were homozygous for quinclorac resistance. In contrast, F₃ progeny segregated into three ratios: 1 : 0, 3 : 1 and 0 : 1 (R : S) in response to ALS‐inhibitor treatment. This segregation pattern indicates that their F₂ parents were either homozygous or heterozygous for ALS‐inhibitor resistance. Therefore, there were clearly two distinct resistance mechanisms encoded by two genes that were not tightly linked as demonstrated by segregation patterns of the F₃.     

广东省水稻田稗对五氟磺草胺的抗性分析

为明确广东省水稻田杂草稗Echinochloa crus-galli对五氟磺草胺的抗性现状及其可能的抗性机理,采用整株剂量反应法测定不同地区稗种群对五氟磺草胺的抗性水平,对不同稗种群的乙酰乳酸合成酶（acetolactate synthase,ALS）基因片段进行扩增测序,分析细胞色素P450酶（cytochrome P450 monooxygenase,P450）和谷胱甘肽-S-转移酶（glutathione-S-transferase,GST）抑制剂胡椒基丁醚（piperonylbutoxide,PBO）和4-氯-7-硝基-2,1,3-苯并氧杂噁二唑（4-chloro-7-nitro-1,2,3-benzoxadiazole,NBD-Cl）对不同稗种群抗性水平的影响,并对替代药剂进行筛选。结果显示,广东省水稻田多数稗种群对五氟磺草胺仍表现敏感,但采自湛江市的1个种群BC-7对五氟磺草胺产生了抗性,抗性倍数达6.5倍。与敏感种群BC-2相比,BC-7种群并未发生已报道的ALS靶标抗性相关突变。PBO和NBD-Cl均可显著提高BC-7种群对五氟磺草胺的敏感性,其干重抑制中量GR₅₀由31.1 g/hm²分别降为11.0 g/hm²和24.7 g/hm²。BC-7种群对氰氟草酯和噁唑酰草胺仍较敏感,但对二氯喹啉酸和双草醚产生了抗性。表明P450和GST介导的代谢抗性是稗BC-7种群产生抗性的重要原因,氰氟草酯和噁唑酰草胺适用于治理该抗性种群。     

大麦抗条纹病基因的定位分析

为发掘大麦中抗条纹病的新基因,采用三明治法通过人工接种大麦条纹病菌Pyrenophora graminea强致病力菌株QWC对甘啤2号(免疫)与Alexis(高感)杂交F_1代及F_2代分离群体进行抗性遗传分析,利用群体分离分析法鉴定与抗病基因连锁的SSR标记,并通过QTL IciMapping软件构建遗传连锁图谱完成对抗病基因的定位。结果显示,甘啤2号与Alexis杂交F_1代对大麦条纹病菌强致病力菌株QWC表现为免疫,F_2代表现3∶1抗感分离,表明甘啤2号对菌株QWC的抗性由1个显性抗性基因控制,将该抗病基因暂命名为Rdg3;该基因位于大麦7H染色体上的SSR标记Bmag206和Bmag7之间,与二者的遗传距离分别为1.78 cM和2.86 cM。经与已定位于7H染色体上的抗病基因比较,发现Rdg3是一个新的抗条纹病基因,可作为大麦抗病育种的新种质资源。     

小偃6号成株期高温抗条锈性遗传分析

为揭示小偃6号抗病机制和培育持久抗病品种,采用常规杂交分析方法,在小麦抽穗期利用小麦条锈菌小种CYR30、CYR32和Su11-4对小偃6号、铭贤169及其杂交F1、F2、F2∶3接种,平均气温达到21℃时对小偃6号进行了抗条锈性调查和遗传分析。结果显示,接种CYR30、CYR32时,F1代表现高感,F2代群体中抗感分离比例符合1 R∶15 S的理论比例。接种Su11-4时,F1代表现高抗,F2代群体中抗感分离比例符合3R∶1S的理论比例。研究表明小偃6号对CYR30、CYR32的抗病性均由2对隐性基因累加作用控制,对Su11-4的抗病性由1对显性基因控制。     

Further studies on the genetics of the carboxylesterase regulatory system involved in resistance to organophosphorus insecticides in Myzus persicae (Sulzer)

Levels of carboxylesterase activity in F₁ clones of Myzus persicae, obtained by crossing sexuales from a resistant, high esterase clone with those from a susceptible, low esterase clone, fell into two distinct groups intermediate between the levels of carboxylesterase in the parent clones. When sexuales of F₁ clones of the lower of these two intermediate levels of carboxylesterase activity were crossed, segregation ratios in the F₂ generation indicated that this lower intermediate activity level (about 0.4 μmol mg^?1 h^?1). which is about twice the level in susceptible clones, is due to mutation at a single regulatory locus. The results obtained with backcrosses, between sexuales of an F₁ clone having the higher intermediate level of carboxylesterase activity and a parent susceptible, low esterase clone, suggest that a second locus may be involved in the expression of higher levels of esterase activity.     

Comparison of screening methods to evaluate the response of St. Augustine grass to Magnaporthe oryzae

The objective of this study was to develop a reliable and high throughput screening method to evaluate the response of St. Augustine grass (Stenotaphrum secundatum) genotypes to the grey leaf spot (GLS) caused by Magnaporthe oryzae infection. Whole plant, detached stolon and detached leaf assays under growth chamber conditions were compared to field conditions on eight commercial and nine advanced breeding lines of St. Augustine grass. Disease was assessed using two variables, lesion size (LS) and overall plant disease severity (SEV). LS and SEV were highly correlated for field and growth chamber screening methods using the whole plant assay (LS r² = 0·79; SEV r² = 0·83; P ≤ 0·001), the detached stolon assay (LS r² = 0·75; SEV r² = 0·72; P ≤ 0·001), and the detached leaf assay (LS r² = 0·46; SEV r² = 0·60; P ≤ 0·001). Genotypic variation for resistance in 17 St. Augustine grass genotypes was identified using all screening methods for LS (P < 0·05) and SEV (P < 0·05). The rank‐sum method was used to classify St. Augustine grass genotypes into highly resistant (HR), resistant (R), moderately resistant (MR), moderately susceptible (MS), susceptible (S) and highly susceptible (HS) classes based on the rank‐sum values of LS and SEV. Two introduced African polyploids used as parents, and two F₁ interploid progeny obtained using an in vitro embryo rescue technique, were classified as highly resistant (HR), or resistant (R), across all screening methods.     

Paraquat resistance in a biotype of Vulpia bromoides (L.) S. F. Gray

A biotype of Vulpia bromoides from a lucerne field in Elmhurst, Victoria, Australia was shown to be resistant to paraquat in pot trials. Application of paraquat at 50 g a.i. ha^?1 killed all of the plants of a susceptible Vulpia bromoides biotype but only 6% of the resistant biotype. The LD₅₀ for paraquat of the resistant biotype was five- to sixfold higher than for the susceptible biotype. The resistant biotype was also resistant to the bipyridyl herbicide diquat, but was susceptible to glyphosate and metribuzin. Application of 100 g a.i. ha^?1 paraquat at anthesis completely suppressed seed set of the susceptible biotype and reduced that of the resistant biotype by 95%. Seed set by the paraquat-treated resistant biotype, however, showed little reduction in germination. This is the fourth species to have been found to be resistant to bipyridyl herbicides in this field, the others being Hordeum glaucum, H. leporinum and Arctotheca calendula. Résistance au paraquat d'un biotype de Vulpia bromoides (L.) S. F. Gray Un biotype de Vulpia bromoides issu d'un champ de luzerne à Elmhurst, Victoria, Australie s'est révélé résistant au paraquat lors d'essais en pots. Des traitements au paraquat 50 g m.a. ha^?1 détruisaient toutes les plantes d'un biotype sensible de V. bromoides mais seulement 6% du biotype résistant. La DLV₅₀ du paraquat pour ce biotype était 5 à 6 fois plus élevée que pour le biotype sensible. Le biotype résistant l'était aussi à l'herbicide bipyridyle diquat, mais était sensible au glyphosate et à la métribuzine. Des traitements au paraquat 100 g m.a. ha^?1 au stade anthèse supprimaient complètement la production de graines du biotype sensible et réduisait de 95% celle du biotype résistant. Cependant, le pouvoir germinatif des graines issues du biotype résistant traité, n'était que peu réduit. Après Hordeum glaucum, Hordeum leporinum et Arctotheca calendula, c'est la quatrième espèce trouvée dans ce même champ résistante aux herbicides bipyridyles. Paraquatresistenz eines Biotyps von Vulpia bromoides (L.) S. F. Gray Ein Biotyp von Vulpia bromoides von einem Luzernefeld in Elmhurst, Victoria, Australien, erwies sich in Topfversuchen als paraquatresistent. Mit 50 g AS ha^?1 wurden Pflanzen eines empfindlichen Biotyps abgetötet, jedoch nur 6% des resistenten. Die LD₅₀ des resistenten Biotyps für paraquat war 5- bis 6mal höher als die des empfindlichen Biotyps. Der resistente Biotype war auch gegenüber dem Bipyridylherbizid Deiquat résistent, gegenüber Glyphosat und Metribuzin jedoch empfindlich. Nach Anwendung von 100 g AS ha^?1 Paraquat vor der Blüte bildeten sich bei dem empfindlichen Biotyp keine Samen aus, bei dem resistenten waren sie um 95% vermindert; die dennoch gebildeten Samen keimten etwas weniger. Dies ist die vierte Pflanzenart, bei der eine Resistenz gegenüber Bipyridylherbiziden beobachtet wurde, die anderen sind Hordeum glaucum. Hordeum leporinum und Arctotheca calendula.     

Genetic Analysis of the Relationship between the Browning Reaction and Bacterial Blight Resistance Gene Xa3 in Rice

The relationship between bacterial blight resistance gene Xa3 and browning reaction was genetically analyzed using F₂ plants from the cross of rice cultivar Kuntulan with Kinmaze. Kuntulan harbors resistance Xa3 and developes a browning reaction to avirulent races of Xanthomonas oryzae pv. oryzae, whereas Kinmaze has a typical susceptible reaction to all known Japanese races of X. o. pv. oryzae. The F₂ plants were tested for their resistance to avirulent race II strain of X. o. pv. oryzae and the development of browning. Of 337 F₂ plants tested, 251 had resistance to the strain. In all the resistant plants, a browning reaction developed around the point of inoculation. The remaining 86 had a susceptible reaction to the strain without a browning reaction. The F₂ population of Kuntulan × Kinmaze had a clear-cut segregation ratio of 3R : 1S. These facts led to the conclusion that the browning reaction is a pleiotropic effect of Xa3. Received 29 January 2001/ Accepted in revised form 24 April 2001     

Leaf chlorophyll fluorescence discriminates herbicide resistance in Echinochloa species

Timely detection of herbicide resistance at an early stage of crop cultivation is essential to help farmers find alternative solutions to manage herbicide resistance in their fields. In this study, maximum quantum yield of PS II [F_v/F_m = (F_m – F_o)/F_m] was measured at the 4–5 leaf stage to discriminate between herbicide‐resistant and susceptible biotypes of Echinochloa species. The differences in F_v/F_m between herbicide‐resistant and susceptible Echinochloa spp. were consistent with the whole‐plant assay based on I₅₀ (herbicide doses causing a 50% inhibition of F_v/F_m) and GR₅₀ (herbicide doses causing a 50% reduction in plant fresh weight) values and R/S ratios (herbicide resistance index), regardless of the mode of action of the tested herbicides. A PS II inhibitor caused the fastest inhibition of F_v/F_m, compared with ACCase and ALS inhibitors, after herbicide treatment. The required time for discrimination between herbicide‐resistant and susceptible Echinochloa spp. was 64 h after PS II inhibitor treatment, much shorter than those of ACCase and ALS inhibitor‐treated plants, which required 168 and 192 h respectively. The leaf chlorophyll fluorescence assay provided reliable diagnostics of herbicide resistance in Echinochloa spp. with significant time savings and convenient measurement in field conditions compared with the conventional whole‐plant assay.