Fusaric acid: phytotoxicity and in vitro production by Fusarium oxysporum f.sp. lilii,the causal agent of basal rot in lilies

The production of phytotoxins byFusarium oxysporum f.sp.lilii, a pathogen causing bulb and scale rot in lilies, was investigated. To determine the toxic activity of culture filtrate, a bioassay with in vitro grown scale bulblets or with callus was set up. The fungus produces toxic components in different culture media. The highest toxicity was observed in Czapek Dox medium. HPLC and GC/MS analyses revealed the presence of fusaric acid at toxic concentrations in this medium. The production of fusaric acid in time coincides with the increase of toxic activity in the culture filtrate. It is concluded that at least part of this toxicity is due to fusaric acid.     

Increasing control reliability of <Emphasis Type="Italic">Orobanche cumana </Emphasis>through integration of a biocontrol agent with a resistance-inducing chemical

Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai is a potential biocontrol agent against the root-parasitic weed Orobanche cumana. In pot experiments with different sunflower cultivars, the application of F. oxysporum was combined with a treatment of BTH (Benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester), a product known to induce resistance against O. cumana in sunflower. The combined treatments resulted in highly reliable control and sometimes in increased control level compared to the Fusarium treatment alone. In laboratory experiments, no enhancing effect of BTH on virulence and growth of the fungus was observed. Future experiments should further investigate the basic mechanisms of the effect achieved by combining the two control strategies as well as the transfer of this innovative control approach into field experiments.     

Short-term Cover Crop Decomposition in Organic and Conventional Soils: Characterization of Soil C, N, Microbial and Plant Pathogen Dynamics

Stages of oat–vetch cover crop decomposition were characterized over time in terms of carbon and nitrogen cycling, microbial activity and damping-off pathogen dynamics in organically and conventionally managed soils in a field and a controlled incubation experiment. A measurement of relative growth consisting of radial growth of a fungal colony over non-sterilized soil divided by that over sterilized soil was used as an assay of suppressiveness. No differences in relative growth of Pythium aphanidermatum and Rhizoctonia solani were detected between organic and conventionally managed soils amended with cover crop residue. Significant effects of cover crop decomposition stage on the relative growth of both pathogens were obtained. Relative growth of P. aphanidermatum was highest just after incorporation and decreased 3 weeks after incorporation. Relative growth of R. solani was highest about 20 days after incorporation, and decreased 2 weeks later in the organic system, but continued to increase in the conventional system. In both experiments, the N or C content, C:N ratio or dry weight of retrieved debris were significantly correlated with relative growth of P. aphanidermatum. Relative growth of R. solani was significantly correlated with the C:N ratio of soil or the C or N content of debris. Microbial activity was not consistently associated with relative growth of either pathogen.     

Influence of caffeine on the survival of leaf-cutting ants Atta sexdens rubropilosa and in vitro growth of their mutualistic fungus

BACKGROUND: Leaf‐cutting ants collect plant fresh material for the cultivation of their mutualistic fungus. Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) cause great economic losses through their foraging activity, mainly in agriculture. The main control method is the application of granulated toxic baits incorporated with an active ingredient (AI). The present goal is to evaluate the effect of caffeine on in vitro growth of the mutualistic fungus and on the survival of the leaf‐cutting ants, aiming to verify the potential toxicity of this secondary metabolite over these organisms. RESULTS: Three distinct patterns of fungal growth correlated with caffeine concentration were observed: (1) no effect (0.01% caffeine); (2) intermediate growth reduction (0.05% caffeine); (3) drastic growth reduction (0.10 and 0.50% caffeine). The highest caffeine concentration causes fungus death in the first week. As for insect survival, caffeine does not seem to exert any effect. The treatments with diet containing caffeine showed similar values of M50, irrespective of caffeine concentration. CONCLUSION: As caffeine was shown to reduce growth of the mutualistic fungus of Atta sexdens rubropilosa, but with no conclusive effect on insect survival, a hypothetical explanation for the selection of different Coffea species by this leaf‐cutting ant species might be associated with caffeine toxicity to the fungus. Copyright © 2011 Society of Chemical Industry     

Nodulation during vegetative growth of soybean stage does not affect the susceptibility to red crown rot caused by Calonectria ilicicola

Soybean cultivar Enrei and its derivative lines, non-nodulating En1282 and supernodulating Sakukei 4, were grown in an experiment field naturally infested with the red crown rot fungus, Calonectria ilicicola, to determine whether nodulation elicits the disease. Infection frequency by the fungus invariably increased with time and reached about 100% 6 weeks after sowing. Disease severity was invariably slight until 8 weeks after sowing. At harvest, however, disease severity was lowest in En1282 and highest in Sakukei 4. Enrei was intermediately susceptible. Sakukei 4 produced many more nodules than Enrei, while En1282 completely failed to nodulate. For three other pairs of nodulating and non-nodulating isogenic lines, all non-nodulating lines had lower severity than their nodulating counterparts at harvest. Pot experiments with Enrei and its derivatives revealed that inoculation with Bradyrhizobium sp. did not affect disease severity during the vegetative stage of plant growth, i.e., 6 weeks after sowing. These results suggested that the production of nodules in the vegetative stage is not, at least directly, related to susceptibility to the disease, but physiologic changes after anthesis vary depending on the nodulation traits in the respective soybean lines, resulting in different levels of susceptibility to red crown rot.     

Factors affecting the efficacy of Orobanche cumana chemical control in sunflower

Broomrapes ( Orobanche spp.) are root parasites, causing severe damage to vegetable and field crops. Their early in situ detection for efficient control is crucial but difficult, because of their sub-surface development. Minirhizotron technology enables the in situ observation of host–parasite interactions. The initial underground development of Orobanche cumana on sunflower roots and its control with imazapic were investigated. Imazapic (2.4 g active ingredient ha⁻¹) was applied post-emergence on sunflower at the eight-true-leaf stage, when O. cumana attachments were first observed. No viable or new attachments were detected on roots of the treated sunflower after herbicide application. However, within the same time frame, the already existing O. cumana attachments in the non-treated controls continued to develop and new attachments appeared. Orobanche cumana shoot emergence was correlated with growing day-degrees (GDD, d °C). This correlation was quantified by a four-parameter logistic equation. Control efficacy was affected by depth and number of parasite attachments per minirhizotron camera frame: it was highest in the topmost layer, and decreased with depth and number of attachments. The results obtained in this study emphasise the need to develop a decision support system based on GDD that should be validated under long-term field conditions.     

Prohexadione-calcium induces sunflower (Helianthus annuus) resistance against the root parasitic weed Orobanche cumana

Prohexadione-calcium (PHDC) is a plant growth retardant that inhibits gibberellin biosynthesis and transiently alters the spectrum of flavonoids and their phenolic precursors. In this study, root chamber and pot experiments were conducted to evaluate the effects of PHDC on Orobanche cumana seed germination and induction of sunflower resistance to this root parasitic weed. Root chamber experiments indicated that PHDC did not interfere with the progress of Orobanche seed germination, but retarded O. cumana tubercle formation and development. In pot experiments, control of O. cumana by PHDC depended on its dose, method of application and sunflower cultivar. In sunflower cv. HA89, PHDC at 10 mg LS⁻¹ (litre soil) as two drenches or at 1 m m as two foliar sprays significantly reduced the total number and dry matter of O. cumana without influencing flower, leaf and root development. In sunflower cv. Albena, PHDC at 20 and 30 mg LS⁻¹, but not at 10 mg LS⁻¹, as two drenches significantly reduced O. cumana infection. Sunflower cv. HA89 was less susceptible to O. cumana and more inducible by PHDC than sunflower cv. Albena. The biochemical analysis of root extracts revealed a significantly higher accumulation of free phenolics in sunflower cv. HA89 after PHDC soil drench, but not in Albena. No significant lignification was observed after PHDC treatments. The results suggest that PHDC reduces O. cumana infection in sunflower by inducing host resistance, not by directly interfering with the parasite. Free phenolics play an important role in sunflower response to the parasite.     

Wheat/faba bean intercropping improves physiological and structural resistance of faba bean to fusaric acid stress

Fusarium oxysporum f. sp. fabae is the causal agent of fusarium wilt. Fusaric acid (FA), produced by F. oxysporum, plays an important role in the occurrence of disease, and intercropping is an effective measure for control of disease and for improving host resistance in plants. The objective of this study was to investigate the physiological and biochemical responses, and mechanisms of tissue structure resistance, of intercropped faba beans following exposure to different concentrations of FA. Results demonstrated that intercropping reduced the occurrence of fusarium wilt, and improved faba bean growth and yield. In addition, wheat intercropping significantly reduced red ink absorption of faba bean (33.2%), increased water content (3.1%), and increased activity of the root antioxidant enzymes peroxidase (POD) and catalase (CAT) (26.3% and 2.2.%, respectively). Furthermore, increased lignin content and callose deposition in plant vessels were observed (12.5% and 42.7%, respectively) when subjected to the highest concentration of FA stress (200 mg/L). Intercropping resulted in more intact root cell morphology, increased occurrence of intracellular vacuoles, increased cell wall thickness, and an increase in the number of mitochondria and rough endoplasmic reticulum. Intercropping alleviated the wilting effect of FA on faba bean via enhanced physiological, biochemical, and tissue structure resistance of faba bean root.     

The effectiveness of eleven sterol biosynthesis-inhibiting fungicides against the take-all fungus,Gaeumannomyces graminis var. tritici,in relation to their physical properties

Eleven sterol biosynthesis-inhibiting fungicides were compared in experiments to determine the physico-chemical properties required for most effective control of take-all by soil treatment. All were active in agar culture against an isolate of the pathogen which causes take-all, Gaeumannomyces grammis var. tritici, with prochloraz being the most toxic (EC₅₀ 0.02 μg ml^?1) and PP 969 the least (EC₅₀ 0.44 μg ml^?1). Penconazole and PP 969 had vapour activity against the fungus in further bioassays on agar. In soil in pots, the most strongly lipophilic compound, buthiobate, was ineffective against take-all in wheat; triadimenol was most effective and, like flutriafol, nuarimol and PP 969, retained some effectiveness after 12 weeks in soil. PP 969, unlike penconazole or nuarimol, was effective in soil treated unevenly by mixing the fungicides in layers. PP 969 is relatively polar, and it is suggested that this property, allowing redistribution in soil water rather than as vapour, outweighed its poor intrinsic toxicity. The ideal soil-treatment fungicide should therefore be polar and also have good intrinsic activity and moderate persistence. None of the compounds tested had all these properties.     

Biocontrol traits of two Paenibacillus polymyxa strains SQR‐21 and WR‐2 in response to fusaric acid,a phytotoxin produced by Fusarium species

The aim of the present study was to investigate the effects of the phytotoxin fusaric acid (FA) on the biocontrol traits of two biocontrol strains Paenibacillus polymyxa WR‐2 and SQR‐21. The results showed that the growth of both WR‐2 and SQR‐21 decreased with increasing FA concentration, and at 70 and 80 μg mL^?1 FA, respectively, the strains were unable to grow. The biocontrol traits of both strains were negatively affected by FA concentration higher than 2·5 μg mL^?1. However, at 2·5 μg mL^?1 FA, biofilm formation and root colonization were not affected and there was even a positive effect on the production of spores and hydrolytic enzymes (protease and β‐l,3‐glucanase). The production of fusaricidin‐type antifungal compounds was increased with an increase in FA concentration up to 50 and 60 μg mL^?1 for WR‐2 and SQR‐21, respectively. The production of antifungal volatile organic compounds by WR‐2 and SQR‐21 was increased only at 2·5 μg mL^?1 FA. The effect of FA on the overall metabolic activity of WR‐2 and SQR‐21 was also determined. This study will help to understand the response of P. polymyxa strains to FA and will help to improve their biocontrol efficiency.     

Identification,characterisation and discriminatory power of microsatellite markers in the parasitic weed Orobanche cumana

Orobanche cumana is an obligate root parasite of sunflower. It represents a major agricultural problem in many countries of southern and eastern Europe. Information on O. cumana population genetics, structure and dynamics is scarce, particularly due to the lack of suitable molecular markers for such studies. The objective of this study was to identify and characterise simple sequence repeat (SSR) markers for O. cumana. Four thousand two hundred SSR‐containing candidate sequences were obtained from O. cumana using next‐generation sequencing, from which 298 SSR primer pairs were designed and 217 of them used for validation. Seventy nine SSR primers produced reproducible, high quality amplicons of the expected size that were polymorphic among 18 O. cumana populations from different geographical locations and hosts (sunflower, wild hosts from the Compositae family). The number of alleles per locus ranged from 2 to 10, with an average polymorphism information content value of 0.37. The O. cumana SSR markers were highly transferable to the closely related species Orobanche cernua. SSR markers showed high resolving power; UPGMA cluster analysis allowed proper classification of Orobanche spp. samples into species (O. cumana and O. cernua), geographical origin and host. The functional SSR markers reported in this study constitute a valuable tool for genetic analyses in O. cumana and related species and will contribute insights into the biology and genetics of this parasitic weed.     

我国向日葵列当发生危害现状调查

向日葵列当是危害我国向日葵最严重的杂草。为明确我国向日葵田列当的发生危害情况及防治现状,采用对角线5点取样法对新疆、内蒙古、吉林和河北等主要向日葵种植区进行调查,对向日葵列当的寄生率和寄生强度等数据进行分析。结果表明,向日葵列当在向日葵产区广泛分布,严重危害向日葵的生产,其对食葵的寄生率高于油葵,对抗性品种的寄生率较低。在所有调查地区中内蒙古地区向日葵列当发生最严重,寄生率高达100%,寄生强度达到38.5,单株寄生数量最高,达118株;新疆地区的向日葵列当寄生率居中,吉林、河北向日葵列当发生相对较轻。通过实地调研结合文献报道,对目前国内外向日葵列当的研究进展进行了综述,研究结果为指导向日葵列当防治提供参考。     

辽细辛提取物对灰葡萄孢菌的抑制效果

采用生长速率法和孢子萌发法测定了辽细辛根的不同溶剂(石油醚、氯仿、乙酸乙酯、乙醇)粗提取物和精油对引起黄瓜灰霉病的灰葡萄孢菌菌丝生长和孢子萌发的作用。结果表明,细辛不同溶剂提取物和精油对灰葡萄孢菌的菌丝生长和孢子萌发均有一定的抑制作用,且对孢子萌发的抑制效果好于对其菌丝生长的抑制效果;石油醚提取物和精油的抑菌效果较好,对菌丝生长的EC₅₀分别为177.44 mg/L和159.98 mg/L,对孢子萌发的EC₅₀分别为173.23 mg/L和125.29 mg/L;试验还显示细辛所含的主要抑菌活性成分易被极性小的有机溶剂所提取。     

Lipoxygenase Metabolites of α-linolenic Acid in the Development of Resistance in Pigeonpea, Cajanus cajan (L.) Millsp, Seedlings Against Fusarium udum Infection

Lipoxygenase (LOX) activity was measured in germinating pigeonpea Cajanus cajan seedlings, resistant (ICP-8863) and susceptible (ICP-2376) to wilt fungus, before and after infection with Fusarium udum. LOX activity was significantly higher in the resistant than in the susceptible cultivars of pigeonpea and was enhanced further in response to infection with Fusarium udum. This increase in LOX activity in the resistant cultivars of pigeonpea appears to be due to the induction of lipoxygenase isozymes in response to infection. Analysis of the endogenous LOX metabolites in pigeonpea seedlings revealed the predominant formation of 13-hydroperoxyoctadecadienoic acid (13-HPODE) in healthy seedlings and 13-hydroperoxyoctadecatrienoic acid (13-HPOTrE) in infected seedlings. Further studies on the effects of LOX metabolites on the growth and multiplication of Fusarium udum showed that HPOTrEs, LOX metabolites of -linolenic acid, are more anti-fungal compared to HPODEs, LOX metabolites of linoleic acid.     

室内条件下向日葵列当和弯管列当在三种不同寄主上寄生能力的比较

以向日葵列当Orobanche cumana Wallr.和弯管列当O.cernua Loefl.为研究对象,利用已有的室内寄生体系来研究两种列当在向日葵、烟草、番茄3种寄主上的寄生能力。结果表明,向日葵列当在室内条件下不仅能够寄生在向日葵上,同时也可以在烟草与番茄上寄生;但其寄生效率在上述不同的寄主之间存在显著差异,而在相同寄主的不同品系间没有差异。交互侵染的结果表明,在寄主番茄上,弯管列当平均每株寄生的瘤结数量为16.3个,向日葵列当只有2.5个;在寄主向日葵上,向日葵列当的平均寄生瘤结数量为25.2个,弯管列当为27.6个,预示着弯管列当在番茄上寄生效率均显著高于向日葵列当,而在寄主向日葵上,二者寄生效率差异不显著,均能高效寄生在向日葵根系上。上述研究结果将为向日葵列当和弯管列当发生严重地区作物轮作对象的选择提供理论依据。     

Growth,population dynamics,and diversity of <Emphasis Type="Italic">Fusarium equiseti</Emphasis> in ginseng fields

Fusarium equiseti is prevalent in ginseng soil, straw mulch and in ginseng root tissues and is the cause of a root surface discolouration on ginseng grown in British Columbia. Population levels of the fungus in ginseng fields ranged from 3.8 × 10³ cfu g⁻¹ soil to 1.4 × 10⁴ cfu g⁻¹ soil and were highest at 0–5 cm soil depths compared to 10–15 cm. Soil population levels were negatively correlated with S content in soil and positively correlated with Zn levels. Barley or wheat straw added to soil significantly increased population levels under laboratory conditions. Mycelial growth in culture was highest at 26–30°C and at pH 7.2–7.8. Samples of flowers and berries, and harvested seed, contained DNA of F. equiseti detected using a Fusarium-specific DNA array and the fungus was isolated from these tissues on agar medium. A high degree of genetic variation in the EF-1 alpha gene sequence was present among 52 isolates of F. equiseti which originated from ginseng fields. At least seven clades were identified. Inoculum dispersal from straw mulch used in ginseng gardens can result in seed contamination by the fungus. In addition, fungal growth near the soil surface under warm summer conditions can result in infection and crown discolouration of ginseng roots.     

锰消除镰刀菌酸对枯草芽胞杆菌R31生物被膜形成的抑制

为了揭示芽胞杆菌类生防因子和镰刀菌病害的互作方式,对镰刀菌酸抑制枯草芽胞杆菌生物被膜形成及其消除开展了研究。首先利用24孔细胞培养板建立了镰刀菌酸抑制枯草芽胞杆菌R31生物被膜形成的生物测定体系,并筛选出抑制R31生物被膜形成所需的最低镰刀菌酸浓度。测定了在该镰刀菌酸浓度处理下的R31生长曲线,并利用显微镜观察了镰刀菌酸处理和对照在振荡培养和静置培养下的菌体形态。然后测定了不同浓度MnSO₄添加消除镰刀菌酸抑制R31生物被膜形成的效果,并用高效液相色谱测定了各处理镰刀菌酸的残留量。结果显示,以24孔细胞培养板为培养容器,以BGM1为培养基的生物测定系统中,显著抑制R31生物被膜形成的最低镰刀菌酸用量为9 μg/mL;该浓度的镰刀菌酸抑制了静置培养的R31菌体形成网状结构和漂浮在液面,并抑制了振荡培养的R31早期菌体增殖。但共培养体系中添加MnSO₄可以恢复R31的生物被膜形成,其中200 μg/mL的硫酸锰不仅能消除毒素抑制,还可显著促进R31的生物被膜形成。镰刀菌酸可能通过影响R31基质产生细胞的分化而抑制其生物被膜形成,硫酸锰可以作为钝化剂缓解镰刀菌酸对R31生物被膜形成的抑制。     

Dimethoxypyrimidines as Novel Herbicides. Part 2. Synthesis and Herbicidal Activity of O-Pyrimidinylsalicylates and Analogues

A new series of the O-pyrimidinylsalicylates was synthesized and their herbicidal activity was examined. Some of these compounds showed very strong herbicidal activity under pre- and post-emergent treatment conditions against various kinds of grass and broadleaf weeds. Among these compounds, O-(4, 6-dimethoxypyrimidin-2-yl) salicylic acid and its methyl ester were found to exhibit the highest activity. The herbicidal symptoms observed after the treatments included early cessation of plant growth followed by chlorosis, necrosis and plant death. The symptoms were similar to those caused by sulfonylureas and imidazolinones, which inhibit branched-chain amino acid biosynthesis.     

Inhibition of Echinochloa crus-galli var. frumentacea seedling root elongation by chiral 1, 3, 5-triazines in the dark

2-z-Substituted benzylamino-4-substituted-amino-6-chloro-1,3, 5-triazines are herbicidal compounds showing leaf-burning and/or growth inhibition with concomitant greening and stunting. Effects of chiral 1,3,5-triazine compounds in a light-independent seedling root elongation test with Echinochloa crus-galli var. frumentacea Wight demonstrated an interaction between chirality and root growth inhibition. The test compounds inhibited root growth, and this inhibition was due to interference with a system or systems other than photosynthesis. 4-(R)-sec-butylamino-2-(α,α-dimethylbenzyl)amino-6-chloro-1,3, 5-triazine showed the highest inhibitory activity, and 4-methylamino-2-(R)-a-methylbenzylamino-6-chloro-1,3,5-triazine was second. The chiral requirement for a strong inhibition of root growth was the (R)-configuration, contrasting with the requirement for the (S)-configuration for an inhibition of photosystem II.     

Fusarium verticillioides as a new pathogen of the parasitic weed Orobanche spp.

A strain of Fusarium verticillioides was isolated from the tubercles of the parasitic weed Orobanche cumana in Israel. The pathogenicity was tested in polyethylene bags on O. cumana, O. crenata, O. aegyptiaca and O. ramosa and in pots on O. cumana and O. crenata. F. verticillioides was highly pathogenic to O. aegyptiaca, O. ramosa and O. cumana in the polyethylene bags. In pots, the fungus caused wilting and necrotic areas on flowering shoots of O. cumana, but did not cause disease symptoms on O. crenata. F. verticillioides grown on liquid Czapek growth medium produced a phytotoxic metabolite, which in leaf-puncture bioassay caused large necrotic areas on Orobanche shoots and on leaves of various crops. An extract of the fungal growth medium caused complete mortality of O. cumana and O. aegyptiaca seedlings in vitro. The toxic metabolite was isolated and identified by spectroscopic methods as fusaric acid. The identity of the compound was confirmed by conversion into the corresponding methyl ester, and by TLC comparison against authentic fusaric acid. No other phytotoxic metabolites could be detected in the growth medium extracts.