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.     

烟草及向日葵上列当Orobanche cumana的发生及其生物防治

 近年,在河北省部分烟草和向日葵种植地发现大量寄生性杂草列当发生并造成严重为害。经鉴定为向日葵列当Orobanche cumana Wallr.。向日葵、烟草、番茄和黄瓜等作物的根分泌物能够刺激向日葵列当O. cumana种子萌发,而油葵根的分泌物则不能刺激向日葵列当种子萌发。利用列当致病镰刀菌L2菌株进行田间生物防治,防治效果达到92.4%。L2菌株对小麦、玉米、棉花、烟草和向日葵等作物生长无影响,L2菌株粗毒素能够抑制列当种子萌发,并造成列当种子萌芽管损伤。     

Resistance to Sphaerotheca pannosa in roses induced by 2,6-dichloroisonicotinic acid

The susceptible rose cv. Madelon and the partially resistant cv. Sonia both responded with reduced development of rose powdery mildew when they were treated with the synthetic inducer 2,6-dichloroisonicotinic acid (INA). The EC₅₀ for number of colonies cm⁻² was approximately 0.4 mg L⁻¹ in both cultivars when treated 4 days prior to inoculation. However, conspicuous differences were observed with respect to number of spores per cm². For sporulation, the EC₅₀ was 0.37 mg L⁻¹ in cv. Madelon and only 0.08 mg L⁻¹ in cv. Sonia. A comparison with the pathosystems cucumber/ Sphaerotheca fuliginea and red cabbage/ Peronospora parasitica is made and the importance of the observed phenomenon for the selection of parents in a breeding programme for (partial) resistance is discussed.     

Benzothiadiazole Activates Resistance in Sunflower (Helianthus annuus) to the Root-Parasitic Weed Orobanche cuman

ABSTRACT The study was conducted to evaluate the potential of induced resistance to infestation of sunflower (Helianthus annuus L.) by the parasitic weed Orobanche cumana Wallr. Treatment of sunflower seeds with 40 ppm of benzo(1,2,3)thiadiazole-7-carbothioic acid S-methyl ester (BTH) for 36 h completely prevented infection in root chambers. In pot studies using 2.86 x 10(-4) g of Orobanche seeds per gram of soil as inoculum, the total number of O. cumana shoots was reduced by 84 and 95% in the 60-ppm BTH treatment in the first and second trial, respectively. Evaluation of the disease incidences revealed that attachment of O. cumana at the sunflower root and the stage of early penetration was reduced in the BTH-treated plants. Chemical analysis of root extracts revealed synthesis of the phytoalexin scopoletin and of hydrogen peroxide in the BTH-treated sunflower roots, but no increase in lignification. Western blot analysis demonstrated accumulation of the pathogenesis-related protein chitinase in roots and stems of induced resistant plants. These results show that the phenomenon of induced resistance is not restricted to viral, bacterial, and fungal disease and demonstrate the great potential of this protection strategy as an effective component of future plant production systems.     

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。     

Molecular analysis of resistance mechanisms to Orobanche cumana in sunflower

Resistance to the dicotyledenous parasite Orobanche cumana in sunflower is characterized by a low number of parasitic attachments and a confinement of the parasite in host tissues leading to its necrosis. To help understand what determines such resistance mechanisms, molecular, biochemical and histological approaches were employed before (early response) and after (late response) attachment of the broomrape parasite to susceptible (2603) and resistant (LR1) sunflower genotypes. The expression patterns of 11 defence-related genes known to be involved in different metabolic pathways (phenylpropanoids, jasmonate, ethylene) and/or in resistance mechanisms against microorganisms were investigated. RT-PCR and cDNA blot experiments revealed that the resistant genotype exhibited a stronger overall defence response against O. cumana than the susceptible one, involving marker genes of the jasmonate (JA) and salicylic acid (SA) pathways. Among them, the SA-responsive gene, def. (defensin), appeared to be characteristic of LR1 sunflower resistance. However, no JA accumulation and similar SA contents (250–300 ng g⁻¹ FW) were measured by GC/MS in both genotypes, parasitized or not. In addition, three cDNAs, isolated by a suppression-subtractive hybridization, were shown to be strongly induced only in the resistant genotype 8 days post-inoculation, when the first O. cumana attachments occurred. These genes, putatively encoding a methionine synthase, a glutathione S-transferase and a quinone oxidoreductase, might be involved in detoxification of reactive oxygen species, suggesting the occurrence of an oxidative burst during the incompatible interaction. Finally, host cell-wall modifications leading to parasite-confinement were correlated with more intense callose depositions in the resistant genotype, concomitant with over-expression of the callose synthase cDNA HaGSL1 .     

Orobanche cumana race F: performance of resistant sunflower hybrids and aggressiveness of populations of the parasitic weed

The production of sunflower is threatened by Orobanche cumana (broomrape) infections in many countries of southern and eastern Europe. The most virulent race of this parasitic weed, race F, is widespread in Spain. Most of the current commercial hybrids of resistant sunflower do not completely prevent broomrape emergence in the field. The performance (broomrape incidence and severity, final yields and oil contents) of four resistant and two susceptible sunflower hybrids was studied in different years in several O. cumana – infested locations. O. cumana – sunflower interactions were characterised by low severity and intermediate incidence in the resistant hybrids; both depended on the environment. An increase in sunflower yield because of the use of resistant hybrids was most noticeable under heavy field infestations and under drought. Characterisation of 20 populations of O. cumana classified as race F in terms of the standardised area under the degree of attack progress curve (SAUDC) and O. cumana incidence (BI) suggested differential intrinsic pathogenicities. These results highlight the variability within race F of O. cumana , mirroring the environmentally dependent horizontal resistance in sunflower.     

向日葵抗列当品种(系)筛选及其应用评价

为了全面评价不同向日葵品种(系)对列当的抗寄生性和其在生产中的应用价值,对‘TP3313’等50个食葵品种(系)、‘内蒙杂4号’等6个油葵品种(系)进行了田间自然寄生试验,结果表明:食葵‘TP3313’为对列当免疫的品种,且病虫害发生较轻,产量相对较高(261.11kg/667m~2),因而具有极高的推广应用价值;‘TP3314’为高抗列当品种,但是受向日葵菌核病危害较重,产量为219.64kg/667m~2;‘SH361-L’、‘SH338-M’等8个品种表现为中感,属耐列当品种(系),并且产量相对较高,在生产中具有一定的应用价值。     

Orobanche aegyptiaca control in tomato fields with sulfonylurea herbicides

Field experiments were conducted from 1994 to 1997 at two locations to study the effectiveness of chlorsulfuron and triasulfuron applied through different irrigation methods (chemigation) for control of Orobanche aegyptiaca Pers. in tomato ( Lycopersicon esculentum Mill). Three split applications of chlorsulfuron at 2.5 g a.i. ha⁻¹ and of triasulfuron at 7.5 g a.i. ha⁻¹, through conventional sprinkler irrigation systems, 10–14 days apart followed immediately by sprinkling with water, controlled O. aegyptiaca by about 90% and 80% and increased crop yield 25–47% and 30%, respectively, without any crop injury symptoms. Repeated applications of the same herbicides at half rates resulted in slightly higher O. aegyptiaca control and crop yield than only one herbicide application at double rate. Chemigation by the sprinkler systems (microsprinklers, 60 m³ ha⁻¹) slightly increased the herbicide efficiency as compared with the high volume spray (800 m³ ha⁻¹). O. aegyptiaca control from sulfonylureas applied by drip chemigation was poor, as this probably requires very accurate timing and the herbicide distribution in the soil was not uniform.     

Effect of broomrape (Orobanche cumana Wallr.) on some agro-morphological and biochemical traits of Tunisian and some reference sunflower (Helianthus annuus L.) accessions

Journal of Plant Diseases and Protection - Orobanche cumana Wallr. is an important new problem for sunflower crop in Tunisia. Little information is available on the behavior of sunflower to O....     

Sensitivity to cymoxanil in populations of Plasmopara viticola in northern Italy

In 1993, control failures were reported on grapevine in northern Italy under severe downy mildew pressure after postinfection application of cymoxanil in mixtures with copper or mancozeb. A monitoring survey was started immediately in Piedmont (north-western Italy) in order to determine the sensitivity of populations of Plasmopara viticola to cymoxanil from those vineyards where the fungicide was not controlling the disease satisfactorily. In 1994 and 1995, monitoring surveys were extended to north-eastern Italy, where cymoxanil mixtures were not performing as well as in the past. Sampled populations were tested on detached leaf discs and on whole potted plants under controlled conditions. In 1993, 12 populations, sampled in Piedmont, showed MIC values (minimum inhibitory concentration) varying from 10 to more than 100 mg L⁻¹ cymoxanil. With a baseline reference population having a MIC value of 3 mg L⁻¹, resistance factors ranged from 3 to more than 30. In 1994, 17 populations out of 27 sampled in Trentino (north-eastern Italy) showed MIC values of 100 mg L⁻¹ or higher and in 1995, 32 populations out of 38 showed the same behaviour. In similar experiments, the MIC values of populations from nontreated plots were between 3 and 10 mg L⁻¹. In whole potted plant tests, populations with MIC values higher than 200 mg L⁻¹ in a leaf disc test were not controlled by 500 mg L⁻¹ of cymoxanil. The results of our study suggest that resistance to cymoxanil in P. viticola may contribute to a lack of disease control in Italian vineyards.     

Quantitative aspects of Orobanche crenata infestation in faba beans as affected by abiotic factors and parasite soil seedbank

The interactions between the root parasitic weed Orobanche crenata Forsk. and its host plant faba bean ( Vicia faba L.) were quantified under controlled and field conditions at ICARDA's Tel Hadya research station. In the field experiments conducted in 1993–94 and 1994–95 faba beans were sown on two dates, in plots with 0, 50, 200 and 600 O. crenata seeds kg^–1 soil, under both limited and sufficient moisture supply. The effects of temperature on the duration of the early developmental stages of O. crenata were investigated in a growth chamber. The extent of O. crenata infestation was closely related to the number of parasite seeds in the soil. The seed-density treatment with 600 seeds kg^–1 soil resulted in complete crop failure. Furthermore, O. crenata infestation was higher under sufficient than under limiting water supply conditions, irrespective of sowing date. Only in the moderately infested plots, did shifting of the planting time of faba bean result in a significant decrease in parasite dry weight and an increase in crop seed yield. The timing of germination, attachment and further developmental stages of O. crenata was not related to faba bean growth stage and was affected primarily by soil temperature. The duration of O. crenata developmental stages was estimated using the thermal time concept. The relationship between total number of parasite attachments at the harvest of the faba bean crop and O. crenata seed density was dependent on maximum faba bean root-length density measured by the start of pod-filling in each treatment combination of sowing date and moisture supply. The results are discussed with reference to implications for the development of a dynamic simulation model for the prediction of faba bean yield losses caused by O. crenata .     

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。     

Host–parasite relationships of Meloidogyne incognita on spinach

Host–parasite relationships in root-knot disease of spinach caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Nematode-induced mature galls were large and usually contained one or more females and egg masses with eggs. Feeding sites were characterized by the development of giant cells containing granular cytoplasm and many hypertrophied nuclei. The cytoplasm in these giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density ( P _i) in a series from 0–128 eggs and second-stage juveniles per cm³ soil and growth of spinach cv. Symphony F₁ seedlings was tested under glasshouse conditions. A Seinhorst model [ y = m  + (1 −  m ) z ^P–T ] was fitted to fresh top- and total plant-weight data for inoculated and control plants. Tolerance limits ( T ) of spinach cv. Symphony F₁ to M. incognita race 1 for fresh top and total plant weights were 0·25 and 0·5 eggs and second-stage juveniles per cm³ soil, respectively. The minimum relative values for fresh top and total plant weights were zero in both cases at P _i ≥ 32 eggs and second-stage juveniles per cm³ soil. Root galling was least at low initial population densities and greatest at 16 eggs and second-stage juveniles per cm³ soil. Maximum nematode reproduction rate was 33·1-fold at the lowest P _i.     

Plant sensitivity to atrazine and chlorsulfuron residues in a soil-free system

The sensitivity of 22 major crops, pastures and weeds from the north-east grain region of Australia to atrazine and chlorsulfuron residues was determined in a glasshouse using a soil-free bioassay system. A logistic equation was fitted to the seedling fresh weights as a function of the logarithm of herbicide concentration by non-linear regression and used to calculate the doses for 10%, 30% and 50% inhibition of seedling growth (ID₁₀, ID₃₀ and ID₅₀). The ID₅₀ for atrazine ranged from 0.03 to 0.04 mg a.i. L^–1 for Salvia reflexa Hornem. and barley to 1.47 mg a.i. L^–1 for sorghum. The ID₅₀ for chlorsulfuron ranged from 0.19 to 0.21 μg a.i. L^–1 for lucerne and snail medic to 102 μg a.i. L^–1 for wheat. Based on ID₅₀ values measured, the predicted responses of each species to a range of concentrations of atrazine and chlorsulfuron were classified into four categories ranging from no damage to severe damage. These sensitivity data will assist in planning cropping sequences in soils previously treated with atrazine or chlorsulfuron.     

A qualitative quick-test for detection of herbicide resistance to tribenuron-methyl in Papaver rhoeas

A qualitative seed-based method useful for the detection of resistance to the herbicide tribenuron-methyl in Papaver rhoeas L. is described. Seeds were germinated on 35 mL of a 1.3% agar medium containing 2 g KNO₃ L^–1 in 8.5 cm Petri dishes in a growth chamber under 20 μmol s^–1 m^–2 of fluorescent light. When 0.24 μM tribenuron-methyl or more was added, growth in susceptible plants stopped after the cotyledon stage and they turned chlorotic. The resistant plants continued developing new leaves. The same effect was achieved when 0.2 g gibberellin (GA₃) L^–1 and 7.68 μM tribenuron-methyl or 0.5 g GA₃ L^–1 and 61.44 μM tribenuron-methyl were added. Germination percentage rose with gibberellin in the presence or absence of the herbicide. Plants developed rapidly, with only about 14 d needed to finish the test but sometimes root growth was reduced because of the addition of gibberellin. In the absence of gibberellin but in the presence of the herbicide, plants grew more slowly and developed smaller leaves with a 17-d evaluation period requirement. The test was validated with pot experiments in a greenhouse and also with field trials. The best combination was found to be 0.2 g GA₃ L^–1 and 7.68 μM tribenuron-methyl, assuring homogenous germination and testing of dormant seeds but avoiding root inhibition associated with too much gibberellin.     

Sensitivity of fungi from cereal roots to fluquinconazole and their suppressiveness towards take-all on plants with or without fluquinconazole seed treatment in a controlled environment

The take-all fungus, Gaeumannomyces graminis var. tritici , was highly sensitive to fluquinconazole ( in-vitro EC₅₀ 0·016–0·018 mg L⁻¹), a fungicide developed for use as a seed treatment to control take-all, and to prochloraz (EC₅₀ 0·006 mg L⁻¹). Fungi of other genera that were commonly isolated from cereal roots were sensitive in varying degrees to prochloraz but were relatively insensitive (e.g. Fusarium culmorum , EC₅₀ > 20 mg L⁻¹) or slightly sensitive (e.g. Epicoccum purpurascens , EC₅₀ 0·514 mg L⁻¹) to fluquinconazole. Gaeumannomyces graminis var. graminis and G. cylindrosporus , weak parasites that can protect roots against take-all, and an unnamed Phialophora sp., all closely related to the take-all fungus, were highly or moderately sensitive to fluquinconazole. Alternaria infectoria and E. purpurascens were most consistently effective in suppressing development of take-all on pot-grown wheat plants dual-inoculated with G. graminis var. tritici and the nonpathogen. Take-all was decreased more on dual-inoculated wheat plants grown from seed treated with fluquinconazole or fluquinconazole plus prochloraz than when only an antagonistic fungus ( A. infectoria , E. purpurascens , Fusarium culmorum or Idriella bolleyi ) or a seed treatment was applied. These fungi were less effective in combination with seed treatments on barley. Gaeumannomyces graminis var. graminis and G. cylindrosporus , tested on wheat, suppressed take-all only in the absence of fungicides. It is suggested that the performance of seed treatment containing fluquinconazole against take-all may in some circumstances be enhanced by its partial specificity for the take-all fungus.     

内生黏质沙雷氏菌LIEH 92对向日葵菌核病的防治效果及其防病机制研究

本研究评价了从向日葵列当体内分离筛选得到的内生黏质沙雷氏菌(Serratia marcescens)LIEH 92对向日葵菌核病进行盆栽与大田防效评价,并测定了该菌株的生理特性和其在根际土与向日葵体内的定殖情况。结果表明,LIEH 92发酵液对向日葵菌核病的室内盆栽防效达73.35%,对大田根腐型菌核病和盘腐型菌核病防效分别达53.48%和38.64%。菌株LIEH 92可产生几丁质酶,并能在根际土和向日葵根、茎、叶内定殖与传导,定殖菌量达102~106 cfu/g。其在向日葵植株的根内定殖数量最大,茎中次之,叶中最少。在灭菌土中LIEH 92在根际土和向日葵根部的定殖菌量小于在自然土中其在相应部位的定殖菌量,而灭菌土中LIEH 92在向日葵茎部和叶部的定殖菌量则大于自然土中相应的定殖菌量。LIEH 92处理可提高向日葵植株PAL、POD和PPO等防御酶活性,从而诱导向日葵对菌核病的抗性。LIEH 92对向日葵菌核病具有生防潜力。     

Biochemical factors involved in vetch resistance toOrobanche aegyptiaca

Experiments were performed to elucidate the biochemical nature of the differential response of resistantVicia atropurpureacv. Popany and susceptibleVicia sativacv. Yovel to the parasitic weedOrobanche aegyptiaca. Plant root material was obtained by growing vetch plants in association withOrobancheseeds on glass microfibre filter sheets inserted in polyethylene bags replenished by nutrient solution. Higher concentrations of bound phenolics, free phenolics and lignin, and higher activity of peroxidase were observed in cv. Popany roots as a result ofO. aegyptiacainfection than were found in cv. Yovel vetch. No differences in hydroxyproline-rich glycoproteins levels were detected between infected and non-infected roots of either vetch cultivar. These results suggest that the resistant vetch defense mechanism involves elevated induction of the phenylproponoid pathway uponOrobancheinfection, conferring mechanical and chemical barriers confronting the invading parasite.     

Nematicidal activity of essential oils and organic amendments from Asteraceae against root-knot nematodes

The essential oil of Chrysanthemum coronarium flowerheads showed strong nematicidal activity in vitro and in growth-chamber experiments. Essential oil concentrations of 2, 4, 8 and 16  µ L mL⁻¹, significantly reduced hatch, J ₂ survival (determined by final value and area under curves of cumulative percentage hatch or mortality) and reproduction rate of Meloidogyne artiellia in vitro , with the lowest values occurring at 16  µ L mL⁻¹. In pot trials with chickpea cv. PV 61, essential oil concentrations of 10–40  µ L per 500 cm³ soil, applied on sterile cotton pellets, also significantly reduced the nematode's reproduction rate. The biological processes of mortality and hatching/reproduction were adequately described by the monomolecular and expanded negative exponential models, respectively. Effectiveness of soil amendment with either flowers, leaves, roots or seeds of C. coronarium , and flowers from several species of Asteraceae ( Chrysanthemum segetum , Calendula maritima , Calendula officinalis and Calendula suffruticosa ) at 5 g per 500 cm³ soil was tested for suppression of M. artiellia and growth of chickpea cv. PV 61 under growth-chamber conditions. In these tests, flowers of all five Asteraceae species and various parts of C. coronarium significantly reduced reproduction rates of M. artiellia , by 83·0–95·9%, with the minimum rates occurring in infected chickpea plants amended with flowers of C. officinalis and C. suffruticosa . The in vitro and in planta results suggest that the essential oil of C. coronarium and organic amendments from Asteraceae species may serve as nematicides.