Interactions between the parasitic angiosperm Orobanche aegyptiaca and its . relations explain responses of tobacco to infection by the root holoparasitic. The damage induced in the crop by broomrape parasitism differs for each Nitrogen and carbon relationships between the parasitic weed. are a root holoparasitic plant devoid of chlorophyll and entirely depending on the host . Studies of structure-activity relationships have led to the finding that the.
However, in combination with other methods, it can reduce the seed bank very efficiently FAO, There is a renewed interest in intercropping linked to the need for reducing nitrogen cost and soil erosion. Intercropping is already used in regions of Africa as a low-cost technology of controlling the broomrapes Oswald et al. Recently it has been demonstrated that intercrops with cereals or with fenugreek or berseem clover can reduce O.
This has been confirmed in a subsequent study, in which trigoxazonane was identified in the root exudates of fenugreek which may be responsible for the inhibition of O. Maize and snap bean as potential trap crops on Orobanche soil seed bank showed better performance in stimulating germination of Orobanche seed bank and raised the germination by 74 and 71 per cent, respectively.
Maize and Snap bean were also complementing each other under inter-cropping and soil seed bank of O. Yield of tomato was significantly increased due to the reduction of Orobanche seed bank in the 3rd season Girma et al. Field experiments noticed that O. The number of O.
Pot and rhizotron experiments confirmed the reduction of infection in faba bean intercropped with cereals. It is suggested that inhibition of O. Crop rotations Rotation with non-host crops is usually suggested. The use of trap crops offers the advantage of preferentially stimulating broomrape suicidal germination. Flax, fenugreek and Egyptian clover are established to be successful trap crops for O.
There are claims that a reduction in infestation has been reported in rotations with rice, due to water flooding Sauerborn and Saxena,however, this has not been substantiated. The incorporation of resistant legumes in crop rotations may also maintain broomrape infestation at low levels. Crop sequences in the two locations, in addition to increase of tomato yield, decreased the Orobanche incidence, branching and seed production.
Experimental results in Tehran indicated that using trap crops namely sesame, brown indian-hemp, and common flax and black-eyed pea decreased broomrape biomass by 86, Reducing broomrape biomass caused increases in the tomato yield. Meanwhile, sesame, brown Indianhemp, Egyptian clover and mungbean increased total biomass of tomato by It was observed that these plants have a great potential to reduce broomrape damage and they can be used in rotation in broomrape infested fields Sirwan et al.
In Tunisia, the results suggested that in fields infested with O. This has been confirmed by experiments showing the pea stimulates germination of O. Whereas in fields infested with O. Fertilization Orobanche tends to be associated with less fertile soil conditions.
High levels of nitrogen fertilizer or chicken manure showed a suppressive effect. In the other side, with increasing of nitrogenous fertilizer, the amount of broomrape germination was decreased. In interaction of type of nitrogenous fertilizers and amount of nitrogenous fertilizer, the maximum yield of sunflower seed in the concentration of 5 ppm of urea fertilizer was obtained.
The minimum amount of broomrape germination also was obtained from the concentration of 5 ppm of urea fertilizer. Urea at and kg N ha-1, ammonium nitrate, and ammonium sulfate at kg N ha-1 and the goat manure at 20 and 30 t ha-1 were found to be most effective in reducing parasitism of Orobanche and enhancing growth of tomato plants. Even though drastic reduction of broomrape infestation was obtained, ammonium nitrate and ammonium sulfate at kg N ha-1 seemed to be injurious to tomato plants.
As nitrogen rates increased, the numbers and dry weights of shoot of branched broomrape decreased and the yields of tomato increased linearly except the yields obtained from the highest rate of ammonium nitrate and ammonium sulfate. This result indicated that broomrape infestation of tomato decreased with increases of soil nitrogen Mariam and Rungsit, The mixtures of chicken manure 20 t ha-1 and sulphur 0, 1, 4, 8, and 12 t ha-1 at all tested rates significantly reduced the dry weight of Orobanche and increased eggplant and potato yield compared with the control Haidar and Sidahmed, Biological methods Like all other plants, broomrapes have natural enemies which can affect their growth and can potentially be used as agents for their control.
Biological control of weeds is defined as the use of natural antagonists to exert pressure on the population of their host to reduce it to levels below economic importance. Unlike chemical compounds, biological control agents have the advantage of being specific to the weed, and do not directly contribute to environmental pollution. This technique utilizes living organisms insects, fungi, viruses, bacteria etc. Pathogenicity toward non-target plants is a major constraint; therefore, it is very important that host-specificity and risk assessment should be made before the release of a control organism into the environment.
The 'bioherbicide approach' employs virulent strains of pathogens viruses, bacteria or fungi which naturally occur on the weed and enhances their destructive activity. The infection build-up of the pathogen is manipulated to the extent of causing significant damage to the parasitic weed.
Pathogens can be used as sole agents or as part of a complex integrated control strategy Sauerborn et al. Biological control is particularly attractive in suppressing root parasitic weeds in annual crops because the intimate physiological relationship with their host plants makes it difficult to apply conventional weed control measures.
Both insects and fungi have been isolated that attack parasitic angiosperms. Most ofthe insects which have been reported to occur on Orobanche species are polyphagous without any host-specificity and thus damage to these parasitic weeds is limited Klein and Kroschel, For biological control, oligo- and monophagous herbivorous insects are of interest.
The fly Phytomyza orobanchia Diptera: Agromyzidae is reported to be host-specific attacking only Orobanche species.
Its distribution is related to the natural occurrence of Orobanche spp. These insects prevent seed production through the development of larvae inside the seed capsules of their target hosts and thus contribute to reduce their reproductive capacity and spread. However, research with both insects has revealed that their effectiveness to prevent seed set is limited and will not be enough to lower the soil seed bank significantly Klein and Kroschel, A factor that may limit the effect of P.
Further limiting factors of cultivation are pesticide applications against crop pests if these coincide with the flight periods of the two beneficial insects. Moreover, Phytomyza and Smicronyx suffer from indigenous antagonists which may have an important impact on their population levels.
Managementof orobanche in field crops: A review
Because of their short lifetime and enormous seed production and the vast damage caused to the host by unemerged plants, Orobanche cannot be regarded ideal organisms for biological control by insects. Approximately 30 fungal genera were reported to occur on Orobanche spp. Boari and Vurro, Soil-dwelling microorganisms have been specifically sampled, since they have a number of advantages in the control of root parasites: Numerous microorganisms potentially useful for the biocontrol of Orobanche species have been isolated and reported, but none has been subject to continuous wide-spread use Boari and Vurro, Results of surveys for fungal pathogens of Orobanche revealed that Fusarium species were the most prominent ones associated with diseased broomrapes.
Fusarium species as soil-borne fungi possess several advantages which render them suitable for the bioherbicide approach. In the soil they are relatively protected from environmental stress of drought and heat, frequently occurring in the area of distribution of Orobanche. The saprophytic nature of Fusarium spp. Because most of the damage to host crops occurs while the parasitic weed is still underground, use of soil-borne biocontrol agents such as Fusarium spp. To date about six Fusarium species are reported to be associated with Orobanche F.
Under laboratory and greenhouse conditions excellent control was repeatedly observed with F. The total number of O. Although data on the efficiency of Fusarium spp.
Thus there has been no successfully demonstrated control of this weed using potential inundative bioherbicides. The question arises, how the efficacy of the pathogens can be improved under field conditions in order to fight the target organism Sauerborn et al.
In the novel approach strategy two or more pathogens are combined and applied before or after parasite emergence. Some applied fungal mixtures caused a significant reduction of the number of emerging O. The feasibility of this approach has been demonstrated in the control of O.
A bioherbicide system was based on two fungal pathogens F. In pot trials, the pathogens gave a low control level when used individually but when applied as a mixture; both fungi caused a significant reduction of the number of emerged O.
The inoculum density of each fungus when applied alone was colony forming units cfu ml The same inoculum level of each fungus was used with the mixture, thus resulting in an inoculum density of 2x cfu ml Another approach, which only recently has shown to provide successful control of O. The combined treatment of the two agents resulted in highly reliable control of O.
The excellent control level in the combined treatments resulted from a lower number and reduced dry weight of O. This could either be due to an enhanced activity of the fungus against the early underground stages of the parasite or to an enhanced induced resistance within the sunflower plant. In laboratory experiments, no enhancing effect of BTH on virulence and growth of the fungus has been observed so far. Yet another approach which receives increasing attention is the engineering of hypervirulence genes into weed specific pathogens, e.
To enhance virulence, two Fusarium species that attack Orobanche have been transformed with two genes of the indoleacetamide pathway that converts tryptophan into the plant hormone indoleacetic acid IAA, Cohen et al. It was shown that overproduction of IAA provided a slight increase in virulence compared to the wild type but not enough to attain a satisfactory level of control.Scotland's Rarest Plants - Broomrape at Spier's
Extreme care should be taken with such genetically modified organisms due to their possible environmental impact, and fail-safe mechanisms should be installed and tested prior to release into the environment. A synergized effect was found between Fusarium oxysporum f. Application of two fungi together to control sunflower broomrape was rusticated to the first weeks after application. Repeated applications are needed for adequate long season control.
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The development of fungal inocula application through drip irrigation system developed in Bari, Italy, opens new horizons in biological control methodology Hershenhorn et al. Myrothecium verrucaria isolated from faba bean roots has been found to inhibit germination of O. Preliminary results demonstrated control of infection of faba bean by O. Pseudomonas aeruginosa, Pseudomonas fluorescens, Bacillus atrophaeus, and Bacillus subtilis reduce the growth of O. The fungus Myrothecium verrucaria isolated from the O.
Colonization by Rhizobium leguminosarum has been reported to decrease O. Also, colonization by the nitrogen-fixing bacterium.
Azospirillum brasilense inhibits germination and radicle growth of O. Colonization by AMF can also provide protection against parasitic weeds.
The fact that AMF colonize roots of most agricultural and horticultural species and that AMF symbiosis reduces Strigolactone production by the host plant opens avenues for its exploitation as an environmentally friendly biocontrol strategy.
Altered patterns in interactions between O. This fact, together with the extreme conservation and structural complexity of the DMI2 protein in plant species, favours a more complex role of this pathway as a general switch of basal defence than initially thought. The autoregulation mechanism limiting host root colonization by the symbiont to below a detrimental level is part of the defence mechanism against parasitic plants, not only in Lotus japonicus L. Crop resistance Goldwasser and Yoder assayed 50 different ecotypes of A.
In Arabidopsis,where natural resistance is not available, mutagenesis has proven successful in identifying resistant lines. In fact, 94 out of 13 A.
In tomato, the low germination stimulant phenotype has recently been reported in mutants owing to reduced exudation of trigolactones Dor et al.
With tobacco cultivars, mutants, or related Nicotiana species, little success has been made in identifying the source of resistance to Orobanche based on low induction of germination.
In legumes, resistance to O. In pea, quantitative trait loci analyses revealed genomic regions involved in the control of low stimulation of O. Two quantitative trait loci were associated with pea roots that had low activity on inducing O. Another preattachment mechanism could be related to the chemotropism responsible for the correct guidance of the Orobanche seedling towards the host root.
Misdirected growth of germinated O. Breeding programs focused on selection of host genotypes for high root exudation levels of germination stimulants could identify better candidates for trap crops to be used in a suicidal germination control strategy.
Genetic variation in this trait has been observed in important cultivars such as soybean. A novel chemical control strategy has been developed during the past few years: SAR can be induced in plants by the application of chemical agents. Recently it has been shown that SAR of host plants can be used for the control of important broomrape species Sillero et al. However, research on the effects of SAR on host-Orobanche systems is still in its infancy.
Recently, Fan et al. Despite no chemical agents were used. Resistance to broomrapes is a multi-faceted response in faba bean and legumes. Several defence mechanisms have been detected in plants resistant to broomrape attack, mainly involving cell wall reinforcement Perez-de-Luque et al,a,production of toxic compounds Lozano et al, and sealing of vascular tissues Perez-de-Luque et al.
Trap crops are commercially valuable crops that are able to reduce the seed bank of parasitic plants. They are false hosts owing to their ability to fool the parasite by triggering germination but not being compatible in the downstream infection process Promising results for trap crops have been reported for many host-parasite interactions, including pepper against O.
In addition to these annual trap crops, leguminous trees and shrubs such as Sesbania sesban L. Trap crops as a control technique should be included in the regular rotation and fallow management of infested fields and integrated with other control measures. Trap crops cannot be expected to eliminate the seed bank in the soil immediately. Regarding faba bean, the mechanisms described to date are pre-haustorial, i. According to Perez-de-Luque et al. The second response lignification occurs after the obstruction of parasite intrusive cells in the host cortex has been overcome, and prevents further penetration into the central cylinder and formation of a haustorium.
In the last five decades, crop yields increased because of chemical control of weeds, especially with selective herbicides. Recently, unfortunately, herbicides have been removed from markets because of toxicity, weed resistance to the herbicides, and environmental concerns Gressel, Developing a new herbicide by chemical companies is difficult, time-consuming, and very expensive.
Accordingly, there is a pressing need for biotech-derived crops not only crops with engineered herbicide resistance adapted over the last few yearsbut also using newer technology based on genomic, protoomic, and metabolomic tools.
Gressel described newer technologies that will assist in meeting the needs for herbicide-resistance crops.
Notably, herbicides that are metabolized by transgenic plants, i. Transgenic herbicide resistance may also pose food safety issues through the expression of the new gene in the crop plant. Concern may also arise regarding the possible gene transfer from transgenic crop plants to wild plants, although different ways to overcome these concerns have been proposed Gressel, Therefore, these parameters should be taken into consideration while applying chemicals to herbicide-resistant crops.
Several tobacco cultivars transformed with a mutant acetohydroxy acid synthase AHAS 3R gene isolated from a sulfonylurea resistant Brassica napus cell line were resistant to the herbicide chlorsulfuron Slavov et al. The effect of chlorsulfuron on broomrape was clearly demonstrated: A very low percentage from 0. Parasitic weeds will rapidly evolve resistance to herbicides because of their prolific seed production. Therefore, resistance to glyphosate, asulam, chlorosulfuron, or imazapyr will eventually appear.
Therefore, herbicide resistance crops should be wisely used or combined with other control methods, and new resistant crops continually developed Ali, Integrated methods Integrated control of broomrape weeds means to combine and to integrate different preventive measures and control instruments into the given farming system.
These are promising combinations for integrated Orobanche control in legume crops: Such a delay prevents the damage caused to the yield but not the continuation of the field contamination with broomrape seeds.
Addition of an imidazolinone herbicide application such as imazapic or imazamox days after planting prevents almost completely broomrape shoot emergence and seed setting of inflorescences present in the field during herbicide application Hershenhorn et al. Furthermore, crop treated with TAL plus chicken manure at 35 g pot-1 was significantly higher in root, shoot and total dry weight as compared to control and other treatments.
Three isolates of Trichoderma species including T. Results of field studies showed that soil treatment with these three fungal agents alone or soil treatment with fungal agents plus aerial spray of glyphosate 50 ppm was efficient and cost-effective method in reducing infection, minimizing the number of spikes parasitic on host plants and increasing yields of peas, faba bean and tomatoes Mokhtar et al.
Conclusion The principal conclusion to be drawn from these studies must be that no single technique provides complete control of Orobanche, and resorting to some of them is unavoidable. Physical methods are very useful to prevent the Orobanche but are tedious, time-consuming and costly.
Chemical, agronomic control methods and host resistance appear to be the most appropriate measures when available and affordable.
Moreover, some biological and crop resistance approaches are promising but they are too expensive and control may not be complete, by this, still need more research. It was claimed that integrated approaches combining several techniques could be more effective. However, these integrated programmes are practiced only on a small scale in a few countries because of cost and technical problems. While avoidance of dispersal of broomrape, crop resistance, and prevention measures could be effective and the most economical methods to reduce this root parasitic weed infestations in agricultural fields.
Advantages of these approaches are no chemical applications and no need for additional labour or complicated management, expensive equipment, or instrumentation, low cost, environmental safety, and may deplete the parasite soil seed bank. It is important both to assess the most severely infested areas in order to target these control measures most effectively, and maintain the seed bank of less infested areas beneath a threshold level of damage.
Acknowledgements The Author gratefully acknowledges Dr. Sanjay, for their assistance, helpful critical reading and comments on the manuscript. Seed germination and tubercle development of Orobanche foetida and Orobanche crenata in presence of different plant species.
Effect of Brassica campestris var. Applied of soil solarization for control of Egyptian broomrape Orobanche aegyptiaca on the cucumber Cucumis sativus in two growing seasons.
Stimulants of Phelipanche ramose germination from oilseed rape roots. Transformation of carrots with mutant acetolactate synthase for Orobanche broomrape control.
Bacterial inhibition of Orobanche aegyptiaca and Orobanche cernua radical elongation. Evaluation of Fusarium spp. Due to their achlorophyllous nature, broomrapes are constrained to obtain their nutritional resources by feeding off other plants using the haustorium, an organ unique in parasitic plants through which the parasite diverts water and nutrients from the host De Candolle, ; Kuijt, ; Musselman and Dickison, ; Westwood, The majority of broomrape species are botanical wonders parasitizing wild host plants in natural ecosystems.
However, seven broomrape species, Orobanche crenata, O. The crops affected depend on the host range of the broomrape species considered but in general, those in the Asteraceae, Brassicaceae, Apiaceae, Fabaceae, or Solanaceae such as sunflower, oilseed rape, carrot, faba bean, or tomato among many others, sustain the major attacks Parker and Riches, The damage induced in the crop by broomrape parasitism differs for each broomrape-host association. In general, parasitized crops suffer from reductions in total biomass at the greatest expense to the reproductive tissue Barker et al.
In some crops, the biomass loss equals to that accumulated by the parasite indicating that damage in the crop is directly attributed to the parasitic sink activity Barker et al. However, in other broomrape-crop associations the damage induced by broomrape extends beyond assimilate diversion.
In those cases, broomrape displays a pathogenic nature promoting disease in the crop mainly through negative effects on the crop photosynthetic machinery and hormonal balance Stewart and Press, ; Mauromicale et al. There are not figures based on rigorous data for the total area affected by broomrape weeds Parker, Sauerborn estimated that 16 million ha in Mediterranean and West Asia regions risked being infested.
In this regard, France is doing valuable work through the Technical Center for Oilseed Crops and Industrial Hemp, Terresinovia, where a nationwide survey of infested fields is actualized online on real time by the farmers with new cases emerging every year and recently toward new regions such as the French Centre region 1 Several studies suggest that large areas of new territory are at risk of invasion by broomrape Mohamed et al.
Several factors contribute to the fact that broomrape weeds remain an uncontrolled agricultural problem. Control strategies designed for non-parasitic weeds such as cultural and chemical methods do not necessarily achieve the required level of control for broomrape due to its mixed traits as weed and as root parasite.