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11. Orobanche minor Smith (1797: 422) . Type:— UNITED KINGDOM (lectotype designated here):—1.. “... [S. E. England / leg. Sutton, C.S.]”. – 2. “See Sowerb. Engl. Bot. t. 422 / This specimen may be considered / as part of the Type! (R...[?])” (K000759346, the sheet contains two specimens of the same gathering, which we choose as lectotype). Heterotypic synonym:— O. minor Sutton (1798: 179), later homonym (Turland et al. 2018: Art. 53.1); O. concolor Duby (1828: 350). Fig. 40. General distribution: —Native and/or naturalised in many parts of the world: Africa (native [Northern Africa] and naturalised), America (naturalised), Asia (native [Western Asia] and naturalised), Europe and Oceania (Australia (naturalised) and New Zealand (naturalised)). Distribution: —Most of localities are in the Samtskhe-Javakheti and Shida Kartli prov., on the rocky slopes of the river Mtkvari and roadsides (Fig. 41). Apparently, Georgia could be the SE limit of its native distribution range. Habitat: —Rocky slopes, roadsides, ruderal habitats, 500‒1000(1600) m. Hosts: —In general, mostly on Asteraceae, Fabaceae and Apiaceae species, here on Anthemis cotula L., Chondrilla juncea L., Lactuca serriola L., Leontodon asperrimus (Willd.) Endl. (all from Asteraceae, and probably on other genera of this family). Phenology: —Flowering May–June (July), fruiting July–August. Conservation status: —Least Concern (LC). The species has a rather restricted distribution in Georgia, mainly in the central part of the country; however, populations are usually numerous. EOO is 5000 km 2 and AOO is ca. 100 km 2. Most localities are located close to roads, on slopes, on embankments or heavily grazed areas. In its global range, the species is often invasive in many regions and requires further observations from Georgia. Taxonomic note: — Orobanche minor was described from near Sheringham (Norfolk County, eastern England, United Kingdom) by Smith (1797) based on material (parasitic on Trifolium pratense L. [“in fields of clover for the most part, to the roots of which it seems to be attached”]) sent to him by Reverend Mr. Sutton, who a year later (1798) would make a much more detailed description of the same species that he knew so especially well, also indicating that Smith (1797) based his drawing (t. 422) on the materials he had sent to him, although he points out some inaccuracies in the drawing, the description (e.g., length of the inflorescence), adds another host-plant (Hypochaeris radicata L.) and some more locations for the species. Sutton (1798) also mentions the name of species described by Smith among its synonyms. We believe that Smith (1797) based his drawing (t. 422) on the specimen (“attached” to Trifolium) that we choose here as lectotype. S pecimens examined: — GEORGIA. Abkhazia: “Abchasia (Nordm. ex Ledeb.)” (Boissier 1879: 512, sub O. minor Sutton); Caucasus N. Sredias[?], Abchasien... Lindemann (P02968681 - hb. E. Cosson [as O. minor Sutt.]); (Gagnidze 1999, sub O. grossheimii; Eristavi et al. 2001: 60, sub O. grossheimii); Samtskhe-Javakheti prov.: NE of Borjomi, Kortaneti, a slope above an asphalt road, roadsides, on Lactuca, Leontodon, 41°53’45”N, 43°26’55”E, 780–790 m, 31 May 2014, R. Piwowarczyk (KTC); Samtskhe-Javakheti, Lesser Caucasus, western part of the Trialeti Mountains, valley of the Mtkvari (Kura) river, between Atskuri and Borjomi, 17–18 kilometers by road before Borjomi, 21 May 2001, G. Schneeweiss & A. Tribsch (WU0022599); Chitakhevi E, roadsides, slopes of the Mtkvari (Kura) river, on Leontodon asperrimus, 41°47’57.7”N, 43°18’50.2”E, 840 m, 16 June 2022, R. Piwowarczyk (phot.); Chitakhevi SW, roadsides, slopes of the Mtkvari (Kura) river, on Chondrilla, L. asperrimus, 41°47’02.8”N, 43°17’40.4”E, 850 m, 17 June 2022, R. Piwowarczyk (KTC); Borjomi distr., NE of Dviri, rocky slopes of Mtkvari river, on Chondrilla, 41°46’54”N, 43°16’00”E, 41°46’42.2”N, 43°17’19”E, 900 m, 2 June 2014, R. Piwowarczyk (KTC); between Dviri and Chitakhevi, NW from Chobiskhevi, slopes of the river Mtkvari (Kura), slopes, roadsides, road embankments, on Chondrilla, 41°46’40.7”N, 43°17’16.8”E, 888 m, 41°46’28.9”N, 43°17’01.2”E, 870 m, 16 June 2022, R. Piwowarczyk (phot.); Dviri N, NW, rocky slopes, roadsides, road embankments, on Chondrilla, 41°46’45.8”N, 43°16’18.1”E, 911 m, 41°46’56.6”N, 43°15’46.2”E, 910 m, 16 June 2022, R. Piwowarczyk (phot.); Shida Kartli prov.: E of Uplistsikhe Cave Town, near Cafe-Restaurant Gamardjoba, foot of rocky slopes in the valley of the Mtkvari River, roadsides, ruderal areas near restaurants and farms, on Anthemis cotula, 41°58’00.5”N, 44°12’48.7”E, 570 m, 8 June 2022, R. Piwowarczyk (KTC).

Root parasitic weeds of the Orobanchaceae, such as witchweeds (Striga spp.) and broomrapes (Orobanche and Phelipanche spp.), cause serious losses in agriculture worldwide, and efforts have been made to control these parasitic weeds. Understanding the characteristic physiological processes in the life cycle of root parasitic weeds is particularly important to identify specific targets for growth modulators. In our previous study, planteose metabolism was revealed to be activated soon after the perception of strigolactones in germinating seeds of O. minor. Nojirimycin inhibited planteose metabolism and impeded seed germination of O. minor, indicating a possible target for root parasitic weed control. In the present study, we investigated the distribution of planteose in dry seeds of O. minor by matrix-assisted laser desorption/ionization–mass spectrometry imaging. Planteose was detected in tissues surrounding—but not within—the embryo, supporting its suggested role as a storage carbohydrate. Biochemical assays and molecular characterization of an α-galactosidase family member, OmAGAL2, indicated that the enzyme is involved in planteose hydrolysis in the apoplast around the embryo after the perception of strigolactones, to provide the embryo with essential hexoses for germination. These results indicate that OmAGAL2 is a potential molecular target for root parasitic weed control.

Damage caused by Orobanchaceae root parasitic weeds is a substantial agricultural problem for global food security. Many studies have been conducted to establish practical methods of control, but efforts are still required for successful management. Seed germination of root parasitic weeds requires host-derived germination stimulants including strigolactones (SLs). Studies on SLs have revealed that a butenolide ring is the essential moiety for SL activity as a germination stimulant. Interestingly, recent studies have revealed that butenolide hormones regulate the biosynthesis of secondary metabolites and mediate communication in actinomycete bacteria. Because of the structural similarity between SLs and the bacterial butenolides, we evaluated the germination stimulatory activity of butenolides isolated from Streptomyces albus J1074 on root parasitic weeds. These butenolides were found to specifically induce seed germination of Orobanche minor. Our findings contribute to understanding the molecular mechanisms of germination stimulant perception and to the development of a method for their biological control.

Orobanche minor Sm. — Habit: Herb. Habitat: LMDF, BZ; up to 3 000 m. Distribution: I. Voucher: Sirimon Track, Alt. 2742– 2847 m, 17 Jul. 2014, CPG 28350 (HIB, PE). References: Bussmann (1994), Agnew (2013)., Published as part of Zhou, Ya-Dong, Mwachala, Geoffrey, Hu, Guang-Wan & Wang, Qing-Feng, 2022, Annotated checklist of the vascular plants of Mount Kenya, East Africa, pp. 1-108 in Phytotaxa 546 (1) on page 88, DOI: 10.11646/phytotaxa.546.1.1, http://zenodo.org/record/6550464, {"references":["Bussmann, R. W. (1994) The forest of Mt. Kenya (Kenya): Vegetation, ecology, destruction and management of a tropical mountain forest ecosystem. Ph. D. dissertation, Universitat Bayreuth Startseite, Bayreuth, 252 pp.","Agnew, A. D. Q. (2013) Upland Kenya wild flowers and ferns, 3 rd edn. Nature Kenya Publications, Nairobi, 733 pp."]}

Orobanchaceae root parasitic weeds cause serious agricultural damage worldwide. Although numerous studies have been conducted to establish an effective control strategy for the growth and spread of root parasitic weeds, no practical method has been developed so far. Previously, metabolomic analyses were conducted on germinating seeds of a broomrape, Orobanche minor, to find novel targets for its selective control. Interestingly, planteose metabolism was identified as a possible target, and nojirimycin (NJ) selectively inhibited the germination of O. minor by intercepting planteose metabolism, although its precise mode of action was unclear. Here, transcriptome analysis by RNA-Seq was conducted to obtain molecular insight into the effects of NJ on germinating O. minor seeds. Differential gene expression analysis results suggest that NJ alters sugar metabolism and/or signaling, which is required to promote seed germination. This finding will contribute to understanding the effect of NJ and establishing a novel strategy for parasitic weed control.

Root parasitic weeds of the Orobanchaceae, such as witchweeds (Striga spp.) and broomrapes (Orobanche and Phelipanche spp.), cause serious losses in agriculture worldwide. No practical method to control these parasitic weeds has been developed to date. Understanding the characteristic physiological processes in the life cycles of root parasitic weeds is particularly important to identify specific targets for growth modulators. In our previous study, planteose metabolism was revealed to be activated soon after the perception of strigolactones in germinating seeds of O. minor. Nojirimycin inhibited planteose metabolism and impeded seed germination of O. minor, indicating that planteose metabolism is a possible target for root parasitic weed control. In the present study, we investigated the distribution of planteose in dry seeds of O. minor by matrix-assisted laser desorption/ionization–mass spectrometry imaging. Planteose was detected in tissues surrounding—but not within—the embryo, supporting its suggested role as a storage carbohydrate. Biochemical assays and molecular characterization of an α-galactosidase family member, OmAGAL2, indicated the enzyme is involved in planteose hydrolysis in the apoplast around the embryo after the perception of strigolactones to provide the embryo with essential hexoses for germination. These results indicated that OmAGAL2 is a potential molecular target for root parasitic weed control.HighlightPlanteose accumulated in tissues surrounding the embryo in Orobanche minor dry seeds and was indicated to be hydrolyzed in the apoplast around the embryo by α-galactosidase during germination.

BACKGROUND Strigolactones (SLs) have a vast number of ecological implications because of the broad spectrum of their biological activities. Unfortunately, the limited availability of SLs restricts their applicability for the benefit of humanity and renders synthesis the only option for their production. However, the structural complexity of SLs impedes their economical synthesis, which is unfeasible on a large scale. Synthesis of SL analogues and mimics with a simpler structure, but with retention of bioactivity, is the solution to this problem. RESULTS Here, we present eight new hybrid‐type SL analogues derived from auxin, synthesized via coupling of auxin ester [ethyl 2‐(1H‐indol‐3‐yl)acetate] and of ethyl 2‐phenylacetate with four D‐rings (mono‐, two di‐ and trimethylated). The new hybrid‐type SL analogues were bioassayed to assess the germination activity of seeds of the parasitic weeds Striga hermonthica, Orobanche minor and Phelipanche ramosa using the classical method of counting germinated seeds and a colorimetric method. The bioassays revealed that analogues with a natural monomethylated D‐ring had appreciable to good activity towards the three species and were the most active derivatives. By contrast, derivatives with the trimethylated D‐ring showed no activity. The dimethylated derivatives (2,4‐dimethyl and 3,4‐dimethyl) were slightly active, especially towards P. ramosa. CONCLUSIONS New hybrid‐type analogues derived from auxins have been prepared. These analogues may be attractive as potential suicidal germination agents for parasitic weed control because of their ease of preparation and relevant bioactivity. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry., Hybrid‐type strigolactone (SL) analogues were prepared from auxin ethyl ester in a two‐step operation. These SL analogues were bioassayed as germination agents for Striga hermonthica, Pelipanche ramosa and Orobanche minor.

Root exudates from Lotus japonicus were found to contain at least three different hyphal branching-inducing compounds for the arbuscular mycorrhizal (AM) fungus Gigaspora margarita, one of which had been previously identified as (+)-5-deoxystrigol (5DS), a canonical strigolactone (SL). One of the two remaining unknown hyphal branching inducers was purified and named lotuslactone. Its structure was determined as methyl (E)-2-(3-acetoxy-2-hydroxy-7-methyl-1-oxo-1,2,3,4,5,6-hexahydroazulen-2-yl)-3-(((R)-4-methyl-5-oxo-2,5-dihydrofuran-2-yl)oxy)acrylate, by 1D and 2D NMR spectroscopy, and HR-ESI- and EI-MS. Although lotuslactone, a non-canonical SL, contains the AB-ring and the enol ether-bridged D-ring, it lacks the C-ring and has a seven-membered cycloheptadiene in the A-ring part as in medicaol, a major SL of Medicago truncatula. Lotuslactone was much less active than 5DS, but showed comparable activity to methyl carlactonoate (MeCLA) in inducing hyphal branching of G. margarita. Other natural non-canonical SLs including avenaol, heliolactone, and zealactone (methyl zealactonoate) were also found to be moderate to weak inducers of hyphal branching in the AM fungus. Lotuslactone strongly elicited seed germination in Phelipanche ramosa and Orobanche minor, but Striga hermonthica seeds were 100-fold less sensitive to this stimulant.

Root parasitic plant germination is induced by the host-derived chemical, strigolactone (SL). We found that a major microbial culture broth component, tryptone, inhibits the SL-inducible germination of a root parasitic plant, Orobanche minor. l-tryptophan (1a, l-Trp) was isolated as the active compound from tryptone. We further found that l-Trp related compounds (1b-11), such as a major plant hormone auxin (8, indole-3-acetic acid; IAA), also inhibit the germination and post-radicle growth of O. minor. We designed a hybrid chemical (13), in which IAA is attached to a part of SL, and found that this synthetic analog induced the germination of O. minor, and also inhibited post-radicle growth. Moreover, we found that N-acetyl Trp (9) showed germination stimulating activity, and introduction of a substitution at C-5 position incresed its activity (12a-12f). Our data, in particular, the discovery of a structurally hybrid compound that has two activities that induce spontaneous germination and inhibit subsequent radical growth, would provide new types of germination regulators for root parasitic plants.

This article belongs to the Special Issue Parasitic Plants Management., The holoparasitic broomrape weeds (Orobanche and Phelipanche species) cause severe yield losses throughout North Africa, the Middle East, and Southern and Eastern Europe. These parasitic weeds form an haustorium at the tip of their radicles to infect the crop upon detection of the host-derived haustorium-inducing factors. Until now, the haustorial induction in the broomrapes remains less studied than in other parasitic plant species. Known haustorium-inducing factors active in hemiparasites, such as Striga and Triphysaria species, were reported to be inefficient for the induction of haustoria in broomrape radicles. In this work, the haustorium-inducing activity of p-benzoquinone and 2,6-dimethoxy-p-benzoquinone (BQ and DMBQ) on radicles of three different broomrapes, namely Orobanche cumana, Orobanche minor and Phelipanche ramosa, is reported. Additional allelopathic effects of benzoquinones on radicle growth and radicle necrosis were studied. The results of this work suggest that benzoquinones play a role in the induction of haustorium in broomrapes. Although dependent on the broomrape species assayed and the concentration of quinones used in the test, the activity of BQ appeared to be stronger than that of DMBQ. The redox property represented by p-benzoquinone, which operates in several physiological processes of plants, insects and animals, is invoked to explain this different activity. This work confirms the usefulness of benzoquinones as haustorium-inducing factors for holoparasitic plant research. The findings of this work could facilitate future studies in the infection process, such as host-plant recognition and haustorial formation., This research was funded by the Spanish Ministry of Science and Innovation (RYC-2015-18961 and AGL2017-87693-R).

Common broomrape (Orobanche minor Sm.) is the most widespread and variable species in the British Isles and is the subject of much taxonomic confusion. Poor preservation in herbaria, coupled with the presence of cryptic host-specific races, have contributed to this. Here we review the taxonomic status of infraspecific taxa of O. minor in the British Isles, and provide a revised identification key, informed by morphology, ecology and molecular data. We describe two new varieties of O. minor s.l. that are ecologically distinct and discuss within the broader context of cryptic taxa in the subsection Minores (Beck-Mannagetta) Teryokhin in the British Isles and continental Europe. We suggest that delineating taxa objectively and reliably will be important for informing conservation priorities. Host identity and ecology, besides morphology, are essential considerations when identifying infraspecific taxa in this taxonomically challenging species.

One of the germination stimulants for root parasitic weeds produced by maize (Zea mays) was isolated and named methyl zealactonoate (1). Its structure was determined to be methyl (2E,3E)-4-((RS)-3,3-dimethyl-2-(3-methylbut-2-en-2-yl)-5-oxotetrahydrofuran-2-yl)-2-((((R)-4-methyl-5-oxo-2,5-dihydrofran-2-yl)oxy)methylene)but-3-enoate using by 1D and 2D NMR spectroscopy and ESI and EI–MS spectrometry. Feeding experiments with 13C-carlactone (CL), a biosynthetic intermediate for strigolactones, confirmed that 1 is produced from CL in maize. Methyl zealactonoate strongly elicits Striga hermonthica and Phelipanche ramosa seed germination, while Orobanche minor seeds are 100-fold less sensitive to this stimulant.

This article belongs to the Special Issue Natural Compound to Biocontrol Agrarian Pests., A new sesquiterpenoid belonging to the subgroup seco-eudesmanolides and named inuloxin E was isolated from Dittrichia viscosa, together with the already known sesquiterpenoids inuloxins A–D and α-costic acid. Inuloxin E was characterized by spectroscopic data (essentially NMR and ESI MS) as 3-methylene-6-(1-methyl-4-oxo-pentyl)-3a,4,7,7a-tetrahydro-3H-benzofuran-2-one. Its relative configuration was determined by comparison with the closely related inuloxin D and chemical conversion of inuloxin E into inuloxin D and by the observed significant correlation in the NOESY spectrum. Both inuloxins D and E induced germination of the parasitic weed Orobanche cumana, but were inactive on the seeds of Orobanche minor and Phelipanche ramosa. The germination activity of some hemisynthetic esters of inuloxin D was also investigated., This research was funded by Programme STAR 2017, financially supported by UniNA and Compagnia di San Paolo grant number E62F16001250003. M. Fernández-Aparicio was supported by projects AGL2017-87693-R and RYC-2015-18961, from the Spanish Ministry of Science, Innovation and Universities.

Strigolactones (SLs) are carotenoid-derived plant secondary metabolites that play important roles in various aspects of plant growth and development as plant hormones, and in rhizosphere communications with symbiotic microbes and also root parasitic weeds. Therefore, sophisticated regulation of the biosynthesis, perception and functions of SLs is expected to promote symbiosis of beneficial microbes including arbuscular mycorrhizal (AM) fungi and also to retard parasitism by devastating root parasitic weeds. We have developed SL mimics with different skeletons, SL biosynthesis inhibitors acting at different biosynthetic steps, SL perception inhibitors that covalently bind to the SL receptor D14, and SL function inhibitors that bind to the serine residue at the catalytic site. In greenhouse pot tests, TIS108, an azole-type SL biosynthesis inhibitor effectively reduced numbers of attached root parasites Orobanche minor and Striga hermonthica without affecting their host plants; tomato and rice, respectively. AM colonization resulted in weak but distinctly enhanced plant resistance to pathogens. SL mimics can be used to promote AM symbiosis and to reduce the application rate of systemic-acquired resistance inducers which are generally phytotoxic to horticultural crops. © 2019 Society of Chemical Industry.

Background Broomrapes attack important crops, cause severe yield losses and are difficult to eliminate because their seed bank is virtually indestructible. In the absence of a host, the induction of seed germination leads to inevitable death due to nutrient starvation. Synthetic analogues of germination-inducing factors may constitute a cheap and feasible strategy to control the seed bank. These compounds should be easy and cheap to synthesise, as this will allow their mass production. The aim of this work is to obtain new synthethic germinating agents. Results Nineteen N-substituted phthalimides containing a butenolide ring and different substituents in the aromatic ring were synthesised. The synthesis started with commercially available phthalimides. The complete collection was assayed against the parasitic weeds Orobanche minor, O. cumana, Phelipanche ramosa and P. aegyptiaca, with the synthetic strigolactone analogue GR24 used as a positive control. These compounds offered low EC50 values: O. cumana 38.3 μM, O. minor 3.77 μM, P. aegyptiaca 1.35 μM and P. ramosa 1.49 μM. Conclusions The synthesis was carried out in a few steps and provided the target compounds in good yields. The compounds tested showed great selectivity, and low EC50 values were obtained for structures that were simpler than GR24. © 2016 Society of Chemical Industry.

Strigolactones (SLs), a group of plant hormones, induce germination of root-parasitic plants and inhibit shoot branching in many plants. Shoot branching is an important trait that affects the number and quality of flowers and fruits. Root-parasitic plants, such as Phelipanche spp., infect tomato roots and cause economic damage in Europe and North Africa&mdash, hence why resistant tomato cultivars are needed. In this study, we found carotenoid cleavage dioxygenase 8-defective mutants of Micro-Tom tomato (slccd8) by the &ldquo, targeting induced local lesions in genomes&rdquo, (TILLING) method. The mutants showed excess branching, which was suppressed by exogenously applied SL. Grafting shoot scions of the slccd8 mutants onto wild-type (WT) rootstocks restored normal branching in the scions. The levels of endogenous orobanchol and solanacol in WT were enough detectable, whereas that in the slccd8 mutants were below the detection limit of quantification analysis. Accordingly, root exudates of the slccd8 mutants hardly stimulated seed germination of root parasitic plants. In addition, SL deficiency did not critically affect the fruit traits of Micro-Tom. Using a rhizotron system, we also found that Phelipanche aegyptiaca infection was lower in the slccd8 mutants than in wild-type Micro-Tom because of the low germination. We propose that the slccd8 mutants might be useful as new tomato lines resistant to P. aegyptiaca.

Strigolactones (SLs), a group of plant hormones, induce germination of root-parasitic plants and inhibit shoot branching in many plants. Shoot branching is an important trait that affects the number and quality of flowers and fruits. Root-parasitic plants, such as Phelipanche spp., infect tomato roots and cause economic damage in Europe and North Africa—hence why resistant tomato cultivars are needed. In this study, we found carotenoid cleavage dioxygenase 8-defective mutants of Micro-Tom tomato (slccd8) by the “targeting induced local lesions in genomes” (TILLING) method. The mutants showed excess branching, which was suppressed by exogenously applied SL. Grafting shoot scions of the slccd8 mutants onto wild-type (WT) rootstocks restored normal branching in the scions. The levels of endogenous orobanchol and solanacol in WT were enough detectable, whereas that in the slccd8 mutants were below the detection limit of quantification analysis. Accordingly, root exudates of the slccd8 mutants hardly stimulated seed germination of root parasitic plants. In addition, SL deficiency did not critically affect the fruit traits of Micro-Tom. Using a rhizotron system, we also found that Phelipanche aegyptiaca infection was lower in the slccd8 mutants than in wild-type Micro-Tom because of the low germination. We propose that the slccd8 mutants might be useful as new tomato lines resistant to P. aegyptiaca.

Highlight Planteose metabolism was uncovered as a key metabolic pathway for germination of Orobanche minor. Inhibition of planteose metabolism by nojirimycin resulted in selective inhibition of O. minor germination., Root parasitic weeds in Orobanchaceae cause serious damage to worldwide agriculture. Germination of the parasites requires host-derived germination stimulants, such as strigolactones, as indicators of host roots within reach of the parasite’s radicles. This unique germination process was focused on to identify metabolic pathways required for germination, and to design a selective control strategy. A metabolomic analysis of germinating seeds of clover broomrape, Orobanche minor, was conducted to identify its distinctive metabolites. Consequently, a galactosyl-sucrose trisaccharide, planteose (α-d-galactopyranosyl-(1→6)-β-d-fructofuranosyl-(2→1)-α-d-glucopyranoside), was identified as a metabolite that decreased promptly after reception of the germination stimulant. To investigate the importance of planteose metabolism, the effects of several glycosidase inhibitors were examined, and nojirimycin bisulfite (NJ) was found to alter the sugar metabolism and to selectively inhibit the germination of O. minor. Planteose consumption was similar in NJ-treated seeds and non-treated germinating seeds; however, NJ-treated seeds showed lower consumption of sucrose, a possible intermediate of planteose metabolism, resulting in significantly less glucose and fructose. This inhibitory effect was recovered by adding glucose. These results suggest that planteose is a storage carbohydrate required for early stage of germination of O. minor, and NJ inhibits germination by blocking the supply of essential glucose from planteose and sucrose. Additionally, NJ selectively inhibited radicle elongation of germinated seeds of Orobanchaceae plants (Striga hermonthica and Phtheirospermum japonicum). Thus, NJ will be a promising tool to develop specific herbicides to the parasites, especially broomrapes, and to improve our understanding of the molecular mechanisms of this unique germination.

Obligate root-parasitic plants belonging to the Orobanchaceae family are deadly pests for major crops all over the world. Because these heterotrophic plants severely damage their hosts even before emerging from the soil, there is an unequivocal need to design early and efficient methods for their control. The germination process of these species has probably undergone numerous selective pressure events in the course of evolution, in that the perception of host-derived molecules is a necessary condition for seeds to germinate. Although most of these molecules belong to the strigolactones, structurally different molecules have been identified. Since strigolactones are also classified as novel plant hormones that regulate several physiological processes other than germination, the use of autotrophic model plant species has allowed the identification of many actors involved in the strigolactone biosynthesis, perception, and signal transduction pathways. Nevertheless, many questions remain to be answered regarding the germination process of parasitic plants. For instance, how did parasitic plants evolve to germinate in response to a wide variety of molecules, while autotrophic plants do not? What particular features are associated with their lack of spontaneous germination? In this review, we attempt to illustrate to what extent conclusions from research into strigolactones could be applied to better understand the biology of parasitic plants.

Certain amino acids induce inhibitory effects in plant growth due to feedback inhibition of metabolic pathways. The inhibition patterns depend on plant species and the plant developmental stage. Those amino acids with inhibitory action on specific weeds could be utilized as herbicides, however, their use for weed control has not been put into practice. Orobanche minor is a weed that parasitizes red clover. O. minor germination is stimulated by clover root exudates. The subsequent seedling is an obligated parasite that must attach quickly to the clover root to withdraw its nutrients. Early development of O. minor is vulnerable to amino acid inhibition and therefore, a series of in vitro, rhizotron, and field experiments were conducted to investigate the potential of amino acids to inhibit O. minor parasitism. In in vitro experiments it was found that among a collection of 20 protein amino acids, lysine, methionine and tryptophan strongly interfere with O. minor early development. Field research confirmed their inhibitory effect but revealed that methionine was more effective than lysine and tryptophan, and that two successive methionine applications at 308 and 543 growing degree days inhibited O. minor emergence in red clover up to 67%. We investigated additional effects with potential to influence the practical use of amino acids against broomrape weeds, whether the herbicidal effect may be reversible by other amino acids exuded by host plants or may be amplified by inducing host resistance barriers against O. minor penetration. This paper suggests that amino acids may have the potential to be integrated into biorational programs of broomrape management., This work was funded by INRA ‘Division Santé des Plantes et Environnement. Appel à projets scientifiques 2015. Catégorie Biocontrôle’. MF-A was supported by the Marie-Curie FP7 COFUND People Programme, through the award of an AgreenSkills fellowship (under grant agreement n° PCOFUND-GA-2010-267196).

Root exudates from the allelopathic plant, black oat (Avena strigosa Schreb.), were found to contain at least six different germination stimulants for root parasitic plants, but no known strigolactones (SLs). One of these germination stimulants was purified and named avenaol. Its HR-ESI-TOFMS analysis indicated that the molecular formula of avenaol is C20H24O7, and thus it contains an additional carbon compared with known C19-SLs. Its structure was determined as 5-((E)-(5-(3-hydroxy-1,5,5-trimethyl-2-oxobicyclo[4.1.0]heptan-7-yl)-2-oxodihydrofuran-3(2H)-ylidene)methoxy)-3-methylfuran-2(5H)-one, by 1D and 2D NMR spectroscopy, and ESI- and EI-MS spectrometry. Although avenaol contains the C-D moiety, the common structural feature for all known SLs, it lacks the B ring and has an additional carbon atom between the A and C rings. Avenaol is a potent germination stimulant of Phelipanche ramosa seeds, but only a weak stimulant for seeds of Striga hermonthica and Orobanche minor.

Allelopathy has been considered not only as an environmentally friendly approach for weed control but also a potential reason causing autotoxicity in crop production. In this study, the responses of seeds of lettuce, wheat, rice, clover broomrape (CB), and sunflower broomrape (SB) to the root exudates of rice cultivars were studied. Lettuce germination was promoted by root exudates of Yliangyou 3218 and I-Kung-Pao. Wheat seedling growth was inhibited by all nine rice species. I-Kung-Pao and Ganxin 203 exerted greater autotoxicity than other cultivars. Yongyou 15 and I-Kung-Pao induced the highest germination rate of CB, while Yongyou 13, Zhongzao 22, and I-Kung-Pao induced the highest germination rate of SB. A significantly correlation was noted between germination-inducing ability on broomrape seeds and allelopathic effects on target plants. It is suggested that using broomrape seeds germination is a better receptor for the identification of rice allelopathic potential.

Cucumber (Cucumis sativus) plants were found to exude at least 12 germination stimulants for root parasitic weeds including 5 known strigolactones, 7-oxoorobanchol, 7-oxoorobanchyl acetate, orobanchol, orobanchyl acetate, and 4-deoxyorobanchol. Two novel germination stimulants were purified from cucumber root exudates and their structures were determined to be 7αand 7β-hydroxyorobanchyl acetate by 1D and 2D NMR spectroscopy, and ESIand EI-MS spectrometry. The stereochemistry was determined by NOE measurement and by comparing the CD spectra with those of the synthetic standards of four stereoisomers of orobanchol. 7αand 7β-Hydroxyorobanchol were detected by LC-MS/MS, and GC-MS analysis of purified sample confirmed their structures. The germination stimulation activities of 7αand 7β-hydroxyorobanchyl acetate on Orobanche minor were comparable to those of orobanchyl acetate and 7-oxoorobanchyl acetate. By contrast, 7β-hydroxyorobanchyl acetate was a highly potent germination stimulant for Phelipanche ramosa inducing more than 50% germination at 10 pM. © Pesticide Science Society of Japan

(+)-Strigone was described earlier in a paper on isolation of strigol and then recently examined for hyphal branching activity in arbuscular mycorrhizal fungi as a strigolactone. Herein, it was isolated from root exudates of Houttuynia cordata, and its structure was confirmed by direct comparison with synthetic standards in LC-MS/MS, GC-MS, and (1)H and (13)C NMR analyses. The stereochemistry of strigone was determined by comparing the CD spectra and RR(t) in chiral LC-MS/MS with those of synthetic (+)-strigone and (-)-strigone. Four stereoisomers of strigone exhibited clearly different levels of stimulation activity on the seeds of three root parasitic plants, Orobanche minor, Phelipanche ramosa, and Striga hermonthica. (+)-Strigone was a highly potent germination stimulant on S. hermonthica and also on P. ramosa, but less active than ent-2'-epi-strigone on O. minor. In addition to strigone, H. cordata was found to produce strigol, sorgomol, and 5-deoxystrigol, indicating that this plant produces mainly strigol-type strigolactones derived from 5-deoxystrigol.

The holoparasitic angiosperm Orobanche minor parasitizes a diverse range of flowering plants from at least 16 orders in both the monocots and eudicots. However, populations of O. minor show host specificity at a local level. Our previous work identified the potential for host specificity to act as a catalyst for genetic divergence among populations of O. minor. Here we have extended this investigation by sampling populations from multiple hosts, across a broad geographic range. Sequence characterised amplified region (SCAR) data identified an exotic host-generalist lineage and a native host-specialist lineage of O. minor, suggesting genetic structure in this species is defined by both host specificity and geography. In addition, host-range overlap, discordant tree topologies, and cryptic morphology indicate the presence of gene flow between alien races and endemic populations. Therefore, repeated introductions of alien races of O. minor from disparate sources leading to introgression with native populations, and cryptic race formation, seem to have contributed to the taxonomic confusion associated with this species. We speculate that radiations associated with broad host range and divergent host ecologies may have promoted the unusually wide geographic distribution and diversification of this species. Finally, evidence of multiple shifts to exotic hosts, coupled with the predicted northward shift in climatic suitability, identify the potential for range expansion in alien races of O. minor, which may threaten nationally scarce native taxa with genetic assimilation. Our phylogenetic analysis provides a framework for identifying host races in Orobanche with a view to setting conservation priorities. © Springer-Verlag 2009.

Small broomrape is a federally listed noxious weed that was first identified in Oregon in 1923. Between 1923 and 1997, there were only six reports of the species in Oregon. Small broomrape is a holoparasitic weed that attaches to the root of its host and can lead to crop failure depending on the level of infestation. Small broomrape was identified in a red clover field in Oregon in 1998. In 2000 and 2001, the Oregon Department of Agriculture surveyed red and white clover fields in Oregon for the presence of small broomrape; 15 infested fields were identified in 2000 and 22 in 2001. The source of the small broomrape seed was not identified although there was speculation that small broomrape seed may have been contaminated clover seed stock. In 2000, a quarantine was established for small broomrape in red clover seed. Research identified effective, easy to implement management strategies for small broomrape including the use of false host crops and imazamox. In 2003, the ODA amended the quarantine to eliminate the mandatory seed sampling and testing and the requirement of reporting infested fields and seed lots. In 2011, there are still populations of small broomrape present in red clover fields in Oregon.

Nine-cis-epoxycarotenoid dioxygenase (NCED), belonging to the family of carotenoid-cleaving dioxygenases (CCDs), is the rate-limiting step in the abscisic acid (ABA) biosynthetic pathway in plants. Abamine is the first reported abscisic acid biosynthesis inhibitor to target NCED. Its utility has also been considered in the inhibition of other enzymes. As CCDs other than NCED are also involved in the strigolactone biosynthetic pathway, abamine may affect strigolactone biosynthesis. In this study, we found that abamine decreases the level of strigolactones in several plant species and reduces the germination rate of Orobanche minor seeds co-grown with tobacco. Taken together, these data suggest that abamine may be used as a scaffold for the development of specific regulators of strigolactone production.

Eleven naturally occurring strigolactones (SLs) were examined for their germination-stimulating activity on the seeds of a root parasitic plant Orobanche minor Sm. Based on their activity, SLs are classified into 3 groups (A–C). Group A, the most active germination stimulant, consists of 3 monohydroxy-SLs, orobanchol, 2′-epiorobanchol, and sorgomol, inducing >80% germination of O. minor seeds at 10 pM. Group B includes 5 SLs, which were ca. 10-fold less active than those in group A. The 3 least active SLs in group C were either more lipophilic or probably less stable than SLs in groups A and B. These results indicate that the germination-stimulating activity of SLs depends on the lipophilicity of the SL molecules and their stability also influences activity. Other structural features for germination-stimulating activity are also discussed.

A number of broomrapes (Orobanche spp.) are major threats for grain legumes in the Mediterranean area. Previous studies have shown very high levels of resistance to Orobanche crenata in Medicago truncatula with little variation among accessions hampering, therefore, its use for genetic analysis. In order to identify alternative systems for ulterior genetic and genomic analysis, we studied early stages of the interaction between M. truncatula accessions and a range of Orobanche species. We found significant differences in the induction of germination on Orobanche aegyptiaca, Orobanche foetida var. broteri, Orobanche minor, Orobanche nana and Orobanche ramosa seeds. Accessions also varied in the number of O. aegyptiaca, O. crenata, O. foetida var. broteri, O. nana and 0. ramosa attachments supported. Applications of the synthetic germination stimulant GR24 increased the germination level of Orobanche cumana and 0. minor. No attachments were observed for any of these species because of physical barriers typical of host resistance. On the contrary, increase of 0. nana germination by GR24 led to an increase in number of attachments albeit the normal development of the nodules was stopped in a later stage. The genetic variation observed for induction of germination and subsequent attachment will be useful for isolating and characterising genes involved in early stages of Orobanche-host plant interaction and for the study of the biosynthetic pathways of production of germination stimulants.