Seed Germination and Radicle Growth - American Chemical Society

Article pubs.acs.org/JAFC

Effect of Fungal and Plant Metabolites on Broomrapes (Orobanche and Phelipanche spp.) Seed Germination and Radicle Growth Alessio Cimmino,† Mónica Fernández-Aparicio,‡ Anna Andolfi,† Sara Basso,† Diego Rubiales,§ and Antonio Evidente*,† †

Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Complesso Universitario Monte S. Angelo, Via Cintia, 4, 80126 Napoli, Italy ‡ INRA, UMR1347 Agroécologie, BP 86510, F-21000 Dijon, France § Institute for Sustainable Agriculture, CSIC, Apdo. 4084, 14080 Córdoba, Spain ABSTRACT: Orobanche and Phelipanche species (the broomrapes) are root parasitic plants, some of which cause heavy yield losses on important crops. The development of herbicides based on natural metabolites from microbial and plant origin, targeting early stages on parasitic plant development, might contribute to the reduction of broomrape seed bank in agricultural soils. Therefore, the effect of metabolites belonging to different classes of natural compounds on broomrape seed germination and radicle development was assayed in vitro. Among the metabolites tested, epi-sphaeropsidone, cyclopaldic acid, and those belonging to the sesquiterpene class induced broomrape germination in a species-specific manner. epi-Epoformin, sphaeropsidin A, and cytochalasans inhibited germination of GR24-treated broomrape seeds. The growth of broomrape radicle was strongly inhibited by sphaeropsidin A and compounds belonging to cyclohexene epoxide and cytochalasan classes. Broomrape radicles treated with epi-sphaeropsidone developed a layer of papillae while radicles treated with cytochalasans or with sphaeropsidin A turned necrotic. These findings allow new lead natural herbicides for the management of parasitic weeds to be identified. KEYWORDS: parasitic weed, allelopathy, fungal toxins, host recognition, broomrape control, nature-inspired herbicides, Orobanche radicle

■

INTRODUCTION Orobanche and Phelipanche species (the broomrapes) are obligate root parasitic plants, some of which represent serious weed problems causing severe yield reduction of many important crops and for which there are few effective control methods.1−4 The main obstacle for long-term management of broomrape infested fields is the durable seedbank with evolved mechanisms of host recognition upon perception of host-derived germination factors. Broomrape seedbank may remain in this way viable for decades. As long as the seed bank is not depleted, the need to apply means to control the parasite will persist whenever a susceptible host is grown in the infested field. In practice, broomrape control relies on the use of resistant cultivars to parasitic plants, and when they are not available, the control relies on the avoidance of the susceptible crop species in the rotation.2 However, even if the farmer completely avoids susceptible crops in the rotation for many years, susceptible autotrophic weed species or volunteer plants from former susceptible crops can keep replenishing the parasitic seedbank by being themselves infected. The use of herbicides has shown some degree of success for the control of broomrape parasitism. However, because of the tight physical and metabolic coordination established between host and parasitic weed though the parasitic attachment to the host root, success in chemical control of postattached parasites is restricted to few crop-broomrape species pairs as there are few herbicides able to selectively control broomrapes without damaging the crop to which it is attached.3,5,6 Preattached parasitic life stages are more susceptible to treatment by chemical control. Two different herbicidal strategies would lead to the © 2014 American Chemical Society

depletion of broomrape seed bank. Compounds that induce suicidal germination in absence of a host are based on the fact that broomrape seed germinated in the absence of a host is unable to survive more than a few days without host-derived nutrient supply. The second strategy is based on the ability of certain compounds to interfere in the parasitic plant process. They can inhibit germination in the presence of host-derived germinationinducing factors or the growth of the seedling radicle therefore reducing the parasitic success on reaching and parasitizing the host root, with lethal consequences to the parasite.2 The extensive use of synthetic chemicals, which frequently have low specificity and are not easily biodegradable, prompted different approaches to discover natural products as templates to develop biopesticides with new chemical structures and mode of actions.7,8 Besides the well-known parasitic seed germination stimulants dihydrosorgoleone, sesquiterpene lactones, and strigolactones,9 other metabolites belonging to different classes of natural compounds were isolated from pea10,11 and common vetch12 root exudates. Similar activity was also shown by some fungal terpenoids and their hemisynthetic derivatives,13−15 while inhibitory effect was exhibited from four new sesquiterpenoids recently isolated from Inula viscosa.16 These results prompted testing of the effect of some plant allelochemicals and several phytotoxins with very different Received: Revised: Accepted: Published: 10485

July 2, 2014 October 1, 2014 October 1, 2014 October 1, 2014 dx.doi.org/10.1021/jf504609w | J. Agric. Food Chem. 2014, 62, 10485−10492

Journal of Agricultural and Food Chemistry

Article

chemical structures isolated from fungal pathogens belonging to Diplodia, Didymella, Phoma, Pyrenophora, and Seiridium genera on the seed germination and radicle growth of four major broomrape species. This work was designed to investigate the ability of metabolites isolated from the above cited plant and fungi to either stimulate suicidal seed germination or inhibit germination induced by a germination-inducing factor on four broomrape species Orobanche crenata, Orobanche cumana, Orobanche minor, and Phelipanche ramosa. Their effect on the radicle growth and their potential as lead compounds to develop new classes of bioherbicides was also evaluated and discussed.

■

MATERIALS AND METHODS Fungal Sources and Tested Metabolites. Sphaeropsidin A, 4, sphaerospidone, 5, and epi-sphaeropsidone, 3; cyclopaldic acid, 1; and epi-epoformin, 2 (Figure 1), were purified,

Figure 2. Phytotoxins isolated from Phoma spp.cavoxin, cavoxone, chenopodolin, chenopodolan C, and 6-hydroxymellein (10−14)and from Pyrenophora seminiperdacytochalasins A and B and deoxaphomin (15−17).

Figure 1. Phytotoxins isolated from Seiridium cupressi and Diplodia spp.cyclopaldic acid, epi-epoformin, epi-sphaeropsidone, sphaeropsidin A, and sphaeropsidone (1−5)and from Didymella pinodesepiherbarumin II, herbarumin II, pinolide, and pinolidoxin (6−9).

respectively, all as white needles from the culture filtrates of Diplodia cupressi,17,18 Seiridium cupressi,19 and Diplodia quercivora.20 Pinolidoxin, 9; pinolide, 8; herbarumin II, 7; and epi-herbarumin II, 6 (Figure 1), were isolated from the culture filtrates of Didymella pinodes.21 Cavoxin, 10, and cavoxone, 11, and chenopodolin, 12; chenopodolan C, 13; and 6-hydroxymellein, 14 (Figure 2), were isolated, respectively, from the culture filtrates of Phoma cava22 and Phoma chenopodiicola.23,24 Cytochalasins A, 15, and B, 16, and deoxaphomin, 17 (Figure 2), were isolated from the solid culture of Pyrenophora seminiperda.25 All the above cited fungal metabolites were freshly isolated from the fungal cultures according to the protocols reported in the literature and were identified by 1H NMR and electrospray ionization mass spectrometry (ESI MS), comparing these data with those previously described. Finally, fusaric acid, 21 (Figure 3), was purchased from Sigma (St. Louis, MO). Plant Source and Tested Metabolites. Inuloxins A, 19, and C, 20, and α-costic acid, 18 (Figure 3), were freshly isolated from the aerial part of Inula viscosa according to the previously reported protocol16 and were identified by 1H NMR and ESI MS, comparing these data with those previously described. Induction of Orobanche Seed Germination by Fungal and Plant Metabolites. The biological activity of the metabolites (Figures 1−3) isolated from Diplodia spp., Didymella pinodes,

Figure 3. Phytotoxins isolated from Inula viscosa, α-costic acid and inuloxins A and C (18−20). Fusaric acid (21).

Phoma spp., P. seminiperda, S. cupressi, and I. viscosa was assayed on O. crenata, O. cumana, O. minor, and P. ramosa seeds. For this purpose, seeds were surface sterilized by immersion in 0.5% (w/v) NaOCl and 0.02% (v/v) Tween 20, were sonicated for 2 min, were rinsed thoroughly with sterile distilled water, and were dried in a laminar air flow cabinet. Approximately 100 seeds of each broomrape species were placed separately on 9 mm diameter glass fiber filter paper disks (GFFP) moistened with 50 μL of sterile distilled water. Subsequently, GFFP disks were placed inside sterile 10 cm Petri dishes, were sealed with parafilm, and were kept for 10 days in the dark at 22 °C to allow seed conditioning. GFFP disks were transferred inside laminar flow cabinet to sterile filter paper to remove excess water, and then they were transferred to a new 10 cm sterile Petri dish. 10486

dx.doi.org/10.1021/jf504609w | J. Agric. Food Chem. 2014, 62, 10485−10492


Article

bi- and tricyclic sesquiterpenes. Finally, cyclopaldic, 1 (Figure 1), and fusaric acid, 21 (Figure 3), are a substituted benzofuranone and a substituted pyridinic acid, respectively. Phytotoxin Activity as Stimulators of Broomrape Suicidal Germination. The stimulation activity of these metabolites on broomrape seed germination was tested on four broomrape speciesO. crenata, O. cumana, O. minor, and P. ramosa. All metabolites belonging to bi- and tricyclic sesquiterpenes class (inuloxins A and C and α-costic acid) induced significant germination on seeds of O. cumana (Figure 4A). The effect of inuloxin A, 19, and α-costic acid, 18 (Figure 3), was stronger than inuloxin C, 20 (Figure 3). Interestingly, O. cumana seeds that germinated with inuloxin C showed short radicles with light brown patches, symptoms that were not observed in seedlings germinated with inuloxin A and α-costic acid. In addition to bi- and tricyclic sesquiterpenes, cyclopaldic acid, 1 (Figure 1), a substituted benzofuranone, induced significant germination of O. cumana seeds (Figure 4A). The rest of the metabolites tested did not induce any germination in O. cumana seeds except for the positive control. P. ramosa seeds were induced to germinate when exposed to inuloxin A and α-costic acid but not when exposed to inuloxin C or cyclopaldic acid (Figure 4B). In addition, epi-sphaeropsidone, 3 (Figure 1), a cyclohexene epoxide, induced significant germination on P. ramosa but not in the rest of the broomrape species tested (Figure 4B). O. crenata and O. minor seeds did not germinate when exposed to any of the compounds tested except for the positive control (data not shown). Phytotoxin Activity as Inhibitors of Broomrape Germination and Radicle Growth. In addition to germinationinducing activity, each compound was also tested as potential inhibitor for broomrape development by inhibiting its germination (Figure 5) and its radicle growth (Figure 6). Each metabolite was mixed with the germination factor GR24 and was applied to conditioned seeds of O. crenata, O. cumana, O. minor, and P. ramosa. epi-Epoformin, 2, and sphaeropsidin A, 4 (Figure 1), significantly inhibited germination of O. crenata and O. cumana seeds (Figure 5A and B). Inhibition of O. minor and P. ramosa seed germination was induced by sphaeropsidin A but not by epi-epoformin (Figure 5C and D). All cytochalasans, 15−17 (Figure 2), inhibited the germination of P. ramosa seeds (Figure 5D), but germination of Orobanche species was not inhibited by this class of compounds except that deoxaphomin, 17 (Figure 2), induced inhibition of O. crenata germination (Figure 5A). Regarding inhibition of radicle growth, all cyclohexene oxides (2, 3, and 5, Figure 1) and cytochalasans (15−17, Figure 2) induced a strong and significant reduction on broomrape radicle length when compared with control radicles (i.e., radicles emerged from seeds induced only with GR24, Figures 6 and 7). This is very significant from a parasitic weed control point of view, as broomrape radicles have limited growth length and constitute the organ that establishes host contact and carries the attachment and penetration organ in its tip. Despite the similar effect on radicle growth inhibition performed by cyclohexene oxides and cytochalasans, there were important differences in the appearance of the radicles treated with each class of compound. While radicles of all broomrape species exposed to cytochalasans quickly turned brown and necrotic (Figure 7B), radicles exposed to cyclohexene oxides although much shorter than the control radicles had a healthy appearance (Figure 7C). In addition, O. crenata and O. cumana radicles exposed to cyclohexene epoxides developed a dense layer of papilla-like structures at the tip of the radicle

Tested samples, dissolved in methanol, were diluted with sterilized distilled water to a final concentration of 10−4 M. The final concentration of methanol was adjusted to 0.70% (v/v). Each disk containing conditioned seeds was treated with 50 μL aliquot of the respective test solution. Each treatment was replicated three times. Seeds treated with distilled water (containing 0.70% methanol) or the synthetic strigolactone GR2426,27 at 0.6 and 0.06 mM were included as controls for comparison. The seeds were incubated in the dark at 22 °C for 7 days prior to examination for germination. Seeds with an emerged radicle were scored as germinated using a stereoscopic microscope at 30 × magnification, and the percentage of germination was established for each dish. Inhibition of Orobanche Seed Germination and Radicle Growth by Fungal and Plant Metabolites. The inhibitory activity of the various above metabolites (Figures 1−3) on seed germination and radicle growth of O. crenata, O. cumana, O. minor, and P. ramosa was assayed as reported previously.28 A solution of the GR24 (10−6 M) was prepared in sterile distilled water. Immediately before use, stock solutions of each toxin prepared in methanol were diluted in the GR24 solution to 10−4 M of each toxin while keeping constant the GR24 concentrations and methanol in order to allow comparisons. Broomrape seeds were surface sterilized and conditioned as described above. GFFP disks containing conditioned broomrape seeds were transferred inside a flow laminar cabinet to a sterile sheet of filter paper to remove excess moisture and were transferred to a 10 cm diameter Petri dish. Fifty microliter aliquots of each toxin-GR24 were applied to each GFFP disk containing the seeds. Petri dishes were sealed with Parafilm and were stored in the dark at 22 °C for 7 days to promote germination and radicle growth. Then, seeds were observed under stereoscopic microscope in order to score levels of allelopathic-mediated inhibition of broomrape seed germination and radicle growth. Statistical Analysis. All the bioassays were performed twice with at least three replicates. Percentage data were approximated to normal frequency distribution by means of angular transformation {180/π × arcsine (sqrt[%/100])} and were subjected to analysis of variance (ANOVA) using SPSS software for Windows, version 21.0 (SPSS Inc., Chicago, Illinois, U.S.A.). The significance of mean differences between each treatment against its respective control was evaluated by the two-sided Dunnett test. Null hypothesis was rejected at the level of 0.05.

■

RESULTS AND DISCUSSION Phytotoxins isolated from plant pathogenic fungi as well as those produced by an allelopathic plant were used in a bioactivity screening on seed germination and radicle growth of O. crenata, O. cumana, O. minor, and P. ramosa, four major broomrape species constraining production of major agricultural crops worldwide. The phytotoxins belong to different classes of natural compounds as sphaeropsidin A, 4 (Figure 1), and chenopodolin, 12 (Figure 2), which are tetracyclic pimarane diterpenes, and as epi-epoformin, 2; epi-sphaeropsidone, 3; and sphaeropsidone, 5 (Figure 1), which are cyclohexene epoxide. epi-Herbarumin II, 6; herbarumin II, 7; pinolide, 8; and pinolidoxin, 9 (Figure 1), are nonenolides, while cytochalasins A, 15, and B, 16, and deoxaphomin, 17 (Figure 2), are 24-oxa[14] and [13] cytochalasans, respectively. Cavoxin, 10; cavoxone, 11; chenopodolan C, 13; and 6-hydroxymellein, 14 (Figure 2), are a chalcone, a chromanone, a furopyran and a hydroxymellein. α-Costic acid, 18, and inuloxins A, 19, and C, 20 (Figure 3), are 10487



Article

Figure 4. Stimulatory effect on (A) O. cumana and (B) Phelipanche ramosa seed germination of the tested phytotoxins. The asterisk (*) indicates differences at the 0.05 level compared with the negative control (seeds treated with water).

herbicide, like inuloxin A and α-costic acid, would be a better candidate for broomrapes post-germination herbicide reducing the parasitic capability of attacking the host crop by reducing the attachment organ length. Some structure−activity relationships could be evaluated within the same class of the natural compounds. The different activity showed on broomrape germination by epi-epoformin, 2 (Figure 1, strong inhibitor of O. cumana seed germination), and epi-sphaeropsidone, 3 (Figure 1, stimulant of P. ramosa seed germination), and sphaeropsidone, 5 (Figure 1, practically inactive), which have the same carbon skeleton, should be due to the different stereochemistry of the epoxy ring and that of the hydroxy group at C-5. On the other hand, common structural features such as the 5-hydroxycyclohexenone-1,6-oxide group in these three compounds induced radicle growth cessation in all broomrapes tested and induced the differentiation of a papillae layer in the radicle tip of O. crenata and O. cumana. No reports have been previously published on these effects on broomrape development mediated by these chemical structures. Sphaeropsidin A, 4 (Figure 1), showed a strong phytotoxic effect by inhibiting both germination and radicle growth on all the broomrapes species tested while chenopodolin, 12 (Figure 2),

(Figure 7C). The papilla layer was not observed in radicles exposed to any other compound in this work. The tetracyclic pimarane diterpene, sphaeropsidin A, 4 (Figure 1), showed a strong phytotoxic effect on all broomrapes species tested inducing inhibition of both germination and radicle growth. Radicles of broomrape exposed to sphaeropsidin A quickly turned brown and necrotic. Inuloxin C, 20 (Figure 3), did not significantly inhibit broomrape germination, and its inducing effect on suicidal germination, in absence of germination-inducing factor GR24, was low and restricted to O. cumana (Figure 4A). Despite this stimulatory activity observed in O. cumana, when broomrape seeds were exposed to a mixture of GR24 and inuloxin C, germinated seedlings developed radicles that were shorter than those in the controls, and this effect was observed in seeds of all the broomrape species tested. In addition, O. crenata and O. cumana radicles exposed to inuloxin C showed light brown patches (Figure 7D), which could point to a cytotoxic effect although this fact needs further investigation. This combined activity allows differentiating inuloxin C from the other sesquiterpenes tested regarding its potential for agronomical use. Inuloxin C, rather than being a good candidate for suicidal germination-based 10488



Article

Figure 5. Inhibitory effect on (A) Orobanche crenata, (B) O. cumana, (C) O. minor, and (D) Phelipanche ramosa seed germination of the tested phytotoxins. The asterisk (*) indicates differences at the 0.05 level compared with the positive control (seeds induced to germinate with GR24).

The different biological activity observed between the three sesquiterpenes tested, with α-costic acid and inuloxins A inducing O. cumana and P. ramosa germination and inuloxin C displaying

is inactive. Both are tetracyclic pimarane diterpenes but strongly differ in the junction between γ-lactone ring and phenanthrene ring system and in the functionalities of the latter. 10489



Article

Figure 6. Inhibition of broomrape radicle growth induced by the tested phytotoxins. The broomrape species tested were (A) Orobanche crenata, (B) O. cumana, (C) O. minor, and (D) Phelipanche ramosa. The asterisk (*) indicates differences at the 0.05 level compared with the positive control (seeds induced to germinate with GR24).

mainly a phytotoxic effect, was due to the different organization of the carbon skeleton and also to their different functionalities and

stereochemistry. These results were in agreement with those reported previously testing the same compounds on O. crenata.16 10490



Article

germination may be confounded with strong inhibition of initial seedling development because of the radicle remaining inside the seed coat. In conclusion, 21 phytotoxins belonging to different classes of natural compounds isolated from different pathogenic fungi and an allelophatic plant were tested on four different broomrape species. The discovery of the negative effect on radicle growth exerted by sphaeropsidin A and compounds belonging to cyclohexene epoxides and cytochalasans is the first step that paves the way for the development of herbicides promoting the interruption of parasitic life cycle before host attachment and crop resource withdrawal by the parasite. Further studies on these compounds could lead to the development of a new and unexplored strategy for broomrape control. In addition to radical growth inhibition, some compounds induced the inhibition of germination in the presence of parasitic plant germination-factor GR24. epi-Epoformin, 2; sphaeropsidin A, 4 (Figure 1); and cytochalasans caused the strongest inhibition of seed germination, and this effect adds to the effect of radicle growth inhibition to strengthen the potential of these substances as candidates for broomrape seedbank management in agricultural soils cultivated with susceptible crop species. Interesting species-specific activity was discovered for some of the compounds tested inducing broomrape seed germination. P. ramosa seed germination was induced by epi-sphaeropsidone, 3, and cyclopaldic acid, 1 (Figure 1), and inuloxin A, 19 (Figure 3), while germination of O. cumana was only induced by sesquiterpenes. Seeds from the O. crenata and O. minor species did not germinate in the presence of any of the compounds tested except for the positive control. This specificity is important from a point of view of parasitic plant germination biology because the unresponsive broomrape species and particularly O. minor are broomrape species with high sensitivity to a broad range of compounds and root exudates.31,32 The strong effect induced by inuloxin A and α-costic acid on O. cumana opens new research addressing broomrape control through a suicidal germination strategy for this broomrape species. Among the rest of the active compounds as broomrape germination inductors, epi-sphaeropsidone and cyclopaldic acid are probably too weak in their current structural form to have practical applications for field delivery as suicidal germinationinducing herbicides; however, as described before, the report of this activity is important because of the special evolutionary strategy of parasitic plants that allows them to germinate in the presence of host-derived factors. The germination biology of parasitic plants is far from completely elucidated, and it has been suggested that combination of compounds may confer specific host recognition patterns. Metabolites promoting low germination inducing activity may have a role on modulation of host recognition in a species-specific manner. In addition, those compounds that showed activities can be subjected to structural modifications in order to increase the intensity of germinationinducing activities. The results represent important findings for further studies on new compounds as tools to be used in the design of new approaches for parasitic weed control such as nature-inspired herbicides or engineering resistant crops by enhancing expression of allelochemicals or phytotoxins against parasitic weed germination and development.33

Figure 7. Radicle growth modification by fungal and plant toxins observed at 7 days after GR24 aplication. (A) Orobanche control radicle, (B) cytochalasin-treated Orobanche radicle, (C) cyclohexene epoxidetreated Orobanche radicle, and (D) inuloxin C-treated Orobanche radicle.

The structural differences between the three cytochalasans tested did not lead to differences in biological activities for broomrape germination and radicle growth. All of them similarly induced phytotoxic effects on broomrape by inhibiting seed germination and radicle growth inhibition and toxicity in radicles. Herbicidal effects mediated by deoxaphomin, cytochalasin A, and cytochalasin B inducing necrosis in tissues of other weeds have been previously reported,29 but this effect was never tested in broomrape germination and radicle growth. Previously, cytochalasins E and B were tested on Striga seed germination, and of them, only cytochalasin E inhibited Striga germination by 50%, cytochalasin B being noninhibitory.30 Unfortunately, these authors did not evaluate the effect of the toxic effects in Striga radicles. We have found that cytochalasans inhibit germination only in the Phelipanche species but not in the Orobanche species. In addition, we observed a strong toxic effect in radicles of all broomrape species tested by inhibiting their growth and inducing darkening in the radicle. The germination bioassays widely conducted on broomrape research are based on the quantification of seeds with emerged radicle through the seed coat. A seed with emerged radicle is counted as germinated. However, in bioassays where the herbicide tested is inducing such a strong reduction on seedling development as that in this work by cytochalasans, it is difficult to discern between inhibition of the strict germination process and inhibition of initial seedling development. Seed germination is a complex physiological process where the seed transforms from dormant to metabolically active, and this process begins with perception of dormancy breaking/germination inducing signals and ends with the beginning of radicle emergence through the seed coat. In the present study, lack of visible radicle in P. ramosa induced by cytochalasans does not mean strictly germination inhibition as the toxins could have allowed germination triggered by GR24, but the seedling development could be inhibited so strongly that the radicle did not make it through the seed coat. Cytochalasantreated P. ramosa seeds showed either no radicle visible or such a short radicle that it was extending in length very little from the seed cover. Inhibitory effect of cytochalasans on P. ramosa

■

AUTHOR INFORMATION

Corresponding Author

*Tel: +39 081 2539178. Fax: +39 081 674330. E-mail: [email protected]. 10491



Article

Funding

(16) Andolfi, A.; Zermane, N.; Cimmino, A.; Avolio, F.; Boari, A.; Evidente, A. Inuloxins A-D, phytotoxic bi- and tri-cyclic sesquiterpene lactones produced by Inula viscosa: potential for broomrapes and field dodder management. Phytochemistry 2013, 86, 112−120. (17) Evidente, A.; Sparapano, L.; Motta, A.; Giordano, F.; Fierro, O.; Frisullo, S. A phytotoxic pimarane diterpene of Sphaeropsis sapinea f. sp. cupressi, the pathogen of a canker disease of cypress. Phytochemistry 1996, 42, 1541−1546. (18) Evidente, A.; Sparapano, L.; Fierro, O.; Bruno, G.; Giordano, F.; Motta, A. Sphaeropsidone and epishaeropsidone, two phytotoxic dimedone methyl ethers produced by Sphaeropsis sapinea f. sp. cupressi grown in liquid cultures. Phytochemistry 1998, 48, 1139−1143. (19) Graniti, A.; Sparapano, L.; Evidente, A. Cyclopaldic acid, a major phytotoxic metabolite of Seiridium cupressi, the pathogen of a canker disease of cypress. Plant Pathol. 1992, 41, 563−568. (20) Andolfi, A.; Maddau, L.; Basso, S.; Linaldeddu, B. T.; Cimmino, A.; Scanu, B.; Deidda, A.; Tuzi, A.; Evidente, A. Diplopimarane, a phytotoxic 20-nor-ent-pimarane produced by the oak pathogen Diplodia quercivora. J. Nat. Prod. 2014, accepted. (21) Cimmino, A.; Andolfi, A.; Fondevilla, S.; Abouzeid, M. A.; Rubiales, D.; Evidente, A. Pinolide, a new nonenolide produced by Didymella pinodes, the causal agent of Ascochyta blight on Pisum sativum. J. Agric. Food Chem. 2012, 60, 5273−5278. (22) Evidente, A.; Randazzo, G.; Iacobellis, N. S.; Bottalico, A. Structure of cavoxin, a new phytotoxin from Phoma cava and cavoxone, its related chroman-4-one. J. Nat. Prod. 1985, 48, 916−923. (23) Cimmino, A.; Andofi, A.; Zonno, M. C.; Avolio, F.; Santini, A.; Tuzi, A.; Berestetskiy, A.; Vurro, M.; Evidente, A. Chenopodolin: a phytotoxic unrearranged ent-pimaradiene diterpene produced by Phoma chenopodicola, a fungal pathogen for Chenopodium album biocontrol. J. Nat. Prod. 2013, 76, 1291−1297. (24) Cimmino, A.; Andofi, A.; Zonno, M. C.; Avolio, F.; Berestetskiy, A.; Vurro, M.; Evidente, A. Chenopodolans A-C: phytotoxic furopyrans produced by Phoma chenopodiicola, a fungal pathogen of Chenopodium album. Phytochemistry 2013, 96, 208−213. (25) Evidente, A.; Andolfi, A.; Vurro, M.; Zonno, M. C.; Motta, A. Cytochalasins Z1, Z2 and Z3, three 24-oxa[14]cytochalasans produced by Pyrenophora seminiperda. Phytochemistry 2002, 60, 45−53. (26) Johnson, A.; Rosebery, G.; Parker, C. A. A novel approach to Striga and Orobanche control using synthetic germination stimulant. Weed Res. 1976, 16, 223−227. (27) Zwanenburg, B.; Mwakaboko, A. S.; Reizelman, A.; Anikumar, G.; Sethumadhavan, D. Structure and function of natural and synthetic signalling molecules in parasitic weed germination. Pest Manage. Sci. 2009, 65, 478−491. (28) Fernández-Aparicio, M.; Cimmino, A.; Evidente, A.; Rubiales, D. Inhibition of Orobanche crenata seed germination and radicle growth by allelochemicals identified in cereals. J. Agric. Food Chem. 2013, 61, 9797−9803. (29) Berestetskiy, A.; Dmitriev, A.; Mitina, G.; Lisker, I.; Andolfi, A.; Evidente, A. Nonenolides and cytochalasins with phytotoxic activity against Cirsium arvense and Sonchus arvensis: a structure-activity relationship study. Phytochemistry 2008, 69, 953−960. (30) Zonno, M. C.; Vurro, M. Effect of fungal toxins on germination of Striga hermonthica seeds. Weed Res. 1999, 39, 15−20. (31) Fernández-Aparicio, M.; Yoneyama, K.; Rubiales, D. The role of strigolactones in host specificity of Orobanche and Phelipanche seed germination. Seed Sci. Res. 2011, 21, 55−61. (32) Fernández-Aparicio, M.; Flores, F.; Rubiales, D. Recognition of root exudates by seeds of broomrape (Orobanche and Phelipanche) species. Ann. Bot. 2009, 103, 423−431. (33) Fernández-Aparicio, M.; Westwood, J. H.; Rubiales, D. Agronomic, breeding, and biotechnological approaches to parasitic plant management through manipulation of germination stimulant levels in agricultural soils. Botany 2011, 89, 813−826.

The research was carried out in part in the frame of Programme STAR, financially supported by UniNA and Compagnia di San Paolo, and in part in the frame of project FP7-ARIMNetMEDILEG. This work was carried out within the COST ACTION FA1206 Strigolactones: biological roles and applications. Monica Fernández-Aparicio has received support from the European Union, in the framework of the Marie-Curie FP7 COFUND People Programme, through the award of an AgreenSkills’ fellowship (under grant agreement n° PCOFUNDGA-2010−267196). A. E. is associated with the Istituto di Chimica Biomolecolare del CNR, Pozzuoli, Italy. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Parker, C. Observations on the current status of Orobanche and Striga problems worldwide. Pest Manage. Sci. 2009, 65, 453−459. (2) Rubiales, D.; Fernández-Aparicio, M. Innovations in parasitic weeds management in legume crops. Agron. Sustain. Dev. 2012, 32, 433− 449. (3) Joel, D. M.; Hershenhorn, J.; Eizenberg, H.; Aly, R.; Ejeta, G.; Rich, P. J.; Ransom, J. K.; Sauerborn, J.; Rubiales, D. Biology and management of weedy root parasites. Hortic. Rev. 2007, 33, 267−349. (4) Rubiales, D.; Fernández-Aparicio, M.; Wegmann, K.; Joel, D. Revisiting strategies for reducing the seedbank of Orobanche and Phelipanche spp. Weed Res. 2009, 49, 23−33. (5) Hershenhorn, J.; Eizenberg, H.; Dor, E.; Kapulnik, Y.; Goldwasser, Y. Phelipanche aegyptiaca management in tomato. Weed Res. 2009, 49, 34−47. (6) Pérez-de-Luque, A.; Eizenberg, H.; Grenz, J. H.; Sillero, J. C.; Á vila, C. M.; Sauerborn, J.; Rubiales, D. Broomrape management in faba bean. Field Crops Res. 2010, 115, 319−328. (7) Rimando, A. M.; Duke, S. O. In Natural Products for Pest Management; Rimando, A. M., Duke, S. O., Eds.; ACS Symposium Series No. 927; American Chemical Society: Washington, DC, U.S.A., 2006; p 388. (8) Vurro, M.; Boari, A.; Evidente, A.; Andolfi, A.; Zermane, N. Natural metabolites for parasitic weed management. Pest Manag. Sci. 2009, 65, 566−571. (9) Yoneyama, K.; Awad, A. A.; Xie, X.; Yoneyama, K.; Takeuchi, Y. Strigolactones as germination stimulants for root parasitic plants. Plant Cell Physiol. 2010, 51, 1095−1103. (10) Evidente, A.; Fernández-Aparicio, M.; Cimmino, A.; Rubiales, D.; Andolfi, A.; Motta, A. Peagol and peagoldione, two new strigolactone like metabolites isolated from pea root exudates. Tetrahedron Lett. 2009, 50, 6955−6958. (11) Evidente, A.; Cimmino, A.; Fernández-Aparicio, M.; Andolfi, A.; Rubiales, D.; Motta, A. Polyphenols, including the new peapolyphenols A-C, from root exudates stimulate Orobanche foetida seed germination. J. Agric. Food Chem. 2010, 58, 2902−2907. (12) Evidente, A.; Cimmino, A.; Fernández-Aparicio, M.; Rubiales, D.; Andolfi, A.; Melck, D. Soyasapogenol B and trans-22-dehydrocamposterol from common vetch (Vicia sativa L.) root exudates stimulate broomrape seed germination. Pest Manage. Sci. 2011, 67, 1015−1022. (13) Yoneyama, K.; Takeuchi, Y.; Ogasawara, M.; Kannai, M.; Sugimoto, Y.; Sassa, T. Cotilenins and fusicoccins stimulate seed germination of Striga hermonthica (Del.) Beth and Orobanche minor Smith. J. Agric. Food Chem. 1998, 46, 1583−1586. (14) Evidente, A.; Andolfi, A.; Fiore, M.; Boari, A.; Vurro, M. Stimulation of Orobanche ramosa seed germination by fusicoccin derivatives: a structure-activity relationships study. Phytochemistry 2006, 67, 19−26. (15) Fernández-Aparicio, M.; Andolfi, A.; Cimmino, A.; Rubiales, D.; Evidente, A. Stimulation of seed germination of Orobanche species by ophiobolin A and fusicoccin derivatives. J. Agric. Food Chem. 2008, 56, 8343−8347. 10492


Seed Germination and Radicle Growth - American Chemical Society

Recommend Documents