Article pubs.acs.org/JAFC
Holadysenterine, a Natural Herbicidal Constituent from Drechslera australiensis for Management of Rumex dentatus Muhammad Akbar,† Arshad Javaid,*,† Ejaz Ahmed,‡ Tariq Javed,§ and Jacob Clary∥ †
Institute of Agricultural Sciences, University of the Punjab, Lahore 54590, Pakistan Institute of Chemistry, University of the Punjab, P.O. Box 54590, Lahore, Pakistan § Centre of Excellence in Molecular Biology, University of the Punjab, P.O. Box 54590, Lahore, Pakistan ∥ Department of Chemistry and Biochemistry, University of California, 1156 High Street, Santa Cruz , California 95064, United States ‡
ABSTRACT: Rumex dentatus L. is a problematic weed of wheat. Bioassay-directed isolation of culture filtrates of a plant pathogenic fungus Drechslera australiensis gave holadysenterine as the main herbicidal constituent against this weed of wheat. Leaf disc bioassay showed that herbicidal activity of holadysenterine was comparable to that of synthetic herbicide 2,4-D. This is the first report of this herbicidal compound from the genus Drechslera. KEYWORDS: Drechslera australiensis, leaf disc bioassay, natural herbicides, Rumex dentatus, weed of wheat
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INTRODUCTION Rumex dentatus L. (family Polygonaceae) is a broad-leaf densely populated weed of wheat (Triticum aestivum L.) fields.1,2 It is an extremely competitive annual herb that causes remarkable reduction in the yield of wheat.3,4 Besides, the weed is also known for its allelopathic activity.5 Anjum and Bajwa3 reported 83% reduction in grain yield of wheat due to R. dentatus infestation. To control this weed, use of chemical herbicides is on the increase to boost up crop productivity.6,7 However, we are now facing new challenges regarding weed control, especially emergence of resistance in weeds to herbicides8 and concerns about herbicide effects in food, soil, groundwater, and atmosphere.9,10 Because of these ill effects of herbicides coupled with increasing demand for organic farming in the world, isolation of new herbicides from natural sources is gaining importance.11,12 Use of natural herbicidal constituents from microbes is one of the alternative strategies to manage the weeds.13,14 There have been many successful attempts to control weeds by metabolites of fungi of genus Drechslera.15−17 Some bioactive compounds have been isolated from some species of this genus and proposed as potent natural herbicides.18−20 Kastanias and Chrysayi-Tokousbalides21 isolated macrodiolide (8R,16R)-(−)-pyrenophorin (8,16-dimethyl-1,9-dioxa-cyclohexadeca-3,11-diene-2,5,10,13-tetraone) from cultures of Drechslera avenae (Eidam) Shoem. The isolated compound inhibited seed germination of wild oats (Avena fatua L.). Another herbicidal compound drazepinone was identified from culture filtrates of Drechslera siccans (Drechsler) Shoemaker.15 Evidente et al.17 isolated a number of herbicidal metabolites from culture filtrate of D. gigantea Heald & Wolf including ophiobolin A that proved to be a potent herbicide against several grass and dicotyledonous weeds including Avena ludoviciana Dur., Phalaris canariensis L., Chenopodium album L., and Sonchus oleraceus L. Ophiobolin A proved to be the most potent phytotoxin as compared to the other related compounds. Preliminary investigations on culture filtrates of some species of © 2013 American Chemical Society
Drechslera from Pakistan, namely D. australiensis, D. hawaiiensis, D. biseptata, and D. holmii, revealed their herbicidal activity against some problematic weeds of wheat and Parthenium hysterophorus.22−24 However, detailed studies regarding isolation of herbicidal compounds from Pakistani Drechslera species are lacking. Therefore, the present study was carried out to identify the herbicidal constituents present in culture filtrates of D. australiensis.
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MATERIALS AND METHODS
Preparation of Culture Filtrates of the Test Fungus. Culture of D. australiensis was procured from Fungal Culture Bank of Pakistan, Institute of Agricultural Sciences, University of the Punjab, Lahore, Pakistan. M-1-D growth medium was prepared by following the procedure described by Evidente et al.17 First, 100 mL of medium was poured in 500 mL conical flasks and autoclaved. These flasks were then inoculated with actively growing culture discs of D. australiensis and incubated at 25 ± 2 °C in an incubator. After 28 days of incubation, cultures were filtered through muslin cloth, centrifuged, and finally filtered through Whatman filter paper no. 1. to get crude fungal culture filtrates free of fungal mycelia and spores. Organic Solvent Extraction. A total of 4 L of crude fungal culture filtrate of D. australiensis was collected and evaporated (45 °C) to yield 1.5 L of concentrated filtrate. Four organic solvents, viz. n-hexane, chloroform, ethyl acetate, and n-butanol, were successively used for extraction. These organic solvents were used in order of their increasing polarity. The organic solvent phases were collected and evaporated under vacuum in a rotary evaporator to yield crude organic fractions.25 Bioassays with Crude Organic Fractions. Bioassays with crude organic fractions were carried out following procedure described by Sarpeleh et al.26 with some modifications. Seeds of R. dentatus were sown in plastic pots under natural environmental conditions. Young leaves from 30-day-old plants were detached, and discs of 1 cm diameter were cut with the help of a cork borer. These leaf discs were Received: Revised: Accepted: Published: 368
September 17, 2013 December 12, 2013 December 23, 2013 December 23, 2013 dx.doi.org/10.1021/jf403860b | J. Agric. Food Chem. 2014, 62, 368−372
Journal of Agricultural and Food Chemistry
Article
Table 1. Herbicidal Effect of Crude Organic Fractions of Culture Filtrate of D. australiensis on Leaf Discs of R. dentatus effect of crude organic fractions n-hexane
DMSO effect
chloroform
ethyl acetate
n-butanol
DMSO conc (μL mL−1)
colora
necrotic spotb
organic fraction conc (mg mL−1)
colora
necrotic spotb
colora
necrotic spotb
colora
necrotic spotb
colora
necrotic spotb
0 1.560 3.125 6.250 12.500 25.000 50.000 100.000
0 0 1 0−1 0−1 0−1 0−1 0−1
4 4 4 4 4 4 4 4
0 0.0625 0.1250 0.2500 0.5000 1.0000 2.0000 4.0000
0 0−1 1 1 1−2 2 2 2
4 4 4 4 4 4 4 4
0 1−2 2 2−3 3 3 3 3
4 4 4 4 4 5 7 10
0 0 1 1 1−2 2 2 3
4 4 4 4 4 4 5 7
0 0 0 1 1 1−2 2 2
4 4 4 4 4 4 4 4
a
Color scale: 0 = no change; 1 = light discoloration; 2 = moderate discoloration; 3 = severe discoloration. bNecrotic spot scale: 4 = no necrotic spot; 5 = necrotic spot ≤ 1 mm; 6 = necrotic spot ≤ 2 > 1 mm; 7 = necrotic spot ≤ 3 > 2 mm; 8 = necrotic spot ≤ 4 > 3 mm; 9 = necrotic spot ≤ 5 > 4 mm; 10 = necrotic spot ≤ 6 > 5 mm. placed on glass slides and punctured with the help of a fine needle. Glass slides were placed in a Petri plate on a filter paper wetted with 2 mL of sterilized distilled water. Then 4 mg of each of the four crude fractions were dissolved in 100 μL of dimethylsulfoxide (DMSO). Final volume of each fraction was raised to 1.0 mL with distilled water to prepare a stock solution of 4 mg mL−1 concentration. The stock solution was serially double diluted by adding distilled water to prepare lower concentrations of 2, 1, ..., 0.0625 mg mL−1. Droplets of 15 μL of each of the seven concentrations were applied on the punctured leaf discs surfaces. Ten leaf discs of the test weed species were used for each concentration. For blank control treatments, 100 μL of DMSO were dissolved in distilled water to prepare a 1.0 mL mixture and subsequent lower concentrations were made by double diluting it with distilled water. Petri plates were incubated at 25 °C under continuous fluorescent light in a growth room. Symptoms regarding appearance of necrotic spot and discoloration of leaf discs were observed after 72 h. Color scale 0−3 and necrotic spot scale 4−10 were used for comparisons following Mahoney et al.27 with some modifications.
Rf =
Six fractions, namely A (Rf 0.096), B (Rf 0.130), C (Rf 0.170), D (Rf 0.269), E (Rf 0.480), and F (Rf 0.576), were isolated from chloroform fraction. TLC fractions were further purified by preparative thin layer chromatography (PTLC). For preparative thin layer chromatography, precoated silica gel GF-254 preparative plates (20 cm × 20 cm, 0.5 mm thick, E-Merck) were used. Solvent system was same as in TLC. When developed with the solvent, the compounds separated in horizontal bands. These bands were scraped from the plates and eluted with methanol. Soluble compounds were carefully collected separately in another vial through filtration and were evaporated at 40 °C to dryness and weighed. Compounds separated through PTLC were further subjected to reversed phase high performance liquid chromatography. For elution, acetonitrile (HPLC grade) with 0.1% formic acid was added and deionized water with 0.1% formic acid was used as solvent system. Gradient elution was employed with initial ratio of acetonitrile and deionized water as 10:90 with an increasing ratio of acetonitrile to water as 100:0. Fractions containing purified compounds were collected in glass vials, and solvent was evaporated under continuous currents of clean air at room temperature. Bioassays with Purified Chromatographic Fractions. Bioassays with purified chromatographic fractions were generally carried out using the same method as was adopted in case of crude organic fractions. Stock solutions of 2 mg mL−1 of the various purified isolated constituents were prepared by dissolving 2 mg of the compound in 50 μL of DMSO and raised the volume to 1.0 mL by adding distilled water. Lower concentrations of 1, 0.5, ..., 0.03125 mg mL−1 were prepared by serially double diluting the stock solutions. In total, seven concentrations were made with distilled water viz. 2, 1, 0.5, 0.25, 0.125, 0.0625, and 0.03125 mg mL−1. A set of blank control treatments with different concentrations of DMSO corresponding to DMSO concentration in various treatments of pure compounds was also included. Different concentrations of a known herbicidal compound 2,4-D (2,4- dichlorophenoxyacetic acid) were also included as positive control to compare with efficacy of the isolated compounds. Symptoms regarding appearance of necrotic spots and discoloration of leaf discs were observed after 72 h. Spectroscopic Analyses. Structural elucidation by 1D and 2D NMR techniques of only the most active compounds was carried out. Less bioactive compounds were not subjected to mass spectroscopy because their bioactivity was far too low as compared to synthetic herbicide in use. Proton nuclear magnetic resonance (1H NMR) spectra were recorded in CD3OD using TMS as internal standard at 600 MHz on Bruker AM-500 nuclear magnetic resonance spectrometers. The 13C
Color Scale 0 1 2 3
= = = =
distance traveled by component distance traveled by the solvent
no change light discoloration moderate discoloration severe discoloration
Necrotic Spot Scale 4 = no necrotic spot 5 = necrotic spot ≤ 1 mm 6 = necrotic spot ≤ 2 > 1 mm 7 = necrotic spot ≤ 3 > 2 mm 8 = necrotic spot ≤ 4 > 3 mm 9 = necrotic spot ≤ 5 > 4 mm 10 = necrotic spot ≤ 6 > 5 mm Isolation of Compounds through Chromatographic Techniques. Crude chloroform fraction of culture filtrate of D. australiensis were selected for thin layer chromatography (TLC) analysis followed by separation of compounds through preparative thin layer chromatography (PTLC) and reversed phase high performance liquid chromatography. A thin strip of aluminum foil backed TLC was used as chromatogram. First, 5 mg of crude chloroform fraction was taken in an Eppendorf tube and was dissolved in 1 mL of methanol. Then 10 mL of solvent (chloroform, ethyl acetate, and n-hexane) in a 10:6:84 ratio was used to elute the mixture of compounds spotted on chromatogram strip. Spots were located under UV transilluminator, both at short and long wavelengths as well as visualized by spraying ceric sulfate solution accompanied by heating with heat gun. Retention factor (Rf) value for each spot was calculated using the formula: 369
dx.doi.org/10.1021/jf403860b | J. Agric. Food Chem. 2014, 62, 368−372
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Table 2. Herbicidal Activity of Purified Chromatographic Fractions from Chloroform Fraction of Culture Filtrates of D. australiensis on Leaf Discs of R. dentatus effect of purified chromatographic fractions DMSO effect DMSO conc (μL mL−1)
colora
0 0.780 1.560 3.125 6.250 12.500 25.000 50.000
0 0 0 0 0 0−1 0−1 0−1
effect of 2,4-D
A
B
C
D
E
F
NSb
2,4-D conc (mg mL−1)
colora
NSb
colora
NSb
colora
NSb
colora
NSb
colora
NSb
colora
NSb
colora
NSb
4 4 4 4 4 4 4 4
0 0.0312 0.0625 0.1250 0.2500 0.5000 1.0000 2.0000
0 0−1 0−1 1 1 1 1 1
4 4 4 4 6 7 10 10
0 0 0−1 0−1 1 1 1−2 2
4 4 4 4 4 6 7 9
0 0 0−1 0−1 0−1 1 1 1
4 4 4 4 4 4 4 4
0 0 0−1 1 1 2 2 3
4 4 4 4 4 4 7 8
0 0 0−1 1 1 1 2 2
4 4 4 4 4 4 4 7
0 0 0−1 0−1 0−1 1 1 1
4 4 4 4 4 4 4 4
0 0 0−1 0−1 0−1 1 2 3
4 4 4 4 4 6 7 9
a
Color scale: 0 = no change; 1 = light discoloration; 2 = moderate discoloration; 3 = severe discoloration. bNS = necrotic spot. Necrotic spot scale: 4 = no necrotic spot; 5 = necrotic spot ≤ 1 mm; 6 = necrotic spot ≤ 2 > 1 mm; 7 = necrotic spot ≤ 3 > 2 mm; 8 = necrotic spot ≤ 4 > 3 mm; 9 = necrotic spot ≤ 5 > 4 mm; 10 = necrotic spot ≤ 6 > 5 mm. NMR spectra were recorded in CD3OD at 125 MHz on the same instrument. EIMS spectra were recorded on a Finnigan MAT 311 with MASSPEC data system.
activity, therefore, spectroscopic analysis of only this compound was carried out. Chromatographic fraction F was identified as compound 1 (Figure 1).
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RESULTS AND DISCUSSION Bioassays with Crude Organic Fractions. Positive reaction showing necrotic spots was recorded on punctured R. dentatus leaf discs surfaces. The chloroform fraction produced the most prominent necrotic spots followed by the ethyl acetate fraction. A 1.0 mg mL−1 concentration of crude chloroform fraction produced necrotic spot, while ethyl acetate fraction produced necrotic spots at a minimum concentration of 2.0 mg mL−1. n-Hexane and n-butanol fractions did not produce any necrotic spot. Severe discoloration was also observed in the case of bioassays that performed well. In the case of the chloroform fraction, severe discoloration was observed due to 0.25 mg mL−1 and higher concentrations. In the case of the ethyl acetate fraction, severe discoloration was observed only at the highest concentration of 4.0 mg mL−1. In the case of n-hexane and n-butanol fractions, discoloration was not much pronounced. Leaf sections treated with DMSO as a positive control exhibited only light discoloration (Table 1). Bioassays with Purified Chromatographic Fractions. In these bioassays, out of six purified chromatographic fractions from crude chloroform fraction of culture filtrate of D. australiensis, four, viz. A, C, D, and F, were found effective in producing necrotic spot on leaf discs of R. dentatus. Among these, A and F were found to be the most herbicidal and produced necrotic spots on leaf discs surfaces at a minimum concentration of 0.5 mg mL−1. Fraction C was found active at a minimum concentration of 1.0 mg mL−1, while fraction D was found active at the highest concentration of 2.0 mg mL−1. Chromatographic fractions B and E did not produce any necrotic spots. In the case of bioassays performed with reference compound 2,4-D, maximum bioactivity was observed at minimum concentration of 0.25 mg mL−1. Discoloration of leaf discs was also observed to a variable extent in all the treatments. Fraction C and F induced severe discoloration at a concentration of 2.0 mg mL−1. In contrast, only light discoloration was observed in case of 2,4-D, even at the highest concentration of 2.0 mg mL−1 (Table 2). Spectroscopic Data of the Isolated Compound. Chromatographic fraction F exhibited the highest herbicidal
Figure 1. Chemical structure of holadysenterine.
Compound 1. Holadysenterine. Colorless amorphous powder; [α]D28 −14.6° (c = 1.0, MeOH); mp 219.5−220.5 °C. EIMS m/z: [M]+ 390 (2.0), 317 (4.5), 354 (3.5), 307 (60), 289 (22), 278 (65), 154 (25), 136 (54), 115 (48), 107 (50), 85 (100). HREIMS m/z: [M]+ 390.3030 (calcd for C23H38N2O3 390.3083). 1H NMR (CD3OD, 600 MHz) δH: 1.19 (1H, m, H1), 1.33 (1H, m, H-1), 1.35 (1H, m, H-2), 1.44 (1H, m, H-2), 2.99 (1H, brm, H-3), 5.44 (brs 1H, m, H-6), 1.84 (2H, m, H12), 1.33 (1H, m, H-17), 4.01 (1H, d, J = 10.9, H-18), 3.70 (1H, d, J = 10.9), 1.29 (s, 3H, H-19), 3.45 (1H, m, H-20), 1.38 (1H, d, J = 7.1 H-21), 2.01 (s, 3H, CO-Me). Compound 1 (holadysenterine) was isolated as amorphous solid from the chloroform extraction. Molecular formula was obtained by HREIMS, showing a peak at m/z 390.3030 for C23H38N2O3 showing six degrees of unsaturation in the compound. Four unsaturations were accounted for by a tetracyclic pregnane type skeleton, and two were due to the endocyclic double bond and was due to the carboxyl function. The UV spectrum was inconclusive. Inspection of 1H NMR spectrum of compound 1 showed olefinic proton at δ 5.44 (1H, br singlet). The spectra showed two doublets at δ 3.70 (1H, d, J = 10.9 Hz) assignable to the hydroxyl methylene protons. At δ 2.99 and 3.45, two broad multiplets were observed and were assigned to the H-3α and 20β, respectively. Two methyl singlets were observed at δ 1.29 and δ 2.0, while at δ 1.38 a 370
dx.doi.org/10.1021/jf403860b | J. Agric. Food Chem. 2014, 62, 368−372
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(6) Ashiq, M.; Muhammad, N.; Ahmed, N. Comparative efficacy of different herbicides against broad leaf weeds in wheat. Pak. J. Weed Sci. Res. 2007, 13, 149−156. (7) Hulting, A. G.; Dauer, J. T.; Hinds-Cook, B.; Curtis, D.; KoepkeHill, R. M.; Mallory-Smith, C. Management of Italian Ryegrass (Lolium perenne ssp. multif lorum) in Western Oregon with Preemergence Applications of Pyroxasulfone in Winter Wheat. Weed Technol. 2012, 26, 230−235. (8) Llewellyn, R. S.; D’Emden, F. H.; Owen, M. J. Herbicide resistance in rigid ryegrass (Lolium rigidum) has not led to higher weed densities in western Australian cropping fields. Weed Sci. 2009, 57, 61− 65. (9) Marín, A.; Oliva, J.; Garcia, C.; Navarro, S.; Barba, A. Dissipation rates of cyprodinil and fludioxonil in lettuce and table grape in the field and under cold storage conditions. J. Agric. Food Chem. 2003, 51, 4708−4711. (10) Rial-Otero, R.; Arias-Estévez, M.; López-Periago, E.; CanchoGrande, B.; Simal- Gándar, J. Variation in concentrations of the fungicides tebuconazole and dichlofluanid following successive applications to greenhouse-grown lettuces. J. Agric. Food Chem. 2005, 53, 4471−4475. (11) Naylor, R. E. Weed Management Handbook; Blackwell Publishing, Oxford, 2002. (12) Jamil, M.; Cheema, Z. A.; Mushtaq, M. N.; Farooq, M.; Cheema, M. A. Alternative control of wild oat and canary grass in wheat fields by allelopathic plant water extracts. Agron. Sustainable Dev. 2009, 29, 475−482. (13) Javaid, A. Herbicidal potential of allelopathic plants and fungi against Parthenium hysterophorusa review. Allelopathy J. 2010, 25, 331−344. (14) Zhang, L.; Kang, Z.; Xu, J.; Xu, W.; Zhang, J.l. Isolation and structural indentification of herbicidal toxin fractions produced by Pythium aphanidermatum. Agric. Sci. China 2010, 9, 995−1000. (15) Evidente, A.; Andolfi, A.; Vurro, M.; Fracchiolla, M.; Zonno, M. C.; Motta, A. Drazepinone, a trisubstituted tetrahydronaphthofuroazepinone with herbicidal activity produced by Drechslera siccans. Phytochemistry 2005, 66, 715−721. (16) Evidente, A.; Andolfi, A.; Cimmino, A.; Vurro, M.; Fracchiolla, M.; Charudattan, R.; Motta, A. Ophiobolin E and 8-epi-ophiobolin J produced by Drechslera gigantea, a potential mycoherbicide of weedy grasses. Phytochemistry 2006, 67, 2281−2287. (17) Evidente, A.; Andolfi, A.; Cimmino, A.; Vurro, M.; Fracchiolla, M.; Charudattan, R. Herbicidal potential of ophiobolins produced by Drechslera gigantea. J. Agric. Food Chem. 2006, 54, 1779−1783. (18) Kastanias, M. A.; Chrysayi-Tokousbalides, M. Herbicidal potential of pyrenophorol isolated from a Drechslera avenae pathotype. Pest Manage. Sci. 2000, 56, 227−232. (19) Zhang, W.; Watson, A. K. Isolation and partial characterization of phytotoxins produced by Exserohilum monoceras, a potential bioherbicide for control of Echinochloa species. Proceedings of the X International Symposium on Biological Control of Weeds, Bozeman, Montana, July 4−14, 1999; Montana State University: Bozeman, Montana, 1999. Spencer, N.R. (ed.). 2000, pp 125−130. (20) Capio, E. R.; Tate, M. E.; Wallwork, H. Phytotoxic metabolites from Drechslera wirreganensis and D. campanulata. Austral. Plant Pathol. 2004, 33, 23−28. (21) Kastanias, M. A.; Chrysayi-Tokousbalides, M. Bioactivity of the fungal metabolite (8R,16R)-(−)-pyrenophorin on graminaceous plants. J. Agric. Food Chem. 2005, 53, 5943−5947. (22) Javaid, A.; Adrees, H. Parthenium management by cultural filtrates of phytopathogenic fungi. Nat. Prod. Res. 2009, 23, 1541− 1551. (23) Akbar, M.; Javaid, A. Management of some problematic weeds of wheat by metabolites of Drechslera sp. prepared in malt extract medium. Pak. J. Weed Sci. Res. 2010, 16, 145−151. (24) Javaid, A.; Javaid, A.; Akbar, M. Herbicidal potential of Drechslera spp. culture filtrates against Parthenium hysterophorus L. Chil. J. Agric. Res. 2011, 71, 634−637.
characteristic methyl doublet was observed having J = 7.1 Hz. The downfield shift of methyl group at δ 2.0 indicated the presence of acetamide functionality in the molecule. A solvent exchangeable proton singlet due to N-hydroxy was observed at δ 4.98,28 indicated its attachment at amine side chain functionality. EIMS spectrum gave peaks at m/z 317 [M + H − CH3CONOH]+ (−C−N bond cleavage), 289 [M + H − C4H8NO2]+ (C17−C20 bond cleavage) and 278 [M + H − C5H8NO2]+ (C13−C17 and C16−C17 bond cleavage). This proves the attachment of a hydroxyl methyl group at the amine center. On the basis of this evidence and comparison with the literature data, compound 1 was assigned as (20S)-20 acetylhydroxylamine,3β-amino,13β-hydroxymethylenepregn-5ene and named previously as holadysenterine.29 Because of a lack of amount, 13C spectrum was unpredictable, however, some 2D NMR spectra (HMBC, 1H−1H COSY) were showing some signals of 13C and from which final structure of compound 1 was concluded. In earlier studies, some herbicidal constituents have been isolated from other species of Drechslera. The culture of Drechslera siccans (Drechsler) Shoemaker is also reported to yield a phytotoxin named as 6,8-dihydroxy-3-(2′-hydroxypropyl) isocoumarin (de-o-methyldiaporthin). Phytotoxicity of this compound has been estimated in terms of necrotic spot area when tested on Avena sativa, Echinochloa crus-galli, and Amaranthus spinosus.30 Capio et al.20 isolated two phytotoxic compounds, namely cytochalasin B and dihydrocytochalasins, from extracts of dried mycelia and liquid culture filtrates of Drechslera wirreganensis Wallwork, Lichon & Sivan and D. campanulata (Lév.) B. Sutton. Similarly, another metabolite namely drazepinone with broad spectrum herbicidal activity has been isolated from Drechslera siccans.15 The present study concludes that herbicidal activity of culture filtrates of D. australiensis is mostly due to holadysenterine.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +92 42 99231846. Fax: +92 42 99231187. E-mail:
[email protected]. Funding
The Higher Education Commission of Pakistan provided funding to accomplish part of this work at the University of California, USA. Notes
The authors declare no competing financial interest.
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REFERENCES
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