Allelopathic Potential of White Top and Syrian Sage on Vegetable Crops

However, the inhibitory materials may be autoinhibitory or heteroinhibitory (Kumari and Kohli, 1987), some White top [Cardaria draba (L.) Desv.] and Syrian sage (Salvia can be highly selective (Stachon and Zimdahl, 1980; syriaca L.) are noxious common weeds of field crops and orchards Sahid and Sugau, 1993), and their effect is concentration in Jordan. This study was conducted to investigate any allelopathic potential of volatiles, foliage leachates, root exudates, and shoot dried dependent (Qasem, 1993). residues of both weed species on cabbage (Brassica oleracea L. var. White top [Cardaria draba (L.) Desv.] and Syrian Capitata cv. Pronzwik), carrot (Daucus carota L. cv. Natus), cucumsage (Salvia syriaca L.) are perennial rhizomatous and ber (Cucumis sativus L. cv. Beithalpha), squash (Cucurbita pepo L. root creeping weeds belonging to cruciferae and labiatae cv. Byrouti), onion (Allium cepa L. cv. Texas Early Grana), pepper families, respectively. They are widespread in cultivated (Capsicum annum L. cv. Red Common), or tomato (Lycopersicon fields in Jordan and invade field crops as well as oresculentum Mill cv. Special Back) through different laboratory and chards. Their deep, penetrating, hard, and extensive glasshouse experiments. Volatiles from Syrian sage fresh shoots recreeping roots make them difficult to eradicate. If the duced germination and inhibited seedling growth of most crops, and weeds were left uncontrolled, they soon colonize a large foliage leachates or root exudates of both weeds were toxic to different area, choking the other plants present. Both are strong crops under laboratory conditions, with most effects on tomato and competitors for soil moisture in arid regions, and their cabbage. In pot experiments, surface-placed shoot residues of both growth increased with increasing water consumption weeds significantly delayed seed germination and reduced seedling growth of all crops with carrot, onion, and tomato being the most (Al-Ahmed, 1982; Qasem and Abu-Irmaileh, 1983). affected. Decayed residues of white top were also toxic at 32 g kg21, Furthermore, both weed species have been reported but lower toxicity was obtained than when fresh materials were used. to possess high allelopathic activity against crops, includFoliage leachates or root exudates of both weed species added or ing wheat (Triticum aestivum L.) and barley (Hordeum released into the soil mixture reduced seedling growth of cabbage vulgare L.) (Qasem and Abu-Irmaileh, 1985; Qasem, and tomato. Results showed that white top and Syrian sage are of 1993, 1994). When shoot and root extracts, water leagreat allelopathic potential against different vegetable crops; cabbage, chates, and dried residues of both weeds were added to onion, and tomato being the most sensitive crops. the soil, all inhibited germination, growth, and development of these crops. The objective of the present work was to investigate M noxious annual and perennial weeds have any possible role of allelopathy mechanism in the interbeen regarded as species with allelopathic potenference between these two common and noxious weed tial and can severely affect crop survival and productivspecies (through their possible volatile materials, root ity (Putnam and Duke, 1978; Rice, 1979; Qasem, 1994). exudates, foliage leachates, and shoot residues) on gerAllelochemicals produced by plants may be released mination and growth of their associated vegetable crops. into the surrounding environment in sufficient amounts with enough persistence to affect neighboring and sucMATERIALS AND METHODS cession species (Akram et al., 1990). Different studies showed that some allelopathic agents Laboratory Experiments are volatile, emanated from different plant parts (OlesExperiment 1. Effect of Root Exudates zek, 1987; Bradow and Connick, 1988); others indicated that they exuded from roots to the root zone and interTen-cm diameter plastic pots were filled with 500 g of soil fere in root growth and functions (Rovira, 1969; Qasem mixture (clay/sand/peat, 3:1:1 of a pH 7.7) and planted with and Hill, 1989) or inhibit seed germination (Rovira, rhizomes of both weed species, separately. After emergence, seedlings were thinned to 10 per pot irrigated with tap water 1969). Plant residues and their decomposition products when needed and left to grow for 2 mo before being harvested. are also implicated in virtually all biochemical processes The soil was loosened, cleaned up from weed roots, and then (Patrick et al., 1963; Bhowmik and Doll, 1984). Some mixed with an equal volume of distilled water and thoroughly allelochemicals are water soluble leached from foliage shaken for 2 h on a shaker. The mixture was passed through parts by rain, mist, dew, or fog drip (Lovett and Lynch, filter paper and immediately assayed for phytotoxicity. For 1979; Qasem, 1994), leading to the monospecies stands the control treatment, 500 g of weed-free soil was mixed with that several perennial weeds form in nature (Rice, 1984). the same volume of distilled water and then similarly treated before used. The effect of soil filtrate was studied by placing 20 seeds Department of Agricultural Resources and Environment, Faculty of of cabbage (Brassica oleracea L. var. Capitata cv. Pronzwik), Agriculture, Univ. of Jordan, Amman, Jordan. Received 29 Nov. 1999. carrot (Daucus carota L. cv. Natus), cucumber (Cucumis sati*Corresponding author ([email protected]). vus L. cv. Beithalpha), squash (Cucurbita pepo L. cv. Byrouti), onion (Allium cepa L. cv. Texas Early Grana), pepper (CapsiPublished in Agron. J. 93:64–71 (2001). QASEM: ALLELOPATHIC POTENTIAL OF WEEDS ON VEGETABLE CROPS 65 cum annum L. cv. Red Common), or tomato (Lycopersicon through Whatman no.1 filter paper. The filtrate was considered a full-strength leachate and immediately assayed. esculentum Mill cv. Special Back) on a filter paper in each of four petri dishes at which 10 mL of the filtrate of either weed Crop seeds were sown in plastic pots (10-cm diam) containing 500 g of the soil mixture. After emergence, seedling species was added per petri dish. In another treatment 10 mL of soil–weed-free filtrate was added per petri dish and treated were thinned to one per pot, then, 150-mL leachates were applied to each of four pots grown by one vegetable species as a control. Dishes were incubated for germination in dark at 248C and at the cotyledon stage. Pots irrigated only with tap water were included and considered as control. The experiment was for 2 to 3 wk, depending on crop species used, before the experiment was terminated. Data on germination and growth harvested at 2 to 4 wk after leachate application, depending on the treated crop species, when stem length and shoot and of different crops were recorded. root dry masses of plants were determined. Experiment 2. Effect of Volatile Materials Experiment 6. Effect of Decayed Residues Ten seeds of each crop species were placed separately in Ground, dried shoots of white top or Syrian sage were each of four sterilized (9 cm diam) petri dish lined with moistadded and mixed thoroughly with the potted soil mixture at ened filter paper. Thirty g of fresh, healthy, and clean shoots a rate of 32 g kg2. The soil shoot residue mixture was placed of white top or Syrian sage, were placed in the bottom of wide in pots of 10-cm diameter, and frequently irrigated with tap mouth 500-mL cups (11-cm diam), using four cups per weed water for 1 mo to allow natural decay of weed residues. The species. Uncovered petri dishes (containing seeds) were placed soil was then loosened, and each pot was sown with 10 seeds over weed shoots inside the cups, which then tightly closed of one crop species. There were four pots per crop species. to eliminate any air diffusion. For the control treatment, dishes Pots filled with the same soil mixture, without any residue sown with crop seeds were placed in similar cups, without added and sown with 10 seeds of the same crop species, were any weed materials added. All cups were incubated as in the included and considered as a control. previous experiments, for 1 to 2 wk, depending on crop tested. All pots were irrigated with tap water when required. The Data on germination and growth of different crops were reexperiment was continued for 2 to 5 wk (depending on crop corded. species used), then plants were harvested from the above soil surface and their stem length, fresh and dry weights, and root Glasshouse Experiments dry weights were determined. Experiment 3. Effect of Surface Placed Residues Statistics and Data Analysis Dried shoots (oven-dried at 808C for 48 h) of both weeds were ground to a fine powder, until they passed through 1.72Treatments in all experiments were laid out in a randomized mm mesh. Plastic pots of 10-cm diameter filled with 500 g of complete block design with four replicates. Data were taken the soil mixture were sown with 10 seeds of each vegetable on germination percentage, stem and total root lengths, and crop. The ground, dried shoot materials were added at a rate shoot and root dry weights after being oven-dried at 808C for of 16 g kg2 soil on the soil surface. For the control treatment, 48 h. All data were statistically analyzed by ANOVA, and seeds of each crop species were sown in the potted soil, but treatments means were compared using the least significant without any weed residue added. differences (LSD) at p 5 0.05. Plants were grown in the glasshouse for 2 to 5 wk, depending on crop species used, then similar data as in the above experiRESULTS AND DISCUSSION ments were taken at harvest. Laboratory Experiments Experiment 4. Effect of Root Exudates Experiment 1. Effect of Root Exudates Pots of 10-cm diameter were filled with 500 g of soil mixture No significant reduction in germination of cabbage and planted with rhizomes of white top or Syrian sage. After was detected with root exudates of either weed species emergence, weed seedlings were thinned to 10 per pot, then irrigated with tap water when necessary. The weeds were added to petri dishes (Fig. 1). However, white top exugrown for 2 mo, before being harvested from the above soil dates significantly reduced total root length of this crop. surface. The soil in each pot was loosened, weed roots and Phytotoxicity of root exudates showed great variation their parts were removed, and then all pots were sown again between both weeds, and the effect was highly dewith seeds of the tested vegetable crops separately, using 10 pending on crop species tested. Certain crops were not seeds per pot. Fresh soil mixture (not used before) was sown affected by these exudates, indicating that allelopathic by the same number of seeds of vegetable crops tested and compounds may be highly selective, less toxins released regarded as controls. Irrigation with 100 mL of full-strength from weed roots to the growing medium or varying crop Hoagland nutrient solution (Hewitt, 1966) was carried out tolerance to allelopathic agents. Stachon and Zimdahl twice a week and with tap water when needed. (1980), indicated that much higher rates of root exudates The experiment was terminated at 2 to 5 wk after emergence and subsequently higher rates of exuded biologically according to crop species used. Germination percentage was recorded at different intervals, then at harvest, data on stem active compounds were required to reduce plant growth. length, and root and shoot dry masses were recorded. Furthermore, Patterson (1981) observed that long-term release of toxic compounds of living plants into the soil Experiment 5. Effect of Foliage Leachates caused strong, harmful effects that would otherwise not appear in short-term experiments. When root exudates One kg of fresh shoots of each weed species was sprinkled were added to the growth medium, growth of crops with tap water, then with distilled water, to remove dust and tested was reduced (Fig. 1) and their roots were clearly soil particles. Shoots were immersed in 1 L of distilled water for 5 min, then leached water were collected and filtered affected. Exuded chemicals from roots of both weed 66 AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001 Fig. 1. Effect of root exudates of white top and Syrian sage on (a) germination at 48 h of incubation, (b) germination at harvest, (c) root length, (d) stem length, (e) root dry weight, and ( f ) shoot dry weight of selected vegetable crops grown under laboratory conditions. species may interfere with nutrient availability and thus crops (Table 1). Results showed that volatile from Syrreduced growth. ian sage fresh shoots inhibited growth of all crops except Root exudates of Syrian sage reduced total root pepper, but the degree of phytotoxicity varied between length of carrot seedlings and severely affected tomato crops. Oleszek (1987) concluded that the toxicity of growth, although germination and stem length of tomato compounds from crucifers was species dependent, and were not significantly affected. Neither squash nor carthe acceptor species react in different ways to volatiles of rot was affected by exudates of either weed species. different donor species. Allelopathic activity of released compounds of different Salvia species have been well Experiment 2. Effect of Volatile Materials established and suggested that volatiles are localized in the leaves of purple sage (Salvia leucophylla Greene) All crops were affected by volatiles of Syrian sage (Muller et al., 1964); and terpenoids could be released shoots, but the degree of inhibition varied between QASEM: ALLELOPATHIC POTENTIAL OF WEEDS ON VEGETABLE CROPS 67 from both S. leucophylla and lance-leaf sage (Salvia reflexa Hornem.) (Muller et al., 1964; Lovett and Lynch, 1979). Similarly, chemical compounds may be released from Syrian sage shoots, since it belongs to the same genus. In addition, inhibitory growth patterns of the affected crop species can be clearly observed in the vicinity and around patches of this weed in nature (Qasem and Abu-Irmaileh, 1985). The exact nature of volatiles released from the donor plant is not yet known. These results suggest chemical characterization of these volatiles needs to be done. Results showed that germination, root length, and root and shoot dry weights of carrot and squash were inhibited, while only dry mass of cabbage was reduced by volatility of this weed species. Glasshouse Experiments Experiment 3. Effect of Surface Placed Residues Crops responded differently to the soil-applied shoot residues of both weed species (Table 2). Shoot residues of white top, when used as a soil mulch, delayed emergence, reduced the number of final emerged seedlings, and stem length and shoot and root dry weights of cabbage, onion, pepper and tomato. Grinding of plant tissues may not represent the exact situation occurring in nature and may enhance release of allelochemicals. This procedure, however, is followed in the present experiment to allow better coverage of pot surface with the relatively small amount of weed residue used. In nature, amount of plant residues is expected to be higher and the decay process of these residues may take place faster than that under glasshouse conditions due to different environmental factors, better prevailing under field conditions, leading to fast release of allelochemicals. However, dried residues of both weeds delayed seedling emergence of carrot and tomato and affected growth of carrot plants. Syrian sage shoot residues significantly reduced stem length and dry weight of cucumber and squash. Experiment 4. Effect of Root Exudates Germination of the different crops was not significantly affected by root exudates. However, stem length and root and shoot dry weights of all crops tested were reduced by root exudates of both weed species (Fig. 2). The degree of inhibition was species-dependent. Qasem (1995) reported that root exudates of redroot pigweed (Amaranthus retroflexus L.) and nettle-leaved goosefoot (Chenopodium murale L.) released to the soil affected growth of squash seedlings showing as mineral deficiency symptoms compared with the control. In the present experiment, nonsterilized root exudates were used since this treatment may change the chemical nature of soil-extracted exudates. Therefore, association of fungal spores or other soil microorganisms with root systems of studied weeds is not to be excluded. However, no T ab le 1. E ff ec t of vo la ti le s fr om sh oo ts of w hi te to p an d Sy ri an sa ge on ge rm in at io n (G ), to ta lr oo t le ng th (T R L ), sh oo t dr y w ei gh t (S H D W t.) ,a nd ro ot dr y w ei gh t (R D W t.) pe r pl an t of ce rt ai n ve ge ta bl e cr op s gr ow n in pe tr i di sh es at 24 8C . C ab ba ge C ar ro t C uc um be r O ni on P ep pe r Sq ua sh T om at o SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D W ee d sp ec ie s G T R L w t. w t. G T R L w t. w t. G T R L w t. w t. G T R L w t. w t. G T R L w t. w t. G T R L w t. w t. G T R L w t. w t. % m m m g % m m m g % m m m g % m m m g % m m m g % m m m g % m m m g C on tr ol 80 53 23 9 82 30 13 4 88 17 1 14 5 23 70 17 11 4 80 15 5 2 85 14 4 19 3 44 80 59 12 4 W hi te to p 70 52 21 8 70 31 13 4 78 17 9 14 3 22 70 15 10 3 75 15 5 1 80 11 3 40 2 41 63 58 12 4 Sy ri an sa ge 75 49 16 6 50 4 5 0 60 10 6 10 4 13 68 8 6 1 58 8 4 1 53 24 12 0 19 50 30 8 4 L SD P 5 0. 05 16 8 2 2 12 5 2 1 15 26 20 4 12 3 2 1 10 4 1 1 15 24 34 3 11 6 2 1 68 AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001 fungal contamination or growth of any disease was observed in the whole study period. Evidences are accumulating and showing that root exudates of certain plant species are toxic to the roots of neighboring plants, and inhibited germination of some other species (Tukey, 1969; Rovira, 1969; Brown et al., 1983). Root exudates of Syrian sage inhibited growth of cabbage, cucumber, and tomato seedlings and the harmful effect on these crops was more pronounced than on other crop species tested. In comparison, white top root exudates were less toxic to the same crops. Experiment 5. Effect of Foliage Leachates Crops were different in their responses to foliage leachates of these weeds. Leached water from foliage parts of white top significantly reduced shoot and root dry weights of pepper, squash and tomato, whereas leached water of Syrian sage reduced shoot and root dry weight of cucumber seedlings (Table 3). Persistent rainfall for a period may leach chemicals from aerial parts of the plants under field conditions. However, allelopathic effects of the leached materials depend on the transfer of chemicals from weed to crop foliage or roots and may depend on both donor and acceptor species. Seedlings growth of different lines of wheat and barley was severely inhibited with white top leachates (Qasem, 1994), and the allelopathic effect of dried shoot residues of the weed species on both crops is well established under field conditions (Qasem, 1994). Inhibitory growth patterns of the affected species are clearly noticed in the vicinity of this weed under field conditions and affected crop plants appeared short in stature with abnormal growth of root systems. In this study, the effect of leachates applied to the soil was less phytotoxic than other treatments. The concentration of leached material and the effect of microorganisms may have been important factors in determining the stimulatory or the inhibitory action of the leached compounds (Patterson, 1981). In this experiment, weed shoots were immersed in water for only a short period of time and low amount of shoots in large volume of water was used. Pepper, cabbage, squash, and tomato seedlings were notably affected by foliage leachates of both weeds; onion and carrot were less so. Higher phytotoxicity was found on tomato than squash and cucumber seedlings and by leachates of both weeds. Leachates of white top were more inhibitory to cabbage, squash, and tomato crops than those of Syrian sage. Experiment 6. Effect of Decayed Residues Results of this experiment showed that cucumber, squash, and tomato suffered more than other crops from decayed residues of white top (Table 4). However, seed germination of most crops was not affected by decaying residues from any of the weeds. Similar results were obtained with the decayed residues of Syrian sage on growth of these crops. Decayed residues of white top, however, reduced root dry weight of cucumber and toT ab le 2. E ff ec t of su rf ac e pl ac ed sh oo t re si du e of w hi te to p an d Sy ri an sa ge on ge rm in at io n (G ), st em le ng th (S L ) pe r pl an t, sh oo t dr y w ei gh t (S H D W t.) , an d ro ot dr y w ei gh t (R D W t.) pe r po t of ce rt ai n ve ge ta bl e cr op s gr ow n un de r gl as sh ou se co nd it io ns . C ab ba ge C ar ro t C uc um be r O ni on P ep pe r Sq ua sh T om at o SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D W ee d sp ec ie s G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. % m m m g % m m m g % m m m g % m m m g % m m m g % m m m g % m m m g C on tr ol 85 58 60 0 34 1 90 76 31 2 14 8 88 10 9 85 8 20 5 70 17 1 26 7 11 1 80 67 68 7 27 2 73 13 5 18 88 32 6 90 66 87 5 25 5 W hi te to p 65 42 28 8 12 2 70 24 24 1 13 3 88 11 0 78 5 20 4 65 13 9 22 1 86 75 53 52 9 15 0 75 14 5 16 65 28 3 65 32 30 8 16 1 Sy ri an Sa ge 83 61 60 0 25 1 75 71 25 1 13 7 73 95 52 5 14 6 78 15 5 26 9 12 1 68 60 51 2 16 7 70 12 2 16 35 32 3 75 55 50 8 22 3 L SD P 5 0. 05 12 8 89 40 15 9 30 28 16 13 10 2 38 17 20 42 20 14 8 71 34 17 25 27 3 31 16 10 10 0 29 mato and seedlings growth of squash. Although decayed QASEM: ALLELOPATHIC POTENTIAL OF WEEDS ON VEGETABLE CROPS 69 Fig. 2. Effect of root exudates of white top and Syrian sage on (a) germination at 1 wk after emergence, (b) germination at harvest, (c) stem length, (d) shoot dry weight, and (e) root dry weight of selected vegetable crops grown under glasshouse conditions. rials, and dried shoot residues of both weeds on germiresidues enhanced growth of certain crop species, the nation and growth of different crop species varied. effect of such treatment on sensitive crops was proUsing closed container technique, volatile materials nounced. from Syrian sage fresh shoots significantly inhibited germination and growth of all crops except pepper, while CONCLUSIONS foliage leachates of both weed species were highly toxic. White top and Syrian sage are perennial weeds widely Root exudates of both weed species resulted in various spread in cultivated land in Jordan. Using different exinhibitory actions, which were donor and receiver deperimental techniques revealed that both have allelopendent. Allelopathic effects of both weed species on vegetable crops under field conditions merit further repathic potential against different vegetable crops. The effect of root exudates, foliage leachates, volatile matesearch. 70 AGRONOMY JOURNAL, VOL. 93, JANUARY–FEBRUARY 2001 T ab le 4. E ff ec t of de ca ye d in co rp or at ed sh oo t re si du e of w hi te to p an d Sy ri an sa ge on ge rm in at io n (G ), st em le ng th (S L ) pe r pl an t, sh oo t dr y w ei gh t (S H D W t.) , an d ro ot dr y w ei gh t (R D W t.) pe r po t of ce rt ai n ve ge ta bl e cr op s gr ow n un de r gl as sh ou se co nd it io ns . C ab ba ge C ar ro t C uc um be r O ni on P ep pe r Sq ua sh T om at o SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D W ee d sp ec ie s G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. G SL w t. w t. % m m m g % m m m g % m m m g % m m m g % m m m g % m m m g % m m m g C on tr ol 73 34 42 7 14 9 80 43 23 3 15 0 75 60 65 4 37 1 85 10 7 31 8 17 6 80 36 26 6 10 8 73 80 12 87 30 4 70 49 28 4 15 8 W hi te to p 70 37 39 9 14 5 65 22 32 4 14 8 90 53 37 4 82 70 72 24 1 13 6 70 35 31 0 10 7 80 54 11 31 23 6 75 50 23 1 12 7 Sy ri an sa ge 70 41 43 9 14 4 67 41 33 2 16 9 75 68 53 3 53 7 63 11 7 34 0 17 4 80 39 33 1 12 0 75 89 14 61 33 8 80 50 23 6 16 6 L SD P 5 0. 05 13 5 74 30 12 8 61 31 15 6 70 36 11 24 60 20 11 6 36 21 11 12 21 1 54 12 8 25 23 T ab le 3. E ff ec t of fo lia ge le ac ha te s of w hi te to p an d Sy ri an sa ge on st em le ng th (S L ) pe r pl an t, sh oo t dr y w ei gh t (S H D W t.) , an d ro ot dr y w ei gh t (R D W t.) pe r po t of ce rt ai n ve ge ta bl e cr op s gr ow n in po ts . C ab ba ge C ar ro t C uc um be r O ni on P ep pe r Sq ua sh T om at o SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D SH D R D W ee d sp ec ie s SL w t. w t. SL w t. w t. SL w t. w t. SL w t. w t. SL w t. w t. SL w t. w t. SL w t. w t. m m m g m m m g m m m g m m m g m m m g m m m g m m m g C on tr ol 11 5 28 8 13 2 88 33 25 99 42 8 15 8 13 5 44 26 82 15 2 10 4 17 7 10 93 37 1 16 7 37 8 10 5 W hi te to p 94 24 7 80 67 31 30 88 42 5 12 4 14 2 50 26 66 88 75 17 1 73 5 30 5 11 3 21 8 59 Sy ri an sa ge 99 24 7 12 2 81 31 23 85 27 3 78 13 1 41 23 67 74 55 15 4 88 0 30 9 16 2 28 8 77 L SD P 5 0. 05 14 62 23 15 6 7 10 93 22 17 11 5 11 23 24 17 14 2 53 13 71 17 QASEM: ALLELOPATHIC POTENTIAL OF WEEDS ON VEGETABLE CROPS 71 species on lettuce, barnyard grass and wheat. Plant Soil 102: ACKNOWLEDGMENTS 271–273. I thank the Deanship of Scientific Research, University of Patrick, Z.A., T.A. Toussoun, and W.C. Snyder. 1963. Phytotoxic Jordan and The Higher Council for Science and Technology substances in arable soils associated with decomposition of plant residues. Phytopathol. 53:152–161. for facilitating this research. Patterson, D.T. 1981. 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