Phytochemical Investigation of Cuscuta campestris Yunck. Stem Extract and Evaluation of Its Bioherbicidal Effect on Amaranthus retroflexus L. and Portulaca oleracea L.

This study focused on characterizing chemically and evaluating in vitro allelopathic and bioherbicidal potential of secondary metabolites extracted from the stem of Cuscuta campestris in seed germination, early seedling growth and early plant growth of Amaranthus retroflexus and Portulaca oleracea. The combined effects of stem extract and a reduced dose of herbicide metribuzin were also examined. Plant extract contained 17 phenolic compounds and the most abundant phenols were flavonoids: quercetin, (+)-catechin, daidzin, luteolin, and rutin. The seeds of P. oleracea were less sensitive than the seeds of A. retroflexus. The seed bioassay confirmed the inhibitory effect of stem extract on germination and early growth of both weed seedlings at concentrations of 0.75 % and 1 %, and a minor inhibitory effect in the plant bioassay. On the other hand, a synergy of C. campestris stem extract and metribuzin was revealed, as their combination achieved better results in the control of both weed species. Based on obtained data C. campestris stem extract could be a potential source of natural-based weed control molecules.

Response of the mushroom pathogen Cladobotryum mycophilum to prochloraz and metrafenone fungicides and Streptomyces flavovirens actinobacteria.

After an outbreak of cobweb disease of cultivated button mushroom in Serbia in 2003, the isolated fungal pathogen was initially identified as Cladobotryum dendroides (teleomorph Hypomyces rosellus) based on morpho-physiological traits. Molecular analysis indicated re-classification of two strains (isolated in 2004 and 2007) as Cladobotryum mycophilum (teleomorph Hypomyces odoratus). However, subsequent analysis of further five strains (isolated over the period 2003-2010) within the frames of the present study, also confirmed their identification as the exclusive cobweb causal agent C. mycophilum. After artificial inoculation, the symptoms observed on harvested and growing mushrooms were consistent with the appearance of cobweb disease. Pathogen sensitivity to fungicides was estimated by probit analyses. Fungicide susceptibility tests showed that C. mycophilum strains were highly sensitive both to prochloraz (ED50<0.087 µg mL-1) and the newly introduced metrafenone (ED50<0.15 µg mL-1). Furthermore, the growth of all examined strains of C. mycophilum was significantly inhibited by the indigenous actinobacterial strain Streptomyces flavovirens A06. A dual culture assay showed after 72 h that the percentage of radial growth inhibition of the pathogen ranged from 22.38 to 55.73%. Our findings suggest that the antagonistic S. flavovirens A06 might be a potential candidate for controlling the cobweb disease of cultivated button mushroom.

Effects of mixtures of allelopathic plant water extracts and a herbicide on weed suppression.

The present study investigated integrated effects of two allelopathic plant water extracts (WE) (Ambrosia artemisiifolia [AMBEL] and Xanthium strumarium [XANST]) and a herbicide (mesotrione) on morphological (height and fresh weight of plants) and physiological (pigments content) parameters of Abutilon theophrasti and Chenopodium album. Also, the study aimed to identify the main components of AMBEL and XANST WE and to evaluate their potential allelopathic effects. Of the 18 investigated compounds, 13 were detected in both tested WE, and p-coumaric acid was the leading component in AMBEL, while quinic acid was the predominant component of XANST. The WE of both weed species and their mixtures with the herbicide exhibited more powerful allelopathic effects on fresh weight and content of pigments than on the height of A. theophrasti and C. album. The results showed that all measured parameters of both weeds were inhibited in treatments with mesotrione and its mix with AMBEL and XANST WE. The data revealed a highly significant difference in effects (P < 0.05) between control weeds and those treated with AMBEL WE and mesotrione, where the inhibition of fresh weight was over 90%, while the inhibition of pigments content exceeded 80%, and plant height was inhibited by over 70%.

Chemical Composition of Ambrosia trifida Essential Oil and Phytotoxic Effect on Other Plants.

This study aimed to identify the main components of an essential oil produced from leaves of Ambrosia trifida and to evaluate its potential allelopathic effect on seed germination and seedling growth of lettuce, watermelon, cucumber and tomato. The essential oil was obtained by hydrodistillation and characterized chemically by gas chromatography (GC) coupled with both mass spectrometry (MS) and flame ionization detector (FID). Total 69 compounds were identified, with limonene (20.7 %), bornyl acetate (15.0 %), borneol (14.7 %) and germacrene D (11.6 %) as the major components. The working solutions of the essential oil emulsified with Tween 20 and dissolved in distilled water were prepared at four concentration levels (0.01, 0.1, 0.5 % and 1 %, v/v). The results obtained showed that increase in essential oil concentration leads to decrease in seed germination, as well as shoot and radical length of lettuce, watermelon, cucumber and tomato. The obtained data revealed a highly significant effect (p<0.05) between control and 1 % and 0.5 % oil concentrations in all treatments. The essential oil of A. trifida exhibited more powerful phytotoxic effects on lettuce, watermelon and tomato than on cucumber regarding germination and early seedling growth.

Bio-herbicidal effects of five essential oils on germination and early seedling growth of velvetleaf (Abutilon theophrasti Medik.).

The evaluation of the inhibition effect exerted by the essential oils of basil (Ocimum basilicum), sage (Salvia officinalis), thyme (Thymus vulgaris), lemon balm (Melissa officinalis) and goldenrod (Solidago virgaurea) on seeds germination and early seedling growth of velvetleaf (Abutilon theophrasti Medik.) weed was examined in a laboratory bioassay. The essential oils were obtained by hydrodistillation and characterized chemically by gas chromatography coupled with both mass spectrometry and flame ionization detector. The working solutions of essential oil emulsified with Tween 20 and dissolved in distilled water were prepared at three concentration levels (0.01%, 0.1% and 1%, vol/vol). The results obtained showed that increase of essential oil concentration leads to decrease of seed germination, shoot and radical length of velvetleaf. The obtained data revealed a highly significant effect (P < 0.05) between control and 1% and 0.1% oil concentrations in all treatments. The essential oils of basil, thyme and lemon balm exhibited more powerful bio-herbicidal effect compared to sage and goldenrod essential oils on the germination and early seedling growth of velvetleaf weed.

Impact of a native Streptomyces flavovirens from mushroom compost on green mold control and yield of Agaricus bisporus.

Thirty-five actinobacterial isolates, obtained from button mushroom (Agaricus bisporus) substrates (i.e., compost in different phases of composting, black peat or casing layer) in Serbia in 2014-2016 were tested in vitro against the causal agents of green mold in cultivated mushroom. Out of six most promising isolates, A06 induced 42.4% in vitro growth inhibition of Trichoderma harzianum T54, and 27.6% inhibition of T. aggressivum f. europaeum T77. The novel strain A06 was identified as Streptomyces flavovirens based on macroscopic and cultural characteristics and 16S rDNA sequence and used in mushroom growing room experiments. Actinobacteria had no negative influence on mycelial growth of the cultivated mushroom in compost in situ. Isolate S. flavovirens A06 enhanced mushroom yield significantly, up to 31.5%. The A06 isolate was more efficient in enhancing yield after inoculation with the compost mold T. aggressivum (26.1%), compared to casing mold T. harzianum (8%). Considering disease incidence, actinobacteria significantly prevented green mold in compost caused by T. aggressivum (6.8%). However, fungicide prochloraz-Mn had a more significant role in reducing symptoms of casing mold, T. harzianum, in comparison with actinobacteria (24.2 and 11.8%, respectively). No significant differences between efficacies of S. flavovirens A06 and the fungicide prochloraz-Mn against T. aggressivum were revealed. These results imply that S. flavovirens A06 can be used to increase mushroom yield and contribute to disease control against the aggressive compost green mold disease caused by Trichoderma aggressivum.

Effect of Cuscuta campestris parasitism on the physiological and anatomical changes in untreated and herbicide-treated sugar beet.

The effects of field dodder on physiological and anatomical processes in untreated sugar beet plants and the effects of propyzamide on field dodder were examined under controlled conditions. The experiment included the following variants: N-noninfested sugar beet plants (control); I - infested sugar beet plants (untreated), and infested plants treated with propyzamide (1500 g a.i. ha-1 (T1) and 2000 g a.i. ha-1(T2)). The following parameters were checked: physiological-pigment contents (chlorophyll a, chlorophyll b, total carotenoids); anatomical -leaf parameters: thickness of epidermis, parenchyma and spongy tissue, mesophyll and underside leaf epidermis, and diameter of bundle sheath cells; petiole parameters: diameter of tracheid, petiole hydraulic conductance, xylem surface, phloem cell diameter and phloem area in sugar beet plants. A conventional paraffin wax method was used to prepare the samples for microscopy. Pigment contents were measured spectrophotometrically after methanol extraction. All parameters were measured: prior to herbicide application (0 assessment), then 7, 14, 21, 28 and 35 days after application (DAA). Field dodder was found to affect the pigment contents in untreated sugar beet plants, causing significant reductions. Conversely, reduction in the treated plants decreased 27% to 4% for chlorophyll a, from 21% to 5% for chlorophyll b, and from 28% to 5% for carotenoids (T1). Also, in treatment T2, reduction decreased in infested and treated plants from 19% to 2% for chlorophyll a, from 21% to 2% for chlorophyll b, from 23% to 3% for carotenoids and stimulation of 1% and 2% was observed 28 and 35 DAA, respectively. Plants infested (untreated) by field dodder had lower values of most anatomical parameters, compared to noninfested plants. The measured anatomical parameters of sugar beet leaves and petiole had significantly higher values in noninfested plants and plants treated with propyzamide than in untreated plants. Also, the results showed that propyzamide is an adequate herbicide for control of field dodder at the stage of early infestation.

Phytotoxicity and allelopathic potential of Juglans regia L. leaf extract.

Implementation of plant extracts that are rich in phytochemicals and have the allelopathic potential for weed management could help reduce the use of chemical herbicides. The present study investigated the herbicidal potential of walnut (Juglans regia L.) leaf extract (WLE) against two weeds, Amaranthus retroflexus L. and Chenopodium album L., by testing in vitro their seed germination and seedling growth, and then evaluated in vivo the oxidative stress of potted plants. The effects of the walnut leaf extract were also tested on maize (Zea mays L.) to eliminate possible negative impacts on a cultivated plant. Total phenolic acids and total flavonoid content in the extract were determined in prior bioassays, followed by separation and analysis of flavonoids and phenolic acids by high-performance liquid chromatography (HPLC). Phytochemical analysis revealed that the obtained extract was notably rich in phenolic compounds, while HPLC analysis confirmed the presence of (+)-catechin, luteolin, myricetin, rutin, (-)-epicatechin, genistin, protocatechuic acid, and caffeic acid as major extract components. The results obtained in bioassays revealed a significant negative impact of the walnut leaf extract on germination and seedling growth of the tested weeds, as well as significant oxidative stress in weeds grown in pots. Although it affected the maize seedling growth in vitro similar to the tested weeds, maize germination was less sensitive to treatment, and the extract did not have a significant negative impact in terms of oxidative stress in maize plants grown in pots. The findings show that walnut leaf extract may have a promising role in replacing chemical herbicides in maize.

Inhibitory Effects of Brassicaceae Cover Crop on Ambrosia artemisiifolia Germination and Early Growth.

Several cover crops (CCs) exert allelopathic effects that suppress weed growth. The aim of the present study was to evaluate the effects of aqueous extracts containing different concentrations [0, 0.5, 1, 2.5, 5, 7.5 and 10% (w/v)] of Brassicaceae CCs (Sinapis alba, Raphanus sativus, Camellina sativa) and of the CCs Fagopyrum esculentum and Guizotia abyssinica on germination and early growth of Ambrosia artemisiifolia L. The allelopathic effects were species and concentration-dependent. C. sativa, for example, caused the greatest potential to inhibit germination, shoot, radicle length and fresh seedling weight, whereas S. alba and R. sativus inhibited germination and early growth of A. artemisiifolia only at concentrations ≥7.5%. In contrast, no inhibition was observed when aqueous extracts of F. escultneum and G. abyssinica were added at any of tested concentration. Liquid chromatography-tandem mass spectrometry detected 15 phenolic compounds in Brassicaceae CCs with the highest content (µg/g) of vanillin (48.8), chlorogenic acid (1057), vanilic acid (79), caffeic acid (102.5) and syringic acid (27.3) in C. sativa. Our results suggest that C. sativa is the most allelopathic CCs and that the fruits of C. sativa are the plant organs richest in allelochemicals.

Infestation of Field Dodder (Cuscuta campestris Yunck.) Promotes Changes in Host Dry Weight and Essential Oil Production in Two Aromatic Plants, Peppermint and Chamomile.

Peppermint (Mentha piperita L.) and chamomile (Chamomilla recutita (L.) Rausch.) are aromatic plants with considerable economic value. These plants and their essential oils are used in medicine, cosmetics, and the food industry. One of the main limiting factors in peppermint and chamomile commercial cultivation is weed competition since weeds are able to decrease both oil amount and biomass yield. The purpose of the present study was to determine the effect of parasitism by field dodder (Cuscuta campestris Yunck.) on peppermint and chamomile dry weight and their essential oil yield and composition. Essential oils from both noninfested and infested peppermint and chamomile plants were obtained by hydrodistillation and characterized chemically by gas chromatography (GC) coupled with mass spectrometry (MS). The amount of dry matter accumulated by peppermint and chamomile plants infested by field dodder was lower (25% and 63%, respectively) compared to noninfested plants. Essential oil yield increased for peppermint (3.87% (v/w) and 3.63% (v/w)), but decreased for chamomile (0.2% (v/w) and 0.5% (v/w)) both from infested and noninfested plants, respectively. The oil composition profile significantly differed in terms of content. In peppermint plants, field dodder infestation increased menthone content by 23%, and decreased the content of both menthol by 11% and pulegone by 67%. Furthermore, δ-cadinene was detected only in oil extracted from infested peppermint plants. Compared to peppermint, chamomile plants were significantly more affected by field dodder in terms of essential oil yield, as well as oil composition and plant dry weight. In chamomile plants, (E)-dendrolasin was detected in the oil of noninfested plants, and 1,4-dimethyl-7-(1-methylethyl)-azulen-2-ol was detected only in the oil of infested plants.