Nikoletta Ntalli

Botanical nematicides: a review.

Despite the uselfuness of nematicidal compounds in agricultural practices, some serious concerns are raised today about their excessive use leading to enhancement of biodegradation mechanisms in soil expressed as lack of efficacy under field conditions and resistance development. Moreover, the phase-out of methyl bromide has led to the need for a valid alternative to organophosporous and carbamate compounds, such us fosthiazate, fenamiphos, oxamyl, and aldicarb. In the past years, intregated pest management strategies have been practised worldwide to maximize crop production while maintaining and contributing to agriculture sustainability. Biopesticides and specifically bionematicides constitute a desirable component of pest management technology and practices. Particularly, in the frame of our ongoing research on natural nematicides of botanical origin, we have reviewed the international bibliography for candidate nematicidal compounds. We report herein the nematicidal activity of plant metabolites on the basis of their chemical characteristics and structure.

Synergistic and antagonistic interactions of terpenes against Meloidogyne incognita and the nematicidal activity of essential oils from seven plants indigenous to Greece.

BACKGROUND Biorational means for phytonematode control were studied within the context of an increasingly ecofriendly pest management global approach. The nematicidal activity and the chemical composition of essential oils (EOs) isolated from seven plants grown in Greece and ten selected compounds extracted from them against second-stage juveniles (J2) of Meloidogyne incognita (Kof. & White) Chitwood were evaluated using juvenile paralysis experiments. Additionally, synergistic and antagonistic interactions between nematicidal terpenes were studied using an effect addition model, with the comparison made at one concentration level. RESULTS The 96 h EC(50) values of Foeniculum vulgare Mill., Pimpinella anisum L., Eucalyptus meliodora A Cunn ex Schauer and Pistacia terebinthus L. were 231, 269, 807 and 1116 µg mL(-1) , respectively, in an immersion bioassay. Benzaldehyde (9 µg mL(-1) ) was the most toxic compound, followed by γ-eudesmol (50 µg mL(-1) ) and estragole (180 µg mL(-1) ), based on 96 h EC(50) values. The most potent terpene pairs between which synergistic actions were found, in decreasing order, were: trans-anethole/geraniol, trans-anethole/eugenol, carvacrol/eugenol and geraniol/carvacrol. CONCLUSION This is the first report on the activity of F. vulgare, P. anisum, E. meliodora and P. terebinthus, and additionally on synergistic/antagonistic nematicidal terpene interactions, against M. incognita, providing alternative methods for nematode control.

Nematicidal activity of (E,E)-2,4-decadienal and (E)-2-decenal from Ailanthus altissima against Meloidogyne javanica.

Methanol extracts of various plant parts of Ailanthus altissima were tested against the root knot nematode Meloidogyne javanica . Extracts of bark (ABE), wood (AWE), roots (ARE), and leaves (ALE) from A. altissima were investigated against freshly hatched second-stage juveniles (J(2)). AWE was the most active extract, with EC(50/3d) of 58.9 mg/L, while ALE, ARE, and ABE did not show nematicidal activity. The chemical composition of the extracts of A. altissima was determined by gas chromatography-mass spectrometry, and (E,E)-2,4-decadienal, (E)-2-undecenal, (E)-2-decenal, hexanal, nonanal, and furfural were the most prominent constituents. (E,E)-2,4-Decadienal, (E)-2-decenal, and furfural showed the highest nematicidal activity against M. javanica , with EC(50/1d) = 11.7, 20.43, and 21.79 mg/L, respectively, while the other compounds were inactive at the concentrations tested. The results obtained showed that AWE and its constituents (E,E)-2,4-decadienal and (E)-2-decenal could be considered as potent botanical nematicidal agents.

Aliphatic ketones from Ruta chalepensis (Rutaceae) induce paralysis on root knot nematodes.

This paper reports on the use of Ruta chalepensis L. extracts as a potential nematicide against root knot nematodes Meloidogyne incognita and Meloidogyne javanica . The essential oil (REO) and methanol extract (RME) of R. chalepensis were tested against second-stage juveniles, with REO inducing paralysis in both species (EC(50/1d) = 77.5 and 107.3 mg/L) and RME being selective for M. incognita (EC(50/1d) = 1001 mg/L). Chemical characterization of extracts was done by means of GC-MS and LC-MS, revealing mainly aliphatic ketones and coumarins, respectively. The first-ranking volatile nematicidal component in terms of individual activity against both species was 2-undecanone (EC(50) = 20.6 and 22.5 mg/L for M. incognita and M. javanica, respectively). This fact together with its high concentration in the most active extract found in this study, namely, REO (2926 mg/kg), categorizes 2-undecanone among the nematicidal principles of R. chalepensis. On the contrary, coumarins rutin and 8-methoxypsoralen were not found to be nematicidal at concentrations of ≤500 mg/L. Interestingly, M. incognita was found more sensitive than M. javanica.

Nematicidal Activity of Mint Aqueous Extracts against the Root-Knot Nematode Meloidogyne incognita

The nematicidal activity and chemical characterization of aqueous extracts and essential oils of three mint species, namely, Mentha × piperita , Mentha spicata , and Mentha pulegium , were investigated. The phytochemical analysis of the essential oils was performed by means of GC-MS, whereas the aqueous extracts were analyzed by LC-MS. The most abundant terpenes were isomenthone, menthone, menthol, pulegone, and carvone, and the water extracts yielded mainly chlorogenic acid, salvianolic acid B, luteolin-7-O-rutinoside, and rosmarinic acid. The water extracts exhibited significant nematicidal activity against Meloidogyne incognita , and the EC50/72h values were calculated at 1005, 745, and 300 mg/L for M. × piperita, M. pulegium, and M. spicata, respectively. Only the essential oil from M. spicata showed a nematicidal activity with an EC50/72h of 358 mg/L. Interestingly, menthofuran and carvone showed EC50/48h values of 127 and 730 mg/L, respectively. On the other hand, salicylic acid, isolated in the aqueous extracts, exhibited EC50 values at 24 and 48 h of 298 ± 92 and 288 ± 79 mg/L, respectively.

Potent nematicidal activity of phthalaldehyde, salicylaldehyde, and cinnamic aldehyde against Meloidogyne incognita.

The nematicidal activity of selected aromatic aldehydes was tested against the root knot nematode Meloidogyne incognita. The most active aldehyde was phthalaldehyde (1) with an EC(50) value of 11 ± 6 mg/L followed by salicylaldehyde (2) and cinnamic aldehyde (3) with EC(50) values of 11 ± 1 and 12 ± 5 mg/L, respectively. On the other hand, structurally related aldehydes such as 2-methoxybenzaldehyde (21), 3,4-dimethoxybenzaldehyde, and vanillin (23) were not active at the concentration of 1000 mg/L. By liquid chromatography-mass spectrometry the reactivity of tested aldehydes against a synthetic peptide resembling the nematode cuticle was characterized. At the test concentration of 1 mM, the main adduct formation was observed for 3,4-dihydroxybenzaldehyde (22), 2-methoxybenzaldehyde (21), and 3,4-dimethoxybenzaldehyde. Considering that 2-methoxybenzaldehyde (21) and 3,4-dimethoxybenzaldehyde were not active against M. incognita in in vitro experiments led us to hypothesize a different mechanism of action rather than an effect on the external cuticle modification of nematodes. When the toxicity of the V-ATPase inhibitor pyocyanin (10) was tested against M. incognita J2 nematodes, an EC(50) at 24 h of 72 ± 25 mg/L was found. The redox-active compounds such as phthalaldehyde (1) and salicylaldehyde (2) may share a common mode of action inhibiting nematode V-ATPase enzyme. The results of this investigation reveal that aromatic redox-active aldehydes can be considered as potent nematicides, and further investigation is needed to completely clarify their mode of action.

Pesticides of Botanical Origin: a Promising Tool in Plant Protection

Future agricultural and rural development is, to a large extent, influenced by the rapidly increasing food demand of 2.5 billion people expected to swell the world population by 2020. Achieving food sufficiency in a sustainable manner is a major challenge for farmers, agro-industries, researchers and governments (Schillhorn van Veen, 1999). The intensification of agriculture to fulfil food needs has increased the number of insect pest species attacking different crops and as a result the annual production losses of the standing crops. In the past, synthetic pesticides have played a major role in crop protection programmes and have immensely benefited mankind. Nevertheless, their indiscriminate use has resulted in the development of resistance by pests (insects,weeds, etc), resurgence and outbreak of new pests, toxicity to non-target organisms and hazardous effects on the environment endangering the sustainability of ecosystems (Jeyasankar & Jesudasan, 2005). In the recent years the EU has employed a fundamental reform of the Common Agricultural Policy (CAP) highlighting the respect to the environmental, food safety and animal welfare standards, imposing farmlands’ cross-compliance with good agricultural and environmental conditions (Schillhorn van Veen, 1999). Due to environmental side effects and health concerns, many synthetic carbamate, organophosphate, and organophthalide pesticides have been banned (Council Directive 91/414/EEC) or are being under evaluation (Regulation 2009/1107/EC OL & Directive 2009/128/EC). On the other hand, industry does not equally sustain the economic cost of research and registration, of all pesticides’ chemical classes. The development of nematicides is rarely supported, even though in some cases, such as in the Netherlands, they represent more than 60% of the total pesticides used in agriculture (Chitwood, 2002). This is due to the fact that nematodes are a rather difficult target and the economic cost of research and registration is an enormous hurdle for a prospective new synthetic nematicide to overcome (Chitwood, 2002). As a result, currently there are only few nematicides left in use, and their limited number makes the repeated applications of the same formulation, inevitable. This fact has led to the enhancement nematicides biodegradation in soil (Qui et al., 2004 , Karpouzas et al., 2004, Arbeli & Fuentes, 2007) and the development of resistance in pests. (Meher et al., 2009) These two phenomena are expressed in field as lack of efficacy of the applied pesticides. All the above facts necessitate the urge for new and alternative pest control methods (Chitwood, 2002). An interesting way of searching for biorational pesticides is screening naturally occurring compounds in plants (Isman, 2006; 2008). Plants, as long-lived stationary organisms, must

Nematotoxic Phenolic Compounds from Melia azedarach Against Meloidogyne incognita

In the present study, evaluated was the paralysis activity of whole Italian and Algerian Melia azedarach, commonly known as chinaberry, fruits and parts (seeds, wood, and kernels) against Meloidogyne incognita second stage juveniles (J(2)). The paralysis activity was evaluated in vitro after 1 h and 1 day immersion periods of nematodes in test solutions. Phenolic constituent components of the extracts were identified and quantified by high-performance liquid chromatography-mass spectrometry, while confirmation was performed by high-performance liquid chromatography-diode array. The water extract of the Italian M. azedarach fruit pulp (IPWE) showed significant nematicidal activity (EC(50/48h) = 955 μg/mL) and among its active ingredient components were p-coumaric acid and p-hydroxybenzoic acid (EC(50/48h) = 840 and 871 μg/mL, respectively). This is the first report of the nematicidal activity of M. azedarach pulp water extract and phenolic acids against the root knot nematode M. incognita.

Nematicidal Activity of the Volatilome of Eruca sativa on Meloidogyne incognita.

Research on new pesticides based on plant extracts, aimed at the development of nontoxic formulates, has recently gained increased interest. This study investigated the use of the volatilome of rucola (Eruca sativa) as a powerful natural nematicidal agent against the root-knot nematode, Meloidogyne incognita. Analysis of the composition of the volatilome, using GC-MS-SPME, showed that the compound (Z)-3-hexenyl acetate was the most abundant, followed by (Z)-3-hexen-1-ol and erucin, with relative percentages of 22.7 ± 1.6, 15.9 ± 2.3, and 8.6 ± 1.3, respectively. Testing of the nematicidal activity of rucola volatile compounds revealed that erucin, pentyl isothiocyanate, hexyl isothiocyanate, (E)-2-hexenal, 2-ethylfuran, and methyl thiocyanate were the most active with EC50 values of 3.2 ± 1.7, 11.1 ± 5.0, 11.3 ± 2.6, 15.0 ± 3.3, 16.0 ± 5.0, and 18.1 ± 0.6 mg/L, respectively, after 24 h of incubation. Moreover, the nematicidal activity of fresh rucola used as soil amendant in a containerized culture of tomato decreased the nematode infection in a dose-response manner (EC50 = 20.03 mg/g) and plant growth was improved. On the basis of these results, E. sativa can be considered as a promising companion plant in intercropping strategies for tomato growers to control root-knot nematodes.

A review of isothiocyanates biofumigation activity on plant parasitic nematodes

Natural isothiocyanates (ITCs) are toxic to a range of soil-borne pest and pathogens, including nematodes and fungi, and can thus be used as natural fumigants called biofumigants. Glucosinolates, β-thioglucoside N-hydroxysulfates, are secondary metabolites of Brassicales plants, stored in the S-cells vacuoles. Upon plant tissue damage myrosinase (thioglucoside glycohydrolase, EC 3.2.3.1), stored in contiguous cells, hydrolyses glucosinalates to an unstable aglycone that eventually eliminates sulfate group producing a wide range of different volatile isothiocyanates that are extremely toxic to root-knot nematodes. In fact, among synthetic commercial nematicidal formulates we can find isothiocyanates as active ingredients. Conventional nematode control practices have included soil sterilants of great environmental impact, most of which are now banned making mandatory the development of eco-sustainable alternative tools. We reviewed the nematicidal activity of isothiocyanates as components of botanical matrixes in the frame of a holistic nematode control approach encompassing secondary beneficial effects on soil structure and microbiology, beneficial preservation, enhanced residual life of biological activity and plant growth.