Chair of Forest Zoology and Entomology, Albert-Ludwigs-Universität Freiburg i.Br. Chair of Forest Zoology and Entomology
Albert-Ludwigs-Universität Freiburg i.Br.

Chair of Forest Zoology and Entomology
Freiburg i.Br.

PAs for nematode management?

Tim Christoffer Thoden

Promotionsprojekt: "Entwicklung neuer umweltfreundlicher Methoden des Nematoden-Managements mit pflanzlichen Sekundärstoffen auf Basis Pyrrolizidin-Alkaloid haltiger Pflanzen", unterstützt vom Stipendienprogramm der Deutschen Bundesstiftung Umwelt.

Thoden TC, Boppré M (2010) Plants producing pyrrolizidine alkaloids: sustainable tools for nematode management? Nematology 12:1-24 link

1,2-dehydropyrrolizidine ester alkaloids (pyrrolizidine alkaloids; PAs) are a class of secondary plant metabolites found in hundreds of plant species. In vitro, PAs are known to affect plant-parasitic nematodes. Thus, PA-producing plants might be used in nematode management. So far, however, Crotalaria is the only PA-producing plant that has been used for nematode control. Consequently, we reviewed the literature on other PA plants and their effects on nematodes. This included the analysis of in vitro experiments with PA plant extracts, host tests with PA plants, as well as experiments in which PA-producing plants were used as different types of soil amendments (mulch, in situ mulching, extracts). Our results clearly show that, in addition to Crotalaria, certain other PAproducing plant species have the potential to be used in sustainable nematode management. This is especially true for management of sedentary endoparasitic nematode species. Promising applications include the use of PA plant extracts and mulches, as well as the use of PA plants for in situ mulching.

Thoden TC, Boppré M, Hallmann J (2009). Effects of pyrrolizidine alkaloids on plant-parasitic and free-living nematodes. Pest Manag Sci 65:823-830 link

Background: The management of plant-parasitic nematodes has been dominated for decades by the use of chemical nematicides such as methyl bromide. Their application is problematic because of negative environmental impacts. A possible alternative to synthetically derived nematicides is seen in the use of plants and/or their secondary metabolites. Those plants could either be used as nematicidal green manure, or as resource for nematicidal extracts. This study aimed to evaluate the effects of 1,2-dehydropyrrolizidine alkaloids (PAs), a group of secondary plant metabolites found in hundreds of plant species throughout the world, on the performance of plant-parasitic and free-living nematodes. Results: All tested PAs induced nematicidal, ovicidal and repellent effects on different plant-parasitic and free-living nematodes. No rating of toxicity was seen for the different structural types of PAs tested. However, the effects were often more pronounced for the tertiary than the oxidised form of PAs (free bases vs. N-oxides). Further, large differences were observed for the susceptibility of different nematode species to PAs. Conclusions: PAs do influence several performance parameters of nematodes. Therefore, PA-producing plant like Crotalaria spp. or Ageratum spp. might be promising candidates for nematode management strategies.

Thoden TC, Hallmann J , Boppré M (2009) Effects of plants containing pyrrolizidine alkaloids on the northern root-knot nematode Meloidogyne hapla. Europ J Plant Pathol 123:27-36 link

1,2-Dehydropyrrolizidine alkaloids (PAs), known to be nematotoxic in vitro, represent a class of secondary plant metabolites from hundreds of plant species worldwide. Pot experiments with the commercially available PA-containing plants Ageratum houstonianum, Borago officinalis, Senecio bicolor, and Symphytum officinalis demonstrate that Meloidogyne hapla is not per se repelled by these plants as all species were infested with nematodes. However, the development of M. hapla juveniles was completely suppressed on A. houstonianum and S. bicolor. Soil in which A. houstonianum and S. bicolor were cultivated and incorporated contained 200–400 times less nematodes than soil treated with Lycopersicon esculentum. Depending on their qualitative composition of PAs at least some of these plants thus appear to be valuable tools for integrated root-knot nematode management.

Thoden TC, Boppré M, Hallmann J (2008) Pyrrolizidin-Alkaloide produzierende Pflanzen: Natürliche Ressourcen zur Nematodenbekämpfung. Mitt Julius Kühn-Institut 417:129link

Sowohl die Ausweitung des ökologischen Landbaus als auch das Verbot zahlreicher synthetischer Pflanzenschutzmittel hat dazu geführt, dass in vielen Bereichen des Pflanzenschutzes nach umweltfreundlichen Bekämpfungsverfahren gesucht wird. Dies gilt auch für die Bekämpfung pflanzenparasitärer Nematoden. Vielversprechend ist die Nutzung pflanzlicher Sekundärstoffe ("botanicals").In den Tropen und Subtropen konnten durch den Anbau verschiedener Crotalaria-Arten Erfolge bei der Nematodenbekämpfung erzielt werden. Der zugrundeliegende Wirkungsmechanismus blieb bislang unklar. Allerdings sind Pflanzen dieser Gattung dafür bekannt, dass sie Pyrrolizidin-Alkaloide (PA) enthalten. Unsere in-vitro Versuche mit verschiedenen reinen PA zeigen nun, dass diese konzentrationsabhängig nematotoxische, nematostatische und auch ovizide Effekte hervorrufen, und dies z.T. schon ab Konzentrationen von 100 ppm. Bei Topfversuchen im Gewächshaus führte der Anbau und die nachfolgende Einarbeitung von PA-Pflanzen wie Senecio bicolor oder Ageratum houstonianum zu einer deutlichen und anhaltenden Reduzierung von Meloidogyne hapla. Dabei drangen die Larven in die Wurzeln ein, konnten sich allerdings nicht weiterentwickeln. Auf diesen Ergebnissen basierend erachten wir PA-Pflanzen als vielversprechende natürliche Ressourcen zur Bekämpfung pflanzenparasitärer Nematoden.

Thoden T, Boppré M, Burzlaff T, Hallmann J (2008) Plants containing pyrrolizidine alkaloids: a potential source for nematode control? Presentation at ICPP 2008

Crotalaria, a plant genus widely used as green manure and fibre crop in tropical and subtropical regions, is well known for its control potential of plant parasitic nematodes. Although the mode-of-action still awaits clarification, Crotalaria spp. do contain pyrrolizidine alkaloids (PAs), a class of secondary plant metabolites with a variety of reported chemoecological properties. So far, PAs have been detected in hundreds of plant species worldwide and we think that other PA-containing plant species besides Crotalaria might be interesting alternatives for nematode management strategies, especially in regions where Crotalaria spp. can not be cultivated for climatic, edaphic or other reasons. Therefore, we tested the nematicidal potential of pure PAs and plants containing PAs. Our in-vitro studies showed nematicidal effects of different types of pure PAs on Meloidogyne incognita at concentrations between 70 and 10,000 ppm. Furthermore, a mixture of purified PAs from Chromolaena odorata suppressed the host finding of M. incognita on lettuce even at concentrations of 70 ppm. Our in-vivo studies showed that cropping of the PA-containing plants Senecio bicolor and Ageratum conyzoides reduced the population density of M. incognita juveniles. In addition, the incorporation of plant material from A. conyzoides, S. bicolor and C. odorata into soil significantly reduced M. incognita infestation of tomato and lettuce. Therefore, PA-based methods like cropping and/or the incorporation of PA-containing plant material might be an environmentally sound alternative for nematode control.

Thoden TC, Boppré M, Hallmann J (2007) Pyrrolizidine alkaloids of Chromolaena odorata act as nematicidal agents and reduce infestation of lettuce roots by Meloidogyne incognita. Nematology: 343-349

1,2-dehydropyrrolizidine alkaloids (PAs) represent a class of secondary plant compounds that are active in defence against herbivory. They are present in Chromolaena odorata, one of the most invasive weeds of Asia and Africa. In-vitro studies demonstrate that pure PAs from C. odorata roots have nematicidal effects to the root-knot nematode Meloidogyne incognita, even at concentrations of 70–350 ppm. In-vivo experiments show that mulch or aqueous crude extracts from C. odorata roots reduce the infection of lettuce by M. incognita. Thus, the use of PA containing plants appears as a valuable element for integrated nematode management.