Banana plant fights off crop's invisible nemesis: Roundworms

The banana variety Yangambi km5 produces toxic substances that kill the nematode Radopholus similis, a roundworm that infects the root tissue of banana plants -- to the frustration of farmers worldwide. The finding by an international team of researchers that includes professors Rony Swennen and Dirk De Waele (Laboratory for Tropical Crop Improvement) bodes well for the Grande Naine, the export banana par excellence, which is very susceptible to the roundworms.

The parasitic nematode Radopholus similis is the invisible nemesis of the banana plant, says Professor Dirk De Waele: "This roundworm infects banana crops worldwide. The nematodes are invisible to the naked eye, but they can penetrate the roots of banana plants by the thousands. Once infected, these plants absorb less water and nutrients, resulting in yield losses of up to 75 percent. Lesions in the roots also make the plant more susceptible to other diseases. Eventually, the roots begin to rot. In the final stage of the disease, the plant topples over, its fruit bunch inexorably lost."

Combating nematodes isn't easy, adds Professor Swennen: "Synthetic pesticides are toxic and expensive. Moreover, pesticides usually do not actually kill the nematodes, they just temporarily paralyze them. Nematodes can also build up resistance to pesticides."

"We have always wondered how the Yangambi km5 fights off roundworms. This study offers an answer."

While the Grande Naine is very susceptible to nematodes, other varieties are known to be resistant to them. Enter the Yangambi km5, a variety first grown in the 1950's at a Belgian research station in Yangambi, DR Congo. The researchers compared the two banana varieties and studied their defense responses to Radopholus similis."Researchers have always wondered how the Yangambi km5 manages to fight off roundworms," says De Waele. "This study goes a long way in answering that."

Metabolites

With colleagues at the Max Planck Institute for Chemical Ecology (Germany), the KU Leuven researchers identified the metabolites that kill the nematodes. "We found nine different nematode-killing metabolites in Yangambi km5. These metabolites are also produced in the Grande Naine, but much more slowly and in lesser quantities. In that banana variety, the nematodes win the fight." The researchers' findings were published in a recent issue of the journal PNAS.

The new insights into metabolites will be helpful in developing edible and pest-resistant banana varieties, says Swennen. "The next step is to screen other banana varieties for metabolites. This method could also be applied to other crops and other species of nematode. Nematodes pose a growing threat to rice production in Asia, for example. Our findings also provide the industry with perspectives to develop a generation of new pesticides against nematodes."

Story Source:

The above story is based on materials provided by KU Leuven. Note: Materials may be edited for content and length.

Journal Reference:

D. Holscher, S. Dhakshinamoorthy, T. Alexandrov, M. Becker, T. Bretschneider, A. Buerkert, A. C. Crecelius, D. De Waele, A. Elsen, D. G. Heckel, H. Heklau, C. Hertweck, M. Kai, K. Knop, C. Krafft, R. K. Maddula, C. Matthaus, J. Popp, B. Schneider, U. S. Schubert, R. A. Sikora, A. Svatos, R. L. Swennen.Phenalenone-type phytoalexins mediate resistance of banana plants (Musa spp.) to the burrowing nematode Radopholus similis. Proceedings of the National Academy of Sciences, 2013; 111 (1): 105 DOI: 10.1073/pnas.1314168110

Cite This Page:

KU Leuven. "Banana plant fights off crop's invisible nemesis: Roundworms." ScienceDaily. ScienceDaily, 5 March 2014. <www.sciencedaily.com/releases/2014/03/140305111050.htm>.

Link:

http://www.sciencedaily.com/releases/2014/03/140305111050.htm

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Toxic Substances in Banana Plants Kill Root Pests

Dec. 11, 2013 — Bananas are a major food staple for about 400 million people in the tropical and subtropical regions of Asia, Africa and Latin America. However, banana yields worldwide are severely threatened by pests.

Dirk Hölscher from the Max Planck Institute for Chemical Ecology in Jena, Germany, and an international team of researchers have discovered that some banana varieties accumulate specific plant toxins in the immediate vicinity of root tissue that has been attacked by the parasitic nematode Radopholus similis. This local accumulation is crucial for the plant's resistance to this pest organism. The toxin is stored in lipid droplets in the body of the nematode and the parasite finally dies. These findings provide important clues for the development of pest-resistant banana varieties.

Banana yields worldwide threatened by pests

Bananas are among the world's most important food crops. Dessert bananas are produced primarily for homegrown consumption in China and India and for export to the northern hemisphere in Latin America. In Europe, they represent the most popular tropical fruit. Plantains (a type of cooking banana) are important components of daily meals in Africa and Southeast Asia. They are highly prized because of their high contents of nutrients, such as potassium, magnesium and vitamins B and C.

Apart from fungi and insects, the parasitic nematode Radopholus similis is considered a major banana pest. It attacks the roots of banana plants, causing slower growth and development of the plant and fruit. In the final stage of the disease plants topple over − often when already bearing an immature fruit bunch. Yield losses up to 75% can be the result of R. similis infestation. In order to control such pests in banana plantations, high doses of synthetic pesticides are used which not only cause ecological damage, but can also have severe negative effects on the health of people who are exposed to these chemicals.

Scientists at the Max Planck Institute for Chemical Ecology and their colleagues from universities in Leuven (Belgium), Jena, Kassel-Witzenhausen, Halle, Bonn and Bremen, as well as the Leibniz Institute for Natural Product Research and Infection Biology and the Leibniz Institute of Photonic Technology in Jena have now taken a closer look at the plant-nematode interactions in the context of resistance versus susceptibility. They compared two banana varieties, a resistant and a susceptible one, and studied their defense responses to Radopholus similis.

Phenylphenalenones: Local accumulation of defensive substances in infected regions of root tissues inhibits further propagation of the pest

The researchers used modern spectroscopic analysis and imaging techniques and were able to identify and localize defense substances in banana roots: The plants accumulated so-called phenylphenalenones only in infected regions of their roots, but not in healthy tissues. This was the case in both the resistant and the susceptible banana variety. The concentration of the most active compound anigorufone, however, was much higher in the immediate vicinity of lesions on the roots of resistant bananas in comparison to infected root tissues of the nematode susceptible banana plants. "The production of the toxin alone is not responsible for the banana plant's resistance to nematodes. It is the differential concentration in specific regions of the roots, which is particularly high at the precise location of the nematode attack, which makes the difference and confers resistance. We measured far higher concentrations of the toxin in these localized regions in the resistant banana variety," Dirk Hölscher summarizes the results.

Lipid droplets containing the active compounds visible in the nematode

The toxic effect of anigorufone and other substances was tested on living nematodes. It turned out that it was in fact anigorufone which was most toxic to the pest organism. By using imaging techniques, the researchers were able to visualize the plant toxin within the body of the roundworm. There the lipid-soluble anigorufone accumulated in lipid droplets which increased in size as they converged and finally killed the nematode. Why these complex lipid droplets are formed and why the nematodes cannot metabolize or excrete the toxin still needs to be clarified. However, it is likely that the growing lipid droplets displace the inner organs of the nematode causing an eventual metabolic dysfunction.

The scientists will now try to find out how resistant banana plants biosynthesize and translocate the defense compounds on a molecular level. Such insights will provide important clues for the development of banana varieties which are resistant to the nematodes. This could help to minimize the excessive use of highly toxic pesticides in banana plantations which jeopardize the environment and people's lives.

Root of the susceptible banana variety Grande Naine (above) and the resistant banana Yangambi km5 (below): visible are the few red, phenylphenalenone containing regions on the resistant Yangambi km5 root within the predominantly healthy, pale root tissue. The root of the susceptible Grande Naine banana is covered in widespread dark, red-brown areas. This massive root damage in the Grande Naine banana will eventually cause the plant’s death. (Credit: Dirk Hölscher, MPI Chem. Ecol.)

Journal Reference:

D. Holscher et al. Phenalenone-type phytoalexins mediate resistance of banana plants (Musa spp.) to the burrowing nematode Radopholus similis. Proceedings of the National Academy of Sciences, 2013; DOI:10.1073/pnas.1314168110

Link:

http://www.sciencedaily.com/releases/2013/12/131211131628.htm

The Ash Dieback Fungus, Chalara Fraxinea, Might Have a Mechanism to Define Territory and to Combat Viruses

Nov. 15, 2013 — The fungus which causes Chalara dieback of ash trees has the potential to defend itself against virus attacks, research by British scientists has shown.

Plant pathologists Dr Joan Webber, from Forest Research, the research agency of the Forestry Commission, and Professor Clive Brasier found that the defence mechanisms which the Chalara fraxinea (C. fraxinea) fungus uses to defend its territory could make it more resistant to virus-based control methods. Their research findings have been published in the journal Fungal Ecology.

Professor Brasier and Dr Webber studied C. fraxinea's genetic recognition system, called a vegetative compatibility (vc) system, in samples of the fungus from three different UK sites. Their results suggest that for most of these UK samples the fungal colonies are likely to be vegetatively incompatible with each other. This has implications for studying the biology of the fungus and for controlling its spread.

Vegetative compatibility (vc) systems are a fungal equivalent of the tissue rejection systems in humans, enabling the fungus to distinguish between self and non-self. Fungal colonies of the same vc-type can fuse to form a single individual, but those of a different vc-type cannot. Vc systems are central to the ecology and survival of a fungus, enabling it to define its territory, to resist viral attack and to promote outbreeding. Initial results show that the vc system of C. fraxinea generates a reaction between incompatible colonies which makes their filaments (the mycelium) collapse, creating a zone between the two colonies where growth is inhibited.

If the vc system is 'switched on' during early infection of ash leaves, then the spores (ascospores) responsible for infection might antagonise one other which could reduce their ash colonizing ability.

Alternatively, if the vc system is 'switched off', the germinating spores might co-operate during ash leaf infection, leading to a greater spread of the fungus. Later, as larger lesions form in ash tissues, the vc system might define the 'territory' defended by each pathogen individual.

Commenting on their results, Professor Brasier said: "This research is still at a preliminary stage. The fact that most isolates of Chalara fraxinea are incompatible with each other could mean that it might be difficult to deploy damaging fungal viruses against the pathogen as a disease control method, since viruses usually spread more readily in a fungal population when the colonies are able to fuse."

Journal Reference:

Clive Brasier, Joan Webber. Vegetative incompatibility in the ash dieback pathogen Hymenoscyphus pseudoalbidus and its ecological implications. Fungal Ecology, 2013; 6 (6): 501 DOI: 10.1016/j.funeco.2013.09.006

Link:

http://www.sciencedaily.com/releases/2013/11/131115094315.htm

Hymenoscyphus pseudoalbidus fruiting bodies on rachis. (Credit: Image courtesy of Forest Research

Mais um passo contra a podridão floral do citros

Da Redação - agenusp@usp.br Publicado em 13/novembro/2013

Lucas Jacinto, da Assessoria de Comunicação da Esalq, acom.esalq@usp.br

Por se tratar de uma das mais comprometedoras doenças nos campos de citricultura, a Podridão Floral do Citros (PFC), causada pelo fungo Colletotrichum acutatum, têm sido foco de diversos estudos. O Estado de São Paulo, que produz 80% do total do setor no Brasil é o principal cenário para estes trabalhos. No entanto, existem ainda lacunas para o processo de erradicação da doença e prevenção contra epidemias.

Podridão Floral do Citros é uma das mais comprometedoras doenças na citricultura

Em contrapartida, com o objetivo de estudar a histopatologia da interação C. acutatum com a laranjeira doce, e complementar os conhecimentos sobre seu patossistema na região sudoeste paulista, o pesquisador João Paulo Rodrigues Marques elaborou em seu doutorado em Fisiologia e Bioquímica de Plantas, realizado na Escola Superior de Agricultura Luiz de Queiroz (Esalq) da USP, em Piracicaba, trabalho voltado para PFC. Ultrastructural Changes In The Sweet Orange Petals Epidermis Infected With Colletotrichum acutatum, como é intitulado, rendeu a Marques Menção Honrosa pela participação no Prêmio Painel da área de Botânica-Biológicas, no último Congresso da Sociedade Brasileira de Microscopia e Microanálise, que ocorreu em outubro deste ano em Minas Gerais.

“Meu foco foi comparar a ultraestrutura da epiderme de pétalas inoculadas e não inoculadas com o fungo, visando compreender as alterações decorrentes da infecção”, contou. O projeto, realizado entre 2008 e 2012, no Laboratório de Anatomia Vegetal, do Departamento de Ciências Biológicas (LCB) e orientado pela professora Beatriz Appezzato da Glória (LCB), em parceria com a Fundecitrus (Araraquara – SP), envolveu os professores, Marcel Bellato Spózito, do Departamento de Produção Vegetal (LPV) e Lilian Amorim, do Departamento de Fitopatologia e Nematologia (LFN). Este trabalho foi financiado pela Fundação de Amparo a Pesquisa do Estado de São Paulo (Fapesp).

Segundo o pesquisador, compreender que o tecido epidérmico das pétalas de citros reagem, estruturalmente, à presença do patógeno é muito importante para entender como a planta interage com o fungo. “Os resultados obtidos pela pesquisa possibilitam interpretar o patossistema sobre a ótica de que os tecidos vegetais das pétalas, mesmo sendo susceptíveis, respondem à infecção, e que este fenômeno pode favorecer estudos futuros que visem um melhor entendimento sobre a interação planta-patógeno neste patossistema”, comenta.

Marques conta que, utilizando microscopia eletrônica de varredura e microscopia eletrônica de transmissão, foi revelado que a pétala sadia apresenta cutícula com estrias paralelas recobrindo a epiderme uniestratificada. “A cutícula é uma camada de material de natureza lipofílica que recobre o corpo do vegetal e é reconhecida como a primeira barreira física a ser ultrapassada pelos fungos durante o processo de infecção”.

No entanto, a cutícula das células epidérmicas infectadas é bastante alterada nos estágios mais avançados da infecção, ou seja, não são mais observadas as cristas devido à deposição de novas camadas cuticulares em placas. “Os resultados observados neste trabalho indicam que as células epidérmicas da pétala respondem à presença do patógeno, promovendo alterações parietais e cuticulares, as quais podem restringir novas infecções”, conclui.

Atualmente, o pesquisador faz seu pós-doutorado no Departamento de Genética (LGN), supervisionado pela professora Maria Lucia Carneiro Vieira.

Foto: Marcos Santos/ USP Imagens

Mais informações: (19) 3429.4109 ou (19) 3447.8613

Link:

http://www.usp.br/agen/?p=161266

Defending Food Crops: Whitefly Experimentation to Prevent Contamination of Agriculture

Nov. 8, 2013 — On November 8th, JoVE, the Journal of Visualized Experiments, will introduce a new technique to aid in the development of defenses against diseases threatening food crops worldwide. The method, published under the title Transmitting Plant Viruses Using Whiteflies, is applicable to such at-risk crops as tomatoes and common bean plants. The whitefly method provides a means of interfering with the plant-contamination process as well as the cultivation of plants that are altogether resistant to infection.

Experimentation with whitefly-transmitted diseases provides a means of interfering with the plant-contamination process as well as the cultivation of plants that are altogether resistant to infection. (Credit: JoVE)

"For example, the described technique is used to develop tomatoes with resistance to tomato yellow leaf curl virus, which is a big problem in tomato production in the southern U.S. and in many parts of the world," said Jane Polston, the principle investigator at the University of Florida's Department of Plant Pathology. In the article accompanying their JoVE video, Polston and her colleagues write that numerous genera of whitefly-transmitted plant viruses (such as Begomovirus, Carlavirus, Crinivirus, Ipomovirus, Torradovirus) are part of an emerging and economically significant group of pathogens affecting important food and fiber crops.

The technique includes reliably rearing whiteflies with a specific virus while omitting the possibility of cross-contamination to other viruses -- an easily encountered problem because of the sheer number of whiteflies used in testing. Such contamination would jeopardize the results of an entire experiment. After exposing large numbers of a particular plant species to a specific whitefly-transmitted virus, a researcher can then note which individual plants resisted infection and why. This article outlines how to generate hundreds or thousands of infected plants year-round by exposing them to whiteflies each week. Therefore, the whitefly-assisted transmission method provides researchers with a powerful means for continued experimentation in developing plant defenses against the threat of whitefly-transmitted disease.

Polston said that she published this technique through JoVE's video format because it was difficult to explain it through traditional text-only journals. "I have never published like this before and wanted to try it," she said, "And it was very difficult to describe some of the details of this technique in writing. Video was a better approach."

Journal Reference:

Polston, J. E., Capobianco, H. Transmitting Plant Viruses Using Whiteflies. J. Vis. Exp., 2013; (81), e4332 DOI:10.3791/4332

Link:

http://www.sciencedaily.com/releases/2013/11/131108102150.htm

UZUM - Sistema especialista para diagnóstico de doenças, pragas e distúrbios fisiológicos em videiras

http://www.cnpuv.embrapa.br/tecnologias/uzum/