Tag Archives: disease

Plant Virus Ecology

Plant Viruses

The latest in the “Pearls” series from PLOS Pathogens is about plant virus ecology. In this short and highly accessible article, Marilyn Roossinck provides an excellent primer for the non-initiated:

  • Plant Virus Biodiveristy
  • Plant Viruses and Invasive Species
  • Viruses, Plants and Insects
  • Persistent Plant Viruses
  • Mutualistic Viruses of Plants

 

Plant Virus Ecology. (2013) PLoS Pathog 9(5): e1003304. doi:10.1371/journal.ppat.1003304
Viruses have generally been studied either as disease-causing infectious agents that have a negative impact on the host (most eukaryote-infecting viruses), or as tools for molecular biology (especially bacteria-infecting viruses, or phage). Virus ecology looks at the more complex issues of virus-host-environment interactions. For plant viruses this includes studies of plant virus biodiversity, including viruses sampled directly from plants and from a variety of other environments; how plant viruses impact species invasion; interactions between plants, viruses and insects; the large number of persistent viruses in plants that may have epigenetic effects; and viruses that provide a clear benefit to their plant hosts (mutualists). Plants in a non-agricultural setting interact with many other living entities such as animals, insects, and other plants, as well as their physical environment. Wild plants are almost always colonized by a number of microbes, including fungi, bacteria and viruses. Viruses may impact any of these interactions.

 

Breathe in, breathe out

Ethylene production from various biological samples Traces of volatile organic compounds (VOCs) – gasses such as ethylene, nitric oxide and ethanol – play an important role in many areas of life sciences ranging from agrotechnology, microbiology, molecular biology, physiology, and phytopathology. In plants, many biological processes can be followed by ultra low-concentration gas emissions. Examples include the circadian rhythm of ethylene production in Arabidopsis thaliana and from fungus-infected tomatoes, and methane emissions from plants – which can produce methane in aerobic conditions. Nitric oxide (NO) plays an important role in plant growth and development, stomatal regulation, and protection against biotic and abiotic stresses – and can also be used to monitor the response of plants infected with pathogens.

A paper in AoB PLANTS describes new methods for online and real-time monitoring of trace gases that are now available. Laser based instruments have a sensitivity at the single part per billion level and a response time of a few seconds. This allows the dynamics of trace gases such as ethylene, nitric oxide and other VOCs released by plants under different conditions to be recorded and analysed under natural conditions. These are indispensable tools for applications which cannot be fulfilled by existing technology, such as gas chromatography.

 

Frans Harren and Simona Cristescu. Online, real-time detection of volatile emissions from plant tissue. AoB PLANTS (2013) 5: plt003 doi: 10.1093/aobpla/plt003

Not so green as they’re cabbage looking

Not so mellow yellow There have been some very interesting papers published recently on how plants withstand diseases. Plants seeingly lack the sophisticated immune system of mamals, so discoveries of how they use the genes they have is noteworthy.

 

The fact that single immune receptors conferring multiple resistances to taxonomically unrelated pathogens may not be exceptional gives plant breeders a strong incentive to identify and to use common virulence targets as leads to discover broad-specificity resistance genes:
Dual disease resistance mediated by the immune receptor Cf-2 in tomato requires a common virulence target of a fungus and a nematode. PNAS USA 06 June 2012 doi: 10.1073/pnas.1202867109 Plants lack the seemingly unlimited receptor diversity of a somatic adaptive immune system as found in vertebrates and rely on only a relatively small set of innate immune receptors to resist a myriad of pathogens. Here, we show that disease-resistant tomato plants use an efficient mechanism to leverage the limited nonself recognition capacity of their innate immune system. We found that the extracellular plant immune receptor protein Cf-2 of the red currant tomato (Solanum pimpinellifolium) has acquired dual resistance specificity by sensing perturbations in a common virulence target of two independently evolved effectors of a fungus and a nematode. The Cf-2 protein, originally identified as a monospecific immune receptor for the leaf mold fungus Cladosporium fulvum, also mediates disease resistance to the root parasitic nematode Globodera rostochiensis pathotype Ro1-Mierenbos. The Cf-2–mediated dual resistance is triggered by effector-induced perturbations of the apoplastic Rcr3pim protein of S. pimpinellifolium. Binding of the venom allergen-like effector protein Gr-VAP1 of G. rostochiensis to Rcr3pim perturbs the active site of this papain-like cysteine protease. In the absence of the Cf-2 receptor, Rcr3pim increases the susceptibility of tomato plants to G. rostochiensis, thus showing its role as a virulence target of these nematodes. Furthermore, both nematode infection and transient expression of Gr-VAP1 in tomato plants harboring Cf-2 and Rcr3pim trigger a defense-related programmed cell death in plant cells. Our data demonstrate that monitoring host proteins targeted by multiple pathogens broadens the spectrum of disease resistances mediated by single plant immune receptors.

And there is also the recent work showing that plants can pass acquired defenses against pests and pathogens on to their offspring: Memory Tools for Plants – how plants pass defenses to offspring through a complex molecular network

 

Plants are clearly a lot smarter than many people give them credit for. The question is, are we smart enough to use these new discoveries to help feed ourselves in the future?

The Top 10 fungal pathogens in molecular plant pathology

Magnaporthe oryzae

Magnaporthe oryzae

Gary has absolutely promised me this will be the last top 10 list. We’ll see :-)

But here it is anyway, the results of Molecular Plant Pathology’s survey of fungal pathologists which asked them to nominate the fungal pathogens they would place in a ‘Top 10′ based on scientific/economic importance:

  1. Magnaporthe oryzae
  2.  Botrytis cinerea
  3.  Puccinia spp.
  4.  Fusarium graminearum
  5.  Fusarium oxysporum
  6.  Blumeria graminis
  7.  Mycosphaerella graminicola
  8.  Colletotrichum spp.
  9.  Ustilago maydis
  10.  Melampsora lini

Don’t agree? (personally I’d have put Botrytis cinerea at number 1) – complain to Molecular Plant Pathology not us!

 

The Top 10 fungal pathogens in molecular plant pathology. Mol Plant Pathol. 06 March 2012
The aim of this review was to survey all fungal pathologists with an association with the journal Molecular Plant Pathology and ask them to nominate which fungal pathogens they would place in a ‘Top 10′ based on scientific/economic importance. The survey generated 495 votes from the international community, and resulted in the generation of a Top 10 fungal plant pathogen list for Molecular Plant Pathology. The Top 10 list includes, in rank order, (1) Magnaporthe oryzae; (2) Botrytis cinerea; (3) Puccinia spp.; (4) Fusarium graminearum; (5) Fusarium oxysporum; (6) Blumeria graminis; (7) Mycosphaerella graminicola; (8) Colletotrichum spp.; (9) Ustilago maydis; (10) Melampsora lini, with honourable mentions for fungi just missing out on the Top 10, including Phakopsora pachyrhizi and Rhizoctonia solani. This article presents a short resumé of each fungus in the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant mycology community, as well as laying down a bench-mark. It will be interesting to see in future years how perceptions change and what fungi will comprise any future Top 10.

Here we go again…

Magnaporthe oryzae In January I wrote about Molecular Plant Pathology’s top 10 plant viruses in molecular plant pathology. Everyone likes a good list, but I had no idea it would be so controversial. Well now they’re at it again, this time with the top 10 fungal pathogens in molecular plant pathology:

  1. Magnaporthe oryzae
  2. Botrytis cinerea
  3. Puccinia spp.
  4. Fusarium graminearum
  5. Fusarium oxysporum
  6. Blumeria graminis
  7. Mycosphaerella graminicola
  8. Colletotrichum spp.
  9. Ustilago maydis
  10. Melampsora lini

Well, I like Botrytis cinerea and I like Fusarium graminearum, but which is best? There’s only one way to find out:

The Top 10 fungal pathogens in molecular plant pathology. Molecular Plant Pathology 06 March 2012, doi: 10.1111/j.1364-3703.2012.2011.00783.x
The aim of this review was to survey all fungal pathologists with an association with the journal Molecular Plant Pathology and ask them to nominate which fungal pathogens they would place in a ‘Top 10′ based on scientific/economic importance. The survey generated 495 votes from the international community, and resulted in the generation of a Top 10 fungal plant pathogen list for Molecular Plant Pathology. The Top 10 list includes, in rank order, (1) Magnaporthe oryzae; (2) Botrytis cinerea; (3) Puccinia spp.; (4) Fusarium graminearum; (5) Fusarium oxysporum; (6) Blumeria graminis; (7) Mycosphaerella graminicola; (8) Colletotrichum spp.; (9) Ustilago maydis; (10) Melampsora lini, with honourable mentions for fungi just missing out on the Top 10, including Phakopsora pachyrhizi and Rhizoctonia solani. This article presents a short resumé of each fungus in the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant mycology community, as well as laying down a bench-mark. It will be interesting to see in future years how perceptions change and what fungi will comprise any future Top 10.


Bananas on the cover – a videoblog

Banana fruit bunch

Banana fruit bunch

We used a bunch of bananas, one of the species I work with, as the main background image on the cover of Annals of Botany two years ago. I am discussing the cover images in Annals of Botany in three video blogs.

The video blog is directly available in YouTube at http://youtu.be/UsjbhWnHQpA – please use the 1080p version if you have a fast internet connection – and a summary with more information is given below.

The video blog is directly available in YouTube at http://youtu.be/UsjbhWnHQpA – please use the 1080p version if you have a fast internet connection.

The plant shown on the cover is healthy and has survived a tropic storm, so shows the wind-damaged leaves adapting to this abiotic or environmental stress. But I was visiting the site to see a biotic – organism caused – stress, the devastating Fusarium tropical race 4 disease on other varieties being grown at the same site (http://aobblog.com/2011/05/bananas-disease-diversity-research-and-the-one-show/). While the picture could have been taken nearly anywhere in the humid tropics or sub-tropics, it was actually taking in Guangzhou, south China, on an island in the Pearl River. Apart from high resolution digital photography, a real advantage for field work has been GPS, and the ability to automatically geotag the locations where photographs are taken, and Google maps can pinpoint the point I stood to take the photograph - 22° 18′ 48″N, 113° 19′ 54″E. Banana originates from the Indo-Malayan Center of diversity, mostly 500 to 2000 km to the south and west of Guangzhou, running from Papua New Guinea through the Malaysian penninsula, parts of China, Thailand and Burma, into India (see for example my review of banana domestication and superdomestication at dx.doi.org/10.1093/aob/mcm191 and from the meeting in China when this photograph was taken). The cover picture shows a cultivar rather than a wild species. The illustrated bunch is a variety called Pisang Awak, and is disease free although rather badly damaged by a tropical storm which came through three days before my visit. However, the main purpose of this visit was to see the devastation of the the tropical race 4 of Fusarium oxysprorum f. sp. cubense, the Panama disease that is destroying the major export variety of banana, Cavendish. You can see me in front of a plant with the infection – the leaves are yellowed and dying, and all the fruit has fallen before ripening. Agronomy and chemical control are essentially impossible for this disease, so only strict biosecurity is controlling its spread outside South East Asia. I made sure I scrubbed my shoes in bleach solution after this visit. More positively, though, as was obvious from the uninfected plants in the same plantation, other banana varieties have resistance to this disease, and hopefully in the next year we will be making more progress to identifying the genes and genetics involved (http://www.mendeley.com/research/genomes-diversity-resistance-gene-analogues-musa-species/)

The mysteries of movement proteins

Prunus necrotic ringspot virus To establish a systemic infection, plant viruses invade neighboring cells via cell to cell movement trough plasmodesmata channels until they reach the vascular system. This cell to cell movement is an active process involving one or more movement proteins encoded by the virus, which interact with other virus and host factors. Exactly how these movement proteins function is still a mystery in most cases. A new paper in PLoS ONE reveals new details on how this process works for Prunus necrotic ringspot virus (PNRSV), a serious pathogen of cultivated stone fruit trees.

A Plant Virus Movement Protein Regulates the Gcn2p Kinase in Budding Yeast. (2011) PLoS ONE 6(11): e27409. doi:10.1371/journal.pone.0027409
Virus life cycle heavily depends on their ability to command the host machinery in order to translate their genomes. Animal viruses have been shown to interfere with host translation machinery by expressing viral proteins that either maintain or inhibit eIF2α function by phosphorylation. However, this interference mechanism has not been described for any plant virus yet. Prunnus necrotic ringspot virus (PNRSV) is a serious pathogen of cultivated stone fruit trees. The movement protein (MP) of PNRSV is necessary for the cell-to-cell movement of the virus. By using a yeast-based approach we have found that over-expression of the PNRSV MP caused a severe growth defect in yeast cells. cDNA microarrays analysis carried out to characterise at the molecular level the growth interference phenotype reported the induction of genes related to amino acid deprivation suggesting that expression of MP activates the GCN pathway in yeast cells. Accordingly, PNRSV MP triggered activation of the Gcn2p kinase, as judged by increased eIF2α phosphorylation. Activation of Gcn2p by MP expression required a functional Tor1p kinase, since rapamycin treatment alleviated the yeast cell growth defect and blocked eIF2α phosphorylation triggered by MP expression. Overall, these findings uncover a previously uncharacterised function for PNRSV MP viral protein, and point out at Tor1p and Gcn2p kinases as candidate susceptibility factors for plant viral infections.

Reactions of Nicotiana species to inoculation with begomoviruses

begomovirus Some Nicotiana species are widely used as experimental hosts for plant viruses. Nicotiana species differ in ploidy levels, chromosome numbers and have diverse geographical origins. Thus, these species are useful model systems to investigate virus-host interactions, co-evolution of pathogens and hosts and the effects of ploidy level on virus resistance/susceptibility.

This research studied the responses of seven Nicotiana species to inoculation with Cotton leaf curl Multan virus (CLCuMV), a monopartite begomovirus, and Tomato leaf curl New Delhi virus (ToLCNDV), a bipartite begomovirus, both from the Indian subcontinent. All Nicotiana species supported the replication of both begomoviruses in inoculated leaves. However, only three Nicotiana species, namely N. benthamiana, N. tabacum and N. sylvestris showed symptoms when inoculated with ToLCNDV, while N. benthamiana was the only species that developed leaf curl symptoms when inoculated with CLCuMV. CLCuMV accumulated to detectable levels in N. tabacum, but plants remained asymptomatic. A previously identified mutation of RNA dependent RNA polymerase 1 was shown to be present only in N. benthamiana. The finding is in line with earlier results showing that the susceptibility of this species to a diverse range of plant viruses correlates with a defective RNA silencing-mediated host defense.

The results show that individual Nicotiana species respond differently to inoculation with begomoviruses. The inability of begomoviruses to systemically infect several Nicotiana species is likely due to inhibition of virus movement, rather than replication, and thus provides a novel model to study virus-host interactions in resistant/susceptible hosts.

Reactions of Nicotiana species to inoculation with monopartite and bipartite begomoviruses. Virology Journal 2011, 8: 475 doi:10.1186/1743-422X-8-475

Improving lives through research on banana biodiversity

Woman standing by banana plant.

Photo: Inge Van den Bergh, Bioversity

Numerous communities in developing countries depend on bananas as a staple food and as a source of income. The vast majority of producers are smallholder farmers who grow most of the world production, estimated by the FAO to be more than 125 million metric tons in 2008. Less than 15% of global production is exported.

Bananas are unusual among major crops in that most of the types grown, either for export or local consumption, are farmer-selected varieties rather than improved hybrids produced by breeding programmes. This situation reflects not only the difficulty of breeding bananas, but also a general lack of appreciation of its importance as a staple crop.

The funds invested in banana research in general are still not commensurate with the importance of the crop and the scale of the problems faced by smallholder producers. Meanwhile, the genetic base on which solutions to these problems depend — either through genetic improvement or a better use of diversity in production systems — is being eroded. Reducing diversity, in turn, has made the crop even more vulnerable to pests and diseases, forcing farmers who have little means for combating them to give up on the more susceptible varieties.

Bananas for sale

Photo: Inge Van den Bergh, Bioversity

But while the production and marketing of this crop pose many challenges, they also present great opportunities for improving the welfare of farmers and consumers in developing countries. Enabling farmers across the tropics to use biodiversity to meet their food security needs and livelihoods aspirations are the main goals of Bioversity International’s work on bananas.

The mission of Bioversity’s banana research group, with headquarters in France and regional offices in Costa Rica, the Philippines, Cameroon and Uganda, is to help people, especially small-scale banana producers and their communities, to improve their well-being through effective use of banana biodiversity.

Banking on Musa

Banana Science.

Photo: Inge Van den Bergh, Bioversity

Bioversity’s approach to research along the banana commodity chain begins with the conservation, within the public domain, of the world’s largest in-vitro collection of Musa. The collection, which contains more than 1,300 accessions, is held at the International Transit Centre (ITC) hosted by the Katholieke Universiteit Leuven (KULeuven) in Belgium.

At the time of its establishment in 1985, quarantine regulations were putting a constraint on germplasm movement. Indexing methods were developed and virus-indexing centres were set up. By the late 1980s, the system to allow the safe movement of germplasm was in place. All the accessions are routinely virus-indexed, and virus therapies have been developed by partners at the University of Gembloux and the French agricultural research institute CIRAD. Virus research commissioned from CIRAD and the University of Minnesota has improved the understanding of banana streak viruses, but their presence in 30% of the collection continues to restrict this part of the collection from general circulation. The ITC has established a collection of lyophilized leaf samples to respond to demands for DNA. By this means, even accessions that are virus-infected can be made available for molecular study.

An extra level of insurance is provided by the conservation of accessions in liquid nitrogen. At these ultra-low temperatures, so-called ‘cryopreservation’ arrests both the growth of plant cells and all processes of biological deterioration, so that the material can be preserved, safely and cost-effectively, and regenerated into fully viable banana plants. So far, most of the collection has been safely cryopreserved and, as yet further insurance, a duplicate set is being deposited for safe-keeping at the French research institute for development IRD.

A Global Conservation Strategy for Musa was developed with partners. Building upon existing strengths at the ITC, and several regional and national collections, the strategy aims to rationalize the global effort to conserve the Musa gene pool and promote the wider use of these genetic resources by scientists, farmers and breeders to produce new varieties.

Bioversity works with specialist research institutes to identify the useful traits embodied in these genetic resources. For example, the ploidy level of the ITC accessions has been entirely characterized by the Institute for Experimental Botany (IEB) in the Czech Republic, using flow cytometry. Another key role is to set up information systems to disseminate the data generated by these characterization and evaluation activities and to make research results available to a wide public.

Hungry for improvement

Woman with an exotic banana

Photo: Inge Van den Bergh, Bioversity

Bananas are known to be difficult to breed. The first ones to try gave up. When the United Fruit Company also abandoned the idea of breeding a commercial banana in 1984, it donated its breeding programme to the Fundación Hondureña de Investigación Agrícola (FHIA) in Honduras, which, capitalizing on more than 25 years’ worth of work on bananas, was soon able to deliver disease-resistant hybrids.

Before they were released, the hybrids were field-tested in the International Musa Testing Programme (IMTP) set up in 1989 and coordinated by Bioversity. One of the explanations offered for the slow progress of banana breeding had been that breeders were receiving little guidance from other disciplines. The IMTP addressed this by making the material they produced available for study by pathologists and other scientists under different environmental conditions.

Forging inter-disciplinary links was further encouraged with the creation in 1997 of the Global Programme for Musa Improvement (ProMusa). At the origin, it consisted of six interlinked working groups, each focusing on a particular subject—genetic improvement, Fusarium wilt, Mycosphaerella leaf spot diseases, weevils, nematodes and viruses—but all from the point of view of providing support to banana breeding efforts. It has since been restructured to further stimulate interaction among specialists and to take into account the difficulty of coordinating such a network with minimal financial support from donors.

Indeed, it has proved increasingly difficult to attract the interest of donors to conventional breeding efforts as a whole. Funding for the IMTP dried up after the first phase (phases II and III were funded by the implementing partners) and public-sector support to FHIA ended in 2004. The lack of international donor interest in networking has however not spelled the end of banana breeding. The field is not as crowded as for the other major crops, but a handful of centres are still at it. In Latin America and the Caribbean, the veterans are the Empresa Brasiliera de Pesquisa Agropecuaria (EMBRAPA) and CIRAD’s Guadeloupe research station. Cuba has also started its own banana breeding programme at the Instituto de Investigaciones en Viandas Tropicales (INIVIT). In India, the National Research Centre for Banana (NRCB) and Tamil Nadu Agricultural University have created numerous hybrids, while in Africa, banana breeding is mainly conducted by the International Institute of Tropical Agriculture (IITA) and the Centre de Recherches Regionales sur Bananiers et Plantains (CRBP).

Given the difficulties inherent in breeding bananas, some scientists have turned their sights to genetic transformation as a way of introducing genes into bananas without disrupting their agronomic qualities. Moreover, the lack of cross-fertile wild relatives in many banana-producing areas and the sterility of most cultivated varieties reduce, to negligible levels, the risk of genes escaping from genetically-transformed bananas. Over the years, Bioversity has coordinated research projects that have contributed to advances in genetically modifying varieties important to smallholders.

Meanwhile, a networking approach is helping researchers make the most of the rapid progress in genomics. Since 2001, most of the genomics work on bananas is being done by scientists who are members of the Global Musa Genomics Consortium (GMGC), for which Bioversity provides the secretariat. Whenever possible, the products developed by GMGC members are placed in the public domain and available from the Musa Genome Resources Centre hosted by the IEB. The sequencing of the genome being done by the French National Sequencing Center, Genoscope, will help identify and use genes of interest for breeding, as well as facilitate parent choice.

Managing diversity

Man with banana harvest

Photo: Inge Van den Bergh, Bioversity

Bioversity and its partners have looked at many dimensions of the challenge of producing slowly evolving bananas in a rapidly evolving world. In other crops, the conventional wisdom is that pest- and disease-resistant varieties provide a sound foundation for integrated crop management strategies but in bananas this principle has been hard to establish. Farmers and consumers have tended to develop strong preferences for their familiar cultivars and, because of the complexity of banana breeding, the disease-resistant cultivars that have been developed rarely substitute directly for existing varieties.

Access to good quality planting material can also be an issue limiting adoption of the new cultivars. Bioversity-led efforts to disseminate improved hybrids in Latin America, Africa and Asia took care to ensure the quality of the initial planting materials and, to some extent, set up mechanisms to encourage further propagation of the new materials by conventional methods. However, these experiences fall far short of establishing national systems to ensure the long-term availability of clean planting material.

Banana nursery

Photo: Inge Van den Bergh, Bioversity

However, Bioversity has worked on institutionalizing such systems in Asia where 17 National Repository, Multiplication and Dissemination Centres have been established in 14 countries. These Centres maintain disease-free mother stocks of potentially useful varieties that can then feed into private- or public-sector systems for larger-scale multiplication. This involves many complementary actions, most successfully undertaken in the Philippines, where a partnership between highly efficient private sector producers of tissue-culture plants (mainly for the export industry) and public sector providers of expertise have teamed up to supply large numbers of high quality plants to small-scale farmers at very competitive prices.

Banana products

Photo: Inge Van den Bergh, Bioversity

Lacking the foundation provided by the banana export industry, smaller-scale tissue-culture laboratories in East and Central Africa provide plantlets at approximately four times the price of their counterparts in the Philippines. Moreover, the upgrading of such systems to ensure quality plantlets at a competitive price represents something of a ‘chicken-and-egg’ situation—in so far as suppliers’ ability to achieve economies of scale depend on an increased demand but it is hard for demand to grow as long as the supply is inadequate.

Part of the demand side of the equation would appear to be the market for processed products. For instance, in East Africa there are indications that improved hybrids can provide an acceptable and profitable supply of raw material for the traditional banana beer-brewing and wine-making industries. In Latin America and elsewhere, the new varieties serve as raw materials for making plantain chips, which have a limited but profitable market as a snack food. Bananas also serve as a raw material for a wide range of flours, ketchups and various high-value confectionary products.

Bananas in the supermarket

Photo: Inge Van den Bergh, Bioversity

Supplying factories or even urban markets with a dependable supply of bananas presents smallholder farmers with quite a different challenge from their traditional one of assuring household and community food security. Varieties remain an important consideration in this new market-oriented game, but production systems that offer high productivity and predictability are also at a premium. Unit sales price for processing is usually lower than for fresh market which also puts great pressure on production costs.

One approach that Bioversity has been experimenting with in both Latin America and Africa involves high-density annual planting particularly of plantains and some cooking bananas. By re-planting annually with clean planting material—and, if necessary, rotating with other crops—farmers may be able to reduce problems of chronic, soil-borne pests such as nematodes, while increasing the productivity of limited land holdings. The dense shade that is established by the banana plants effectively reduces weeds while, through mechanisms that are poorly understood, a microclimate seems to be established that under certain conditions can reduce the incidence of black leaf streak.

The high cost of synthetic pesticides and growing resistance of the pathogen to conventional products remain strong incentives for the development of new products and approaches. And how can we harness biodiversity to sustainably enhance the productivity and resilience of farming systems? This includes research on soil and root health and on the threats posed by epidemic diseases, as well as advocacy to develop concerted action in response to such threats. Projects in Latin America have looked at a wide range of plant and compost extracts for their effectiveness in reducing pathogen attack, either by boosting the plant’s defence mechanisms or through direct toxicity to the fungi. Researchers are also finding that bacteria and fungi living ‘endophytically’ within the tissues of plants without causing disease may help to protect the host plant against disease-causing agents.

Bioversity pursues many of these actions through four regional research-for-development networks: MUSALAC in Latin America and the Caribbean, BAPNET in Asia and the Pacific; BARNESA in Eastern and Southern Africa, and the Innovation Platform for Plantains in West Africa. The networking approach of Bioversity is ideally suited to mobilizing the complementary resources of partners in these concerted global efforts. Its trademark approach of sharing knowledge and the task of testing new options is ideally suited to identifying a range of solutions, tailored to the individual situations and aspirations of the small banana producers and their communities.

Guest blog by Inge van den Bergh, Stephan Weisse, Anne Vezina and Nicolas Roux for Bioversity International.