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Archive for the ‘Plant Pathogens’ Category

Global change alters microbial life in soils

Posted in Bacteria, Climate change, Fungi on February 28, 2021| Leave a Comment »

FEBRUARY 25, 2021

Global change alters microbial life in soils—and thereby its ecological functions

by German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig

soil
Credit: CC0 Public Domain

Soil microorganisms play a critical role in the survival of life-sustaining ecosystems and, consequently, human well-being. Global assessments continue to provide strong evidence that humans are causing unprecedented biodiversity losses. However, existing information is strongly biased towards selected groups of vertebrates and plants, while much less is known about potential shifts in below ground communities.

Soil microbial communities are largely an unseen majority, even though, according to first author Dr. Carlos Guerra (iDiv, MLU), “they control a wide range of ecosystem functions that have implications for both human well-being and the sustainability of our ecosystems.” The published results provide evidence that climate change has a stronger influence on soil microbial communities than land-use change like deforestation and agricultural expansion.

The scientists focused especially on bacteria and fungi, which are the most diverse groups of soil-dwelling organisms across the globe. They studied a comprehensive database of soil microbial communities across six continents, whilst incorporating temperature, precipitation and vegetation cover data. Established climate and land-use projection datasets were used to compute various temporal change scenarios, based on a projection period from 1950 to 2090. To understand this complex system with multiple interdependent variables, four structural equation models were developed for bacterial richness, community dissimilarity, phosphate transport genes and ecological clusters. These models are particularly useful for distinguishing between the direct and indirect effects of external environmental variables (vegetation type, temperature, precipitation, etc.) on the aforementioned biodiversity variables.

The authors were able to show that local bacterial richness will increase in all scenarios of climate and land-use change considered. Although this increase will be followed by a generalized community homogenisation process affecting more than 85% of terrestrial ecosystems. Scientists also expect changes in the relative abundance of functional genes to accompany increases in bacterial richness. These could affect soil phosphorus uptake, which in turn could limit plant and microbial production. The results of the ecological cluster analysis suggest that certain bacteria and fungi known to include important human pathogens, major producers of antibiotic resistance genes, or potential fungal-transmitted plant pathogens will become more abundant.

While increases in local microbial diversity might seem positive at first glance, they hide strong reductions in community complexity in the majority of terrestrial systems, with implications for ecosystem functioning. Future ecosystems are therefore expected to have a greater number of bacterial lineage communities at the local scale, making several bacterial species groups potentially more abundant in soil communities under global change scenarios. Assuming the links between functionality and taxonomy remain constant through time, this suggests that similar bacterial groups with similar functional capabilities will live in soils across the globe, reducing specialization and potentially the adaptation capacity of ecosystems to new environmental realities.

The published results are at odds with current global projections of aboveground biodiversity declines, but do not necessarily provide a more positive view of nature’s future. Major changes in microbial diversity driven by climate and land-use change have significant implications for ecosystem functioning. “The results also help to fill an important gap identified in current global assessments and agreements,” says group leader Prof Nico Eisenhauer (iDiv, UL). They also lay the groundwork for incorporating soil organisms into future assessments of ecosystem response to global change drivers. According to mathematician Dr. Eliana Duarte (MiS), “the application of mathematical and statistical methods to the study of the soil microbiome will play an increasingly important role as more data on soils becomes available.”

Explore further Research delineates the impacts of climate warming on microbial network interactions

More information: Carlos A. Guerra et al, Global projections of the soil microbiome in the Anthropocene, Global Ecology and Biogeography (2021). DOI: 10.1111/geb.13273Journal information:Global Ecology and BiogeographyProvided by German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig

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Relationship between Nitrogen and crop disease

Posted in Abiotic stress, Plant Pathogens, Uncategorized on February 28, 2021| Leave a Comment »

Relationship between Nitrogen and crop disease

  1. The Crescent News
  2. By Hoorman Soil Health Services
  3. Feb 25, 2021 Updated Feb 25, 2021
  4.  

Nitrogen (N) is the fourth most abundant plant nutrient with about 80-85% N sequestered in protein, 10% in genetic components (DNA & RNA), and 5% in amino acids (protein building blocks). Nitrogen makes proteins like enzymes (speed up chemical reactions), hormones (regulate plant functions), and N increases cell growth. Nitrogen strengthens plant cell walls (cellulose), is used in plant energy transfer (ATP), and in photosynthesis (chlorophyll); effecting many plant processes. If a plant has balanced N, it has less disease; but when N is either deficient or in excess, expect more disease and insect problems in the field, garden, with ornamentals, or house plants.https://e58b06d6ddf80758d88dccc3cc17f20d.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html

The rate of N application and the form depends on the plant’s life cycle. Nitrogen deficiency or excess N may change the cell wall to become leaky, promoting more diseases. Early on, plants need more nitrates for growth with ammonium sources increasing as the plant matures to increase yield. N stressed deficient plants can’t make full proteins while excess N lowers plant defenses to both disease and insects. Plants typically absorb N in the oxidized form as nitrate (NO3-) or the reduced form as ammonium ( NH4+). Ammonium is 25% more plant efficient than nitrates because it can be easily converted to amino acids but to avoid toxicity, plants need it in small doses and it is easily converted to soil nitrate. Soil health keeps these N forms plant available to optimize plant growth and yield.

Nitrogen interacts with many other plant nutrients. Potassium (K) promotes the increase of nitrates and plant growth, but too much K decreases yield. Adequate phosphorous plus chlorine decreases nitrates and enhances plant ammonium N forms to increase yield. In soybeans, calcium and cobalt are needed for Rhizobium microbes to fix atmospheric N into protein. Supplementing cobalt (a micronutrient) and calcium in soybeans at the right time may increase soybean yields by 3x. Molybdenum, manganese, iron, and magnesium are involved in nitrogen transformations and protein synthesis. As my high school math teacher (Dave Laudick) use to say: It’s as clear as mud. Soil organic matter is a storehouse of many essential micronutrients and allows soil microbes and plants to thrive in a buffered and safe environment. Yes, it’s complicated but worth knowing if yields improve.

Common N related corn diseases are gray leaf spot, stalk rot due to late season N stress (N deficient), and increased aflatoxin due to high nitrates. In soybeans, to much N increases mosaic virus and Rhizoctonia. In wheat, take-all is increased by nitrates, decreased by ammonium; too much N increased powdery mildew; but higher N levels decreases Stagonospora nodurum. Balanced N fertilization is a key to decreasing most diseases.

Time of N fertilization is important. Corn side dressing reduces N leaching and denitrification losses but also decreases Pythium and Rhizoctonia BUT may increase Fusarium and Gibberella stalk rot. Adding a N inhibitor to fertilizer or liquid manure may decrease corn stalk rot by keeping N in the ammonium form late season. In soybeans, avoid over using glyphosate because it chelates or ties up manganese, iron, calcium, and zinc which can affect plant N fixation. In wheat, delaying N fertilizer until spring promotes take-all but avoids excess winter N when its cold and wet, so less Rhizoctonia. Best solution, put on a small amount of N in fall to promote tillering and delay spring N applications until late spring using granular or urea forms of N to reduce foliar leaf stress from liquid N sources.

There are four strategies to reducing diseases associated with nitrogen. The 4 R’s are the right form, right time, right rate, and right place. Use a balanced N fertilizer program with sufficient N in the right form for optimum growth. For corn starter, 25% nitrates and 75% ammonium, is a good mix but placement (2”X2”, 2”X4”) is critical to avoid root stress. Weather, pH, soil conditions (compaction), soil texture, moisture, biological activity, etc. all affect N transformations and plant uptake. Building SOM buffers soils and helps control or moderate these factors. Make timely N applications to avoid N deficiency, excesses, or losses. Modify the soil environment by changing pH (lime), add cover crops to build soil organic matter, reduce soil compaction, add a N inhibitor, avoid over using glyphosate, or supplement with micronutrients to assist in optimal N utilization and less crop disease. Source: Mineral Nutrition and Plant Disease, 2018.

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Plant evolution driven by interactions with symbiotic and pathogenic microbes

Posted in Plant Pathogens on February 22, 2021| Leave a Comment »

Plant evolution driven by interactions with symbiotic and pathogenic microbes

Science
https://science.sciencemag.org/content/371/6531/eaba6605.full

From PestNet

Authors: Pierre-Marc Delaux and Sebastian Schornack

Abstract

During 450 million years of diversification on land, plants and microbes have evolved together. This is reflected in today’s continuum of associations, ranging from parasitism to mutualism. Through phylogenetics, cell biology, and reverse genetics extending beyond flowering plants into bryophytes, scientists have started to unravel the genetic basis and evolutionary trajectories of plant-microbe associations. Protection against pathogens and support of beneficial, symbiotic, microorganisms are sustained by a blend of conserved and clade-specific plant mechanisms evolving at different speeds. We propose that symbiosis consistently emerges from the co-option of protection mechanisms and general cell biology principles. Exploring and harnessing the diversity of molecular mechanisms used in nonflowering plant-microbe interactions may extend the possibilities for engineering symbiosis-competent and pathogen-resilient crops.

Read on: https://science.sciencemag.org/content/371/6531/eaba6605.full

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Crop disease basics

Posted in Control tactics, Plant Pathogens, Uncategorized on January 31, 2021| Leave a Comment »

 Crop disease basics that matter

TAGS: FUNGICIDEPEANUTSCORNCOTTONJason Brock, University of Georgia, Bugwood.orgsouthern corn rust

I would like to outline a few basics when deploying disease management strategies for row crops, such as corn, soybean, peanuts and cotton.

Bob Kemerait | Jan 29, 2021

Disease and nematode management for your 2021 crops starts now. Now is the time to carefully select the most appropriate varieties, to settle upon most effective crop rotations and to begin “filling in the blanks” for choice of fungicides and nematicides.  

Working with county agents, consultants and growers to develop best management plans, I assume that we share some basic understanding of diseases and nematodes.  This is not a fair assumption if no one has ever taken the time to teach you.https://ba27f553dad04d5abb5535d198f6ee3d.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html

In mid-December, I invited my team and a few other student workers to lunch anticipating the Christmas Season.  Most of my guests selected meals of moderate, even modest cost, practicing what I thought was established etiquette: consideration for your host.  A pair of young men, however, proceeded to order the largest, most expensive steak on the menu and then ordered additional sides.  Neither cleaned their plate, but both expressed with satisfaction that they had sampled “the very best” that this restaurant had to offer. 

While eating, I noted that one of the students (most at the table attended college) was wearing a “Magellan” T-shirt.  Always the professor, I asked if anyone could tell me ANYTHING about Magellan.  There was silence.  After an awkward period, one young man replied, “Dr. Bob, I thought that this was just the name of a brand of shirts.”  Needless to say, I was stunned at what I felt were breaches in common etiquette and common knowledge.  Later, after considerable angst, I realized that the problem was less with my young guests and more with the fact that no one had ever taken the time to teach them.  I won’t make that mistake with growers.

To best protect your crop against diseases and nematodes, it is essential to understand the basics. So I sleep better at night, I would like to outline a few basics when deploying management strategies to our row crops:ADVERTISING

  1. Fungicides can be essential tools for the control of crop diseases.  Unlike insecticides, where we often talk of thresholds, or herbicides, where we consider the size of the weed, fungicides are best used preventatively.  Once established, diseases become much more difficult to control, largely because of difficulties in reaching the target after infection occurs. 
  2. Fungicides can be split into two broad groups, protectants and systemics.  Protectant fungicides are preventative and MUST be applied prior to infection.  Systemic fungicides are best used preventatively; however, because they can penetrate plant tissues, they have some curative activity.  Curative activity is limited, and like cancer in humans, if plant diseases are not caught early enough, they will be impossible to stop. 
  3. Even in the absence of a specific crop, disease-causing pathogens and parasitic nematodes survive in a field, poised to attack at the next opportunity.  Survival occurs when the next crop is also susceptible, or when weeds are susceptible.  Survival occurs when pathogens and nematodes hunker down, killing time until a suitable host returns. 
  4. Some pathogens, like those causing rust diseases, must have a living host; in the absence of a susceptible crop, they remain a threat only until their short-lived spores die.  Other pathogens survive in infected crop debris.  Peanut leaf spot, corn blight, and target spot pathogens survive in the debris left at harvest. A few pathogens, such as the peanut white mold fungus, produce survival structures that can remain viable for years.
  5. Warm and moist conditions are favorable for development of diseases.  First, growth and development of many pathogens is enhanced during periods of warmth.  Second, infection by fungi and bacteria, and activity of plant-parasitic nematodes occurs more readily with wet weather.  Third, disease-causing organisms are spread over significant distances, in wind and blowing rain.  Finally, excessive rain can keep growers out of the field and frim timely fungicide applications.
  6. The value of a resistant variety should be fully recognized.  Where a variety has complete resistance, the plants may be immune to damage from a disease or nematode.  Where a variety has partial” or rate-limiting resistance, development of disease will be delayed and slower as compared to a susceptible variety.  Planting resistant varieties results in less need for use of fungicides and nematicides; it may also reduce the risk to losses in future crops as well.
  7. Timeliness is critical for best and most effective use of fungicides.  Timeliness may require applications when the crop reaches a critical growth stage.  Timeliness may require early detection of a disease.  Putting a scout and “boots” in the field are essential l for the best management.

Having a “basic” understanding matters in life and it matters in farming.  My initial angst at young men and women for poor manners and lack of common knowledge was replaced with understanding that someone should have spent more time teaching them.  I feel the same for crop production; guys like me need to take the time to make sure you have what you need for success.  You deserve it.

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Understanding disease-induced microbial shifts

Posted in Viruses on January 9, 2021| Leave a Comment »

NEWS RELEASE 5-JAN-2021

EurekAlert

Understanding disease-induced microbial shifts may reveal new crop management strategies

AMERICAN PHYTOPATHOLOGICAL SOCIETY

Research NewsSHARE PRINT E-MAIL

IMAGE
IMAGE: ORANGE FIELDS AND LAB WORK view more CREDIT: DR. NICHOLE GINNAN

While humanity is facing the COVID-19 pandemic, the citrus industry is trying to manage its own devastating disease, Huanglongbing (HLB), also known as citrus greening disease. HLB is the most destructive citrus disease in the world. In the past decade, the disease has annihilated the Florida citrus industry, reducing orange production for juice and other products by 72%. Candidatus Liberibacter asiaticus (CLas) is the microbe associated with the disease. It resides in the phloem of the tree and, like many plant pathogens, is transmitted by insects during feeding events. Disease progression can be slow but catastrophic. Symptoms begin with blotchy leaves, yellow shoots, and stunting, and progress into yield decline, poor quality fruit, and eventually death.

Currently, the only thing citrus growers can do to protect their crops from HLB is control the insect vector. Dozens of researchers are trying to find ways to manage the disease, using strategies ranging from pesticides to antibiotics to CLas-sniffing dogs. Understanding the plant microbiome, an exciting new frontier in plant disease management, is another strategy.

Dr. Caroline Roper and first author Dr. Nichole Ginnan at the University of California, Riverside led a large research collaboration that sought to explore the microbiome’s role in HLB disease progression. Their recent article in Phytobiomes Journal, “Disease-Induced Microbial Shifts in Citrus Indicate Microbiome-Derived Responses to Huanglongbing,” moves beyond the single-snapshot view of the microbial landscape typical of microbiome research. Their holistic approach to studying plant-microbe interactions captured several snapshots across three years and three distinct tissue types (roots, stems, and leaves). What is so interesting about this research is the use of amplicon (16S and ITS) sequencing to capture the highly intricate and dynamic role of the microbiome (both bacterial and fungal) as it changes over the course of HLB disease progression.

Ginnan et al. surmised that HLB created a diseased-induced shift of the tree’s microbiome. Specifically, the researchers showed that as the disease progresses, the microbial diversity increases. They further investigated this trend to find that the increase in diversity was associated with an increase in putative pathogenic (disease-causing) and saprophytic (dead tissue-feeding) microbes. They observed a significant drop in beneficial microbes in the early phases of the disease. Arbuscular mycorrhizal fungi (AMF) were one such beneficial group that the authors highlighted as showing a drastic decline in relative abundance.

The depletion of key microbial species during disease might be opening the door for other microbes to invade. Certain resources may become more or less available, allowing different microbes to prosper. Dr. Roper and Dr. Ginnan hypothesize that when HLB begins, this depletion event triggers a surge of beneficial microbes to come to the aid of the citrus tree. They suspect that the microbes are initiating an immune response to protect the host.

As the disease proliferates, the citrus tree and its microbiome continue to change. Dr. Ginnan, the lead author on this study, found that there was an enrichment of parasitic and saprophytic microorganisms in severely diseased roots. The enrichment of these microbes may contribute to disease progression and root decline, one side effect of HLB.

Survivor trees, or trees that did not progress into severe disease, had a unique microbial profile as well. These trees were enriched with putative symbiotic microbes like Lactobacillus sp. and Aureobasidium sp. This discovery led the researchers to identify certain microbes that were associated with slower disease progression.

Dr. Ginnan says their “aha” moment during the research was in the data analysis. “Originally we were looking for taxa that increased and decreased in relative abundance as disease rating increased,” she said. “Our differential abundance analysis ended up revealing clear enrichment patterns replicated in multiple taxa.” This is the moment they began to develop the individual patterns they were seeing into a broader disease model.

This research is the foundation for future projects and collaborations that the authors are excited to continue to develop. They are motivated by the potential function of the microbiome to manage crop diseases. In the near future, they hope that these discoveries and an understanding of beneficial microbes can help establish a microbiome-mediated treatment plan to protect crops from diseases like HLB. In addition, the model they’ve developed can be applied to understanding diseases of other tree crop systems.

###

This research article was a part of Dr. Nichole Ginnan’s Ph.D. thesis under the mentorship of Dr. Caroline Roper (the lead researcher). Dr. Ginnan is now a Postdoctoral Researcher in Dr. Maggie Wagner’s Lab at the University of Kansas. She hopes to continue in academia with a research faculty position. Dr. Caroline Roper is a tenured professor at the University of California Riverside. She mentors several Ph.D. students, undergrads, and postdoctoral scholars on cutting edge research in plant-microbe interactions.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

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New Zealand: New app to detect plants at risk from myrtle rust

Posted in Fungi, Pest diagnostics, Uncategorized on December 16, 2020| Leave a Comment »

SunMedia

New app to detect plants at risk from myrtle rust

Capsules (also known as gumnuts) of Eucalyptus pilularis. Features like this can enable users of the NZ Myrtaceae Key to identify species of interest. Supplied photo.

People keen to support the fight against the fungal disease myrtle rust, which threatens many of Aotearoa-New Zealand’s native trees, shrubs and climbers, now have a new tool to help identify vulnerable plants in the myrtle family.

Manaaki Whenua – Landcare Research and Biosecurity New Zealand have partnered in the development of the NZ Myrtaceae Key – a free app that makes it easy for citizen biosecurity volunteers to identify susceptible plants and keep an eye out for the fungal disease myrtle rust.

Myrtle rust has already spread across the top half of the North Island and cases have been recorded as far south as Greymouth.

“We know how much damage plant pests and diseases are causing overseas, and science partnerships, like this, will help us stay ahead,” says Veronica Herrera, MPI’s diagnostics and surveillance services director.

The NZ Myrtaceae Key is a Lucid identification tool envisaged and funded by Biosecurity New Zealand and developed by botanists from Manaaki Whenua, the National Forestry Herbarium, Unitec, and other experts.

The app is easy-to-use, interactive and comprehensively illustrated with more than 1,600 fully captioned images built in and it is downloadable for both iPhone and Android smartphones.

“The key includes more than 100 of the most commonly found Myrtaceae species, subspecies, hybrids and cultivars in New Zealand. Of these, 27 species, such as the iconic pōhutukawa, mānuka and kānuka, are indigenous to New Zealand: others, such as feijoa and eucalyptus, are exotics of economic importance,” says Dr Herrera.

Manaaki Whenua – Landcare Research researcher, Murray Dawson says the arrival of the windborne myrtle rust in 2017 gave a new importance to being able to identify Myrtaceae as heavily infected plants inevitably die.

“The disease is a threat to the important and substantial mānuka and kānuka honey industry. Using the new app to accurately identify species of Myrtaceae in New Zealand will make it easier to monitor and report cases of myrtle rust.

“By using the key, anyone, from farmers and trampers to gardeners and park users, will be able to identify plants to check for and report the tell-tale yellow spores, and diseased leaves,” says Mr Dawson.

To use the app, the characteristics of the plant being identified are entered, the app then sorts plants possessing these features, and it rejects those that don’t match. By progressively choosing additional features, the key will eventually narrow the results to just one or a few matching species.

Once you’ve correctly identified a plant in the myrtle family and if you think you see signs of the disease on it, don’t touch it.

If you have a camera or mobile phone you can take a photo and submit it to the iNaturalist website. Experts can check to confirm whether it is myrtle rust.

Capturing this information makes it available to agencies and scientists to analyse the rate of spread and observed impacts.

The NZ Myrtaceae Key is available from the Google Play (Android) store and the iPhone app store as a mobile (smartphone) app suitable for undertaking identifications in the field, or through a web-based browser hosted by Manaaki Whenua.

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EPPO Datasheet: Aphelenchoides besseyi

Posted in Nematodes, Uncategorized on September 17, 2020| Leave a Comment »

Aphelenchoides besseyi

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EPPO Datasheet: Aphelenchoides besseyi

Last updated: 2020-07-24

IDENTITY

Preferred name:Aphelenchoides besseyi
Authority: Christie
Taxonomic position: Animalia: Nematoda: Chromadorea: Rhabditida: Aphelenchoididae
Other scientific names: Aphelenchoides oryzae Yokoo, Asteroaphelenchoides besseyi (Christie) Drozdovski
Common names in English: rice leaf nematode, rice white-tip nematode, strawberry crimp disease nematode, white-tip nematode
view more common names online…
Notes on taxonomy and nomenclature

The taxonomy used in this datasheet reflects developments suggested by several recent publications, summarised in Decraemer & Hunt (2013), which place Aphelenchoides in the Order Rhabditida, Suborder Tylenchina. This contrasts with the taxonomy nomenclature occasionally used by some authors (such as the CABI Invasive Species Compendium CABI, 2019; Wheeler & Crow, 2020), which place Aphelenchoides in the Order Aphelenchida, Suborder Aphelenchina (Hunt, 1993). Whilst this makes no difference to classification from the level of Superfamily (Aphelenchoidea) to species level (Aphelenchoides besseyi), those studying the species might need to be aware of differences in the literature.EPPO Categorization: A2 list
EU Categorization: RNQP (Annex IV)
view more categorizations online…
EPPO Code: APLOBE HOSTS 2020-07-24 GEOGRAPHICAL DISTRIBUTION 2020-07-24 BIOLOGY 2020-07-24 DETECTION AND IDENTIFICATION 2020-07-24 PATHWAYS FOR MOVEMENT 2020-07-24 PEST SIGNIFICANCE 2020-07-24 PHYTOSANITARY MEASURES 2020-07-24 REFERENCES 2020-07-24 ACKNOWLEDGEMENTS 2020-07-24 How to cite this datasheet? Datasheet history 2020-07-24

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Kenya: Unidentified rust in maize

Posted in Emerging/invasive pests, Fungi, Plant Pathogens, Uncategorized on July 16, 2020| Leave a Comment »

Thursday, 09 July 2020 12:42:00

From PestNet

Grahame Jackson posted a new submission ‘UNDIAGNOSED RUST, MAIZE – KENYA: (BARINGO)’

Submission

UNDIAGNOSED RUST, MAIZE – KENYA: (BARINGO)

ProMED
https://promedmail.org/

Source: The Standard, FarmKenya [edited]
https://www.farmers.co.ke/article/2001376657/fears-as-deadly-maize-rust-affects-3-000-acre-field
Farmers contracted to grow certified maize seeds in Baringo are staring at losses following [an] outbreak of maize rust disease. There are 8 farmer-managed schemes contracted to plant seed maize on 3000 acres [1214 hectares].
[One farmer] said the crop germinated evenly, but was hit by the fungal disease at the flowering stage and [the disease] was spreading fast. “Several varieties of maize were grown, but the disease affected one variety that we fear might cause us more losses,” [he] said. Leaves of the crop appeared brown and rusty.
Kenya Seeds Company that contracted [the] farmers are inspecting the farms. [They] attributed the disease to cold weather following heavy rains, saying it could be managed by spraying fungicides. Extension officers have been sent to the ground to find mitigation measures.
—
Communicated by:
ProMED-mail
<promed@promedmail.org>
[There are 3 rusts affecting maize: common rust caused by _Puccinia sorghi_; southern rust caused by _Puccinia polysora_; and tropical rust caused by _Phakopsora zeae_. (For more information, see previous ProMED-mail posts in the archives and links below.)
Rust spores are wind dispersed over long distances. They can also be spread by mechanical means (human or insect activities) and on contaminated materials (equipment, clothing, crop debris). The fungi need living tissue to survive between seasons. Volunteer crop and wild host plants may generate a “green bridge” providing inoculum to infect new crops. Disease management relies mainly on timely fungicide applications, choice of crop cultivars, and control of volunteer crop plants. Early discovery of infection is important so action can be taken to limit pathogen spread as well as build-up of inoculum.
Maps
Kenya:
https://www.nationsonline.org/maps/kenya_map.jpg and
http://healthmap.org/promed/p/48354
Kenya counties:
https://www.mapsofworld.com/kenya/kenya-political-map.html
Pictures
Symptoms of some maize diseases via:
http://www.ipmimages.org/browse/Areasubs.cfm?area=72
Links
Information on common and southern maize rusts via:
http://maizedoctor.cimmyt.org/pests-diseases/list and
https://www.pestnet.org/fact_sheets/maize_common_rust_225.htm
List of major diseases and pathogens of maize:
https://www.apsnet.org/edcenter/resources/commonnames/Pages/Corn.aspx
Fungal taxonomy and synonyms via:
http://www.indexfungorum.org/Names/Names.asp
– Mod.DHA]

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Madagascan bananas

Posted in Emerging/invasive pests, Fungi on July 14, 2018| Leave a Comment »

Madagascan bananas may soon be extinct

Sunmbo olorunfemi
holger-link-683121-unsplash
Photo: ‘Green Bananas’ by Holger Link on Unsplash

Bananas we buy across the world could be threatened with extinction in the future. This claim is due to the decline of wild banana species which could be the last resort for saving the world’s most popular banana, the Cavendish.

According to a BBC article, a wild banana (Ensete perrieri) has been classified as Critically Endangered by the IUCN. These are only found in Madagascar, where there are just five mature trees left in the wild.

In light of this, scientists are advocating its conservation as it may hold the secret to saving the Cavendish banana. This cultivar could go into extinction in years to come due to its vulnerability to Fusarium (a disease also known as Panama disease that attacks the root of banana trees).

It is thought that the Madagascan banana, E. perrieri, could have certain properties making it resilient to attack from certain pests and diseases, and from drought. The species grows large seeds, making it difficult for humans to eat, but it could be crossbred with another more edible variety or cultivar (such as Cavendish) to create a more resilient cultivated banana.

To find out whether this could be done, Richard Allen, senior conservation assessor at the Royal Botanic Gardens, Kew, stated in the BBC article that more research had to be carried out on the species, but first of all it has to be saved.

Therefore, the race is on to develop new banana varieties that are both tasty and resilient enough to survive attack from pests and diseases such as Panama disease.

Sunmbo Olorunfemi is a graduate of Sustainable Agriculture and Food Security and currently working as an intern with the Plantwise Knowledge Bank.

Coming soon from CABI Books: Handbook of Diseases of Banana, Abacá and Enset

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3D structure of the geminivirus is revealed

Posted in Viruses on June 24, 2018| Leave a Comment »

John Innes Centre

Devastating plant virus is revealed in atomic detail

One of the world’s most lethal families of plant viruses has been revealed in unprecedented detail in a new study that may provide clues to preventing the global spread of the pathogen.

The complex 3D structure of the geminivirus  is revealed in the joint study carried out by researchers at the University of Leeds and the John Innes Centre.

Geminiviruses are responsible for diseases affecting crops such as cassava and maize in Africa, cotton in the Indian subcontinent and tomatoes across Europe.

Revealed in unprecedented detail – geminiviruses are a global plant pathogen

Being able to see its structrure in great detail is vital as it could help virologists and molecular biologists better understand the virus lifecyle, and develop new ways to stop the spread of these viruses and the diseases they cause.

These viruses are named for their curious shape. Viruses usually have a protective shell of protein, or capsid, that acts to protect their genetic material in the environment. In most viruses, this capsid is roughly spherical, but the geminivirus has a ‘twinned’ capsid formed by two roughly spherical shapes fused together.

The molecular details of how this twinned capsid is achieved – and how it assembles in cells or expands to release the genome and start a new infection – has remained a mystery, despite the risk posed by the virus to agricultural economies worldwide.

Researchers at the Leeds University’s Astbury Centre for Structural Molecular Biology used cryo electron microscopy techniques to study geminivirus structure at undprecedented resolution, and in the process have begun to untangle its assembly mechanisms.

Published in Nature Communications, the study reveals how the capsid of the geminivirus is built and how its single-stranded DNA genome is packaged.

“In many other types of virus, the spherical capsids are built from a single protein that adopts three different shapes, which then fit together to form a closed container,” explains Professor Neil Ranson, who led the research team at the Astbury Centre.

“But geminivirses are not spherical, so must be using a different set of rules. Using cryo-EM, we’ve been able to show that they do use three different shapes of the same protein, but with a completely different rulebook for assembly”

One of the difficulties in studying geminviruses is growing them in sufficient quantities for structural studies.

The team studied a type of geminvirus transmitted by whitefly called ageratum yellow vein virus, which was produced in tobacco plants under carefully controlled conditions by researchers at the John Innes Centre.

The team at the John Innes Centre led by Dr Keith Saunders and Professor George Lomonossoff also developed a method for assembling geminivirus particles within plants in the absence of infection.

This highlighted the role played by the single-stranded DNA in particle formation.

“Having worked for many years to understand the diseases geminiviruses cause, it was very satisfying to apply modern genetic methods to generate these geminate structures,” said Dr Saunders.

“The big surprise arising from this study was that fact that the virus coat protein can adopt different conformations that are dependent upon its location in the structure – it is different at the equator than at its apexes. That helps to explain how the particles form during virus infection. With this new knowledge, it now means that future studies can be directed to seek ways to disrupt geminate structure maturation by making antivirals that target those areas.”

Dr Suanders said the John Innes Centre team had been studying ageratum yellow vein virus for 20 years and their knowledge of the diease made it a good candidate for closer inspection.

It is part of white-fly transmitted group responsible for  tomato yellow leaf curl disease, a disease affecting tomato production in many countries around the Mediterranean Sea and cotton leaf curl disease affecting cotton plants in India and Pakistan.

Both diseases give rise to tremendous crop losses and so are economically very damaging.”

The work was funded by the Biotechnology and Biological Sciences Research Council.

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