Researchers at the University of California, Davis, and in the Netherlands have discovered how three fungal diseases have evolved into a lethal threat to the world’s bananas.
The discovery, reported in the online journal PLOS Genetics, better equips researchers to develop hardier, disease-resistant banana plants and more effective disease-prevention treatments.
“We have demonstrated that two of the three most serious banana fungal diseases have become more virulent by increasing their ability to manipulate the banana’s metabolic pathways and make use of its nutrients,” said UC Davis plant pathologist Ioannis Stergiopoulos, who led the effort to sequence two of the fungal genomes.
“This parallel change in metabolism of the pathogen and the host plant has been overlooked until now and may represent a ‘molecular fingerprint’ of the adaption process,” he said. “It is really a wake-up call to the research community to look at similar mechanisms between pathogens and their plant hosts.”
Bananas and the disease threat
The banana is one of the world’s top five staple foods. About 100 million tons of bananas are produced annually in nearly 120 countries. But the fruit suffers from an “image problem,” giving consumers the appearance that it is and always will be readily available, said Stergiopoulos. It’s an image problem that he fears could prove fatal to the entire banana industry in the very near future.
In reality, the global banana industry could be wiped out in just five to 10 years by fast-advancing fungal diseases. And that would prove devastating to millions of small-scale farmers who depend on the fruit for food, fiber and income. Already, Sigatoka — a three-fungus disease complex — reduces banana yields by 40 percent.
Three diseases in one
The Sigatoka complex’s three fungal diseases — yellow Sigatoka (Pseudocercospora musae), eumusae leaf spot (Pseudocercospora eumusae) and black Sigatoka (Pseudocercospora figiensis) — emerged as destructive pathogens in just the last century. Eumusae leaf spot and black Sigatoka are now the most devastating, with black Sigatoka posing the greatest constraint to banana production worldwide. The constant threat of the disease requires farmers to make 50 fungicide applications to their banana crops each year to control the disease.
“Thirty to 35 percent of banana production cost is in fungicide applications,” Stergiopoulos said. “Because many farmers can’t afford the fungicide, they grow bananas of lesser quality, which bring them less income.”
And for those growers who can afford fungicide, the applications pose environmental and human-health risks.
To make matters worse, all commercial “dessert” bananas — those most commonly found in grocery stores — are of the Cavendish variety. And unlike a tomato or green bean, which are grown from seeds, bananas are grown from shoot cuttings.
“The Cavendish banana plants all originated from one plant and so as clones, they all have the same genotype — and that is a recipe for disaster,” Stergiopoulos said, noting that a disease capable of killing one plant could kill them all.
Probing the genomes for solutions
Stergiopoulos and colleagues sequenced the genomes of eumusae leaf spot and black Sigatoka, comparing their findings with the previously sequenced yellow Sigatoka genome sequence.
They discovered that this complex of diseases has become lethal to banana plants not just by shutting down the plant’s immune system but also by adapting the metabolism of the fungi to match that of the host plants. As a result, the attacking fungi can produce enzymes that break down the plant’s cell walls. This allows the fungi to feed on the plant’s sugars and other carbohydrates.
“Now, for the first time, we know the genomic basis of virulence in these fungal diseases and the pattern by which these pathogens have evolved,” Stergiopoulos said.
When people take the psychedelic drug LSD, they sometimes feel as though the boundary that separates them from the rest of the world has dissolved. Now, the first functional magnetic resonance images (fMRI) of people’s brains while on LSD help to explain this phenomenon known as “ego dissolution.”
As researchers report in the Cell Press journal Current Biology on April 13, these images suggest that ego dissolution occurs as regions of the brain involved in higher cognition become heavily over-connected. The findings suggest that studies of LSD and other psychedelic drugs can produce important insights into the brain. They can also provide intriguing biological insight into philosophical questions about the very nature of reality, the researchers say.
“There is ‘objective reality’ and then there is ‘our reality,'” says Enzo Tagliazucchi of the Royal Netherlands Academy of Arts and Sciences in Amsterdam. “Psychedelic drugs can distort our reality and result in perceptual illusions. But the reality we experience during ordinary wakefulness is also, to a large extent, an illusion.”
Take vision, for example: “We know that the brain fills in visual information when suddenly missing, that veins in front of the retina are filtered out and not perceived, and that the brain stabilizes our visual perception in spite of constant eye movements. So when we take psychedelics we are, it could be said, replacing one illusion by another illusion. This might be difficult to grasp, but our study shows that the sense of self or ‘ego’ could also be part of this illusion.”
It has long been known that psychedelic drugs have the capacity to reduce or even eliminate a person’s sense of self, leading to a fully conscious experience, Tagliazucchi explains. This state, which is fully reversible in those taking psychedelics, is also known to occur in certain psychiatric and neurological disorders.
But no one had ever looked to see how LSD changes brain function. To find out in the new study, Tagliazucchi and colleagues, including Robin Carhart-Harris of Imperial College London, scanned the brains of 15 healthy people while they were on LSD versus a placebo.
The researchers found increased global connectivity in many higher-level regions of the brain in people under the influence of the drug. Those brain regions showing increased global connectivity overlapped significantly with parts of the brain where the receptors known to respond to LSD are found.
LSD also increased brain connectivity by inflating the level of communication between normally distinct brain networks, they report. In addition, the increase in global connectivity observed in each individual’s brain under LSD correlated with the degree to which the person in question reported a sense of ego dissolution.
Tagliazucchi notes in particular that they found increased global connectivity of the fronto-parietal cortex, a brain region associated with self-consciousness. In particular, they observed increased connection between this portion of the brain and sensory areas, which are in charge of receiving information about the world around us and conveying it for further processing to other brain areas.
“This could mean that LSD results in a stronger sharing of information between regions, enforcing a stronger link between our sense of self and the sense of the environment and potentially diluting the boundaries of our individuality,” Tagliazucchi said.
They also observed changes in the functioning of a part of the brain earlier linked to “out-of-body” experiences, in which people feel as though they’ve left their bodies. “I like to think that our experiment represents a pharmacological analogue of these findings,” he says.
Tagliazucchi says the findings highlight the value of psychedelic drugs in carefully controlled research settings. He plans to continue to use neuroimaging to explore various states of consciousness, including sleep, anesthesia, and coma. He also hopes to make direct comparisons between people in a dream versus a psychedelic state. Meanwhile, researchers at the Imperial College London are investigating other psychedelic drugs and their potential use in the treatment of disorders including depression and anxiety.
Learn more: How LSD can make us lose our sense of self
The Royal Netherlands Academy of Arts and Sciences (Dutch: Koninklijke Nederlandse Akademie van Wetenschappen, abbreviated: KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands.
The Academy is housed in the Trippenhuis in Amsterdam.
In addition to various advisory and administrative functions it operates a number of research institutes and awards many prizes, including the Lorentz Medal in theoretical physics, the Ariëns Kappers Medal in neuroscience, the Leeuwenhoek Medal in microbiology, and the Dr. A.H. Heineken Prizes.
The Academy advises the Dutch government on scientific matters. While its advice often pertains to genuine scientific concerns, it also counsels the government on such topics as policy on careers for researchers or the Netherlands’ contribution to major international projects. The Academy offers solicited and unsolicited advice to parliament, ministries, universities and research institutes, funding agencies and international organizations.
- Advising the government on matters related to scientific research
- Assessing the quality of scientific research (peer review)
- Providing a forum for the scientific world and promoting international scientific cooperation
- Acting as an umbrella organization for the institutes primarily engaged in basic and strategic scientific research and disseminating information