Tuesday, December 21, 2010

Ergot in the Rye

Stopping at the charity field on the way back from pollinating, I noticed a ripening rye cover crop the next field over - and decided to look for my friend, ergot.*

I couldn't believe my luck! There were little black pods sprouting from rye spikes all over the edge of the field. This is a very exciting creature to a plant pathologist - and one that's had quite an impact on European history...


Ergot is a plant disease caused by Claviceps purpurea, a member of one of my favorite fungal families, the Clavicipitaceae. Its lifecycle begins in the spring when infective spores are forcibly ejected from reproductive structures that sprout from overwintering pods of black, hardened mycelium called "sclerotia." These spores are launched into the air in the same season that rye and other susceptible grasses are flowering and float on the breeze until they come in contact with one of these plants. Upon landing on a susceptible flower's stigma, the spore germinates and grows into the ovary, destroying it and growing into a fluffy mass of hyphae - covered with asexual spores and a nectar-like substance that encourages insects to track it to yet to be infected flowers elsewhere.

While spores continue to infect new rye flowers, our original fungal infection continues to develop - growing into a long, thin and progressively harder pod where a particular rye grain should have been. One or many of these sclerotia (aka "ergots") may be found in any given rye head, where their little black nubs can be seen poking out of the head (the one in the picture is unusually large). Many of these sclerotia fall from their host during harvesting. They survive the winter in the litter of the field, protected in part by a potent mix of more than 40 toxic and psychotropic alkaloids within them, including lysergic acid diethylamide (LSD) derivatives.**

While we're well aware of the danger inherent in these little black pods today (and can remove them from infested grain), Medieval Europeans were not so fortunate. Ergots were routinely milled into flour, and in bad years could reach frighteningly high levels. The ergots were not identified as a source of this disease until 1670 (partially because these little sclerotia were so common that they were included in botanical illustrations of rye!). The primary effects of ergot alkaloid poisoning include hallucination and vasoconstriction. The resulting loss of blood flow to the extremities of afflicted persons produced intense burning sensations, followed by blackening and the loss of hands and feet - a condition commonly known as St. Anthony's Fire (so named due to the symptoms and the religious order that became known for caring for the afflicted).*** This disease was especially tragic as it was most likely to strike the poorest individuals and intensified the worst harvests - rye is extremely cold tolerant and was, for many Europeans, either a staple or food of last resort.

Historians have invoked outbreaks of this disease (legitimately or not) to help explain all manner of sociological unrest, including the European and Salem witch trials, the "Great Awakening" and the French Revolution. Peter the Great's crusade for a warm water port at Constantinople was ended when an ergotism outbreak poisoned his soldiers and horses. In recent centuries, doctors have taken advantage of these chemical cocktails to induce labor, prevent postpartum hemorrhage and treat migraines. Some domesticated strains have been developed that contain 20% alkaloid chemicals by sclerotium dry weight (versus the natural 1%).

Today, ergotism is thankfully known primarily as a disease of livestock (though outbreaks occasionally occur where starving people are forced to eat contaminated grain or wild grasses). In the present, as in the past, unlucky livestock can be diagnosed by the loss of tails, ear tips and eventually feet.

Can't get enough of the Clavicipitaceae?

A sister of Claviceps is Cordyceps, the parasitic "caterpillar fungus" that sprouts from infected insects and is being driven to oblivion by harvesters. One of a handful of fungi able to colonize living insects (and then fruit from within them), Cordyceps sinensis is prized for its mythical curative powers and the "loosing of miraculous athletic feats!"

Recently, many new Cordyceps species have been discovered in tropical regions where they are capable of zombie-fying certain ants - forcing them to climb to exposed perches where they die and sprout infective spores.

David Attenborough narrates this incredible 3 minute video (and time-lapse photography!) of insects enslaved and succumbing to Cordyceps.

The Clavicipitaceae also contains a number of grass endophytes (Epichloe, Balansia, Atkinsonella and Myriogenospora). These symbiotic fungi live between and around the shoot and leaf cells of certain grasses and sedges. Some of these fungi can penetrate their host's seeds (a rare feat for a microbe!), allowing them to spread to the next generation. Others inhibit flowering of their hosts (decreasing sexual recombination that might allow the host to repel future generations of fungi). One species does this by binding the tips of leaves and flowers, preventing proper development and causing the grass leaves to stick in big loops. Another, which infects a grass species with both closed (inbreeding) and open (outcrossing) flowers, spares the inbreeding flowers and destroys the outcrossing flowers. Meanwhile, these fungi produce sugary masses of sexual spores that are cross-pollinated by insects.

So do the manhandled grasses get anything out of this? Yep! Like their other family members, these fungi are packed full of alkaloids, which in this case can confer drought and herbivore resistance to the host. It's actually a real problem in forage, where it causes diseases such as fescue toxicosis (warning: this review contains some gross pictures of symptoms such as "fescue foot"). This disease is a major livestock disease of the eastern U.S. and shares some of the symptoms of ergot poisoning, slowing weight gain at best and killing livestock at worst (another more colorful name for this type of endophyte poisoning is "the blind staggers"). In the case of fescue toxicosis, prevention (there is no cure) is accomplished by managing pastures for the absence of endophytes (or the presence of low-toxin strains).

* It was July, and and the winter squash and melons were coming on strong. The beans were already gone and the cantaloupes (for non-Americans, muskmelons) were so incredibly ripe that they might as well have been filled with an 80+ degree sorbet. I opened one up with my corn knife and shared it with my co-workers. Not a good day to have a beard, but a great end to a long day in the corn fields.
** I once knew a girl from Oberlin who claimed that generations of students cultivated this hallucinogenic fungus on rye bread in a closet. She also claimed that there was a girl who kept a pet bat under her shirt at all times...
*** Not to be confused with St. Elmo's fire.

Alexopoulos, C.J., Mims, C.W., Blackwell, M. 1996. Introductory Mycology. John Wiley & Sons.
Schumann, G. (2000). Ergot The Plant Health Instructor DOI: 10.1094/PHI-I-2000-1016-01
Stone, R. (2008). MYCOLOGY: Last Stand for the Body Snatcher of the Himalayas? Science, 322 (5905), 1182-1182 DOI: 10.1126/science.322.5905.1182
Roberts, C., & Andrae, J. (2004). Tall Fescue Toxicosis and Management Crop Management DOI: 10.1094/CM-2004-0427-01-MG

4 comments:

  1. What fun! I knew Ergot, but the rest of this creapily cool family is new to me!

    ReplyDelete
  2. Eeeeeeew! Bug fungi give me the willies! Ew ew ew ew ew ew!

    ReplyDelete
  3. Dude, you sure some poor grad student in chemistry didnt plant this crop to produce a "Natural, Organic" LSD? Sounds like a profitable venture to me...

    ReplyDelete
  4. "Bump. Can I get ergot on my rye if I'm sprouting it? Nervous... but it's SO delicious.

    Liz (email deleted)"

    I doubt it. It usually infects plants through their flowers and takes some time.

    ReplyDelete

Share!

LinkWithin

Related Posts with Thumbnails