Fungi that only reproduce asexually are also known as the imperfect fungi. I for one think all fungi are perfect in their own right, but when you look at the morphological complexity of the higher fungi, I understand the acceptance of this terminology. We are probably most familiar with this fungal group, more commonly known as molds, as they infiltrate our homes and ruin those strawberries we had forgotten about. At FFN, I have written about a recently discovered mold strain that has the enzymatic potential to actually break down plastic. This may prove to be a trait us humans must utilize if we are to have any chance of reducing the piles of plastic debris we have created. In the past, we have used the secondary compounds these fungi produce to create the first antibiotics. Doesn’t penicillin ring a bell? Today, I’d like to revisit one of these molds, Botrytis cinerea. Although this species is a common pest that causes agricultural hardship ruining crops around the world, it actually is a welcomed site in some vineyards.
At a wine tasting, I was asking the sommelier about grape vine-soil interactions, mycorrhizae and then Botrytis had come up. I had known little about this opportunistic fungus prior, but Missy, the sommelier really broadened my understanding of these species interactions. This imperfect fungus here isn't used medicinally or as a waste management tool and actually live in harmony within vineyards. Wine producers around the world for millennia have learned how to use these infected grapes, also known as noble rot.
I learned that outbreaks of Botrytis cinerea on vineyards are localized, and don’t impact the entire crop. If Botrytis cinerea spread throughout the crop, I doubt it would be welcomed so warmly. When you look at this species ecological strategy, its localized nature makes perfect sense. Let’s use those forgotten strawberries as an example. When they start to turn, you can pick out the moldy ones, rinse and enjoy. Without rain or strong winds in your fridge, the mold spreads slowly from the point of initial infection, as their conidia (asexual spores) don’t disperse well alone.
Over millions of years, this group of fungi has lost the ability to reproduce sexually, because this strategy for nutrient acquisition works so well. Molds are notorious for utilizing nutrient rich substrates like fruits. With so many available carbohydrates, these fungi rapidly produce these asexual spores, where they can then re-infect the fruit. Although Botrytis cinerea spores can become airborne, its potential clones disperse more readily via rain, as rain drops splatter conidia on neighboring fruits. With these traits, this mold grows in self-contained sections of vineyards when conditions are just right.
So why would grapes infected by the fungus be welcomed by wine makers? Well, one of the main interactions involves the perforation of grape skin once infected. Water is removed from the fruit, resulting in more concentrated, sweeter wines, similar to grapes used in ice wines. Ice wine producers utilize grapes left on vines until the freezing months. Most of the water remains in a solid state while being pressed, so just the sugars and other dissolved solids become extracted. Frozen grapes along with botrytized grapes yield much less juice, but they’re sweeter, and have more intense flavor.
Besides being more concentrated versions of their non-botrytized counterparts, these noble rot wines have distinct earthy tones. In 2015, Barbara Blanco-Ulate and her team of scientists wanted to study these fungal-grape interactions from a metabolic and biochemical perspective. Their intense study showed exactly why these earthy, umami undertones present themselves in these unique wines. They focused on a white grape variety called cv Sémillon, studying its development and chemical composition. Interestingly, they found that fungal infection induced the genetic expression of ripening pathways, some that are only found in red grape cultivars. Thus, once botrytized these white grapes soon carry traits that totally different varieties possess.
For example, the metabolism of phenylpropanoid, a process nearly absent in white varieties yet normally found during the ripening of red skinned grapes was significantly enhanced in these fruits infected by the fungus. Besides this metabolic alteration, the synthesis of several other compounds increased in infected grapes. All in all, this inconspicuous imperfect fungus reprograms grape development and shifts its metabolic pathways resulting in grapes that carry significantly different characteristics, sometimes only found in red cultivars.
Imperfect fungi offer a diverse array of functions. They can be used to enhance our future by potentially reducing plastic waste. Additionally, they have been utilized in our past to synthesize the first ever commercial antibiotics. After reading this, I hope you have learned yet another service these perfect, imperfects provide. Their presence ultimately provides human enjoyment. Paired with different grapes, these fungi alter the fruits chemical makeup, allowing novel nuances to exist that would otherwise be silenced. Before the existence of humans, Botrytis lived all over the world, as a parasite and necrotroph, infecting fruits and other nutrient rich plant and animal parts on the forest floor. Fast forward millions of years, and these molds are still here interacting with a numerous number of Earth’s species.
I'd like to thank Missy Winkler from Winkler & Samuels located on 500 Seneca St. in Buffalo NY. She was so knowledgeable and passionate, that the $35.00 wine tasting seemed like burglary. Good sommeliers are not experts on wine, they are experts of geography, fermentation, soil chemistry and plant/fungal traits. If you are ever in the area an have a taste for wine, definitely schedule a tasting with her.