Viruses are tricky. A fungus can sometimes be controlled with an antifungal agent, a bacterium with an antibiotic, a competing weed with an herbicide, etc. That’s not really an option with viruses. Usually once you’ve got one, you’re stuck. So I’m going to talk about three AWESOME ways a person can protect a plant from catching a virus: cultural practices (like keeping insects away), using cleaned germplasm (starting off with a healthy plant), and GMOs (plants that the virus can’t infect because of genetics). If you read the previous post I wrote about viruses, you’ll notice that not all of them are bad for plants, but some of them are. Ok. Let’s go! It’s not gonna be boring because you’re having this knowledge adventure with me!
Our first way to avoid viruses is protecting a plant we already have growing from being infected by a virus. Remember, readers, that while viruses are sort of like living beings in that they can reproduce, they’re different from us in that they can’t move around unassisted. Viruses are reliant on other beings (or forces) to move from plant to plant. These beings can be insects, nematodes, or even people. There is a whole big chunk of literature about how viruses go into and out of insects, which I am not super excited about because (sorry entomologists) I don’t love insects. But if we’ve got leafhoppers or aphids, and we’ve got weeds or crop plants that are harboring viruses, those viruses might be hopping or squishing around on all our other plants. Ew.
All of this means that all the other ways we protect our plants from harm, meaning, by controlling the levels of insect infestation and managing weeds (the other two big areas of IPM), we’re also probably managing disease. Wow! Such synergy! Nematodes that live in soil can carry viruses also and maybe deserve their own post or at least a scan-through of this http://vegetablemdonline.ppath.cornell.edu/NewsArticles/Potato_Virus.htm. And, of course, we alive humans can be dumb and move viruses from one plant to another by using the same tools on one tree as the one before it without cleaning our tools because we’re humans and consequently bums. So practicing good hygiene and managing other aspects of a growing system is basically awesome for virus prevention.
All of this is no use, through, if the plant we start off with already has harmful viruses in it. Lots of viruses can be transmitted through seeds from the parent plant, and it’s possible, and sometimes a good idea, to buy seeds that are certified healthy. The biggest, most crazy adventure, though, is when we grow plants that are propagated vegetatively, which means that we grow new plants from little bits of old plants. An example is our friend the noble potato. Yes, potatoes can come from potato seeds inside potato fruits but, much like we discussed with apples, most of the potatoes we grow come from other potato tubers. This means that if a parent potato had a virus, there is a really good chance that all the new potatoes will too. Yum! Potatoes get attacked by lots and lots of viruses, so there can be a great advantage to a grower in buying certified virus-free potatoes to grow from. Cornell has a secret isolated potato breeding facility in a hidden location where they breed potatoes away from other potatoes so that the seed potatoes can be screened for viruses and a clean bit of germplasm can be produced for a new variety. This is important! I’m sure other places have secret facilities too, but I didn’t go to their schools so I don’t know.
- First of all, I recommend that everybody check out this (bch.cbd.int/database/attachment/?id=12294) 30-page summary from 2007 of what virus-resistant GMOs are, plus a review of studies about whether they’re safe, so that 1. you get a good visual sense of what viruses do, because there are great pictures and 2. you understand the concepts of a GMO as explained in the most understandable way possible (seriously, acronyms are explained on the side and everything) and 3. you hear a really good discussion of what risk is and what the risks with transgenic virus-resistant plants are, with the eventual goal that 4. you don’t sound dumb when you talk about this issue, because I like you and I want you to not sound dumb! Here’s a link again. bch.cbd.int/database/attachment/?id=12294 Even if you just skim it, I definitely recommend taking a look. I love this review article. It’s ideal. It’s got stories about papayas! It’s got pictures and diagrams! It’s one of the best things I ever saw at school.
With that said, I’ll briefly restate in a more convoluted and less illustrative way! Viruses have RNA so that they can get proteins made, and sometimes if we can put a copy of a section of that RNA into a plant’s genome, the plant will simply degrade the RNA of the virus when it is exposed to it. I like to imagine that when the plant finds itself expressing this non-plant protein, it gets super skeeved out and squashes all traces of the protein in itself or anyone else, sort of like if a person found himself saying the annoying catchphrase from a TV show, and got mad at himself, he might decide to never say that again, and also turn off the TV anytime that show was on. (Memes! Genes! Oh gosh!) A GMO plant that encounters a virus won’t let the virus replicate, and won’t get sick or show any symptoms, and will eventually crush the virus with its mighty defense system, which the GMO addition has triggered.
Because people are nervous about a lot of factors, most of the GMO options are not legal to sell for commercial use but they work so well and eliminate so much of the bad stuff that otherwise tends to happen. Papayas and some squashes have had genes from viruses in them since the mid-1990’s and got grandfathered in to the law, which is good for people who eat papayas and squashes, because viruses can be devastating in those crops, and every other GMO that’s been introduced has been withdrawn from the market or never offered. That’s in the US. I guess there are other crops that are GMOs that are legal in China. GMOs are definitely the most workable prospect for virus prevention in some crops (not all the crops, obviously!) but also if no one wants to eat them because people are scared, that’s a pretty big problem.
Um ok! This took a long time and is a long post!