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!
Anonymous said: Melon = King O' Produce? Discuss
I don’t know if the melon is the king o’ produce. Maybe it is because it commands love and because the melons I ate this winter were really good and from Guatemala and Honduras and stuff. Maybe it is not because produce has no king.
Thanks for asking, kiddo.
Maybe you’re reading this blog and thinking to yourself, “Um, shoot! I know that plants can get sick, because I see all your pictures of deformed apples and rotten spots and all. But I don’t think I’ve ever actually EATEN a sick plant!” Maybe you’re a picky produce consumer, and you don’t buy anything fuzzy, or with mushy spots, and you use everything right away so it doesn’t show any symptoms of anything it’s caught. Ok! That’s cool! But what about viruses?
The internet tells me that there are something like 1000 different viruses that we know infect plants. You know what viruses are – they’re little dudes who aren’t alive, they need living cells to replicate themselves, they pump cells full of their own weird genetic goo, they can’t usually be fixed with medicine, etc etc. I don’t know why I’m making this list. You’re not dumb. You know all this. But maybe you didn’t know that even the foods you know from the plants you love can be full of viruses! Maybe your tummy is right now full of plant viruses from eating sick plants. Good thing that these viruses are so host-specific and probably don’t even recognize that you’re a thing.
You’ve had a human-infecting virus before in your own human meat body, right? You know that sometimes your body responds by fighting the virus off, degrading its genetic materials as best as possible, and sometimes your body doesn’t fight it off, so the virus just stays in your body latently. Sometimes you get behavior changes, like fevers and a case of the pukes. Sometimes, according to medicine science (which I know nothing about!!!!), viruses can get into our bodies and help protect us against other diseases, and have generally beneficial effects! Wow!
Plants are like this too! Plants can try to fight off plant viruses, either by directly breaking up viral genetic codes (using RNAi and stuff) or by shutting down infected cells to try to isolate the virus (the hypersensitive response! (remember, a virus can’t survive in a dead cell)). Sometimes plants get infected and don’t respond to the virus and don’t show symptoms. And sometimes plants get sick and get behavioral changes. Unless the viral infection is so bad as to make the produce unmarketable, any of these plants with viruses in them are totally edible by you!
You’ve definitely eaten things that were sick with viruses. For example, sometimes you get spinach that’s really, really crinkly. Maybe it’s sick with a virus! Viruses make spinach do that. Maybe you’re expecting to find a big, tasty, cheap sweet potato at the store, but instead you find a tiny, wood-flavored, expensive sweet potato. It might have been hit with a heavy viral load and have come out all unappealing. And onions get viruses, and zucchinis and all the squashes, and potatoes, and basically so many plants.
Ok! So plants get sick with viruses! And we eat them, and we’re fine!
We can detect viruses in tissue of any living thing using ELISA tests, which are complicated. Sometimes when we test, we find out that a plant has a virus but doesn’t show any symptoms at all, because that plant is tolerant of the virus. Plants can be more than fine too, like when a virus in a tulip plant makes the color break, or when a virus in an apple rootstock makes the scion tree come out small (with a higher fruit:wood ratio, which is a good thing if you’ll remember my rootstock posts). This is such a cool subject to my mind, because it’s a case where we’re obviously working towards plant health for our human goals instead of plant health for the plant. (It’s the nafka mina, if you will!) Usually we want plants to grow up big and strong and make many seeds, which is what the plant wants too, but sometimes we want a plant to grow small and convenient, so we allow it to get viruses, which is probably a metabolic handicap on the “natural” goals of the plant.
Some viruses are pretty bad, though, and we want to protect plants from them. I’m going to talk about three ways we deal with harmful plant viruses in my next post.
I found this article http://www.apsnet.org/publications/apsnetfeatures/Pages/bacterium.aspx about a pretty bacterial disease in beans that has a cool history and interesting developments that continue until today!
It’s always so satisfying when we feel like the micro-level differences in the little dudes manifest themselves in visible changes on our macro-level. I know for me, knowing only a little bit about taxonomy of our different microorganisms (just enough to be confused about which names are the current ones and which names are obsolete, depending on what bit of literature I’m reading) it’s really nice to imagine that the organization that we use has some relevance to the biological reality of these little dudes. These bacteria make different colors on mature dry beans, and the varieties that make each color have their own other characteristics and virulence patterns as well!
I’m not scienceing so frequently these days, but I really enjoyed that article and wanted to share it with anyone who is interested in seeing some cool pictures and writing about sick beans. Also, I love beans!
For those in suspense, playing along at home, that apple had cedar apple rust, sooty blotch, flyspeck, and what looks to me like black rot. How many of you got all four?
I didn’t know about this apple but I saw it looking so cute in the vending machine in the Plant Science building so I went for it. Throwback Monday, as they say!
It’s small and pinkish red on a custard yellow background, and it’s got yellow stripes and white lenticels. The shape is really good! It’s pentagonal from top and bottom, and almost circular from the side, excepting for the calyx and stem cups. It even has an adorable little waist! I hope you can see from the picture how cute this one is. I’m really excited to eat it. It’s not too shiny and not too dull. It looks ideal.
Mmmm! Wow! The flavor is really interesting! It definitely tastes stored, with that sort of sugary wet flavor, but it tastes spicy too, like bell peppers or mango maybe. The skin is medium thickness, and the texture of the flesh is sort of mushy, presumably from storage, so it’s hard to know for sure what its noise or snap is like. The juice is sugary and dries my mouth. There is no tartness, only sugar and vegetable spice. The flavor is also very up front, with only a small afterkick. The vegetable flavor gets stronger closer to the core and makes me think of lettuce. There is sweetness throughout but it is sweetest just at the skin.
So, this apple was pretty good! Really pretty and pretty tasty! Not the #1 top apple but a good snack for a midmorning free time moment!
Ok, so, shoot. I’m trying so much to make my blog have disqus comments and it just isn’t working. I thought it worked for one post but I just learned that the only reason that other post had an option to answer it was because the title had a question mark in it, I guess that is a native thing to tumblr? I do not know how comments work! Help me!
If you’ve talked to me over the past season about what I do at work, I’ve probably given a sort of rosy view of what it’s like and usually it is pretty rosy! (Haha get it Rosaceae???) But there are some things that if you talked to me on the day I did them I’d probably grumble a bit. One of those things is chopping rootsuckers. Rootsuckers get lopped off with loppers at the soil line from around lots of trees, because they get in the way and they’re a super problem. If you look in the picture that I put up, you might see that it looks like there are branches coming out from the soil all around the trunk. That’s rootsuckers!
Why are there rootsuckers?
Let’s backtrack a little bit before we answers this!
Why do plants grow in predictable shapes????
Imagine an apple tree (or any plant mostly!) and think about its general shape (this is going to be very general and YMMV for any particular plant but I just want to give you an idea of where I’m coming from). Most plants are taller than they are wide, right? And most branches also! Longer than they are wide! Here’s why. The tip of the shoot is made of a special kind of tissue called meristem that can divide its cells and develop and grow. There is meristem in the very end, or apex of the shoot, and we call it apical meristem, but there’s also meristem near the tips of the rest of the bits of the shoot, which we call lateral meristem, that can also grow and divide. The reason plant sections get to be longer usually from the central bit and have shorter side bits is…hormones! Yeah! Plants have hormones! We call them plant growth regulators and they’re a bit different from the kind that we have. But they work in a similar way: they get produced in some tissues and circulated out to other tissues and the effect varies with the dose, etc etc! So the hormone auxin is involved in convincing the little bits of meristem that the apex should grow a lot, and it flows down to the closer-in bits of the branch to convince the little bits of lateral meristem that they should just hang out for a bit and not develop so much. It’s super complicated and you could look up more information on the internet if you’re curious about how awesome plants are. It’s called apical dominance and it’s a cool topic!! For, like, science fair or something! Or just if you feel like playing with houseplants!
Because get this- if you take off the apical meristem, it stops producing auxin, which stops telling the lateral meristems to chill, and they grow like CRAZY and compete to become the new apex. This is the principle we use when we prune trees- we take off some branches, and this actually encourages the plants to be more productive. If a plant makes its fruit on its one-year-old spurs, for example, we can take out old wood to encourage new spurs to grow and get more fruits. In our tall spindle pruning systems (like in our high-density block) we usually try to preserve the central leader (that’s the main trunk at the top) at all costs, because if it breaks out, the lower branches go crazy with growth and focus on getting tall instead of making fruit.
But not all plants are the same at this thing! It can really vary by cultivar. Some plants really want to grow and as soon as you take off their apex they’re gonna make a mad dash for it with tons of limbs, and some plants are more relaxed. This is part of what we talk about when we talk about vigor. Vigor is a characteristic of a particular variety, and it’s a little different from, although related to, size. Some apple trees want to get really big, and some don’t mind staying small. That’s why rootstocks are described in their dwarfing skills by percentages- if this rootstock takes a tree down to 1/3 of the size it wants to be, it is a dwarfing rootstock but the tree might still be larger than a less-dwarfing rootstock that’s supporting a variety that likes to get large. A large tree is usually more vigorous than a small one, but even small trees can be really vigorous if they’re the kind that want to replace EVERY BRANCH YOU TAKE OFF with A MILLION BRANCHES.
Let’s think about rootstocks! Then we will know why they make rootsuckers. A rootstock gets another tree grafted onto it, and usually just one original limb, the “nurse limb” is left, to keep the nutrients flowing into the scion. As soon as the scion is healthy and growing and the tree is popped into the ground in its in-ground home, the nurse limb is chopped off and the rootstock is in a weird position. Some rootstocks are fine to just accept the scion as their apex and the auxin coming down from the new scion is plenty to chill out their vigor. They might make no rootsuckers at all. But some rootstocks are MAD vigorous, and they don’t take kindly to being told to just chill out. They feel decapitated or whatever! I don’t know! They worry that they don’t have a trunk or branches or anything! Now, of course, the sensible thing to do would be to realize there’s a tree up there and just chill out, but we can’t always chill out when we should! As I mentioned earlier, often when the apical bud is removed, the rest of the limbs go CRAZY with competition trying to all be the new main stem. That’s what rootsuckers are. They come from the roots of the rootstock and they suck energy out of it and just shoot up like little trunks all around the trunk of the grafted tree. I’ve never seen any get reproductive, just vegetative growth, but I don’t know how far they’re willing to take it.
So we go outside and chop off the rootsuckers. The vigorous rootstock says ‘oh shoot my apex just got removed AGAIN’ and makes rootsuckers to compensate. We chop them off. The cycle gets repeated. It’s crazy how much effort these trees are willing to put into rootsuckers. They’re so pointless. Plus, they get in the way of everything, including herbicides on the ground, and regular pruning, and harvesting, and life, and they might not be a vacuum but they just suck. They can be feet away from the tree they’re from, and they can be really pretty, like some of our Bud rootstocks, which have pretty pink and purple wood and leaves, and all sorts of things. But some of them are tough, and all of them need to get chopped off low down, usually more than once for each tree, and, oh man. It’s tough.
That’s that. You know everything now.