Archive | January 24, 2015

How Vaccinations Can Make You Think About Tomato Disease Resistance


… or better titled as “odd things that run through a horticulturist’s mind while on Facebook”.

This morning I had some down time while I was waiting for a few of my Saturday morning tasks to ‘do their thing’.  Sitting there in the kitchen, I got on my phone and looked through my Facebook feed to see what was new and interesting with people.   One of my Facebook friends had a post about how she did not understand why unvaccinated kids made vaccinated kids sick.

Of course, the scientist-that-used-to-teach-college-classes-and-believes-knowledge-is-power that is in me responded about infectivity, virulence, gene mutations, and the like.

Vaccinations do not make one 100% immune to a disease. Giving a vaccine to an individual stimulates their immune system to recognize the pathogen and develop adaptive (acquired) immunity. The adaptive immunity allows the person to have more resistance to the particular disease and reduce the risk of death should they contract it.

The reason why those without the vaccine can infect those with the vaccine comes down to the basics of resistance, pathogenicity, and genetic mutation. An unvaccinated child can increase the risk of disease for everyone that is exposed to him or her because exposure is not a “yes or no” kind of thing that is determined by if you did or didn’t get vaccinated. For the vaccinated individual, the concentration of viroid particles they are exposed to (i.e. did they walk past the infected person in a store? or did they sit next to them for hours?), the virulence of the virus strain, and their overall health (i.e. existing conditions, diet, etc.) determines if they will be able to fight off the disease with antibodies or if they will get sick.

Unlike an organism like you or I that are multicellular and complex, a virion (a single virus particle) is nucleic acid (DNA and RNA) enclosed in a capsid (a protective protein shell). They are not even as complex as a single cell and therefore not living because they require a host cell to fulfill their life cycle. Once a virion enters your body, it attaches to a particular cell that has specific components that will be needed for its replication process (usually white blood cells). Once attached, the virion penetrates the cell wall through endocytosis (energy-requiring cell absorption) and injects the nucleic acid into the host cell. The host cell replicates the nucleic acid and creates many new virus particles. The host cell bursts open and the released newly made virus partcles go attack more host cells. When an individual has had a vaccination, their body develops antibodies. Once an antibody recognizes a virion (the antigen), it attaches to the surface and destroys the virion by opsonization and the formation of a membrane attack complex.

Viruses are quite perceptive to their environment and can adapt and mutate easily. While the antibodies in a vaccinated individual can have a field day of attacking fun, the virus’s virulence and vaccinated person’s health can play major factors in the quality of the job the antibodies do. If a particular virus strain is virulent, it has mechanisms that help it to avoid the antibodies. A pyrogen fever is one of these, as the virus induces the fever to shift the body’s temperature outside of the ‘ideal’ range to reduce the ability of the antibody to function. If a virion attaches to a cell that it not the healthiest and replicates, it is possible for antigenic shift or genetic recombination to occur. Antigenic shift is where the DNA or RNA sequence is recombinated or reasserted. Genetic recombination is the process in which the DNA is broken and rejoins at the opposite ends. It occurs rampantly. By either process occurring, all new virus particles created in the host cell and in the successive host cell attacked will not be recognized by the antibodies developed through vaccination. You have now created a pandemic by a virus that is not resistant to the antibodies in everyone that has been vaccinated with that particular disease.

It’s not hype or somebody just saying it – it is true because it is well documented and can even be demonstrated by a student in any lab. I used to work with Tobacco Mosaic Virus in disease resistant and non-resistant tomatoes and Potato Virus Y and Potato Spindle Tuber Viroid on Andean potatoes that my professor brought back from her germplasm expansion trips. I easily manipulated these same principals to test resistance and give my professor parameters to use for her future breeding projects. While I’m sure people would argue that plants are a lot simpler than people, the same principles still apply because viruses, not complexity of the host organism, is the common factor.

You are not alone in thinking that vaccinated or resistant means 100% coverage – probably 75% of the tomato calls I received when I worked in the seed industry were from people calling in to grump that my company had sold them bad seed because their precious resistant tomato still caught blight. It doesn’t mean it’s perfect, just means that it can tolerate it a little bit better. Flora or fauna, disregard of science will not lead to perfection.

Further comments back and forth dealt with the logistics behind the recent outbreak of measles related to Disneyland.

I’m sure that some of her FB friends and some of mine read this and thought I was pulling out my soapbox and railing against the world on the benefits of vaccination.  Not so to the soapbox, and hopefully not so to people thinking that.  It is more a “old Mert planned to put up a sentence or two, and then her talkative nature attacked her brain and made it spew out every detail it knew on the subject because there is always background details that are important and somehow pulled plants into it just because plants thoughts are always there lurking around”.

It’s true:  plants are always on my mind. Even to the point of where I sometimes have dreams of feeding homegrown vegetables to children that live on chicken nuggets and ice cream.  And of course my comment pulled in Tobacco Mosaic Virus and various potato viruses.

Diseased Tomatoes

But, I royally digress.  This all, in a very roundabout way, it made me think of a very common question I got while working in the seed industry and here on my blog:

 

“Why did my disease resistant tomato catch blight/verticillium/etc. and die?”

 

As previously stated in a more vaccination-oriented format, resistance is not a 100% shield that goes around your plant and makes it indestructible.  It doesn’t matter if we are talking about a virus, bacteria, or fungus.

For example, lets say that you planted your Resistant Lacking Tomato next to a Big Beef VFFNTASt Hybrid Tomato.  Your Resistant Lacking Tomato will get a disease — blight, verticillium, etc. — and within a week or two your Big Beef plants has it too.  Doesn’t mean that the seed from the company you bought it from is bad. Keep in mind these are “resistant” varieties, not completely disease-proof. They can maybe hold out for longer, but are not immortal.  In areas of very high concentrations of disease organisms, the resistance may not be enough to overcome these odds.

Former customers of mine at my old unnamed workplace were always quick to point out that heirloom and open pollinated varieties where not disease resistant because they “don’t have the letters”.  Don’t let that fool you too.  Hybrids ALWAYS have the letters because the breeder/vendor that is selling it to your mailorder seed company of choice has done the testing to find out what it has the edge on.  It is a marketing tool to get you to prefer their variety over another.  Of course, the question is always what their variety was compared to in the testing…

Just because an heirloom or open pollinated variety doesn’t ‘have the letters’ doesn’t mean that they are going to keel over at the first sign of disease.  The fact of the matter is that 99% of these varieties have not been tested.  Most land-grant universities have breeding programs and heirloom testing is a matter of $$$ rather than finding a truly good, resistant plant.  First of all, most open pollinated or heirloom varieties sell wholesale for a couple dollars a pound.  Hybrid varieties sell for a LOT more than that — upwards of $100s per pound depending on what supposed resistance or other desirable traits they have.  What professor is going to do research to determine the resistance of the old heirloom seed his grandma used to grow rather than developing a new variety that can sell for a ton and earn him some nice royalities?  Um, hello — from my experience I can tell you that a lot of PhD holders are willing to sell their soul to the industry rather than do the right thing for a lot less minor things that determining disease resistance.

Back in 2010 when I was growing a trial garden for the company I worked for, I had in a bunch of new hybrids that they were thinking about including in their next catalog and about 25 varieties that were already being offered by the company but had poor catalog and internet pictures.  That year we had a horrible time with late blight because we had a very humid, warm summer.  As I watched the blight spread through the tomato patch, it was interesting to see that the first to die were not the heirlooms, but many of the hybrids!  So much for that resistance!  As the varieties still standing became a handful of names, I was left with a couple Japanese numbered hybrid varieties (which had beautiful looking fruits with the texture of moist cardboard), Matt’s Wild Cherry (heirloom) , and 3 heirloom varieties that were already in the company’s catalog.  Interestingly enough, the next year the 2 Japanese hybrid varieties and a number of the other hybrids that had died were added to the catalog.  The Matt’s Wild Cherry was not added, and 2 of the heirlooms that we had already offered that survived were cut to make room for the hybrids.  Remember, it’s all about marketing.

So, the next time you have a tomato, hybrid or otherwise, that is having disease issues in your garden, don’t blame the seed company.  Look at what you are doing in your cultural practices and learn from the experience:

1.  Grow more than one variety because there is always one that won’t get as sick as the others. Not including the varieties I grow for sale, I have 4 staple varieties that are always in my garden.

2.  Rotate your crops so your tomatoes (and other Solanaceae family members) will not be in the same spot for four years.

3.  Don’t water your garden after 4 pm in the afternoon.  Tucking your garden in bed for the night with wet feet is a perfect way to start just about any disease.

4.  When the growing season is done, clean up your garden.  As tedious as it may be, pick up every leaf, stem, fruit, etc. out of the garden.  Heap it up in a pile, dry it down, and burn it on a good winter day  or bag it up and take it to the dump/put out for garbage collection.  DO NOT COMPOST IT!  DO NOT TILL IT IN!  While people will tell you the benefits of green manure or how much your compost pile will grow by, the small ‘reward’ is not worth the trouble you will reap.  It only take one small particle of infected material to be incorporated into your soil or compost to create problems down the road.  Don’t believe me?  Ask the 1800s Irish how their practices worked… Famine much?

5.  Keep your plants healthy by giving them the care to help them grow healthy.  Water, fertilize, cultivate, trellis, etc. as needed to make your plant grow to it’s best potential.

 

(And 6. Your horticulturist recommends vaccinating your children using the 1981 schedule.  ;-D   )

 

 

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2015. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.