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Thoughts on genetic diversity and varietal slip.

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Dean

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As an orchid grower and breeder , a grand champion holder and what I think to be a fair understanding of plant genetics I am looking for opinions on varietal slip through the generations.

in what most of us are doing, growing small amounts of seed in a home garden, selecting the best of that crop to seed is speeding up,genetic divergence. I'm not saying this is a bad thing but it will be happening.

a commercial grow selects a lot more plants and open pollinates to mix genes of the grown strain evening it out across the next grow or buys in select seed to plant.

i am looking for opinions on the diversity of things like TN90 once grown and selfied many times, some of the others with numbers as well as even my growing of let's use TN90 as an example may differ to another growers preferred plant to use. With each generation we must be moving away from the original characteristics that made this a varietal.

i don't think things like growing conditions, which I hear a lot in the oriental section change the genetics, they may change the taste but the same applies to them, open pollinated is better, it spreads the genes out and causes less slip than growing just one plant on for seed.

here in OZ we don't have that luxury. We are stuck with whatever we can produce and save seeds from. In a decade even we will have new strains based on other countries plants but not the same, NZ will be close to us.

is the Grinn still holding originals of everything? They need to I think, we are not GM ing strains deliberately but we are not doing them any favours either. Look at Turkish locational varieties to see what a small change in genetics can do.

i think in only 5 generations of selfings I may not have the same plant I started out with, in 10 generations I will have a deferent strain. For the good or bad this is how strains were developed and cultivated and register but the gene pool is continually changing to accommodate the shift in farmer preference especially on selfings of individual plants.

i am not writing this to be argumentative, more as a heads up and a discussion point to keep our vars pure.
 

leverhead

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I think this is a handicap of amateur growers that will be hard to get past. For me, I would need a much more rural area before I would dare trying open pollination. I think the best, or maybe the worst we could do is to swap same variety seed amongst ourselves and mix them to get a larger number of plants represented. Growing and saving 10 years worth of seed might be a better strategy, that would stretch 5 selfings out over 50 years. Time isn't a constant, change is. The trick would be to become very good at keeping viable seed.
 

Dean

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Well said... I couldn't agree more.

I'm not saying what we are doing is bad but if we were to keep strains pure open pollination would be the only way to do that on a sustainable level. I am worried about the 'pure' strains offered here, I keep my opinions on them close to the chest and will assume a strain derived from in a decade from now. I will say again this is not a bad thing but TN90 from you to me in 10 years may be a completely diff beast. We need to keep that in mind, maybe work some open pollination into the mix when keeping a strain for the forum. This would keep the movement of the strain to the same rate as the farmers.
 

Dean

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You guys are coming into a state of growth, maybe there could be a collective of growers willing to grow put single strains, or stagger their growing to produce open pollinated plants. A swap for what they want in smokes by trusted growers. ThTs a whole lot of bull crap to do but it would reserve the strains better than individual growers keeping and breeding off one plant.
 

leverhead

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I don't live in the city, but there's too many people within a 1/2 mile to know what's growing around me. Open pollination isn't an option for me.
 

Dean

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I understand open pollination isn't an option for the majority and there lies the food for taught. I am alone here but still seed true by bagging. I an guilty of genetic change and I don't have an option to stop it.

This is is why I asked the question, I want real time feedback on a real tobacco world issue. I think this is something many have not thought of, many think a bag makes it ok. The real world ramifications are varied and uncontrollable.
 

DGBAMA

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For me this idea is where my seedlng selection criteria plays in. After germination, thinning out both the largest and smallest seedlings and growing out the healthiest of the MOST UNIFORM seedlings would seem to have the best likelyhood of keeping the variety "true to form" for the next generation.
 

deluxestogie

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The issue raised is one of genetic homozygosity (the absence of recessive, unexpressed traits). For most plant geneticists, 7 seasons of selfing a stable tobacco variety is considered to firmly establish a homozygous state. (Perhaps Jessica could clarify this.)

The rules of thumb used for most plant varieties assume a relatively low number of seeds produced per plant per generation. A single, typical tobacco plant may produce a quarter million seeds. If you were to start 100 of those seeds, it represents only a negligible fraction of the gene pool available in 250,000 seeds.

Skychaser and I argue over the math. However, if you grow, say 50 plants, bag 10 of them, and harvest the seed (mixing from all 10), the math is overwhelmingly in favor of maintaining that variety's homozygosity. With at least 1/2 mile separation between varieties, open pollination within a variety fertilizes only a minuscule fraction of the seed, since self-pollination of tobacco is its primary mode of fertilization, and often occurs just before the blossom opens.

I think that the major advantage of growing a larger number of plants of a chosen variety is that you can more reliably select for seed production those plants that are true to type. From the math, bagging 10 plants vs bagging 1 plant is pitting 10[sup]1[/sup] (number of plants bagged) against 10[sup]5[/sup] (number of seeds produced per plant). Bagging multiple plants does, however, improve your odds of avoiding failure due to weather or budworms.

The question of "hybrid vigor" is unclear to me. Where plants or animals are not homozygous, cross-fertilization is well documented to improve the "vigor" (whatever that might mean for a specific tobacco variety). With a homozygous gene pool, cross-fertilization seems to me to have no meaning.

My recommendation for seed production is to grow as many of a variety as you are able, select those true to type, and bag as many of these as your time and resources allow.

Bob
 

skychaser

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Skychaser and I argue over the math. However, if you grow, say 50 plants, bag 10 of them, and harvest the seed (mixing from all 10), the math is overwhelmingly in favor of maintaining that variety's homozygosity. With at least 1/2 mile separation between varieties, open pollination within a variety fertilizes only a minuscule fraction of the seed, since self-pollination of tobacco is its primary mode of fertilization, and often occurs just before the blossom opens.

I think that the major advantage of growing a larger number of plants of a chosen variety is that you can more reliably select for seed production those plants that are true to type. From the math, bagging 10 plants vs bagging 1 plant is pitting 10[sup]1[/sup] (number of plants bagged) against 10[sup]5[/sup] (number of seeds produced per plant). Bagging multiple plants does, however, improve your odds of avoiding failure due to weather or budworms.

Bob

The 20/100 rule for a minimum number of plants is a well established rule that every reputable seed producer follows. For inbreeding plants you want a minimum of 20, for out breeding plants you want 100. More is even better. I do agree that tobaccos are one of the most forgiving plants to bend the rules on a little, due to the reasons Bob mentioned. But there is still a risk of "bottle-necking" the gene pool with growing smaller numbers. Genes that may not express themselves in a current generation can be lost. As an example, these may be genes that are only active atduring times of stress, such as adverse weather conditions, disease or predation. One example is something many of us have seen for ourselves during abnormally cool and cloudy weather conditions early in the growing season. A normally inactive gene(s) becomes active and causes the plant to bolt to flower as a means of ensuring some seed is produced. You may also have noticed some types that mature very early often go through a second growth and bloom period. Little Cuba is one I had last season that is an excellent example. These are part of the plants survival strategy that ensures its survival into next year.

Growing a large number of plants also lets you select plants that are true to type. Rouging out plants not true to type is something we do with everything we grow. Plants that are abnormally small, have excessive suckering, premature blooming, or abnormally large plants are culled. We cull anything that even remotely looks like a possible viral or bacterial infections are they culled immediately when spotted. I have culled plants that have probably had nothing but some weather fleck on the leaves and were fine, but could possibly also be a bacterial infection. Not having a lab at my disposal, I go with better safe than sorry and pull it. When rouging plants you must resist your human nature to keep "that really big one" for example, and try to maintain an average normal variation among the population.

Open pollination is always the best way to go when feasible. Numerous studies have shown the germ rate and viability of OP plants to be a few percent higher, no matter what type of plant you are growing. Open pollinated tobacco of different varieties grown side by side in rows will cross at a rate of 2-10%, depending on the number of pollinators present. (I found that info on the ars-grin site somewhere once) Open pollination among the same variety should yield a slightly number percentage mixing. I know of no real data to support that theory other than what other seed growers tell me, but it does seem logical that mixing among identical types would be slightly higher than with different types. Large populations of open pollinated plants will always give you a better mixing of genes and a higher viability that any other method does. Saving seed from a large population of selfed plants is the second best way to go.

To establish a variety in a homozygous state, 5-7 successive generations must be grown. The most widely accepted number seems to be 7 generations, as Bob mentioned. If there is a specific trait you are trying to reinforce, then selfing seems it would be the best way to do it in the earliest generations, with lots of culling done in each grow. But if the trait you are after is reproduced with good consistency in generation 1 & 2, I would think open pollination and lots of culling would be the best way to establish it in successive generations and not bottle neck out other genes that may contribute to the plants overall survival in ways not easily observed. But I really do not know for sure. I am NOT an expert on genetics by any means. I'm just a guy with a high school diploma and a passion for reading and growing plants. :)

Sky
 

skychaser

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i don't think things like growing conditions, which I hear a lot in the oriental section change the genetics, they may change the taste but the same applies to them, open pollinated is better, it spreads the genes out and causes less slip than growing just one plant on for seed.

I agree. Growing conditions, both good or bad, don't change a plants genetics. And least not in the short run. Growing a plant for many generations in the same location would however slowly alter the plants genes by reinforcing beneficial ones to that particular location or climate, and slowly losing genes of no benefit to that location. Open pollination would maintain the original gene pool for a longer period than in selfed plants, even though the genes may not be expressed at a given time or location.
 

deluxestogie

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Genes that may not express themselves in a current generation can be lost. As an example, these may be genes that are only active atduring times of stress, such as adverse weather conditions, disease or predation.
This is an excellent point, and an issue that is seldom addressed in determining "homozygosity" by means of morphology or chemical analysis. The switching on/off of particular genes is regulated by epigenetic factors that are subject to environmental influences. While environmentally induced epigenetic changes can persist (without altering the genome), it is extremely difficult to identify these potential morphologic changes when plants are only examined under "normal" growing conditions.

Outrageous example:
If there is a "switched off" gene that only becomes functional when the plant is grown during March Madness, then you might never know that a few percent of your "pure" strain tobacco will produce orange basketballs. The larger the grow-out, and larger the number of plants from which seed is collected, then the lower the risk of ending up with a crop that predominantly shows such a grim, athletic deformity.

Bob
 

istanbulin

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Homozygosity is a theorical aim/state for truebred organisms (plants in this case). In Mendelian genetics, this means that an organism must be homozygous for every trait for which it is considered true breeding.

Hybridization in tobacco is rather new so I don't want to talk about that for now. What people are doing for long years is selection.

There're two types of selection ;

1.Single plant/True bred selection, is (basically) selecting single plants (200 to 1000) from a population (let's say from a field) and controlling their progeny. Because of selfing homozigous plants for years (at least 7) these varieties are called truebred line variety.

2. Mass selection, is selecting phenotypically similar plants (at least 200 for not to miss anything) and mixing their seeds. This is what people in seed busines do to keep seeds pure.
There're two drawbacks of this selection type;
2.a. If the zygosity (if they're heterozygous or homozygous) of the starting plants are not known, even after 7 years selfing, they may show different expansions. In this case another phenotype selection should be applied.
2.b.The environmental conditions are effective on their growing habit and purity. Because of this selecting plants according to phenotype can't give an idea if plant's "superior" phenotype is because of genotype or growing/environmental conditions. Because of this, mass selection is not widely used as single plant selection for breeding lines especilly for self fertile (otogamy) plants. Tobacco is both self fertile (otogamy) and allogamy (cross pollination). So, this type of selection is generally used for keeping seeds pure for long years of growing and distributing.

On the otherhand, environmental variance (F1) is important as phenotypical variance (F2) to check and determine the degree of heredity.

h[SUP]2 [/SUP]= (Var[SUB]F2[/SUB]-Var[SUB]F1[/SUB]) / Var[SUB]F2 [/SUB]
 

jekylnz

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What if you were to put say 6-12 plants of the same variety in one big bag? Would this help..or would you still need open pollination of more..like a field. ..I'm thinking portable little frost cloth houses that would fit a dozen or something? ?
 

leverhead

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It would be allot of work, but what would manual manipulation of the flowers do? Like "crossing" two varieties, except keeping the pollen swap between two or more plants of the same variety.
 

DGBAMA

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What if you were to put say 6-12 plants of the same variety in one big bag? Would this help..or would you still need open pollination of more..like a field. ..I'm thinking portable little frost cloth houses that would fit a dozen or something? ?

You would also have to enclose pollinators, ie bees, butterflies, humingbirds; within the same "tent", while ensuring that others from outside dont come and go as they please.
 

Dean

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I think leverhead has hit the nail on the head, how technical do I need to talk, I'll keep it simple. I would think a small selection of in crossings would preserve the strains better, take pollen from x amount of var. in cross for that var. between grown plants. It wouldn't be that much of a job if you were only using 1 or 2 flowers per plant. I would think pulling pollen from several plants shaking it up in a small baggy and pollinating the var. could come down to something like open pollinating. The more plants the better obviously but on the small scale I believed it would be better than the statistics for selfing. This is only my theory but I can't see a negative and far better than selfings of plants being produced season after season. Something like this would keep the vars. diversity within containable limits to call it a pure strain after many generations.
 

Dean

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You guys can refresh every year so the net worth may not be applicable. For those under a Nazi government are not going to be so lucky. If I utilise my long season and grow 2 lots a year I'm strange in 3.5 years as an example, I know I can keep seed here for up to 6 years and still have reasonable results but fresh seed always grows better. The data provided by above posters eases my mind a bit but I am still not convinced natural selfings are the way to go. Especially in a small self contained plot. We have times of year like first sowing that does not many pollinators present, second crop is when the bees and wasps get happy. Without using these natural pollinators and as read it will be less than 10% I am in crossing a strain and limiting the genetic diversity with every generation.

This is is something we use in orchid production to intensify traights we want to keep, like vigour, size and especially flower size and count. All this can be manipulated over as little as 3 generations.

has there been any research into diploid and triploid ploydy counts on baccy, this is something I could look into in the lab, it would require mericloning all plants but doubling the ploydy count could and would give larger plants, leaves and harvest. This would have to be done at a cellular level. A small piece of growing tissue is taken, treated and then cloned into protocorms, it is done a lot with pine plantations, we got the idea from you guys re foresting and growing for sustainable harvests. It is not a hard thing to do but is time consuming.

many triploid and quadraploid plants can only be produced by cloning.

A great eat example would be the opium poppy, the one used for drug production it is a triploid plant and as such produces overly large leaves and flower pods so the latex production is more and more intensified than a normal garden variety poppy of the same var.
 

leverhead

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I still think the best bang for the buck would be keeping seed better and only selfing every 10 years. The Nazis didn't last 20 years, like any pest, they do keep coming back in different places.
 

JessicaNicot

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sheez. I know this isn't the first time we have had this discussion in the last year even. unless someone is making their own crosses or getting open pollinated seed, EVERYONE should have HOMOZYGOUS materials (because you're hopefully getting your seed from a reputable source who doesn't open pollinate). PLANT BREEDERS ELIMINATE GENETIC DIVERSITY TO CREATE GENETICALLY UNIFORM VARIETIES. even corn hybrids, which get 50% of their genome from each inbred parent, are genetically uniform from plant to plant, except for whatever the natural mutation rate is. The exception is the rise in popularity of supposedly "heirloom" varieties (formally known as "landraces"; but keep in mind the word heirloom is not regulated, just like "natural") which were never inbred as much as modern day cultivars. I think it would be much more useful if you thought of all of your plants of a single variety as identical twins- they are exactly the same in every way except for the interactions they have with their immediate environment (which goes back as far as the womb/seed capsule).

I preserve the genetic diversity of tobacco by maintaining numerous inbred lines that capture the gene pool of the whole species. if you are seeing phenotypic variation in your tobacco plants that originate from GRIN it is because (in order of likelihood):
A- micro environmental interactions which include: soil chemistry and physical properties, shade, temperature, water availability, etc
B- stresses from soil borne pests including bacteria, fungi and nematodes
C- you did indeed witness an aberrant genetic mutation that led to a noticeable change in phenotype

the science of epigenetics and environmental imprinting (DNA methylation) is a hot topic these days as new technology has really allowed people to ask and answer some really interesting things. however, I can say that we have vastly altered the plant architecture of TN90 using an accelerated breeding technology over the course of a number of generations and when the technology was removed, the resultant plants reverted true to type (and statistically the plants were not significantly different from the original TN90 seed lot in morphology or chemistry). to be honest, I was a skeptic of said technology for fear of the imprinting it might cause, but the evidence won the day. I think you need not worry about the environmental imprinting of tobacco unless you're considering along the magnitude of hundreds of years (with genetic mutation still being the predominant driver of change).
 
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