joseph
Junior Member
Market farmer
Posts: 57
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Post by joseph on Aug 15, 2012 21:51:16 GMT -8
I'm also torn between keeping pedigrees like Tom does, and not keeping track like Joseph does. I keep pedigrees after a fashion... I generally allow uncontrolled pollination, so I don't know who the father is. But I often write the mother's identity or at least phenotype on the seed package. And sometimes a phenotype is so distinct that it's descendants are easily identified many generations later, even with uncontrolled pollination. If I do a manual cross pollination I record the father and mother. The children will often be saved as a family group for several generations. I grow a lot of things as family groups, or as phenotype groups. I might not know the exact pedigree, but I know things like "Every butternut squash in my garden is a descendant of a plant that produced fruit during the 88 day frost free growing season of 2010", or every cucumber in my garden survived the summer solstice frost of 2012, or every mother fruit in these seeds weighed more than 20 pounds (or less than 2, etc), or the radishes survived 2 consecutive years of grasshopper attacks. I don't have the inclination, or the skills to keep detailed records, I'm much too disorganized, so rather than stew over what is beyond my ability, I work with what I have. I am able to harvest into a basket with a label attached to it, and to keep track of that label long enough to dry the seed and get it into a labeled seed storage container. Of the many dozens of commercial varieties of potatoes that I have grown, there was only one variety that set a fruit or two on perhaps 5% of the plants in the patch. And I gotta wonder if that was only because it got pollinated by something from my landrace. I wasn't selecting at the time for fruitfulness, so it may be possible to find fruitful commercial varieties. And I think that potato fruiting is dependent on location and climate, what sets seed in a particular garden in a given year might not the next year in the same garden.
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Post by DarJones on Aug 16, 2012 23:37:11 GMT -8
Joseph, see if you can get some Shepody to grow. I've had extremely high fruit set from it.
DarJones
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nuts
New Member
Posts: 20
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Post by nuts on Aug 21, 2012 10:45:01 GMT -8
Throwing away pedigré information is often a bad idea. (Allthough it's an essential part in the process of creating what erroneously is called "landrace" ) In the case of a "landrace"lol that consist of a number of selfing lines with some exceptionel crosses you won't be able to make the distinction between a plant from a self pollination and a cross pollinisation,When you keep the lines separate you can often indentify a cross by being different from the parent . When the "multiline"(this could be more a appropriate term) consist of a collection of crosses,but selfing,the different lines will be segregating and it will be more difficult to see the difference between a cros and a self but even then you better keep the lines separated to avoid "drift" Drift is loss of genotypes due to random effects,as exemple,if you mix the seeds of two lines and you plant two plants,you have 50% chance to loose one of the lines. But of course you must be kind of organised to do this. When you have a population with very high % of outcrossing (natural or by hand) keeping lines separated makes less sense or even may be useless.
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Post by oxbowfarm on Feb 14, 2014 13:17:05 GMT -8
I get perturbed when I read that stuff because it shows poor understanding of genetics. It is very misleading. 1. You can't select what is not there no matter how many generations you grow. There are abundant examples of plants that have resistance genes in one species but not in another. Both tomato and potato are really good examples. Unless you include the resistant species in your breeding program, you will never be able to incorporate the required genes into your project. So if you want to incorporate really good resistance to Septoria in a tomato, you would have to include S. Peruvianum, S. Chilense, and S. Penneli in the breeding program. Unfortunately, that means you would have a problem because you can't cross Peruvianum or Chilense with domestic tomato (S. Lycopersicum) without some form of embryo rescue. Chestnut is a good example in this category. Castanea Dentata is totally susceptible to chestnut blight. There is no useful resistance in the species. Castanea Mollissima is the opposite. Very high levels of tolerance to chestnut blight are in this species. If you want to breed an American Chestnut with resistance to chestnut blight, you will have to include Chinese Chestnut in the breeding program. Keep your ideals, just add a healthy dose of reality. Next time you read about "horizontal" vs "vertical" resistance, ask yourself if the article is founded in reality. See if it can deal with the situations above. DarJones Having just read Raoul Robinson's Potato Breeding Manual, and Return to Resistance, I am very interested in Tom's view of these works. I have found them fascinating. I don't think Dar understands the context of the breeding schedule mariol posted. Robinson is recommending breeding for horizontal resistance. He rationale for avoiding vertically resistant genetics is because they prevent you from selecting for increased horizontal resistance. The vertical resistance acts as a block on the selection pressure for increased horizontal resistance. I would like to discuss the relative benefits of vertical vs horizontal resistance in potatoes. In fact, I would very much like to hear Tom's opinion. Having read Robinson's work, I am certain he fully understands genetics.
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Post by DarJones on Feb 14, 2014 19:32:13 GMT -8
Oxbow, The intent is to avoid single gene resistance because it is relatively easy for a disease to overcome. Unfortunately with potato and tomato, this viewpoint ignores a very simple conundrum. Resistance genes (referred to as "R" genes) in the potato family come in discrete packages. A single R gene might block late blight race 1. Another R gene might block late blight race 2. If you stack the two R genes into the same variety, you get resistance to both race 1 and race 2. This type gene is always a '1 for 1' relationship where one gene blocks one disease variant. Unfortunately, the newly stacked genes would not block late blight race 3. So now you need to find another R gene to block race 3 and try to stack it into the line with R1 and R2. Each of these R genes represents a different genetic block to the disease organism and to the guy who is using "horizontal" resistance breeding, he thinks he is making progress when in reality, he is just stacking multiple R genes into a single line. According to RR's writings, an R gene stack would be horizontal resistance. According to the 1 gene 1 resistance model, an R gene stack is just a bunch of single resistance genes that a disease can relatively easily overcome.
What should be considered is sequential polygene resistance. This is where one gene blocks a disease, but if that gene is overcome, it is backstopped by another gene and another and another. This is the intent behind the concept of "horizontal" resistance.
Raoul Robinson is a plant scientist, not a geneticist. It is the same concept as someone saying they are a computer programmer. Show me the programs you have written. Then I will know that you are a programmer. He is a plant scientist and I have no doubt he has some understanding of genetics, but he is NOT a geneticist.
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Post by oxbowfarm on Feb 15, 2014 8:26:52 GMT -8
So you are saying that someone who works as an agricultural plant pathologist can somehow get away with an entire career with no understanding of plant genetics? And what I'm saying is that since you haven't read his book, you are apparently unaware that he extensively covers everything you just discussed, including stacked vertical resistance genes. If I direct you to this link, please examine chapter 18, specifically the section beginning on page 177. Robinson's purpose for advocating horizontal resistance is to breed for the capacity withing a species to tolerate a pathogen, AFTER it has been successfully been colonized by the pathogen. Thus, a cultivar with high horizontal resistance and no vertical resistance is colonized instantly, but the disease is not fatal, or even noticable. The crop and the pathogen are able to coexist, a lethal pathogen becomes a non-lethal parasite. In effect, breeding for a situation identical to that which exists in wild potatoes in the Mexican center of origin for Phytophthora infestans. The situation is similar to Chinese Chestnuts versus American. Chinese chestnuts have high levels of horizontal resistance to Chestnut Blight. American Chestnuts have low levels of horizontal resistance. A disease that is a parasite of Chinese Chestnuts is a deadly pathogen for American Chestnuts, until we can breed horizontal resistance into them. I'm saying read his work. He's a plant pathologist, he understand plant pathogens. He is advocating for a completely different methodology for breeding dealing with plant pathogens. I'd like to debate whether or not horizontal resistance actually exists. When you read the entire book and the reference papers it is pretty hard to logically refute. I'm asking you to read his work itself, not just an exerpt, before saying stuff about his knowledge of genetics.
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Post by DarJones on Feb 15, 2014 22:14:13 GMT -8
Oxbow, I read the book in its entirety. In the past, I had read about 2/3 or it. He is NOT a geneticist. He does not correctly account for or even understand the reasons various resistance mechanisms are present in plants. He is only presenting one facet of a complex living system.
Neither Mendel based nor biometric based genetics is entirely correct. Why do you think plants have multiple levels of defense against pests and pathogens. It is because each defense in a plant has a purpose. Where we have taken a detour is in not recognizing the damage monocropping does to a plants defensive systems. Look what happened to rubber tree plantations when a disease got loose in the plantings. The same thing can happen with any monocultured crop.
RE chestnuts, the resistance is based on 3 genes and for his purposes, he would describe them as vertical resistance genes. Those 3 genes have been effective for thousands of years in chinese chestnut. Do you magically re-classify them as horizontal resistance genes because they have not broken down?
From a geneticist's viewpoint, it does not matter whether resistance can be broken or not, all that matters is that the gene is there and it functions. It doesn't matter whether it is a single gene that blocks infection or multiple genes that stack together to provide a barrier to infection or if it is a gene that produces a toxin that kills the infectious agent. All that matters is that the genetics are there and they function in a way that yields a result.
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Post by oxbowfarm on Feb 16, 2014 5:20:45 GMT -8
Oxbow, I read the book in its entirety. In the past, I had read about 2/3 or it. He is NOT a geneticist. He does not correctly account for or even understand the reasons various resistance mechanisms are present in plants. He is only presenting one facet of a complex living system. That is an interesting statement. I'd like you to back it up with specifics. Where specifically is his understanding of genetics faulty? Since Return to Resistance is entirely about different forms of plant resistance, I felt he covered the different ypes of plant responses to pathogens and parasites extensively, with an intriguing perspective. Its quite easy to make flat statements like "He's not a geneticist", "He has no understanding of plant resistance mechanisms". Where, specifically, are his positions incorrect or invalid? If you disagree with the entire concept of horizontal resistance, that's an interesting conversation. I'd just like you to explain that position.
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Post by DarJones on Feb 16, 2014 9:39:22 GMT -8
Oxbow, it is a false dichotomy because he tries to separate genetic resistance mechanisms into one or the other of two positions. There are multiple positions, therefore it is not a dichotomy. Here are examples to prove it.
Potatoes have a leaf surface protein that prevents infection by many forms of late blight. But some variants of late blight have devised a chemical key that attaches to these proteins and opens a path to infect the cells. Robinson equates this to a key/lock based resistance mechanism and calls it "vertical" resistance.
Tomatoes produce a chemical called tomatene which you can think of as a general purpose anti-infection alkaloid. Production of tomatene is regulated by genes that can be up-regulated, in other words, the amount of tomatene produced can be increased or decreased by the plant. The plant breeder can selectively breed from plants that over-express tomatene production with the resulting plant exhibiting much higher general resistance to fungal infections. This system can be equated to horizontal resistance from his book.
But then there are other genetic systems such as turning on or off a gene in a plant which is required for an infection to occur. Southern Blight in tomato exhibits this pattern where a tomato gene is deactivated resulting in the plant being highly resistant to infection. This mechanism is not truly vertical resistance, nor is it horizontal resistance as he defines the terms.
So my statement that it is a false dichotomy is because plants are not limited to just two categories of resistance genes. Or put another way, a geneticist is not limited to black and white, he also can see red, blue, orange, green, yellow, etc.
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billw
Junior Member
Posts: 76
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Post by billw on Feb 16, 2014 10:42:14 GMT -8
I think the strategy that he outlines for eliminating outright resistance in order to look for intermediate forms is a good one for the plant breeder that doesn't have any information about the resistance genes in the plants that he is working with. But, just as with any component of phenotype, there is no reason to think that this reflects a particular genetic arrangement without additional work.
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Post by oxbowfarm on Feb 18, 2014 18:31:10 GMT -8
So my statement that it is a false dichotomy is because plants are not limited to just two categories of resistance genes. Or put another way, a geneticist is not limited to black and white, he also can see red, blue, orange, green, yellow, etc. Geneticists may not be limited to black and white, but most amateurs are. Sophisticated and accomplished polymaths such as yourself may be able to cook up cultivars with stacked resistance genes in their greenhouse, but most of us require fully staffed research institutions for that. Is it truly a false dichotomy if you take into account the intended end users of his book? I would describe it as a valid simplification of terms. He is detailing a system for amateur plant breeders for selecting populations for improved resistance using recurrent mass selection. It also doesn't indicate a convincing lack of understanding of genetics on his part, merely organizing of traits into classes as a rule of thumb for his intended audience.
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Post by DarJones on Feb 20, 2014 15:59:29 GMT -8
Thank you Oxbow, but I am not a polymath. Maybe a minimath at times, but not a polymath. Your response echoes a lot of what I see as problems for plant breeders today. We need better tools to work on genetics.
Contrary to what you may think, I have a lot of respect for this book. It gives a very good description of most plant immune system responses. It is state of the art for 1980's plant breeding, but can't begin to describe what is feasible today.
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Post by oxbowfarm on Feb 22, 2014 10:24:31 GMT -8
I agree that science has advanced greatly since the 1980s. I don't see how it makes his proposed approach obsolete. Even the rather simplified description of his proposed breeding and selection schedule that mariol posted represents a major commitment for a group or individual over a long time scale. Not something to be entered into lightly.
A truth that I see, for all the advances in genetic knowledge, much less plant breeding is being done in the public interest than in the 80s. Most public sector breeding projects are slowly being down-scaled and underfunded. More and more private breeding work is now transgenic and almost all of it is proprietary and bound by various forms of intellectual property law.
I am excited by a book offering grassroots methods to counter this trend, even if the techniques are not state-of-the-art.
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Post by nathanp on Feb 23, 2014 17:21:00 GMT -8
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Post by nathanp on Feb 23, 2014 17:25:16 GMT -8
linkAnd I just ran across this article from 2012 about Tom's methodology vs traditional breeding for resistance ( GM gene insertion is what is compared here, but the theory of vertical resistance is identical - it has the same weaknesses as traditional breeding for vertical resistance).
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