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Post by mariol on Jul 27, 2012 6:29:54 GMT -8
Hi Tom and other potato fans,
I live on a small mixed organic farm in the Pacific North West where I study gardening/farming. We have the opportunity to present a topic of our choice to our teachers and other students, and I chose potato breeding!
This led me to read Raoul Robinson's Return to Resistance as well as his potato breeding manual.
I'd like to talk specifically about how to set up an amateur breeding program to improve horizontal resistance in potatoes. The farm had blight pretty bad last year so it is very relevant. Eventually and ideally I'd like to start breeding in a year or two.
I think I have a general understanding of how to proceed (from Robinson's books), but I'd like to get a second point of view.
What are the different steps you would go through if you were an amateur potato breeder trying to create new varieties with horizontal resistance to blight?
I was going to write my own understanding of it and more questions but it's time to go harvest! I'll come back to this later
Thanks for your help!
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Post by DarJones on Jul 27, 2012 23:15:39 GMT -8
The first step is to understand basic potato genetics. Potatoes come in diploid and tetraploid varieties. The complexity of a tetraploid cross make targeted breeding much more difficult than diploid breeding. At the same time, the size and yield of tetraploids makes them potentially much more rewarding. A good next step is to learn to make crosses. You will probably make 100 crosses before you get up to 10% success rate. Collecting pollen can be a pain. Finding right age flowers may never happen. Lots of environmental things can go wrong. Then you need a good stock selection to be able to pick potentially complementary parents. And that means you have to grow a LOT of potatoes. Which gets down to some really hard work. Having a tractor and land and a source of income to support your potato endeavor is one of those must be things. Add the grueling physical labor to the low to no reward for your potatoes and you have a recipe for a nervous breakdown. I'll let someone else tell you a few of the pitfalls. I've given the high points. DarJones
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Post by mariol on Jul 29, 2012 12:18:48 GMT -8
Thanks for you reply, that was an interesting read.
From what I understand, tetraploids make it harder to understand what is happening in a cross, but maybe it doesn't matter for reccurent mass selection?
I do see the importance of building skills before heading on into even a small breeding program. This year my intention was to graft scions of two different varieties onto their own tomato rootstocks and hand cross them. The experiment half failed as I ended up with only one graft that may or may not produce flowers. But I might still get some flowers on the graft and be able to find some pollen on my potato beds to get some crosses happening.
You seem to emphasize that a specific program targeted at horizontal resistance would be very hard work. Maybe, for a small scale grower/amateur breeder, the solution would be to just have horizontal resistance build up be a side effect of saving TPS?
Anyway, I also wanted to share my understanding of what a breeding program for horizontal resistance would look like. This comes mostly from reading Robinson's work, so I'd like to get your input on this:
****Breeding cycle:
- Start with 10-20 parents that have desirable traits (e.g. yield/quality), but not chosen on the basis of their resistance (avoid varieties that have vertical resistance). (note: flower production might be an issue) - Graft a scion of each parent on an indeterminate tomato rootstock. Have two grafts of each just in case. - Potato scions will hopefully survive and produce flowers
*Cross-pollination:
- Each day, emasculate flowers the day before they open (save at least one to use as a male parent) - The next day, use the anthers of the male parent to drop pollen on the emasculated flowers - Switch male parents every day, so that all parents are represented equally
- Save seeds; do not bother labelling, we will mix them all together
Each fruit will contain up to 300 seeds. We are aiming for >100,000 seeds. One good graft can produce up to fifty fruits, with up to 300 seeds per fruit, totalling some 15,000 true seeds
*Sowing:
- After the last frost, direct sow the seeds every two inches. Let pest/disease do their work. - Rescue the survivors or the best plants. If only a few survivors (early breeding cycles), transplant into pots and nurse them. If lots of survivors (later breeding cycles), transplant the best to a potato field with a normal spacing and make final selections later.
- In later breeding cycles, inoculation/infestation might be necessary. Avoiding rotation, planting susceptible varieties around the experiment might be amateur ways to do so?
- Use scions from the 10-20 selected plants to produce more seeds for the next year via grafting on tomato rootstock (?). (Can this be done at the end of the season late summer/early fall in a temperate climate??).
I am actually unsure of this last part as Robinson doesn't really tells how to go from the selected plants to producing more seeds.
We then start a new breeding cycle.
We need 10-15 cycles/years for optimum resistance.
************ Any input regarding this whole process? Thanks
Sorry for the format, a lot of this is from my note taking, and I haven't formatted it clearly on paper or in my head yet.
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Post by DarJones on Jul 29, 2012 22:25:33 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.
2. There is absolutely no reason to avoid "vertical" resistance genes. Just understand their impact and how they work. One reason this is a non-issue is because there is almost always something that can overcome single gene resistance. With tomato as an example and late blight as the disease, you can combine ph2 and ph3 genes to get highly effective late blight tolerance. But this tolerance can be overcome by some strains of late blight. It is not a complete tolerance. In other words, you will always be able to tell when more resistance genes are impacting the breeding lines therefore you can always do more work to incorporate resistance genes.
3. There are always side effects of cumulative breeding. One of those side effects can be that the result is inedible. For example, you could breed a potato with increased levels of solanine and other alkaloids. It would be highly resistant to many diseases and pests. It would also be inedible for humans.
4. There are abundant examples of R genes in potato that convey resistance to one and only one strain of a disease. The problem is that the disease organism mutates faster by far than the potato plant can produce new variants of the R genes to fight off the infection. In other words, you are fighting a battle that simply cannot be won if you try to stack R genes to produce tolerance to multiple variants of the disease. This does NOT mean the R genes are useless. You can indeed achieve some useful results by stacking them into a single cultivar.
5. A good example of stacked genes conveying increased tolerance can be found in the tomato. Several breeders have been working to improve the ability of plants to tolerate various fungal infections. They have combined ph2, ph3, eb, and various other genes which gives some level of increased resistance to fungal infections. I have a line of tomatoes with this background. This summer, I sliced one of them in half and at the same time sliced a normal tomato in half and put them on a tray in the back porch of my house. 3 days later, the normal tomato was covered in white fungal growth. The resistant tomato was almost untouched. I tasted some of the resistant tomatoes and could easily detect some unusual flavors that my tongue said were some kind of alkaloids such as tomatene.
6. There are plenty of other side effects to consider. For example, you might be able to combine genes for highly effective resistance to late blight, early blight, septoria, and gray mold. But unfortunately it turns out that the gene for septoria resistance just happens to make the resulting plant susceptible to tomato mottle virus.
7. You can't treat natural inbreeders the same as natural outbreeders. Tomato and potato have species in both groups. Lets say you want to bring in some genetics for tomato from a species that has the S gene. This gene results in self-incompatibility. The plant is an obligate outbreeder. You would have to understand the effect of the S gene and how to overcome it before you could incorporate the desired resistance genes into your breeding lines.
8. Genetics in plants is the science of 2, 4, 6, or sometimes 8. Most species are diploid with two sets of chromosomes. But with potato there are plenty of species that are tetraploid with 4 copies. You can't use quite the same approach with breeding the diploid as you would use with the tetraploid. If you want an example of a hexaploid, look at clover. IIRC, Kura clover is a hexaploid. You can cross it with ordinary white clover which is a diploid. The result is a tetraploid with 3 sets of chromosomes from Kura clover and 1 set from white clover. I give you thirty-three guesses what happens when you try to grow out the tetraploids and produce segregating offspring.
9. Corn is a really good example to use in this case. You can actually achieve a lot of your goals by relatively simple selection with corn. Corn has an exceptionally high level of diversity with 97% of its genome common among the various strains and 3% that you can do a ton of selection work with. The best example I know of where multiple genes convey high levels of resistance to a disease are Rust in corn. The thing is that corn is a rampant outcrosser. A few generations under very high levels of selection pressure and you can achieve incredible results. Tell me how you are going to do the same with potato please?
10. There are examples where a single gene conveys durable resistance to a disease. In other words, it is a lock so effective that the disease will never find a key to open it. Is there any reason you can think of why a breeder should avoid such a gene?
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
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nuts
New Member
Posts: 20
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Post by nuts on Jul 30, 2012 1:01:01 GMT -8
So,you don't only need a tractor,but you need to understand potatoe genetics. If you're realistic enough you'll drop the whole idea.
I'm a bit more optimistic about the potentials of such an approach. In fact,in reality breeding for horizontal resistance is what's happening if y-ou're playing with crosses,if you want it or not.In fact that's what happened for thousenths of years without man having any knowledge of modern genetics.
My believe is that new features can emerge by recombinations of existing genes and not only by introduction of preexisting genes/features.
The succes of such breeding program depends on the genetic variety of the initial population and the rate of new crosses that are generated. The idea of masscrosses by hand is interesting.
In the ideal world potatoes would be good outcrossers,Some varieties are good outcrossers.This would be a top feature choosing the initial population,so you could nature let do the work. It's very difficult to obtain information about the ability of varieties to naturally outcros. But I hope Tom can say something about this.
I read some articles of Raoul Robinson,I wouldn't say he has a bad understanding of genetics. I didn't find anything very recent from him. What happened to him?Murdered by the seedcompanies?
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Post by wingnut on Jul 30, 2012 8:07:54 GMT -8
I grow about 300 varieties from Tom wagner, most from his TPS program. I do not have a tractor, only a 16" broadfork and a HOSS PUSHPLOW. It takes me about an hour to weed/hill HUNDREDS of feet of potatoes. I do specific hand pollinations as well as bulk open pollinations between all plants. I will be breeding for disease resistance, just because those plants with better resistance are the ones that flower/set seed the best. Many of the varieties I am useing have already been bred extensively for disease resistance such as Sarpo Mira, muruta, victoria, and others.
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joseph
Junior Member
Market farmer
Posts: 57
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Post by joseph on Jul 30, 2012 8:40:19 GMT -8
Recurrent mass selection works well without requiring an understanding of genetics.
I think that you would be better off growing potato seedlings, and selecting for cultivars that flower and set seed in your garden than you would be to do weird and unusual and labor intensive stuff trying to get a plant to bloom. That tomato grafting thing would be way too much work for me...
We can't know ahead of time what pre-existing components will recombine in new and unique ways in order to provide better resistance to disease or pests. But we can start with as wide a diversity as possible so that there are more opportunities for recombination.
When I got serious about my potato breeding program, the first thing I did was make a potato salad and eliminate every cultivar that is not abundantly fruitful from my breeding program. I figured that there was no sense trying to overcome fertility issues. Better to start with fertile plants.
Blossoms with abundant pollen shed it like crazy when jostled: So jostle 30 flowers and collect the pollen into a test tube, and use a brush to apply the pollen to other flowers. That greatly increases the diversity of the manual pollination without destroying perfectly good flowers. As far as I'm concerned, potatoes with clumpy pollen are not worth growing. And pay attention during potato bloom time: Learn which insects are visiting the flowers. Learn how to cultivate higher populations of those insects on your farm: Hover flies, bumble bees, tiny wasps, other insects that would require a macro lens to see clearly, etc.
Potato seeds are too small to be able to do any sort of precision seeding of a large area...
And they grow slowly. Direct seeding of potatoes doesn't work in my garden, because weeds grow much faster than potato seedlings. But it might work if the potatoes were seeded into weed free soil.
In my climate, I only get one chance at a potato seed crop. So I plant tubers before the last spring frost, and harvest them with the fall frost. It is very common for a potato seedling to produce berries during it's first growing season.
In my experience, it can take as little as 2-3 growing cycles to end up with a variety that is very well adapted to my garden. The first year eliminates things that are extremely unsuitable. The second year selects very suitable plants, and the third year is magical.
If I had any advice, it would be go ahead and start on a small manageable scale, forget about labor intensive attempts to trick the plant into blooming: instead start with potato plants that are known to be sexually promiscuous. And make sexual promiscuity one of the selection criteria for your mass selection program. You will be glad that you did. You can always make a triploid later on if sterility is important to developing a commercial cultivar.
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Post by mariol on Aug 4, 2012 19:10:56 GMT -8
thanks for all the replies, this is very helpful. i'd love to read about Tom Wagner's methodology to breed for resistant varieties. Is it mostly about preserving a large pool of genetic diversity?
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Post by rickmachado on Aug 5, 2012 8:15:19 GMT -8
I met Raoul Robinson some years back at a seed conference, and he did a slide show and presentation on horizontal resistance. It was very well put together and he was certainly very experienced and seemed to know a lot about it.
Everyone that has commented on this thread has something important to say, I feel. I suppose I can cherry pick this and that that I agree with, and other comments I feel, are not really relevant nor important to your purpose.
I don't have blight in my extremely dry area, so it's hard to breed for it. But if I did, I would have someone who does have it culture it, expand it, and somehow have it bottled and shipped to me. I would then set aside a toxic nursery ( something we should all have I think ) , and then spray it on every plant. I would weed out every plant that had no resistance to it.That would be my take on it.
I saw a slide show at the same conference on spinach breeding, and a guy in Texas used the same technique, he sprayed every plant, a big field, with whatever he was having problems with, maybe Phytophthera, and then proceeded to weed out every plant that was diseased. Very impressive.
I breed for heat and drought tolerance. Like others have said, make your work load as light as possible and as important as possible. Try not to veer off into dead ends. I keep a strong pool of diversity, like you said. I look for multiple genes that point to my end. I look for lots of berries, like Joseph said,and dump all else, no matter how much I like the finished tuber. I plant in the heat and harvest in the heat. I stress them by withholding water and nutrients. I plant 2, 3, sometimes 4 crops in a row in the same field and not fertilizing. I pay little attention to yield in the early years. Smaller leaves are helpful, less leaf mass for the sun to beat on. I crowd them. I push them to finish in less than 90 days. I am always looking for germaplasm that comes from hot area of the planet, although that is no sure thing. I taste them. And if I can make a smaller plant with a good yield, I will take it.
That's my take on it. I wish there were more people doing heat and drought work with tubers, but there really is only the fabulous Tom, Israel, and David Levy. They are the ones that I know about, and maybe a few others I don't know about. Tom has forgotten more than I will know in six lifetimes.
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Post by mariol on Aug 5, 2012 12:01:56 GMT -8
Thanks Rick, it's very interesting to hear your experience
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Post by mariol on Aug 11, 2012 10:07:29 GMT -8
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Post by rickmachado on Aug 13, 2012 6:53:36 GMT -8
Great article from Tom about potato genetics and disease. Thanks.
Interesting that he should mention the variety Leona, and it's resistance to blight . We grew it for the first time this year, and it set a bucketful of berries for us. But alas, no tubers, even after 120 days. No doubt another short day adaptation.
I was going to pull it, but after reading that article, I will wait until frost or pests kill it, and I might get a tuber or two.
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Post by Tom Wagner on Aug 14, 2012 7:05:23 GMT -8
Thanks, Mariol, for reminding me of my addressing the horizontal resistance issue some two years ago. No wonder I did not try to re-write that post!! I should continue where I left off. Regarding Leona: I have planted just weeks ago a yellow version of Leona (PI 660358). There are two accessions of LEONA available as tuber lines. I have in quotes the two lines below. I will have to go back and check my TPS of LEONA and the various crosses of it. Seems I have lots of the clones and TPS that are more like the second accession....red skin with yellow/red flesh. Hmmm...Oh, yes... PI 233118 = PASPUELA X LEONA. WRF 1782 - 233117 x 233118 HYBRID SEED Yes, good drought resistance via notes of 2006/2007. Lots of berries. Late maturing and late tuber set. Since I goodly part of my better late blight resistance derives through many generations of varieties going back to LEONA...I wonder...and suspect...my breeding lines are mostly from the yellow clone? LEONA is in the pedigree of Atzimba, Rosita, Tollocan, Maria, etc which are from the Mexican clone Note the following... Whenever there are conflicts due to an identical name but different clones....one must be careful on assigning a genetic trace. My guess is that the Mexican clone is better adapted to drought and heat and should be able to tuberize without a hitch here is the USA. The mystery continues...at least for me. The yellow potato below is from a Peru site peruviancuisinefortheworld.com/web/?p=1856
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Post by rickmachado on Aug 14, 2012 15:05:00 GMT -8
Tom, thanks for lineage and info of Leona and the clarification between the two clones.
I have the one from Ecuador, and I have it planted in two places. One plant has some sort of spider web trying to grow over it, trying to kill it. It has a red fungal like powder on the stems, it may not make it.
The other one looks healthy, but no tubers yet. I'll just wait it out as long as I can.
I have pulled all of Joe's tubers he left me, and was disappointed to see so many white./white varieties.
Some standouts, though, we Dobro and Bjorna, massive yields and size, even though early yields I try to stay neutral. Other were Picasso, Teena, and Chiloe Ancud, nice color, plant growth and general vigor.
I will post pictures as I go.
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Post by mariol on Aug 14, 2012 20:58:04 GMT -8
Thanks everyone. I did a presentation of principles of TPS and potato breeding to my teachers and 9 fellow gardening students and it was very well received. Works of Tom, Joseph, Raoul Robinson were mentioned alongside Niederhauser, Simmonds etc
The farm I am on is being hit with blight for the 2nd year in a row and after my presentation breeding is now being considered as a solution.
I'm a bit wondering how that would start... Maybe saving true seeds from our current commercial varieties (the ones that fruit), as well as getting a variety of seeds from Tom? And then seeing which ones work well, and making some crosses?
I'm also torn between keeping pedigrees like Tom does, and not keeping track like Joseph does. Seems like keeping pedigrees would help preserve genetic diversity and helps when sharing seeds with other farmers, so it seems important that some people like Tom do it. On the other side, just making mass crosses and creating genetically dynamic landraces seems like the way to go to create varieties that work well on a given farm. Any thoughts? Maybe doing both in parallel is the solution?
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