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Post by gilbert on Dec 22, 2016 16:38:09 GMT -5
From Joseph on the Tomatoville forums.
This is interesting, considering that there are probably more varieties of tomato then of any other garden crop. So are all those tomato varieties just sharing a tiny pool of genes? It would make sense that they are all inbred, considering how fragile they are. But I'm just wondering about other vegetables with much less (seeming) diversity. Do they make up for it by having greater inter variety diversity?
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Post by philagardener on Dec 22, 2016 18:49:23 GMT -5
In 1970 15% of the US hybrid corn crop (estimated value at the time of $1 Billion USD) was lost to an nationwide outbreak of Southern corn leaf blight. The problem was traced to big ag's reliance on a single elite male-sterile cytoplasm to make hybrid lines. Losses could have run higher (as it was, some states lost a full half of their crop) since 90% of the entire nation's corn planting that year was susceptible to the virus. en.wikipedia.org/wiki/Southern_corn_leaf_blightLuckily, by quickly turning to other elite lines and genetic diversity on hand, a crisis was averted, but it shows how a narrow genetic base can imperil a crop (and the humans that rely on it). |
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Post by steev on Dec 22, 2016 19:47:16 GMT -5
Commercial bananas are another example of the potential peril of concentrating on a very narrow genome.
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Post by blueadzuki on Dec 23, 2016 8:09:08 GMT -5
So is Chocolate (or why they keep saying that in a few years chocolate will be so rare only the rich can afford it)
Probably the ULTIMATE genetic bottleneck in commercial fruit is the Mangosteen (though that one really isn't humanities fault) Due to a tendency towards parthenocarpic seed production and those seeds ALWAYS outgrowing the sexually produced ones, all Mangosteen trees on earth have IDENTICAL genotypes (barring, I suppose the odd random mutation). They are, in essence clones of each other. So one disease and the whole SPECIES goes extinct. Being natural there probably isn't much we can do about via breeding, but I sometimes hope that, as modern tech gets cheaper and more available to the developing world, some South East Asian agricultural scientist will plop some mangosteen tissue or seeds in some sort of mutagen (be it chemical or radiation based) cultivate the results (via tissue culture or embryo rescue) and see what he or she can do about making a little broadening of the base.
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Post by walt on Dec 23, 2016 16:07:19 GMT -5
From Joseph on the Tomatoville forums. This is interesting, considering that there are probably more varieties of tomato then of any other garden crop. So are all those tomato varieties just sharing a tiny pool of genes? It would make sense that they are all inbred, considering how fragile they are. But I'm just wondering about other vegetables with much less (seeming) diversity. Do they make up for it by having greater inter variety diversity? Most, almost all, tomato varieties are totally inbred. The ONLY exceptions are what is being called landraces here. Tomatoes are natural selfers, and only one fruit can provide enough seeds for an average garden. So every gardener saving only one variety of tomato is effectively only saving one set of genes. But that doesn't explain why worldwide, nearly, there is so little genetic variation. So a little history. Way back, tomatoes were domesticated in the Andes Mountains. Go back to the Andes and you'll find plenty of variation, for the Andes. But not neccessarily variaton useful for other places. Sure some genes for resistance to various diseases and insects and nematodes, etc. Variation in flavor, growth habit, etc. That is where you'll find variation but not always useful in another environment. So about 1,000 years ago, maybe more, someone took a tomato, or a very few tomatoes to Mexico. not much variation shows up there compared to the Andes but a lot compared to the rest of the world. Why? Because the Spanish took a few (or one) variety to Europe. It caught on there eventually, and people selected mutants for smaller, larger, colors, flavors etc. But mostly tomatoes from those in Europe are all but clones of each other, except for those desirable mutants that were selected for. From Europe, tomatoes were taken to Asia and to North America other than Mexico and southwestern USA. So that is how tomatoes became one of the world's most inbred crops. Africa may have gotten different types from Mexico via the slave trade. I don't know. Niger, where I was a tomato breeder back in 1978-81, didn't have tomatoes until WWII. But along the coast, who knows? If you want genetic variation, go to Native Seeds/Search and you might get more variation than all of Seed Savers Exchange, other than those that got to SSE from South America or Latin America or the desert southwest USA. GRIN or Tomato Genetics Coop, would have novel genes from Mexico or S. America. You might think about shopping there. |
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Post by gilbert on Dec 23, 2016 16:15:27 GMT -5
Thanks Everyone! That is interesting. It sure explains why tomatoes are so finicky and disease prone. So SSE's thousands of tomatoes make even less sense, then.
It is interesting to see all these crops that have such a narrow genetic base. One of the really exciting things about this site is all the folks working on restoring diversity to crops such as garlic or sweet potatoes.
Do you think anything could be done to help out bananas?
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Post by walt on Dec 23, 2016 16:42:30 GMT -5
Back in 1977, I did a term paper on banana breeding. Back then, the gene base of bananas was being broadened by breeding at the diploid level then crossing improved diploids with the triploid Gros Micheal and getting tetraploids, which could also be inter-bred. Then the improved diploids and the improved tetraploids could be intercrossed to get more sterile triploids. The reason for needing sterile cultivars was that banana seeds can break a tooth if you bite down on it.
People would be hired to sit all day squishing bananas to find a seed, maybe one in 100 bananas. But some people will work really cheap, so that didn't keep the crosses from being worthwhile. I mean un-economical.
But the problem with bananas is that there are a couple of diseases spreading for which there is no resistance in the whole world-wide gene pool, wild and everything.
So the only hope presented by the huge banana companies is gene splicing. I'm not entirely against that, but I know some people who will give up bananas when those get on the market.
Another solution is to only grow bananas in small-holdings that are relatively isolated and effectively in quarantine. But that would be a lot of trouble and hurt the stock price of banana companies. So GMOs it is, right?
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Post by gilbert on Dec 23, 2016 17:32:00 GMT -5
No resistance even in the wild? That's tough. Do you suppose once these diseases sweep through some will evolve or emerge? Or will the bananas be too slow? I'm hoping to put some bananas in a greenhouse here in Denver. Maybe once the disease sweeps through, and the big companies switch over to GMOs and own all the fertile breeding stock remaining, I'll be able to give bananas back to the world!  |
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Post by Joseph Lofthouse on Dec 23, 2016 18:22:46 GMT -5
In addition to two bottlenecks, I think that another reason that tomatoes became so inbred is the Heirloom Seed Movement. Because people started selecting for inbreeding tomato varieties, and against "impure" tomato varieties that are more prone to out-crossing. There seems to be an attitude among seed savers that inbred tomato ==> good, and promiscuous tomato ==> bad.
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Post by philagardener on Dec 23, 2016 19:03:10 GMT -5
Do you think anything could be done to help out bananas? is a very informative site hosted by Wageningen University in the Netherlands. There are efforts to find resistant germplasm and surmount the breeding barrier, but the fungus (actually there are several strains) is spreading very quickly. |
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