Updating Cassava

[mrg]

As discussed by an article from THE ECONOMIST ("Cassava Nova", 20 February 2016), the cassava plant -- AKA tapioca and manioc -- is of little economic importance in the developed world, but it feeds a half-billion Africans. Due to its unimportance in the developed world, it has not been the target of much crop research, but that's now changing. Chiedozie Egesi of the National Root Crops Research Institute in Umudike, Nigeria, who leads the NextGen Cassava project, says cassava is now getting a major overhaul.

 

Cassava is a starchy root, with its origins in South America. It was brought to Africa by the Portuguese from their colony in Brazil, but such strains as survived transplantation represent only a small range of the plant's genetic diversity. African agronomists would like to bring in other New World varieties, but most such imports fall prey to cassava mosaic disease -- a virus that does not exist in South America. Egesi and his colleagues are trying to deal with the sensitivity of imported cassava strains through a genomics-based breeding program.

 

They began with 6,128 different cassava specimens from all over Africa, and genotyped them using a technique named "SNP analysis" -- with the acronym standing for "single-nucleotide polymorphism", a place in the genome where a single genetic letter varies from strain to strain. They found more than 40,000 SNPs that they could use as markers for genetic variation.

 

Examining and testing full-grown plants from the collection for desirable characteristics AKA "phenotypes", allowed Egesi and his team to find correlations between particular patterns of SNPs and particular phenotypes. They then picked out 100 specimens with especially promising SNP patterns and crossed them, to produce nearly 10,000 hybrids. They grew these, checked the SNP patterns of the offspring to see which their computer model predicted would have the desired characteristic -- in this case, resistance to cassava mosaic virus being at the top of the list -- picked once again the 100 most promising, and repeated the process.

 

They are now in the third cycle of the procedure, each generation of plants requiring a year to raise and process, and judge that one more cycle will be needed to get to the desired level of resistance. Furthermore, there's nothing to prevent other properties from being enhanced in parallel. Egesi believes that SNP-based breeding will double cassava yields from their average value of about 10 tonnes a hectare, as well as increase the amount of starch in the plant's root, increasing its nutritional and economic value. He also hopes to improve the plant's resistance to other plant pathogens, including brown-streak virus and bacteria blight.

 

Along with methodical breeding, Egesi wants to improve monitoring of crop samples. The project is therefore experimenting with hand-held infrared spectrometers that need only be held up to the cut surface of a cassava root in order to measure its levels of chemicals such as beta carotene, a precursor of vitamin A. Egesi believes that modern agro-science promises to elevate cassava as a global crop, by improving the yield and quality of flour and starch made from cassava. Considering that most African cassava farmers are women, a more salable cassava would mean more money for family budgets in some of the world's poorest countries.

 

ED: It is interesting to note that Egesi and his team did not use genetic modification (GM) in their cassava work -- but they did use genetic analysis, notably using a computer model to determine which sets of SNPs were most useful for their purposes. Of course, that leads to the question of if, given an optimized set of SNPs provided by the model, it might be most efficient to build a GM cassava plant based on that set. The interesting aspect is: would it even be officially judged a GM plant? No -- it would simply be a collection of genes from a range of different cassava plants, and would incorporate no genes from other organisms.

 

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This is an older article that I just cleaned up and now put into my personal notes.  It is not a copy of THE ECONOMIST article, instead being considerably condensed.  Any objections to me posting this, let me know.   Cheers -- MrG (Greg Goebel)

[exchemist]

As discussed by an article from THE ECONOMIST ("Cassava Nova", 20 February 2016), the cassava plant -- AKA tapioca and manioc -- is of little economic importance in the developed world, but it feeds a half-billion Africans. Due to its unimportance in the developed world, it has not been the target of much crop research, but that's now changing. Chiedozie Egesi of the National Root Crops Research Institute in Umudike, Nigeria, who leads the NextGen Cassava project, says cassava is now getting a major overhaul.

 

Cassava is a starchy root, with its origins in South America. 

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I never knew what tapioca, a.k.a. the "frogspawn" we used to get at school, came from, so thanks for this. I thought chocolate tapioca pudding was quite good but a lot of school kids hated it. I think it has died out now.

 

But evidently cassava remains important in Africa. 

Edited May 23, 2017 by exchemist

[mrg]

But evidently cassava remains important in Africa. 

 

I get tapioca pudding from the supermarket every now and then -- prefer it when it gets a bit rubbery.

 

Bananas -- of all stripes, like plantains, not just the familiar Cavendish -- are also a big crop in Africa, as is sorghum.  Sorghum is used for broomstraw, bread, beer ... handy stuff, and not too fussy about growing conditions.  Grown a bit here in Colorado, in the east of the state; don't know what the commercial use in the States is.

[JMJones0424]

Sorghum is used for broomstraw, bread, beer ... handy stuff, and not too fussy about growing conditions.  Grown a bit here in Colorado, in the east of the state; don't know what the commercial use in the States is.

In Texas, especially West Texas where rainfall is sporadic and soils are not ideal, sorghum is a staple crop grown for livestock feed.  I do not grow crops for livestock, but my basic understanding is that if corn is not profitable in your area, then sorghum can be.  Of course, this rule of thumb misses soy bean, alfalfa, and other livestock feeds that are common, so maybe this isn't a good rule of thumb at all.  Sorghum was an important source of sugar in areas far from climates that could support sugar cane and beets, but I think human consumption of sorghum is a novelty in the US now.  While those in Northern US and Canada may know of the importance of Maple sap as a sugar source, my parents used sorghum as their syrup.

[mrg]

Very interesting, JMJ, thanks for the feedback.

 

West Texas?  I went down to Midessa for the Commemorative Air Force airshow some years back:  "Sure is flat around here!   And why do they have yardsticks in the hollows in the roads?"  To keep from being drowned, doofus.

[JMJones0424]

They began with 6,128 different cassava specimens from all over Africa, and genotyped them using a technique named "SNP analysis" -- with the acronym standing for "single-nucleotide polymorphism", a place in the genome where a single genetic letter varies from strain to strain. They found more than 40,000 SNPs that they could use as markers for genetic variation.

 

Examining and testing full-grown plants from the collection for desirable characteristics AKA "phenotypes", allowed Egesi and his team to find correlations between particular patterns of SNPs and particular phenotypes. They then picked out 100 specimens with especially promising SNP patterns and crossed them, to produce nearly 10,000 hybrids. They grew these, checked the SNP patterns of the offspring to see which their computer model predicted would have the desired characteristic -- in this case, resistance to cassava mosaic virus being at the top of the list -- picked once again the 100 most promising, and repeated the process.

I'm not sure that this breeding program is remarkable other than that it is more well-informed than those that existed before for other species.  Of course, informed crossing is beneficial.  It is not necessarily the case that this will produce a line that contains a desired disease resistance while still maintaining other useful qualities of the crop, especially if the desired resistance relies on multiple DNA differences.  It seems clear to me that constructing a cassava plant that has exactly the DNA characteristics that are desired is preferable, but that doesn't mean that this route is the most likely to produce a strain that is widely accepted.

 

I would find it interesting to see how anti-GMO activists would argue against a GM cassava that contained 100% cassava genetics.  

[mrg]

It's mostly remarkable to the extent that cassava has been kind of neglected by plant breeders, since it's not a staple crop in developed countries.   I do think the software that they used to statistically link SNPs to desired traits was interesting.

 

In Europe, any sort of gene-splicing is legally regarded as GM.  In the US, the definitions are looser.  For example, vanillin produced by GM yeasts is not regarded as a GM product.   Why should it be?   It's the same molecule,no matter how it was derived.  Also, since the vanillin wouldn't be chemically synthesized, the yeast product would be legitimately labeled as "natural".   Gotta love it!

Edited May 27, 2017 by mrg