He Liping, chief reporter of The Paper
The potato is the world's most important tuber-based food crop, with 1.3 billion people feeding on potatoes, the third largest staple food in the world and the fourth largest staple food in China. In recent years, Scientists in China have been working on a "Good Potato Project."
On the evening of June 24, Beijing time, the top academic journal Cell published a study completed by Huang Sanwen and others at the Shenzhen Institute of Agricultural Genomics of the Chinese Academy of Agricultural Sciences (hereinafter referred to as the "Institute of Genomes") online, entitled "Genome design of hybrid potatoes". The paper reports on the research team's research results in the field of hybrid potato breeding, which is a milestone breakthrough since the implementation of the "Excellent Potato Project".
Zhang Chunzhi, the first author of the paper and a researcher at the Institute of Genomics, told the media including the surging news (www.thepaper.cn) reporter that the team has cultivated the first generation of high purity (>99%) diploid potato inbred line and hybrid potato strain "Youshu No. 1". The community test showed that the yield of "Youshu No. 1" was close to 3 tons/mu, which had significant yield heterosis advantages. At the same time, "Youshu No. 1" has the characteristics of high dry matter content and high carotenoid content, and the cooking quality is good.
It is worth noting that for 99% of the purity, Huang Sanwen believes that it is not easy, which is achieved under the continuous progress of technology. "For seed-propagated rice, corn, wheat, 100% homogeneity is not a problem, but it is difficult for potatoes." Thousands of years ago, in the Andes Mountains of South America, potatoes were domesticated by farmers and have been propagated in potato chunks to this day, "long-term vegetative reproduction makes the potato genome highly hybrid, turning this highly heterozygous vegetative propagation species into seed propagation species is a major scientific challenge." ”
The success of the "Youshu No. 1" breeding proves the feasibility of the hybrid potato breeding system of Huang Sanwen's team, "which can make potato breeding enter a rapid iterative process." Zhang Chunzhi said.
It is worth mentioning that in the field of hybrid breeding, corn and rice are the "predecessors" of potatoes. Just last year, on November 8, the "Youshu Project" team received guidance from Academician Yuan Longping. Academician Yuan Longping gave a high evaluation to the potato hybrid seed propagation technology at that time, believing that replacing potato block propagation with hybrid seeds can effectively solve major potato industry problems. Academician Yuan Longping also specially wrote an inscription for the "Excellent Potato Project": "Potato hybrid seed propagation technology is a subversive innovation that will bring about a green revolution in potatoes."
The paper published this time also paid special tribute to Academician Yuan Longping in the acknowledgment, thanking him for his guidance and encouragement of the "Excellent Potato Plan".
The potato industry needs a "green revolution"
Founded in 1952, the multinational restaurant chain KFC sells a large number of Fries from russet Burbank, an American fries processing variety, but The history of Russet Burbank actually predates KFC's founding by half a century and is still the largest potato variety in the United States.
A similar situation is also observed in China, where the largest cultivar ,Kexin No. 1," was bred in 1958 and has been cultivated for more than 60 years.
A variety can be used for more than a hundred years, not because the variety is perfect. "It's because it's hard to breed, and breeders haven't been able to breed a variety to replace this for so many years, so that's the problem of breeding difficulty." Zhang Chunzhi said.
Unlike cereal-based food crops, cultivated potatoes are homologous tetraploid species that rely on potato chunks for asexual reproduction. Its genome is highly heterozygous and genetic analysis is complex, resulting in a slow process of genetic improvement of potatoes, with breeding cycles typically 10-15 years.
This is the first structural obstacle to the potato industry, and the second is the low reproductive coefficient of potato blocks, high storage and transportation costs, and easy to carry diseases and insect pests. "After we plant 1 potato, we can get 10 potatoes when we harvest, that is, about 1/10 of them cannot be used as food or vegetables, and we have to stay and then use them as seed potatoes."
Zhang Chunzhi further mentioned that potato seed potato seeds need 200 kilograms per mu of land, "one is that it is expensive; the second is that seed potatoes can not be produced in every place, if you want to plant potatoes in Guangdong, we need to transfer seed potatoes from the north, the cost of storage and transportation is very high; and in the process of storage and transportation, it is easy to be infected with various diseases and insect pests, and the loss is relatively large." She gives a statistic that about 13 percent of all potatoes harvested are directly depleted, "which is a huge waste." ”
In order to completely solve the above problems faced by the potato industry, with the support of the Ministry of Agriculture and Rural Affairs, the Chinese Academy of Agricultural Sciences and Shenzhen Municipality, Huang Sanwen, together with Yunnan Normal University and other domestic and foreign advantageous units, launched the "Excellent Potato Plan". That is, the theory and methodology of "genome design" are used to breed hybrid potatoes, double sports species are used instead of quadruple sports seeds, and hybrid seed propagation is used to replace potato block propagation.
The research team concluded that this is a new underlying technology for potato breeding and reproduction, and a disruptive innovation in the potato industry.
Zhang Chunzhi showed the seeds of "Youshu No. 1" at the scene, which is only 1/6 of the weight of sesame seeds, if you plant an acre of land, the original seed potato needs 200 kg, and now the seed is only two grams. "This makes the transportation very convenient, a courier solves, and the seeds are clean and basically do not spread pests and diseases." If we can transform the potato industry from the current tetraploid potato block propagation system to a diploid seed model, it will be equivalent to a subversive innovation for the industry and can completely solve the problems facing our current industry. Zhang Chunzhi stressed.
The research team also pointed out that in the diploid seed model, we can use the southern winter idle field to grow potatoes, "which can effectively alleviate the pressure on national food security, especially to fill the gap in feed grain." ”
According to reports, the "Good Potato Plan" has formulated three "five-year plans." During the "Thirteenth Five-Year Plan" period, the scientific and technical problems involved in the construction of diploid potato inbred lines were solved, and the first conceptual variety "Youshu No. 1" was cultivated; during the "Fourteenth Five-Year Plan" period, the key problems involved in the diploid potato industry were solved, excellent hybrid combinations were selected and bred, and small-scale promotion began; during the "Fifteenth Five-Year Plan" period, a series of new diploid potato hybrid varieties that met market demand were cultivated, and large-scale demonstration and promotion began.
Overcoming two key obstacles to the successful selection of "Sweet Potato No. 1"
In fact, on a global scale, potato doubles have become a research hotspot. Scientists from the Netherlands, China and the United States have also called for research and breeding of potato diploids in recent years.
However, two key obstacles need to be overcome to achieve diploid hybrid potato breeding: incompatibility and decline in inbredness.
Inbred incompatibility refers to the phenomenon that plants do not produce seeds after pollination from flowers. To cultivate inbred lines, it is first necessary to solve the problem of incompatibility. In the previous study of Huang Sanwen's team, they knocked out the S-RNase gene that controlled potato inbred incompatibility through genome editing technology, screened the natural mutants of S-RNase, and cloned the inbred affinity gene from wild species, completely solving the problem of inbred incompatibility.
Self-inbred decline refers to the decline of physiological functions of organisms after self-inbringing, which is manifested as a decrease in vitality, a decrease in resistance, and a decrease in yield. The research team pointed out that potatoes, as heterogeneous crops, accumulate a large number of hidden harmful mutations in the long-term asexual reproduction process, and once self-inbred, the adverse effects of harmful mutations will appear, resulting in self-inbred decline.
Unlike inbred incompatibility, which is controlled by a few genes, inbred recession involves many genes and is more difficult to overcome. In terms of research in the same field, Dutch scientists announced the progress of hybrid potatoes in 2011, but after 10 years, they still face the problem of low purity of inbred lines, limiting large-scale commercial promotion, mainly because they cannot overcome the problem of self-inbred recession.
In view of this problem, Huang Sanwen's team systematically analyzed the genetic basis of potato inbred decline in the early stage. They found that the mosaic of harmful mutations that cause inbred decline was distributed across two sets of potato genomes and could not be completely phased out by recombination. "One implication to us is that breeders can't weed out every mutation, and we have to be able to tolerate some degree of harmful mutation." Zhang Chunzhi said.
However, the research team also found that harmful mutations in different potatoes have individual differences, and the effects of harmful mutations in hybrids can be masked by hybridizing on inbred lines with large differences in genetic background. "One of the implications for us is that we can choose two materials with relatively large differences, that is, two materials with strong complementarity to hybridize."
These studies also show that breeding strategies based on phenotypic selection are difficult to overcome the problem of self-inbringing decline, and must be designed and bred with the help of genomic big data to effectively eliminate harmful mutations.
Schematic of the genome design of potato hybrid breeding.
On this basis, Huang Sanwen's team used the advantages in genomics research to use genomic big data for breeding decisions and established a hybrid potato genome design breeding process, which mainly includes four links.
The first step is the selection of the starting material for breeding inbred lines, the criteria for selection are the low genomic heterozygosity of the starting material and the small number of harmful mutations; the second step is the genetic analysis of the inbred population of the starting material, mainly based on the partial separation analysis and phenotypic evaluation of the whole genome, to determine the distribution of large-effect harmful alleles and excellent alleles in the genome; the third step is the selection of inbred lines, eliminating harmful mutations with large effects according to the prospect and background, and polymerizing excellent alleles. In particular, it is necessary to break the linkage between large-effect harmful mutations and excellent alleles; the last step is the selection of hybrids, according to the results of genome sequencing, select inbred lines with relatively high genome complementarity for hybridization, and obtain hybrids with significant heterosis.
Using the above process, Huang Sanwen's team has cultivated the first generation of high purity (>99%) diploid potato inbred line and hybrid potato strain "Youshu No. 1". Zhang Chunzhi introduced that the community test conducted this year showed that the yield of "Youshu No. 1" has approached 3 tons / mu, "this has been similar to the current mainstream tetraploid yield, indicating that our hybrid has significant yield potential." At the same time, "Youshu No. 1" has the characteristics of high dry matter content and high carotenoid content, and the cooking quality is good.
Hybrids have a strong hybrid advantage.
Huang Sanwen also stressed that "Youshu No. 1" will continue to iterate in the future. "We also need to improve several traits that improve it, including disease resistance, including adaptability to the photoperiod." At present, we can only cultivate in the south, can we cultivate varieties that can be cultivated in the north? All of these further improvements, he argues, require genomic design to speed up the process.
Fortunately, if you use quadruple sports seeds, the cycle is about 10-15 years, but with seed breeding, the cycle is 3-5 years, only 1/3 of the original. "The shorter the breeding cycle, the more iterates, and the breeding is iterative, that is, each round of breeding is better than the previous one, which is different from the tetraploidy, which is very random." Huang Sanwen said.
Thesis link: https://doi.org/10.1016/j.cell.2021.06.006
Editor-in-Charge: Li Yuequn
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