LIFE SCIENCE

After coming to China for more than 60 years, kale-type rapeseed has practiced “half-winter” skills


Rape flower field Courtesy of the Oilseeds Institute of the Chinese Academy of Agricultural Sciences

Rape flower Courtesy of oil feeder of the Chinese Academy of Agricultural Sciences

The growing period is only about 200 days, and the yield of rapeseed per mu reaches 130 kg, forming a seamless connection with rice… This is the cabbage type rape that came to China in the mid-1950s.

After more than 60 years of continuous improvement, it has adapted to the climate environment of All Corners of China, not only mastered the new skills of “half-winter”, but also gradually increased its output.

Recently, Nature Genetics published online the basic genomics research results of Chinese scientists on the genetic improvement of rapeseed, revealing the molecular basis of yield improvement and adaptive improvement in the breeding process, and providing an important theoretical basis and rich genetic resources for high-yield rapeseed breeding.

A classic case from “winter sex” to “half winter sex”

“Today, the cabbage-type rapeseed grown in a large area of China can produce up to 130 kilograms of rapeseed per mu.” Wu Xiaoming, the corresponding author of the paper and a researcher at the Oilseed Research Institute of the Chinese Academy of Agricultural Sciences, said in an interview with China Science News that however, more than 60 years ago, rapeseed oil was still a rarity on the market, because the traditionally grown cabbage and mustard rapeseed in China had low yields and weak resistance. But they have a short growth period and wide adaptability, forming a perfect crop rotation system with crops such as rice.

As a result, the high-yielding and highly resistant kale-type rapeseed (also known as rapeseed) of European origin was introduced to China. “But its growth period is long, and it is not suitable for rice-oil rotation.” Wu Xiaoming said that the newcomers to the cabbage type canola are not satisfied with the water and soil in China.

Therefore, breeders continue to improve cabbage-type rape through breeding channels such as interspecific hybridization and mutagenesis. After more than 60 years of efforts, the growth period of cabbage rape has been shortened from more than 300 days to about 200 days; the yield level has increased from more than 30 kg/mu in the 1950s to more than 130 kg/mu; and the quality has been improved from “high canuric acid and high thioside” to “low erucic acid and low thioside”.

As a result, China’s unique and new kale type rape “half-winter” ecological type suitable for China’s “rice oil” rotation system has been formed, which has made important contributions to improving the supply level and quality of domestic vegetable oil.

The so-called semi-winter rapeseed is sown at the end of September and the beginning of October every year before the Harvest of the following year, and the growth period is about 200 days; in the european hometown, the winter rapeseed is generally sown in the autumn and matures in the summer of the following year, and the whole growth period is long, up to about 330 days.

Rape carob Courtesy of oilseeds of the Chinese Academy of Agricultural Sciences

Wu Xiaoming said that through modern breeding and improvement, kale-type rapeseed has been successfully domesticated from “winter nature” to “semi-winter nature”, basically replacing the cabbage type and mustard type rape planted in China, which is widely promoted and applied in China, with a perennial promotion area of more than 100 million mu, becoming a classic case of changing crops to adapt to the new environment through modern breeding.

However, “the use of traditional breeding methods to improve the quality and yield of kale-type rapeseed has entered a bottleneck period.” Wu Xiaoming said that if you want to continue to break the bottleneck of production, you must summarize the historical experience of success, find out the genetic mysteries hidden under the increase in production, and then seek new paths and more efficient technologies.

However, the molecular basis for the increase in yield and adaptive improvement of “semi-winter” rapeseed is not clear.

Improvement: “Survive” and then “Live Well”

In order to reveal the molecular basis of rapeseed yield and adaptive improvement, the team selected 418 global cabbage germplasm resources with ecological type, geographical origin and breeding period representative, and systematically identified 56 traits closely related to yield formation in multiple environments.

Tian Shilin, the corresponding author of the paper and chief scientist of the R&D and Cooperation Center of Nuohe Zhiyuan, introduced that through resequencing, they carried out genome-wide genotype identification, and based on the large-scale phenotype group and genomic variation data obtained, the genetic analysis of the excellent germplasm and important traits of cabbage-type rapeseed was systematically carried out.

The results showed that “semi-winter” rapeseed and “winter” and “spring” rapeseed could not be clearly divided into different taxa at the genomic level.

Wu Xiaoming said that this shows that in the modern breeding process, the overall level of the kale rapeseed genome has not changed dramatically. The formation of “half-winter” high-yield kale type rapeseed is the result of the selection and aggregation of multiple key genes, and this process mainly involves two stages: environmental adaptation selection and high-yield and high-quality selection.

At that time, when breeding kale-type rapeseed, breeders first tried to adapt it to China’s natural environment, and then went to improve its yield. “We proved with genes that have been selected at different times that breeders do exactly that. They believe from experience that cabbage canola must first be able to grow, develop and flower normally in China, otherwise it will not be able to talk about production. Survive first, and then you can live well. Wu Xiaoming said.

Tian Shilin told China Science News that they found that breeders initially selected 4 types of genes related to environmental adaptability, including: biological clock rhythm regulation genes and flowering genes were strongly selected, so that the growth and development rhythm of “semi-winter” rapeseed coincided with the law of light temperature change in China, so as to effectively use light temperature resources; hormone-related genes were selected, so that the angle of leaves in the overwintering period changed from creeping or semi-upright, and creeping leaves were suitable for resisting the cold climate of Europe. Upright leaves are more suitable for increasing the photosynthetic leaf area in China’s relatively mild winter and accumulating more photosynthetic products in a short period of time; genes related to chlorophyll synthesis and leaf aging are also selected, and the chlorophyll content during the overwintering period is significantly lower than that of “winter” rapeseed, which is conducive to improving the winter photosynthetic efficiency; cold resistance related genes are selected, which is more suitable for China’s relatively mild winter. These adaptive improvements ensure yield increases in multiple directions.

The second phase focuses on the selection of high-yielding and high-quality genes. 2 plant type (plant height) genes and 14 yield traits (1,000 grain weight, grains per corner, number of main inflorescence carobs, whole plant siliques, etc.) genes were selected, resulting in plant height, 1,000 grain weight and grain per corner increasing, thereby increasing yield levels; some allele frequencies related to yield and quality gradually increased, such as genes that control erucic acid content, genes that regulate thioside content, and the selection of these key genes is consistent with China’s “double low” high-quality and high-yield breeding goals.

Using big data in genomics, scientists will accurately identify what deficiencies in the breeding process can be improved, for example, which yield-related genes have not yet been polymerized in place and have not been used well, thus laying the foundation for future breeding and production practices. “And previous breeders couldn’t do that.”

Regulatory networks that analyze yield traits

Through large-scale genome association analysis, the team identified 628 genetic loci that controlled 56 important traits in 6 categories (growth period, plant type, morphology, disease resistance and stress resistance, yield composition), and clarified the genomic hotspots of the genetic traits of rapeseed for the first time.

“The next job is to get those partially perfect varieties from single or multiple champions to all-around champions.” Wu Xiaoming said that although there is an idea, it does not mean that it has been completed, it is just the first step.

In crops, many important agronomic traits are often controlled by multiple gene loci, and the results show that there are interactions between the 56 traits, suggesting that there may be a co-regulatory network of genetics between them.

“Because the trait of 1,000 grain weight is the highest and most stable. So we focused on the genes associated with a thousand grain weights. Wu Xiaoming explained that the higher the inheritance power, the greater the influence of genes on traits, and the less affected by environmental factors. The weight of a thousand grains is one of the important genes that determine the yield of rapeseed.

The study unearthed a total of 100 sites associated with the 1,000-particle weight, which form a regulatory network. Therefore, in order to regulate yield traits, it may be necessary to adjust multiple genes.

At the same time, different regulatory networks, such as the network that regulates the strain type and the network that regulates the granular weight, sometimes overlap or intersect, or have mutual correlations, or there is an upstream and downstream relationship.

In the past, scientists may only see the function of one or two genes; later, they may have to parse the relationship between the network and the network, or even layer by layer, in order to increase production more effectively.

Reviewers believe that this study reveals the genetic basis for a large number of important agronomic traits in rapeseed through genome-wide association analysis, and the work of this research is very commendable because the phenotypes of these traits have been collected for many years in multiple environmental locations. The large number of genetic resources unearthed by this study is very valuable and impressive, and will make a clear contribution to the study of cabbage-type rapeseed, which will greatly help to clarify the genetic characteristics of cabbage-type rapeseed.

Wu Xiaoming believes that in order to cope with the impact of global climate change on crop production, the rapid selection and breeding of new varieties of crops suitable for new climatic conditions has become a common issue faced by all crops. The successful analysis of the classic case of cabbage yield and adaptive improvement from the genetic basis not only lays a theoretical foundation for further improving the yield of rapeseed, but also provides a new idea for the rapid improvement of new varieties of crops that adapt to new environments in the genomic era. (Source: China Science Daily Li Chen)

Related paper information:https://doi.org/10.1038/s41588-022-01055-6



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