How are high-quality seeds cultivated?
High-quality seeds are important means of production for ensuring high and stable corn yields. Their production is a systematic project, the result of perfect execution of all processes including parental seed propagation, production technology research, field seed production, seed processing, and quality monitoring throughout. Understanding the internationally accepted seed production process and mastering every link of key production technologies means the one who knows and acts first wins.
Parental seeds:
Determining the purity of hybrids
When breeding hybrids, the female parent and male parent come from two independent heterotic groups. The female parent group has advantages such as short plants, large ears, uniform silking, smooth silking, and good overall resistance, while the male parent group has advantages such as tall plants, large pollen volume, and a long pollen-shedding period. Such parents inherently possess the advantages of easy seed production and high yield.
When a hybrid performs excellently and obtains market approval, the breeder has only a small amount of parental seeds on hand. These seeds are propagated and identified ear-row by ear-row, and uniform ear rows are selected for mixed harvest, producing breeder seeds. Breeder seeds are the parental source for future seed production and the initial determining factor of seed purity.
After breeder seeds are handed over to the production department, they undergo 1 generation of expanded propagation to obtain pre-basic seeds, which can be stored in cold storage for many years. Each year the production department takes out a portion of the pre-basic seeds, and after 2 generations of isolated propagation, reaching the seed quantity needed for field seed production, hybrid seed production can proceed. Quality control of pre-basic seeds is very critical, largely determining the purity of hybrids, so the purity, cleanliness, and germination rate of each batch of pre-basic seeds must be strictly tested.
Production research:
Efficiently producing high-quality seeds
Before starting field seed production, scientists in the seed production department must conduct seed production research, the purpose of which is to answer “how to efficiently produce high-quality seeds at a designated seed production base.” This kind of research begins before the hybrid is launched on the market. For domestic seed companies, the best time to start is from the first year of regional trials, and preferably at the future seed production base. Before large-scale seed production, seed production research must be conducted for at least 2 to 3 seasons.
This research is divided into several parts. First, the seed production suitability of the parents, which means observing and recording the development of tassels and ears, the flowering period gap, and yield traits of the parents under the seed production environment. Only combinations with high yield, low risk, and low seed production cost will be approved for market launch and further seed production research. Second, seed production technology research. This part of the work mainly involves gaining a detailed understanding of a variety's parental characteristics, traits, flowering period, optimal sowing time window, and responses to temperature, light, water, and other factors, with the purpose of adjusting the sowing dates of the parents to ensure flowering synchronization, exploring the row ratio of parents to ensure yield, and determining high-yield planting density and management models. Third, further optimization of seed production technology, studying how to further increase yield and reduce costs by improving various agronomic techniques.
Field seed production:
Isolation and detasseling, neither can be omitted
After mastering a sufficient quantity of parents and seed production technology, field seed production can be arranged. The key technical links at this stage are isolation, detasseling, and cultivation management.
Isolation is to reduce contamination of the seed production field by foreign pollen and ensure seed purity. The internationally required isolation distance for corn seed production is 300 m, and international seed companies can strictly select, plan, and plant seed production fields according to this standard.
Detasseling is the removal of the tassels of the female parent, ensuring that only the male parent can shed pollen in the seed production field to produce hybrid seeds. The quality of this work depends on the size of the area managed by the field technician, their sense of responsibility, and their management ability. In recent years, high-power intelligent detasseling machines have developed rapidly in Xinjiang. Detasseling machines can operate 12 to 16 rows at the same time, with infrared detectors installed on each detasseling mechanical hand to accurately determine the height of corn tassels. After receiving information on tassel height, the detasseling machine immediately adjusts the position of the detasseling mechanical hands, thereby achieving accurate detasseling without excessively damaging the male parent plants.
Male sterility technology:
The core competitiveness of seed companies
Field detasseling during corn seed production is time-consuming and labor-intensive, and incomplete or untimely detasseling can affect seed purity. Therefore, developing new male sterility technology is of great value to seed companies. After years of research, the American company Pioneer launched a new patented seed production technology, SPT. Traditional corn male sterile lines are cytoplasmic male sterile lines (CMS), and the commonly used T-CMS is highly susceptible to southern corn leaf blight and carries great risk. In the new SPT technology, sterility is controlled by nuclear genes, and the core of the technology is a transgenic maintainer line. This maintainer line contains a fertility gene, a sterility gene, a pollen lethality gene, and a fluorescent marker gene from goldfish, and can produce two types of pollen: one fertile and one sterile. After selfing, the maintainer line produces sterile lines and maintainer lines. The maintainer line carries the fluorescent marker gene and appears red, while the sterile line is normal yellow or light yellow. After screening by a specially designed color sorter, the two types of seeds can be distinguished. The greatest advantage of this technology is that because the sterile line is an ordinary nuclear sterile line containing no transgenic components, the hybrid produced after crossing with a normal non-transgenic restorer line is non-transgenic seed. Therefore, SPT technology is a method of using transgenic technology to produce non-transgenic seeds (of course, the technology can also be used to produce transgenic seeds). Another advantage of SPT technology is the protection of germplasm resources. At the seed production base there are only restorer lines and sterile lines, but no core maintainer line, which can effectively protect the variety's female parental inbred line from being easily lost.
Seed processing:
A powerful means of enhancing the brand
After harvest, seeds enter the seed processing stage. Seed processing refers to the entire process from ears entering the factory to finished seeds leaving the warehouse, and includes numerous management and technical points. They cannot all be listed here, so only two technologies important to domestic seed companies will be discussed: ear drying and seed coating.
Ear drying means directly transporting the ears harvested from the seed production field from the field edge to the factory and using drying equipment to rapidly reduce seed moisture. Ear drying reduces mechanical mixing caused by farmers threshing, advances the time for seeds to enter the factory, and improves processing efficiency.
Seed treatment is another secret weapon for improving seed quality and value. It can improve the commercial quality of seeds and fully demonstrate the yield-increasing potential of seeds. International seed companies pay close attention to research progress in the international agricultural chemical field, and through specialized agronomy departments study fungicide and insecticide formulations suitable for planting regions, as well as supporting seed coating technology. Seed treatment has become a powerful means for international seed companies to increase product differentiation and enhance their brands.
Quality monitoring:
Controlling germination rate and purity
From parental seed propagation, through field seed production and seed processing, until finished seeds are shipped out of the warehouse, quality monitoring runs throughout this long seed production process. Every portion of parental seeds, every seed production field, every batch of harvested hybrid seeds, and seeds after each processing step must undergo quality testing by the quality monitoring department, and unqualified plots and seeds must be resolutely eliminated.
Germination rate and purity are the two core indicators of seed quality.
The germination rate testing methods of international seed companies are simpler, more standardized, and easier to repeat, and are more reliable than the sand table method commonly used domestically. In addition, low-temperature germination tests and accelerated aging tests are stricter than ordinary germination rate testing and closer to actual field conditions. Therefore, the seeds of international seed companies are more tolerant of harsh environments in production and emerge more uniformly.