Rapeseed

Rapeseed, known scientifically as *Brassica napus subsp. napus*, is a vital member of the Brassicaceae family.

This plant is globally significant because it is the third-largest source of vegetable oil. It also serves as the second-largest source of protein meal in the world. While the seeds are naturally rich in oil, they also contain erucic acid, which can be mildly toxic. To make the plant safer for human consumption, scientists developed cultivars with very low levels of this acid. These specific varieties are known as canola.

In Canada, canola is officially defined by its low erucic acid and low glucosinolate content.

The anatomy of the rapeseed plant is quite distinct. The plant features hairless, fleshy, and glaucous lower leaves that are stalked. Its upper leaves lack petioles, which are the small stalks connecting a leaf to a stem. The flowers are bright yellow and exhibit a radial, cross-like shape with four petals and four sepals.

Flowering occurs through an indeterminate racemose process. This means the flowers bloom in a sequence, starting from the lowest bud and moving upward. The reproductive parts include two lateral stamens with short filaments and four median stamens with longer filaments. After flowering, the plant develops green, elongated pods called siliquae.

Each siliqua contains an inner central wall that creates two compartments for rows of seeds. These seeds are round, hard, and black at maturity, with a diameter of approximately 2 millimeters.

Farmers categorize rapeseed into different types based on their growth cycles and climate needs. Winter rapeseed is the most common form in Europe and Asia. It requires a process called vernalization, which is exposure to cold temperatures, to trigger flowering. Farmers sow it in autumn, and it stays in a leaf rosette on the soil surface during winter. In the spring, it grows a long vertical stem and flowers in late spring.

Spring rapeseed is grown in Canada, northern Europe, and Australia. This variety is not winter-hardy and does not require vernalization. Instead, it is sown in the spring and begins stem development immediately after germination.

The history of rapeseed cultivation spans thousands of years. Plants in the *Brassica* genus were among the first crops widely cultivated by humans, dating back 10,000 years. Evidence shows rapeseed was grown in India as early as 4000 B.C.E. It eventually spread to China and Japan about 2000 years ago. In 1973, Canadian scientists launched a marketing campaign to promote canola. This helped transform how the world uses rapeseed oil for food. By 2009, the entire genome of *B. napus* had been sequenced through a global collaboration.

Growing rapeseed requires careful management of soil and nutrients. The plant grows well in well-drained soils with a pH between 5.5 and 8.3. It has a moderate tolerance for soil salinity. Rapeseed has an exceptionally high demand for nutrients, particularly sulphur. Because atmospheric sulphur levels decreased in the 1980s, sulphur fertilization became a standard practice.

While the plant is predominantly wind-pollinated, bee pollination can nearly double the grain yield. However, the use of nitrogen fertilizers can lead to environmental concerns. An estimated 3% to 5% of the nitrogen used is converted into N2O, a greenhouse gas.

Maintaining a healthy crop involves defending against many biological threats. The plant faces various diseases, such as canker, light leaf spot, and stem rots like sclerotinia. Canker can cause leaf spotting and premature ripening.

Insects also pose a major challenge. Pests like the cabbage stem flea beetle, pollen beetles, and various weevils feed on the leaves, flowers, or developing seeds. To protect the crops, farmers may use synthetic pyrethroid insecticides or molluscicide pellets to stop slugs from attacking the plants.

Modern science continues to change how we interact with rapeseed through genetics. In 1998, a genetically modified variety was developed to be tolerant to the herbicide glyphosate. By 2009, 90% of rapeseed in Canada was this type of variety. This led to significant legal discussions regarding patent infringement and the movement of pollen between fields. Researchers also use molecular breeding tools, such as SNP arrays, to improve crops. Understanding the epigenetics and the complex genome of *B. napus* helps scientists prepare for the challenges of climate change, which may decrease both the yield and oil quality of future crops.