The main botanical characteristics of Beta.vulgarisL. species are: annual or perennial, herbaceous, hairless, alternate leaves, basal leaves, and the main leaf shapes are shield-shaped, heart-shaped, tongue-shaped, and rectangular. Nearly entire, petioles long, flowers bisexual, solitary or in clusters of 2 to 4, axillary to form compound spikes, perianth 5, united at the base, stamens 5, sometimes 6; stamens and calyx are opposite in number, no petals Ovary is semi-inferior, stigmas are 2-3 lobed, some are 4-lobed, the lower part is conjoined with the base of the perianth, the seeds are transverse, flat, the embryo is ring-shaped, the endosperm is rich, the fruit is hard, there are longitudinal ridges on the back, the fruit can be solitary or 2- 4 combined into irregular bulbs. When several flowers are clustered together, it is called polyflora.

Beet flowers

Beet seeds and bulbs

As sugar beet used for sugar production, some characteristics of its leaves, flowers and seeds are used in genetic breeding. It has important value in production and production. Root shape, leaf shape, seed granularity and uniformity, and root tube quality are often used as important indicators to identify a variety or purity.

(1) Root tuber and root shape

Cultivated beetroot has a tap root system, which is composed of main root, lateral root and branch root. The fleshy root formed by the enlargement of the main root is a hypertrophic taproot, also known as a tuberous root, which is divided into three parts: root head, root neck and root body.

When sugar beet emerges, the seedlings extend about 15cm deep into the soil. When harvested, the main root can reach a depth of more than 2m. A longitudinally slightly depressed root groove can be seen on the surface of the main root. The branch roots (also known as branch roots) attached to the main root are Root hairs) are generally concentrated in the root furrow and expand to the surroundings. There are also individual plants with three rows of root furrows. However, this type is not inherited to future generations. After a self-crossing, the next generation will return to the two-root furrow shape.

Beets have four main root shapes: cone, spindle, wedge, and hammer. The root bark is yellow-white or white. Root shape is hereditary. The root shapes of the offspring of inbred lines are relatively uniform, while the offspring of hybrids have the root shape of both parents, with the root shape of the hybrid being the dominant one. Root shape is affected by soil and cultivation conditions. When the soil structure is poor, the soil is hard, or there is damage from underground pests, the root shape will change, often becoming shorter and thicker, or the taproots will have many and large forks.

Shape of beet root

The epidermis, vascular bundle rings and inter-ring parenchyma can be clearly seen in the cross-section of the mature root. The number of vascular bundle rings is 8 to 12. Between the vascular bundle rings are filled with parenchyma cells. Different types of varieties have different numbers and distribution densities of vascular bundle rings in their roots. Generally, high-sugar varieties have a large number of vascular bundle rings and a high density; high-yielding varieties have a small number of vascular bundle rings, a low density, and wide parenchyma tissue between the rings. From the cross-sectional analysis, the middle layer has the highest sugar content, the inner layer is the highest, and the outer layer is the least. The vascular bundle ring has a higher sugar content than the parenchyma.

Cross-sectional diagram of the distribution of sugar () in beet roots (standard type)

(2) Leaf shape and leaf cluster posture

The main leaf shape is shield shape, heart-shaped, plowshare and tongue-shaped. Within the cultivated species, the diploid leaf area is smaller, and the leaf shape is mostly plowshare-shaped and tongue-shaped. Tetraploid leaves have a larger area, and heart-shaped and shield-shaped leaves account for a larger proportion.

The ground posture of the leaves also has certain significance for cultivation and breeding. The leaf area is larger, the leaves are wider, and the semi-oblique leaf cluster posture is not conducive to ventilation and light transmission between rows, so it is not conducive to dense planting. The leaf area is small and narrow, and the leaf clusters stand obliquely on the ground at an angle of more than 70°, which is conducive to ventilation and light transmission between rows and dense planting.

(3) Flowers

Beets are bisexual flowers, cross-pollinated, and self-fertilizing does not produce fruit under normal circumstances. When beet pollen matures, the pollen sacs are filled with yellow pollen grains. When the pollen sac ruptures, the pollen grains disperse and spread by the wind, and the horizontal spread distance can reach 4 to 5 km. In the other type, the development of the tapetum layer is blocked during the formation of anthers, which cannot supply nutrients, resulting in underdeveloped pollen grains. When the pollen matures, there are almost no mature pollen grains in the pollen sacs, and there is no pollination ability. This type of flower is called Male sterile flowers. According to the development status of anthers, the characteristics of pollen grains and the ability to disperse pollen, male sterile beet flowers can be roughly divided into 4 types.

1. Totally sterile type

The anthers are white or milky white, translucent, not dehiscent, have no pollen grains or a small amount of early degenerated pollen grains, and the outer wall is unclear.

2. Semi-sterile type 1

Anthers are light yellow or greenish-yellow, opaque, not dehiscent, with a small amount of pollen grains, clear pollen film, and no viability.

3. Semi-sterile type 2

The anthers are orange or yellow, opaque, relatively plump, indehiscent or there is a mixture of dehiscent and dehiscent anthers and pollen grains on the same plant. There are many pollen grains, varying in size, the anther membrane is clear, and a small number of pollen grains are viable.

4. Restore fertile type

The anthers are yellow, large, plump, and full of pollen grains. After flowering and powdering, the anthers fall off. The pollen grains are numerous, round and large, and there are also small pollen grains. The pollen film is clear, the pollen has the ability to survive, and it is easy to rupture when absorbing water. The pollen development status of the male sterile maintainer line used in breeding is the same as that of the normally restored fertile type.

(4) Seeds

On sugar beet seeds, a single flower or several flowers are clustered in axillary branches, forming a flower cluster containing one or several seeds, also called a seed. ball. A seed ball containing only one seed is called a single seed, a ball containing 2 seeds is called a double seed, and a ball containing 3 to 5 seeds is called a multiple seed. On multi-grained sugar beet plants, a small number of double-grained and single-grained seeds may appear at the end of the flowering branches or on the later flowering branches. A small number (1 to 2) of double-grained bulbs often appear on the tops of the flower branches of single-grained seed plants, which does not hinder the inheritance of the single-grained type.

Beet leaf shape

Single and multi-seeded bulbs