(A) Roots

The roots of kohlrabi are conical. The base of the main root is fat, the tip grows underground, the base of the main root gives rise to many lateral roots, and many fibrous roots occur on the main and lateral roots, forming a very dense network of absorbing roots. Its roots into the soil is not deep, the main root group distribution in the soil layer below the ground within 60cm, to 30cm of the cultivated layer of the most intensive; root group lateral extension radius in the range of 80cm, when the ball of the mature leaves can reach 100cm range. Therefore, the drought-resistant ability of nodular kale is not strong. However, the regeneration ability is very strong after root breakage, and new adventitious roots are easy to occur after the main root and lateral roots are broken during transplanting, therefore, nodular kale is suitable for seedling transplantation.

(B) Stem

The stem can be divided into short stem and flowering stem. The shortened stem is basically shortened throughout the nutrient growth stage although it is slightly elongated in the rosette stage or bulb stage, and the shortened stem is divided into the outer shortened stem and the inner shortened stem. The outer phallus is outside the leaf ball and bears rosette leaves, while the inner phallus bears the bulb leaves, which is the center column of the leaf ball. Generally, the shorter the inner shortening stem, the more compact the leaf ball, the quality is also better, which is one of the important basis for identifying the quality of kale (Figure 10-8). Kale into the reproductive growth stage after the flower shoots called flower stalks, flower stalks can be branched to produce leaves, the formation of inflorescences. The length and thickness of the flower stem is related to the type of leaf ball, variety and nutritional status, and the nutritional supply is sufficient, the flower stem is thick and sturdy, and there are many branches. Generally round spherical varieties, the main flower stem is obvious, while the bull's-eye and flat round varieties of lateral branches are more developed.

Figure 10-8 Kale center column and leaf bulb internal structure

1. short center column, leaf bulb tight 2. center column medium long, leaf bulb tight medium tight 3. center column long, leaf bulb sparse

(3) leaf

Kale leaves can be divided into cotyledons, basal leaves, seedling leaves, rosette leaves, bulbous leaves, and cauliflower leaves. In addition to the ball leaves for storage organs, the rest are assimilation organs, and the leaf morphology of different periods varies greatly. The cotyledons are kidney-shaped opposite. The first pair of true leaves, the basal leaves, are opposite, perpendicular to the cotyledons, wingless, and have long petioles. The seedling leaves that subsequently occur are ovoid or elliptic, reticulate-nerved, with distinct petioles, and alternate on shortened stems. This is followed by the gradual growth of a strong rosette of leaves, also called outer leaves. The number of outer leaves in kale ranges from 10 to 30. Early-maturing varieties generally have fewer outer leaves, and mid- and late-maturing varieties generally have more outer leaves. The outer leaves occurring in the late rosette stage become wider and wider, and the petiole gradually becomes shorter and shorter, so that the leaf margin reaches the base of the petiole, forming a sessile leaf. Accordingly, it is possible to judge varieties with different characteristics and predict the arrival of the onset of nodulation. Outer leaf color can be yellow-green, green, gray-green, blue-green, etc. The outer leaf of purple kale is red or purplish red (Figure 10-9). Outer leaf shape varies by variety and is generally vertical elliptic, oval, round, horizontal elliptic, elliptical, and inverted oval. Leaf tip shapes are generally categorized as convex, flat, or concave (Figure 10-10). Most varieties have smooth, glabrous leaf surfaces, and wrinkled-leafed kale has wrinkled leaf surfaces. The leaf surface is covered with white wax powder, and generally the more wax powder there is, the more drought and heat tolerant it is. The midribs of leaves that reoccur into the nodulation stage are bent inward, encompassing the terminal bud. Thereafter, as new leaves continue to be produced, the individual leaf blades encompassing the terminal bud increase in size and eventually form a tightly packed leaf bulb. The leaves that make up the ball are sessile and yellowish-white in color. The shape of the leaf bulb is generally categorized as round, pointed, or oblate (Figures 10-3 through 10-7). The color of the leaf bulb varies from yellow-green, green, gray-green, and blue-green, with the outer leaves of purple kale being red or purplish-red (Figure 10-11). Leaf bulb inner bulb leaves also vary in color from white, light yellow, yellow, light green, and purple (Figure 10-12). The leaves on the flowering stem are called cauline leaves and are alternate, with smaller blades, pointed at the apex, broad at the base, and sessile or very short petioles. Knotty kale has 2/5 and 3/8 leaf inflorescences, both left- and right-handed.

Figure 10-9 Color of the outer leaf of kale

1. Yellow-green 2. Green 3. Gray-green 4. Blue-green 5. Purple

Figure 10-10 Shape of the leaf tip of the outer leaf of kale

1. Concave 2. Flat 3. Convex

Figure 10-11 Color of the leaf bulb of kale

1. Yellow-green 2. Gray-green 4. Blue-green 5. Purple

Figure 10-12 Color of bulbous leaves within the ball of the knotty kale leaf

1. White 2. Light yellow 3. Yellow 4. Light green 5. Purple

(d) Flowers

Knotty kale inflorescences are compound racemosities, with a first-order branch occurring between the leaf axils on the central main flower stem.

Second-grade branches occur between the leaf axils of the first-grade branches, and third- and fourth-grade branches can occur if there are enough nutrients and good management conditions.

Branching habit varies greatly among different ecotypes of nodular kale picking plants. Generally speaking, round ball-shaped varieties of seed plants, the main stem growth potential is very strong. And pointed spherical and oblate varieties, the main stem growth potential is not as strong as the round spherical varieties, but the first, second and even third level of branching is more developed. The number of flowers per robust seed plant, depending on the variety and cultivation and management conditions, usually 800 to 2000. The order of flowering, usually the main branch first, then the first-class branches flowering, then the second, third and fourth-class branches gradually in turn. From a flowering branch, regardless of the main branch or branch, buds are gradually opened from the bottom up.

The flowering period of nodular kale is usually 30~50d, and there are some differences between different types of varieties in terms of early and late spring flowering time and the length of flowering period. Generally speaking, under the same cultivation and management conditions, the pointed spherical and oblate varieties bloom about 7d earlier than the round spherical varieties, but the flowering period is about 5d shorter.

The flower of nodding kale is a complete flower, including calyx, corolla, pistil, stamen, nectar several parts. When the flower is in bloom, four petals are arranged in a cross shape, the inner side of the petals bear six stamens, two of which are shorter, four longer, each stamen is bearing an anther at the top, the anther naturally split after maturity, and pollen is dispersed.

Kale is a typical cross-pollinated crop, in natural conditions, pollination by insects as a medium. When two different varieties are planted together in alternate rows, the natural hybridization rate can reach about 70% at flowering.

The vitality of the stigma and pollen is strongest on the day of flowering. However, the stigma can receive pollen for fertilization 6d before flowering and 2-3d after flowering. Pollen was viable 2d before and 1d after anthesis. If the anthers are removed and stored in a desiccator, pollen viability can be maintained for more than 7d under dry, room-temperature conditions, and longer under low-temperature drying conditions below 0℃.

The time required from the beginning of pollination to the completion of the fertilization process: under the conditions of heterogamous pollination and temperature of 15～20℃, the pollen tubes start to grow after 2～4h, and they pass through the stylar tissues after 6～8h, and fertilization is completed after 36～48h. The optimum temperature for pollination is 15～20℃, below 10℃ pollen germination is slower, while higher than 30℃ it affects the normal fertilization activity.

(E) fruit and seed

Knotting kale fruit for the long angle fruit, cylindrical, smooth surface slightly like rosary, thickening and hardening of the cell wall at maturity, the seeds are arranged on both sides of the septum. Each plant generally has 700 to 1500 effective angle fruit. The number of angiosperms varies greatly depending on the cultivation and management conditions. On a plant, most of the effective drupes are concentrated on the first branch, followed by the second branch and the main branch. Each hornbeam has about 20 seeds, and on a branch, the upper and lower hornbeams contain fewer seeds, while the middle hornbeam has the most seeds. The seeds are reddish-brown or blackish-brown, with a thousand-seed weight of 3.3-4.5g, and about 50g of seeds can be harvested from a well-grown seed plant.

Knotting kale seeds generally mature about 40d after pollination, but the time needed for maturation often varies depending on temperature conditions. Generally in high temperature conditions seed maturation faster, lower temperature maturation slower - some. In North China, the seeds are generally harvested in late June. Therefore, after mid-May flowers, even if the completion of fertilization is often unable to form fully mature seeds, even if the formation of a small number of seeds, the germination rate is also very low. Knotting kale seeds should be stored under low temperature and dry conditions. Northern dry areas, fully mature seeds in general indoor conditions can be saved for 2 to 3 years, while in the humid south can only be saved for 1 to 2 years, but in the desiccator or sealed cans to save 8 to 10 years of seeds still have a fairly high germination rate.