After reading this article you will learn about:- 1. Origin of Beetroot 2. Production of Beetroot 3. Botany 4. Genetics 5. Breeding Objectives 6. Selfing and Crossing 7. Breeding Methods 8. Biotechnology 9. Seed Production 10. Varietal Groups.
- Origin of Beetroot
- Production of Beetroot
- Botany of Beetroot
- Genetics of Beetroot
- Breeding Objectives of Beetroot
- Selfing and Crossing of Beetroot
- Breeding Methods of Beetroot
- Biotechnology of Beetroot
- Seed Production of Beetroot
- Varietal Groups of Beetroot
1. Origin of Beetroot:
The earliest form of domesticated beet was leaf beet. The leaves were eaten and the roots were used for medical purposes only. According to Campbell (1979), this species is believed to have originated from Beta maritima, known as sea-beet which is indigenous to Southern Europe.
Genus Beta is primarily found in Asia and Europe. The modern table beet is one of the progenitors of the sugarbeet. The evolution of Beta crops is illustrated in Fig. 24.1.
2. Production of Beetroot:
Beetroot (Beta vulgaris ssp vulgaris, 2n = 2x= 18) is an important vegetable crop in eastern and central Europe and belongs to family Chenopodiaceae. It is known as garden beet or red beet or table beet. The swollen roots are consumed as vegetable and salad. Table beet is a member of crop complex from the genus Beta that includes Swiss Chard, mangel and sugarbeet.
All three of these crops are derived from same species vulgaris and are often represented by different subspecies. Table beet and Swiss chard are mostly used as vegetables, the mangel and its derivatives as animals feed and sugarbeet as source of sugar. Beetroot is a major vegetable crop globally and occupies a unique niche in Europe, North America, the Middle East, and parts of Asia including India.
In India 40-50 tons of seed of beetroot is imported and sold annually by private sector seed companies. Table beet is rich in vitamin B (folic acid), betalain pigments which cause the colouring in the leaves and roots and have been shown to be a powerful anti-oxidant.
3. Botany of Beetroot:
The beetroot is closely related to sugar beet, with which it is cross-compatible. It has the almost unique characteristic (in the vegetable kingdom) of being wind-pollinated like its related species spinach, and is therefore a very prolific pollen producer.
Breeding work with this species should be carried out under pollen proof conditions employing filtered air and this may be one of the reasons why this crop has been largely neglected by vegetable breeders.
It belongs to family Chinopodiaceae. Garden beet is a biennial producing enlarged hypocotyl (roots) and a rossette of leaves in first year and flowers and seed in second year. Enlargement of hypocotyl is due to growth of several concentric vascular cambia which comprise the rings of beet.
It requires cold temperature (4-10°C) treatment for 2 weeks or longer for flower induction. The inflorescence is a large spike. The flowers are small, inconspicuous without corolla, but with green calyx which becomes thicker and covers the seed completely.
This forms what is called the beet seed or multi-germ seed which, botanically is a fruit containing usually 2-6 seeds. The true seeds are small, kidney shaped and brown.
4. Genetics of Beetroot:
At least 2 genes govern root colour and red colouration is dominant to yellow or white, but the intensity of red colouration is influenced by minor polygenes. Further, 5 alleles, R, Rt, r, RP and Rh have been identified at the R locus and 3 alleles, Y, Yr and y at Y locus.
The R-Y-genotype produces phenotypes with red roots, hypocotyls and petioles, while in the presence of rr, genotype Y-gives yellow coloured roots, petioles and hypocotyls. The R-yy genotype roots are white with red hypocotyls. The rr yy genotype produces yellow hypocotyl and white root. For details Pink (1993) may be referred.
Male sterility has been reported to be governed by gene X in S cytoplasm, with fertility dominant to sterility. A second gene Z causing partial male fertility has also been reported. This is dominant to male sterility and independent of and hypostatic to X.
5. Breeding Objectives of Beetroot:
i. High root yield
ii. Round to globe shaped roots
iii. Dark red, uniformly coloured roots
iv. Improved colour and sweetness
v. Uniform root shape
vi. Absence of internal white rings in roots
vii. Increased betalain concentration
viii. Slow bolting
ix. Mono-germ seed
x. Resistance to downy mildew (Peronospora farinosa f. sp. betae), powdery mildew (Erysiphe communis f. sp. betae), Cercospora leaf spot (Cercospora beticola), Rhizoctonia root rot (Rhizoctonia solani)
6. Selfing and Crossing of Beetroot:
Garden beet produces small flowers in clusters of 2 to 6. It is wind pollinated. The pollen is dust like and produced in abundance. For selfing, the entire plant or a few flowering branches are enclosed in a thick muslin cloth bag or preferably in a Kraft-paper bag. The bag should be shaken once or twice daily to ensure better pollen dispersal and better seed-setting. The bags should not be opened on windy days.
If marker genes are available, to identify selfed plants in seedling stage or root stage, emasculation shall not be required and crosses can be made by enclosing flowering shoots of two parental cultivars in the same pollinating bag. Shaking the bag occasionally will effect pollination but both self and cross seed will be produced and hybrids can only be distinguished from plants resulting from selfing if a suitable genetic marker is available.
If the pollen parent does not possess any marker gene, it will be necessary to emasulate the flowers before crossing, although emasculation is difficult in beetroot. During pollination care must be taken to avoid contamination from foreign pollen carried by wind. The pollination must be done when the air is still, preferably in a glass house or plastic cage.
7. Breeding Methods of Beetroot:
Beetroot when subjected to self-pollination, shows considerable inbreeding depression. Therefore, as a rule, this crop is improved by mass selection or by more sophisticated techniques involving progeny testing. Although the introduction of cytoplasmic male sterility has resulted in the development of some hybrids, most cultivars are still produced by mass selection.
For mass selection, selected roots should be grouped together, for flowering in the year after selection. If a large number of roots has been selected, it is advisable to divide them into groups of not more than 10 plants. These should be seeded together in isolation from other groups or various groups would be seeded together under a fine muslin bag or cage at the same place.
Mass pollinated seed will be collected separately from each group or possibly from single plants for progeny testing and sown separately. It is most likely that some group progenies will perform better than others and further selections could be made only from these.
While selecting the roots, quality of each root can be assessed by cutting a vertical wedge and replacing it afterwards. Selected sampled roots can be grown on to produce seeds. Growing in relatively infertile soils accentuates colour differences and makes it easier to choose the darkest coloured roots. Premature bolting occurs most readily in the long days and at relatively low temperatures.
Early sowing and growing at northerly latitudes encourages bolting and can aid selection for resistance to bolting. Selection for resistance to bolting can also be achieved very easily by subjecting a large number of seedlings to long days (16 hrs. of daylight supplemented by artificial light from tungsten bulbs), selecting those which did not produce flowering heads from 8-10 weeks of treatment, and mass-pollinating the plants which grew on to produce high quality roots.
Chemical mutagens (dimethyl sulphate, DMS; N-methyl-N-nitroso urea, MNU; N-ethyl- N-nitroso urea, ENU) and physical mutagens (gamma rays and ultraviolet irradiation) have been used to induce variation in beetroot.
Avon Early has been bred by selecting from among a population derived from a large number of cultivars of the Detroit type. The plants were raised early in the year and subjected to continuous light followed by cold treatment to induce bolting. The level of resistance has then to be maintained by selection during seed multiplication. This variety has good resistance to downy mildew.
As in onion and carrot, beetroot hybrids are developed using CMS. The first four maintainer lines developed in US have been W32, W162, W163 and W187. Once sterile and maintainer pairs are available, sterile lines could be used as females in various hybrid combinations with restorer lines, populations or maintainer lines used as pollen parrot. In easily developed hybrids, there was not much superior horticultural performance over open-pollinated cultivars.
However in second series of hybrids developed in USA, heterosis for a variety of horticultural characteristic was apparent in various hybrid combinations. In USA, table beet inbreeds have been released as A and B pairs where A lines refer to sterile phenotype (Sxxzz) and the B lines refer to the maintainer of sterility (fertile) phenotype with genotype Nxxzz.
All inbred lines released are biennial and thus carry the b allele in the homozygous recessive condition. For line development, with wild type table beet germplasm, direct selfing was not possible. However, with introduction of the SF allele, self-pollination has been feasible.
8. Biotechnology of Beetroot:
Development of transgenic sugar beet having herbicide resistance in USA is now a reality. Little, if any, work has been done on transgenics in beetroot. However, it is quite likely that any genetic transformation accomplished in sugarbeet likewise can be translated in beetroot.
There are reports on significant genetic variability for regeneration ability from leaf disk callus in sugarbeet. SNP markers have been developed for each of nine linkage groups in sugar beet and similar developments are expected in beetroot.
9. Seed Production of Beetroot:
Table beet has a biennial life cycle and requires specific environment stimuli to promote switch from vegetative to reproductive stage. It is an obligate long-day plant. Vernalization (exposing plants to relatively short period of temperature slightly above freezing) is required to produce flowering stimulus. The minimum and maximum temperatures for vernalization in sugar beet are 0 and 15°C respectively.
Seed production of beet root seed needs two seasons:
1. Mild winter with average seasonal low temperature of – 8°C.
2. Cool dry summer with average seasonal high temperature of 24°C.
Stock seed is planted into a plant-bed in late June-early July in USA at spacing required for commercial crop. Plants grow vigorously for 6-10 weeks. Based on foliage colour and shape, off type plants are rogued out. By early October, well developed roots are seen. The foliage is cut-off mechanically.
Within 10 days of topping plants, roots are lifted and piled into windrows, with each windrow representing four to six rows of beetroots. Sometimes these windrows are pushed into shallow pits, 15 cm deep and 1 m wide. The roots are covered with 30 cm soil from all sides. This ensures protection of roots from freezing temperature.
Roots are digged out between middle of March and early April. The roots meant for seed production are called stecklings. These stecklings are examined for shape, prominence of taproot, absence of disease, internal root colour, acceptable pigment levels.
This is done in two ways:
1. Cutting approximately 1/10-1/15 of root mass diagonally, off the side of the root.
2. Slicing the root diagonally starting at the centre of the apical growing point thereby cutting the root into two equal halves.
These methods allow the breeders to see both the overall intensity of colour and presence of zoning which is differential colouring between cambial rings. Roots are firmly placed into the soil, 90 x 60 cm apart. After planting of stecklings, an early irrigation is done.
Isolation distance of beet seed field from other beet seed production plot is 1.2 – 1.6 km and 2.4 – 8.3 km from Swiss chard, mangel and sugar beet. It is wind-pollinated and pollen can travel up to 20 km.
A gene conditions fasciation of flower stalk. It causes flattened flower stem with petioles coalesced into a twisted ribbon-like appearance. Fasciation due to could be useful in beet seed production as fascinated plants tend to exhibit heavy seed set with seed maturity occurring in a synchronous manner.
10. Varietal Groups of Beetroot:
Goldman and Navazio (2008) have described following varietal groups/varieties. In some cases, varietal groups and name of a particular variety have become synonyms.
This population was introduced to U.S. from Germany in 1868 by the Ernst Benary Company. It was listed in seed catalogues as Extra Early Egyptian and Dark Red Egyptian. It is early, has small foliage, flat roots. Root shape is flattest among founding populations. Roots are small-sized and suitable for canning.
It was developed by Josiah Crosby of Arlington, Massachusetts, from a population of Flat Egyptian. It was listed in seed catalogues as back as in 1885. It has increased depth of roots and less rough root exterior. Thus, it is much rounder and smoother than Flat Egyptian from which it has been developed. It matures in 55-60 days. It shows pronounced white zoning in warm weather.
Light Red Crosby:
This population was first described in 1904 by D.M. Ferry and Co. as a vermillion or light-red coloured beetroot. The root and exterior skin colour of this population is lighter than the original Crosby.
This population was first listed in 1911 by F.H. Woodruff and Sons and S.D. Woodruff and Sons catalogues. It is derived from Crosby Egyptian. It is rounder in shape than Crosby Egyptian. Its foliage is robust and it is suitable for fresh market.
Detroit Dark Red:
This population has been developed from a population known as Early Blood Turnip by Mr. Reeves of Port Hope, Ontario, Canada. In 1892, it was listed as Detroit Dark Red Turnip beet by D.M. Ferry and Co. This population is most widely adapted. It is appropriate for fresh market, processing and market garden production. Roots are smooth and round. Foliage is dark green.
It has several synonyms such as Detroit Blood, Detroit Early Dark Red, Early Detroit Dark Red. Morse Detroit is a selection from Detroit Dark Red and offered by C.C. Morse and Co. in 1928 as Morse’s Improved Detroit. In Indian conditions, it matures in 80-100 days.
This population was developed at Ohio Agr. Exp. Stn., USA and released in 1932. Its skin, flesh and foliage colour is similar to that of Detroit Dark Red. It has reduced amount of differential colouring between cambial rings (zoning) and therefore is an excellent choice for canning.
Long Dark Blood:
This is perhaps the oldest founding population of beetroot in U.S. It may have been introduced from France to U.S. It is long rooted type with cylindrical roots.
This is an introduction by private seed companies for direct seed sale in India. The seed is imported from Italy, etc. and packed and sold. The roots are red and round. White zoning is less pronounced.