Specificities of carrot cultivars

Through genetic improvement, Embrapa Hortaliças has been focusing over the last few decades on the challenge of developing carrot cultivars adapted to planting in regions of Brazil, characterized by

17.01.2018 | 21:59 (UTC -3)

Until the mid-1980s, carrot cultivars available on the Brazilian market were of European or American origin and were only suitable for winter cultivation, as there were high incidences of foliar diseases in summer. This seasonality in the cultivation of the crop meant that the price fluctuated greatly throughout the year. The main leaf disease that made its cultivation unfeasible in the summer was leaf blight. This disease is a complex involving two fungi (alternaria dauci e Cercospora corotae) and a bacterium (Xanthomonas hortorum p.v. carotae) that can be together or isolated on the same plant, leaf or lesion.

The carrot's center of origin, as well as the regions where it was cultivated for millennia, have different climatic conditions than most of the Brazilian territory, especially in the hottest months of the year. So much so that carrots could only be grown in the winter period in the Southeast and South regions of Brazil. Thus, at the end of the 70s, the Embrapa Hortaliças Carrot Genetic Improvement Program was created, with the aim of developing cultivars suitable for cultivation in the hottest months of the year in all Brazilian regions. Carrot germplasms from local populations in the Rio Grande (RS) region were collected and went through several selection cycles in Brasília, Federal District, in the search for selecting plants that were more resistant to leaf burn and with root patterns similar to those of cultivars from the Nantes group, which have cylindrical, smooth roots and an intense orange color. The result of this effort was the launch of the Brasília carrot cultivar, in 1981, considered until then one of the results with the greatest impact within Brazilian agricultural research. The success of this cultivar was so great that currently “Brasília” refers to the group of cultivars adapted to summer cultivation. Furthermore, the launch of this cultivar made it possible to explore new agricultural frontiers, such as the regions of São Gotardo, in Minas Gerais, and Irecê, in Bahia.

After the launch of the Brasília cultivar, the Genetic Improvement Program continued work to improve the qualities of the Brasília cultivar. The result of this improvement was the launch of the BRS Alvorada cultivar in 2000. This cultivar, in addition to greater root uniformity in terms of color and size, has approximately 35% more carotenoids, which are the precursors of vitamin A. In 2009, Embrapa Hortaliças launched the BRS Planalto cultivar, which, in addition to root quality, has high productivity, high resistance to leaf burn and tolerance to root-knot nematodes.

Currently, carrot production centers are located in distant geographic regions. This distance causes cultivars to exhibit different behavior depending on where they are being grown, which is known by breeders as genotype x environment (GxE) interaction. For example, Irecê in Bahia is located in a region of the Brazilian semi-arid region and has a climate, soil, among other attributes, different from the region of Marilândia do Sul, in Paraná. This distinction between environments creates difficulties for breeding programs, as, most of the time, a genotype with high potential in a given region does not present the same performance in another. In this way, the breeder defines a new cultivar based on the average behavior of the genotype in the locations where it was evaluated.

Embrapa Hortaliças is the only Brazilian public institution that develops carrot cultivars adapted to summer conditions in Brazil. Currently, research is focused on the development of free-pollinated cultivars and hybrids that can be grown in summer conditions in the main carrot-producing regions in Brazil.

From the formation of the base population to the launch of a new summer carrot cultivar, many steps need to be carried out. The first consists of crossing two promising genotypes, in order to generate a population with sufficient genetic variability so that successive selective cycles can be carried out for the characters of interest. Under the conditions of the Federal District, it is possible to do one selection cycle per year. It all starts in November each year, when the populations are sown in the field to select the best roots. During this stage the attack by pathogens or insects occurs naturally, and no chemical control is carried out.

Before harvesting, 90 days after sowing, plants are selected that show superior behavior to the BRS Planalto cultivar in terms of leaf burn severity, premature flowering, lodging and agronomic value. 100 days after sowing, harvesting takes place, when the roots with the best commercial standards are selected. At this stage, length, diameter, absence of pigmentation in the upper part of the root (green or purple shoulder), smoothness, root shape, absence of attack by pests and diseases and general appearance are evaluated. Then, the selected roots are vernalized (breaking dormancy) so that they can flower and produce seeds in the winter period. This process is carried out in cold chambers at temperatures between 4ºC and 6oC for a period of approximately 40 days. After this process, the roots are removed from the cold chambers and cut into a bevel in the lower third, in order to eliminate roots with internal defects such as cotton heart or uneven color. Then, the cut roots are transplanted to the field where those of the same origin are placed in the same screen so that crossing occurs between selected individuals from the same population. During the flowering period, recombination between these selected plants is carried out by house flies. At the end of the cycle, seeds from the selected plants are harvested individually and sown again the following month of November, thus closing a selection cycle, which is called recurrent selection because it is a cyclical process.

Improving a population can take up to dozens of selective cycles. When the breeder finds that a certain population is promising, it needs to go through a process called validation. At this stage, the population is evaluated in different regions for several years (minimum of three) compared to traditional commercial cultivars. The locations commonly used by Embrapa Hortaliças to validate carrot populations are Brasília, in the Federal District, Irecê, in Bahia, São Gotardo, in Minas Gerais, and Canoinhas, in Santa Catarina.

This assessment is necessary because each region has its particularities and affects the development of culture. Irecê, in Bahia, for example, is located in a semi-arid region, with alkaline soil and low use of technologies. On the other hand, São Gotardo, in Minas Gerais, is located in a cerrado region, with high altitude, with cold nights from October to December and intensified use of technologies. The Marilândia region, in Paraná, has acidic and very heavy soils, which makes it difficult for the roots to lengthen. With all these adversities, a new population is only launched as a cultivar if it performs better than commercial controls based on the average of all regions where it was validated.

In Brasília, in the Federal District, in addition to validating new populations in the conventional system, populations are validated for the organic system. This assessment makes it possible to recommend cultivars that are more adapted to the organic system, in which the use of inputs and pesticides is restricted.

The minimum period for evaluating populations is three years. Thus, the most stable population during this period in all evaluated locations is characterized and registered with the Ministry of Agriculture, Livestock and Supply (Mapa), to then be launched as a new cultivar and recommended for planting in the main carrot-producing regions in Brazil.

Unlike large crops, where pre-cultivars are evaluated in dozens of locations respecting agricultural zoning, carrot pre-cultivars are evaluated only in the main production areas. This is due to the evolution of carrot genetic improvement programs in relation to large crops and the smaller number of limiting factors to which the crop is exposed. For example, lack of water is not a limiting factor for carrots, as in the regions where it is grown there is regular rainfall distribution or the producer has an irrigation system.

However, in the last ten years there have been major changes in carrot breeding programs, such as the replacement of free-pollinated cultivars by hybrid cultivars. Although hybrids are more expensive, they have high productivity due to the high uniformity of the materials. This fact, associated with improved cultural practices, doubled carrot productivity in high-technology regions, such as São Gotardo, Minas Gerais. In these regions, some crops are still planted with free-pollinated cultivars, due to the lack of hybrid seeds available on the market.

In the future, the influence that each environment has on the performance of a given genotype will be capitalized in its favor, that is, future cultivars will benefit from the attributes of the environment where they will be grown. Therefore, the tendency will be to develop specific cultivars for each producing region.

Based on the demand for hybrid cultivars in the seed market, Embrapa Hortaliças has developed work to incorporate male sterility and extract lines for the production of future summer hybrids. These hybrids will maintain the focus of what was accomplished with the free-pollinated cultivars already launched, such as resistance to early bolting, leaf blight, root-knot nematodes and root quality. The program will also aim to incorporate aspects such as precocity, uniformity and productivity of materials.

Box – The carrot

A Carrot cultivation occupies a prominent place within vegetable agribusiness in Brazil. It is currently among the five most important and cultivated in the country. It occupies approximately 25 thousand hectares, with production estimated at more than 750 thousand tons. The main carrot producing regions in Brazil are São Gotardo, Minas Gerais; Marilândia do Sul, in Paraná, and Irecê, in Bahia.

The center of origin of cultivated carrots (Daucus carota L.) is located in the regions where Afghanistan and Turkistan are located today. These countries have an arid to semi-arid climate with hot summers and cold winters. From this region, this species began to be cultivated in the 10th century in Asia Minor. It was then introduced to Europe in the 11th century and to China in the 13th century. Around the 17th century, orange carrots appeared in northern Europe, and there were already many local varieties with good root quality. In Brazil, carrots were introduced along with other “garden plants” by the Portuguese in the 7th century in Rio Grande do Sul, where these introductions adapted to the climate and formed local populations with great genetic variability.

 Click here to read the article in issue 78 of Cultivar Hortaliças e Frutas.

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