DAHLIA: CHARACTERISTICS, HABITAT, CULTIVATION AND REPRESENTATIVE SPECIES - BIOLOGY - 2024

The dahlia (Dahlia) is a genus of herbaceous and perennial flowering plants in the Asteraceae family. This genus is made up of 35 species endemic to Mexico, of which only four genera constitute the genetic base of commercial crops.

These plants are characterized by developing a fleshy root or fasciculate tuber that represents the main means of vegetative reproduction. The opposite, simple or pinnate leaves are triangular in shape with smooth serrated margins and pale green in color.

Dahlia (Dahlia). Source: pixabay.com

The ligulate flowers are grouped in erect or sloping heads of various shades of red, purple, pink, orange or yellow. Flowering usually occurs during the summer or late autumn, constituting the main commercial attraction of the crop.

At present, dahlias are cultivated worldwide, being their main ornamental use, as flowers in pots or cut flowers. However, recent studies have made it possible to determine certain medicinal properties for the treatment of diabetes and as a nutritional supplement.

General characteristics

Morphology

Species of the genus Dahlia are herbaceous plants with shrubby appearances, sometimes epiphytic or climbing, and with perennial or deciduous habits. Its size varies from creeping plants of 0.3-0.5 m, to erect plants 1.2-1.5 meters high with multiple branches.

Root

The underground root that emerges from the neck of the plant is of the widely fasciculated tuberous type. Indeed, the tuberous root of the dahlia lacks nodes or internodes, and constitutes a storage and reproduction structure.

Leaves

The leaves depending on each species can be simple or compound, also in opposite or whorled arrangement. Likewise, the entire or divided leaf blade is oval in shape with straight or serrated edges and a pale green color.

flowers

The flowers are arranged in inflorescences grouped in campanulate heads of variable size, shape and color depending on the species. Shapes vary from hemispherical, simple, or cluster, and the predominant colors include white, red, pink, orange, or purplish.

The inflorescences have two types of flowers, the ligulates located on the outside, generally sterile and of a great variety of colors. As well as the central ones arranged on the disk or receptacle, tubular, hermaphroditic, fertile and colored yellow, orange, red or purple.

Dahlia growing plant. Source: Krish Dulal

Taxonomy

- Kingdom: Plantae

- Subkingdom: Tracheobionta

- Division: Magnoliophyta

- Class: Magnoliopsida

- Subclass: Asteridae

- Order: Asterales

- Family: Asteraceae

- Subfamily: Asteroideae

- Tribe: Coreopsideae

- Genus: Dahlia Cav. 1791

- Species: 30 species, 20,000 varieties

Species

Pseudodendron section

Epiphytum section

Entemophyllon Section

Dahlia Section

Habitat and distribution

The Dahlia genus is native to the Mesoamerican high valleys of Mexico, El Salvador, Guatemala, Honduras, Nicaragua, and Costa Rica. As well as some regions of South America and some northern states of Mexico where they were introduced as wild crops.

Wild dahlias. Source: Nilfanion

The great diversity of Dahlia species includes a wide altitudinal range, from 200-500 masl to 1,500-2,500 masl as the Dahlia australis. The genetic diversity of the crop adapts to frequently calcareous, stony, rocky, volcanic and even clay soils.

This crop comes from and adapts to tropical and subtropical climates, but has become accustomed to various environmental conditions. In Europe they were introduced by the Spanish, being in Belgium the place where the first commercial crops were established.

Culture

Floors

The dahlia is an undemanding plant on soils, although it adapts to loamy and well-drained soils. In addition, it has a high content of organic matter and nutritional elements, as well as a pH range of 6-8.

Weather

The optimal climatic conditions for this crop should range between 18-23 ºC in average temperature and 75-78% relative humidity. Most varieties of dahlia are susceptible to low temperatures and occasional frosts.

This crop is generally managed under controlled irrigation, so high rainfall in the productive phase of the crop is favorable. Likewise, it requires natural or artificial protections against the wind, since it does not tolerate strong winds.

illumination

Dahlias are commercially grown in sunny areas, although they are well suited to semi-shady conditions. However, full sun exposure should be avoided, as strong radiation tends to burn the leaves and young shoots.

Irrigation

During the establishment of the crop, irrigation should be moderate to avoid damage due to waterlogging or the incidence of diseases of the root system. In the growth and production phase, it is necessary to increase the frequency of irrigation, also during dry periods and summer.

Ornamental cultivation of dahlias. Source: pixabay.com

Spread

Dahlia is propagated by various methods of reproduction, through seeds, tuber division, cuttings and even through in nitro cultivation.

Propagation by seeds

Technique used for genetic improvement purposes, in order to obtain pure varieties and avoid the crossing between cultivars. In fact, it is used in potted crops under a nursery, where rigorous control of edaphoclimatic conditions is maintained.

The ideal time to sow dahlias by seed is at the beginning of spring, on a substrate rich in organic matter mixed with sand. Maintaining an average temperature of 15-18 ºC, the seeds begin to germinate 15 days after sowing.

The plant requires 1-2 chimes during its development phase in order to select vigorous plants and favor their adaptation. Finally, a transplant is carried out to the final terrain, trying to maintain a 0.8 m spacing between plants.

Tuber division

The division of tuberous roots or tubers is the most used propagation method to multiply dahlias due to its ease and high effectiveness. Indeed, the dahlia develops a series of tuberous roots that act as a storage structure that are used for its reproduction.

These tubers can be stored for a certain time under special conditions for use as a means of propagation. Indeed, the tubers are placed in germination trays with a fertile substrate, in conditions of humidity and warm temperature.

At the beginning of sprouting, the tubers are divided, trying to keep 2-3 vegetative buds for each fraction to guarantee grip. It is advisable to carry out this procedure during the spring and sow the fractionated tubers directly in the final field.

Spread

The technique consists of placing selected cuttings in cultivation under greenhouse conditions to promote the sprouting of vegetative buds. It is advisable to sow the tuber in a substrate of peat and sand, ensuring humidity and average temperature of 15-20 ºC.

The shoots emerge from the portion of the tuber that remains on the substrate. When these new seedlings reach a height of 5-10 cm they are separated from the mother plant, keeping part of the tuber.

These cuttings are placed on growth trays with enriched peat, constant humidity and a temperature of 18ºC. After 15-20 days the cuttings open vigorously rooted to be transplanted to their final soil.

Spread

In vitro propagation of dahlia is the best alternative since it guarantees clonal multiplication due to the genetic variability of the genus. This technique is carried out using selected meristematic tissues from healthy, vigorous and productive plants.

Commercial cultivation of dahlias. Source: Phoebe

Driving

Sowing, either by division of tubers or cuttings, is done during the first month of spring. In commercial crops, different planting frames are managed, for large flower species 1 x 1 meters, and for small flowers 0.5 x 0.5 meters.

Floors

The various varieties of dahlia prefer non-calcareous soils, with pH adjustment to neutral, preferably fertilized with composted manure.

Fertilization

When preparing the soil, a fertilizer with a high content of phosphorus and potassium is recommended, as well as a maintenance fertilizer with nitrogen. Organic fertilizers or fertilizations with high nitrogen content can cause physiopathies at the foliage level.

Indeed, excess nitrogen weakens the stems, promotes leaf production and can damage flower buds. On the other hand, phosphorus and potassium make the stem stiff, intensify flower color and ripen the tubers.

Irrigation

It is appropriate to carry out regular and abundant waterings, trying to keep the substrate moist. However, the application of irrigation on the leaves and the waterlogging of the soil or substrate should be avoided in all stages of development.

Pinching

The practice of pinching or pinching is done on young seedlings when they are 15-20 cm high. Indeed, the clamping is carried out on the third pair of true leaves counted from the base of the stem.

This technique seeks to eliminate secondary shoots and flower buds located in the axils of the leaves, keeping only the main shoot. The objective of this practice is to achieve that the stem that supports the main flower reaches a length of better commercial value.

Unbuttoned

With the unbuttoning it is intended to obtain flowers of better size and quality of the cut. This technique seeks to guide and control flowering by eliminating flower buds located in the leaf axils.

This activity is carried out when the fabrics are still tender, before the buttons are 5 cm long. With this maintenance pruning, the production of a main flower with stems 60-70 cm in length is achieved.

Dahlia flower bud. Source: Soumendrak

Plagues and diseases

- Pests

Aphids (

The adults and nymphs suck the sap from the leaves, causing yellowing and general weakening of the plant. In addition, they secrete a molasses on which a fungal disease called bold develops.

Low incidence of the pest allows its biological control with Adalia bipunctata and Aphidius colemani. For larger incidents, preventive control is carried out by applying a systemic insecticide.

Red spider (

It occurs in low humidity conditions and manifests as small yellowish spots, curling of the leaves and defoliation. In addition, the presence of cobwebs on the surface of the leaves is common.

The control is carried out through management increasing the humidity of the crop, or using the biological controller Phytoseiulus persimilis. In severe attacks, the application of sulfur-based chemicals is recommended.

White fly (

Damages are caused by adults or larvae feeding on the sap of the leaves, causing yellowing and weakening of the plant. The control is carried out with systemic insecticides when observing the presence of adults on the crop.

Trips (

The damage appears as small whitish spots with a leaden appearance surrounded by black spots on the leaf blade. Preventive control with anti-thrips traps or biological control with Orius or Amblyseius swirskii is recommended.

White worms and wire worms

This type of pest is coleopteran larvae that settle in the soil causing damage to the root system. The preventive control is carried out with disinfection of the substrate, in severe attacks it is recommended to apply systemic insecticides.

- Diseases

White coal (

Symptoms of the disease are rounded spots on the leaves that influence the commercial quality of the crop. The control is carried out in a preventive way, eliminating diseased plants, disinfection of the substrate or tools, and with expansion of planting density.

Wilt (

The main symptom is the change in color of the older leaves and the internal tissues turn brown. The general damage extends to the upper part of the plant and is favored by practices such as watering, handling and presence of weeds.

The control is preventive through the use of healthy plant material, elimination of diseased plants and reducing the frequency of irrigation. Chemical control is deficient, so preventive measures are adequate, including disinfection of work material.

Bacterial diseases

Among the main bacteria that affect dahlia cultivation are Erwinia chrysanthemi, Agrobacterium tumefaciens and Corynebacterium fascians. The recommended control is through preventive measures such as disinfection of tools, elimination of diseased plants, sanitation pruning and weed control.

Virosis

Cucumber mosaic virus (CMV) and dahlia mosaic virus (DMV) are the main viral problems of the crop. The symptoms vary from spots at the level of the veins, depigmentation of the leaves, to irregular growth of the leaves.

Prevention is accompanied by the control of pests such as aphids. In addition to the disinfection of work material, elimination of diseased plants and weed control.

Representative species

Dahlia coccinea

Known as red dahlia or chalihuesca, it is an ornamental plant belonging to the compound family or Asteraceae. Species native to Guatemala and Mexico, it is one of the main ancestors of the current ornamental dahlias.

Dahlia coccinea. Source: Prsjl

Dahlia imperialis

The so-called Catalina dahlia is located from central and southern Mexico to Colombia, being a herbaceous or shrubby species. Dahlia imperialiss is a perennial and tuberous plant that reaches high altitude, generally between 8-10 m in height.

Dahlia imperialis. Source: Louise Docker

Dahlia merckii

Native plant of northeast and central Mexico. It is a highly branched and compact plant, with divided leaves with numerous heads with lilac-whitish ligulate flowers.

Dahlia merckii. Source: Marktee1 at en.wikipedia

Dahlia pinnata

Species distributed between Guatemala and Mexico. It is characterized by simple and divided leaves, with long petioles with fleshy bracts, and ligulate flowers of purple or violet tones with some yellow spots.

Dahlia pinnata. Source: SGS

Dahlia variabilis

It is a hybrid herbaceous plant of certain Mexican species that reaches 0.70-1.50 meters in height and has a thick tuberous root. The current varieties are hybrids originating from Dahlia pinnata, D. coccinea and D. purpurea.

Dahlia variabilis. Source: Nic McPhee, Morris, Minnesota, USA

References

1. Carrasco-Ortiz, M., Lino, GM, Castro-Castro, A., Vargas-Amado, G., Harker, M., & Rodríguez, A. (2019). Wealth, geographical distribution and conservation status of the genus Dahlia (Asteraceae) in Mexico. Acta Botanica Mexicana, (126).
2. Castro-Castro, A., Zuno-Delgadillo, O., Carrasco-Ortiz, MA, Harker, M., & Rodríguez, A. (2015). News in the genus Dahlia (Asteraceae: Coreopsideae) in Nueva Galicia, Mexico. Botanical Sciences, 93 (1), 41-51.
3. Dahlia. (2019). Wikipedia, The Free Encyclopedia. Recovered at: es.wikipedia.org
4. The cultivation of the Dahlia (2018) Infoagro Systems, SL Recovered in: infoagro.com
5. Garzón Solís, C. (2007) Phenological development of the Dahlia campanulata (Dahlia campanulata Saar.) A new species for ornamental horticulture. Chapingo Autonomous University. Regional University Unit of Arid Zones. (Thesis).
6. Hanan Alipi, Ana María and Mondragón Pichardo, Juana (2009) Dahlia coccinea Cav. Conabio. Recovered at: conabio.gob.mx
7. Jiménez Mariña, L. (2015). Dahlia cultivation. Tropical Crops, 36 (1), 107-115.
8. Mera Ovando, LM, & Bye Boettler, RA (2006). The Dahlia a beauty native to Mexico. University Digital Magazine. Volume 7 Number 11. ISSN: 1067-6079.