AVOCADO: CHARACTERISTICS, DISTRIBUTION, CULTIVATION, PESTS - BIOLOGY - 2024

The avocado (Persea americana Mills.) Is an arboreal species belonging to the Lauraceae family, native to the Mesoamerican region. The word avocado comes from the Aztec language "Nahuatl" resulting in the simile "ahuacatl", alluding to the shape and position of the fruit.

In a natural way, the species is distributed in America from Chile to Mexico, locating in Peru, Ecuador, Colombia, Venezuela and Central America. In this regard, the species currently cultivated comes from plants cultivated since pre-Columbian times.

Avocado (Persea americana Mills.) Source: pixabay.com

The avocado fruit is an edible berry with a high content of calories, lipids, proteins, vitamins and unsaturated fats. In fact, the pulp is creamy in texture, green or light yellow in color and has an aromatic flavor similar to hazelnut.

On a commercial level, the success of avocado production depends on the effective selection of the appropriate variety for the specific agroclimatic region. In this case, continuous production, higher yields, lower incidence of pests and diseases, and better fruit quality are guaranteed.

characteristics

The avocado is a large, perennial-growing plant that, under natural conditions, can reach a height of 10-12 m. It has an abundant crown, globular or bell-shaped, which can reach a diameter of 25 meters.

With a taproot and branching, the secondary and tertiary roots expand in the first 60 cm of the soil. The superficial root system responsible for absorbing water and nutrients, tends to be susceptible to excess moisture in the soil.

The stem is made up of a cylindrical woody trunk, with rough bark and longitudinal grooves at the surface level. In addition, from the third quarter of height it presents an abundant branching.

Likewise, the foliar area is made up of numerous light and weak branches, brittle due to the weight of the fruits and the action of the wind. The leaves are simple unifoliate with a smooth and leathery texture, reddish in color, turning a deep green color over time.

Flower buds in avocado. Source: pixabay.com

Persea americana is a species that exhibits a floral behavior called dicogamy and protogyny, that is, the flowers unfold in two phases. In fact, the female and male structures function separately, in order to avoid self-pollination.

For this reason there are varieties classified on the basis of floral behavior as type A and type B. Type A flowers initially unfold as female and type B unfold as male in the second phase.

As for the fruit, it is a fleshy berry, generally pear-shaped, with a rough or smooth texture, and a characteristic green color. In this regard, the shape and color of the berry, the texture of the rind and the consistency of the pulp depend on each variety.

Avocado life cycle

Avocado is a perennial plant, with an effective life span of 25 years in wild cultivars. However, in improved varieties the life cycle can be shortened to 15-18 years.

These plants have a continuous growth throughout their life cycle, as a result of the apical dominance and slow growth of the terminal buds. Process that favors the development of axillary buds, source of flowering and subsequent fruiting.

The life cycle of avocado goes through four well-defined stages:

1. Production of plant material: 7-10 months.
2. Growth and development of the plant to the juvenile stage: 1-4 years.
3. Start of production and stabilization of flowering: 4-8 years.
4. Adult state, full production until decay: 8-25 years.

Origin

The varieties of avocados that are currently marketed come from native plants of the Oaxaca region, in southern Mexico. However, the predecessors of the genus Persea comes from the northern part of North America, migrating in later times to Mesoamerica.

Scientific evidence suggests that the origin of the Persea americana species results from the profound geological changes that occurred in the region where Mexico currently sits, finding fossil remains of similar species to the north of present-day California.

Avocado fruit. Source: pixabay.com

The domestication of this genus began in 5,000-3,000 BC, in the Mesoamerican area. Today there are three varieties of P. americana, from the wild varieties: Antillean, Guatemalan and Mexican.

The Antillean variety comes from the Antilles region, and the Guatemalan variety from the high mountains of Guatemala. The Mexican variety is native to the central and eastern region of Mexico.

Over time the three varieties have crossed naturally, creating particular native hybrids. Since the 20th century, producers have made a controlled selection, creating productive cultivars, characteristic of each region and agroclimatic conditions.

Taxonomy

• Kingdom: Plantae
• Subkingdom: Viridiplantae
• Underkingdom: Streptophyta
• Superdivision: Embryophyta
• Division: Tracheophyta
• Subdivision: Spermatophytina
• Class: Magnoliopsida
• Superorder: Magnolianae
• Order: Laurales
• Family: Lauraceae
• Gender: Persea
• Species: Persea americana

The genus Persea Mill. Was defined by Miller (1754), and the species Persea americana was represented in the 8th edition of Gardener's Dictionary (Miller 1768).

Varieties

The Persea americana Mill. Species presents a varietal classification based on ecological conditions. P. americana var. americana (Antillean variety), P. americana var. guatemalensis (Guatemalan variety) and P. americana var. drymifolia (Mexican variety).

Antillean variety

The variety Persea americana var. americana, is native to the hot and humid lands of Central America. Characterized by large fruits of up to 2.5 kg, oval in shape, smooth rind, bright green and abundant pulp.

It adapts to tropical conditions, 18-26º C and heights below 1,000 meters above sea level. Among the cultivars of this variety we can mention: Lorena, common or criollo, Russell, Pinelli, Venezuelan, Curumani, Fuchs, Peterson, and Hulumanu.

Guatemalan variety

From the high mountains of Guatemala comes the variety Persea americana var. guatemalensis. It is a variety that is conditioned at altitudes between 1,000-2,000 meters above sea level, which is characterized by its long period between flowering and harvest of up to 15 months.

The berries are pyriform in shape, medium to large in size, dark green to purple in color. The pulp of high protein content, excellent aroma and texture, has more than 20% of unsaturated fats.

Among the cultivars of this variety are: Edranol, Hass, Itzama, Linda, Mayapan, Nabal, Pinkerton and Reed.

Mexican variety

The Mexican variety Persea americana var. drymifolia, is native to the high mountains of central Mexico. It reports its best growth and development in areas between 1,700-2,500 meters above sea level.

The ovoid-shaped fruits of light green color, have low fiber and sugar pulp (2%), and high fat content (25-30%). Of the cultivars of this variety are Bacon, Duke, Gottfried, Mexicola, Puebla, Topa-topa and Zutano.

Cultivars

There are numerous cultivars obtained based on tests and trials in different geographical areas, but the most common and commercially cultivated are:

• Criollo: native to Central America and Mexico, it is the original unselected variety. It has a very thin and dark rind when ripe, becoming edible.
• Hass: Native to California, it has a rough and rough skin, creamy pulp and low in fiber. The berry is dark green in color when ripe and the bark peels off easily.
• Méndez: native to central Mexico, it is one of the original varieties. It has rough, thick rind, dark green in color and creamy pulp and low in fiber.
• Bacon: native to California, it is characterized by the smooth and thin bark, of a bright green color.
• Strong: native to Central America and Mexico, with a rough rind that comes off easily from the pulp.
• Pahua or avocado: fruits with thick skin and pulp with a greasy texture, aromatic flavor.
• Torres: cultivar obtained by hybridization and selection in Argentina, in the Famaillá area, Tucumán province.
• Negra de La Cruz: also called Prada or Vicencio. Obtained by natural hybridization in Chile, in the Valparaíso region. The bark is very dark purple in color, turning black.
• Blue or black: crop produced in the southern region of Mexico, it presents a fruit with thin skin and abundant pulp, which requires great care during transport and marketing.

Distribution and habitat

Avocado cultivation occurs in the tropical and subtropical regions of the five continents. However, the highest level of production and productivity is obtained in America, with Mexico being the world's leading producer of avocados.

Avocado cultivation requires certain agroecological conditions related to altitude, temperature, humidity, soil and topography, to achieve an abundant harvest. In fact, it is a species that shows effective growth and development between 400-1,800 meters above sea level.

As for temperature, it adapts to a range between 17-30ºC, being highly susceptible to low temperatures. It requires an average of 1,200-2,000 mm of annual precipitation and a relative humidity of 60%.

It adjusts to soils with slopes less than 30%, of medium texture, deep, well drained and with a pH of 5.5-6.5. The ideal texture is sandy clay loam and organic matter content of 3-5%.

The establishment of crops in clay soils, with high salinity content and shallow, that limit the development of the roots, is not recommended. In the same way, this is a crop that does not support the watering of the soil, and is susceptible to strong winds.

Propagation of plant material

The appropriate method to propagate this species begins with the preparation at nursery level of rootstocks from native seeds. The rootstocks must come from healthy plants, of good development and production, resistant to drought, pests and diseases.

The seedlings are established in medium-sized polyethylene bags in rows of three to four rows. An effective agronomic management of the patterns is essential, ensuring irrigation, fertilization and control of pests and diseases.

Commercial propagation is carried out by the grafting technique, selecting plant material from varieties adapted to the production area. This technique allows obtaining better quality fruits, resistant plants, with better agroclimatic adaptation and excellent production.

The graft is obtained from healthy and good looking seeds, collected directly from the tree. The seeds, with a time no longer than 20 days after being extracted from the fruit, must be cleaned, washed and treated with fungicides.

At the time of sowing, a cut is made in the narrow part of the seed, a quarter of the total length. In order to discard unviable seeds and facilitate the germination process.

The sowing is done in plastic bags placing the seed with the cutting area facing up. In this way, germination begins approximately 30 days after sowing.

Graft

The grafting is carried out when the stem of the rootstock or pattern has reached a diameter of one centimeter. This condition requires an approximate time of four to six months after sowing.

Graft in avocado. Source: ventadeplantadeaguacates.com

In avocado, the type of graft most used is lateral plating, due to its practicality and the high percentage of effectiveness (80-90%). The process is carried out in a cool and airy place, making the graft at a height of 20-30 cm from the base.

The 10-12 cm twigs to be grafted should have 3-4 well-developed buds. The technique consists of inserting the rod in the rootstock cut, taking care that the cambium of both tissues is in contact.

Subsequently, the firm tying with plastic tape is carried out, protecting the union of the tissues to be grafted. After four or six weeks, the success of the graft is determined, proceeding to eliminate the pattern 5 cm above the graft site.

When the grafted plants have reached 20-25 cm in height and show calluses at the graft point, they can be transferred to the final field. In fact, the plants are ready for sowing in the plantations 4-6 months after the grafting process begins.

Land preparation

The avocado is a monoculture that requires clear land, free of stones, weeds, trunks and roots. However, in some regions it is grown in association with the coffee tree, although it requires special care in terms of pest and weed control.

The planting structure is determined by various factors such as topography, climatic conditions, variety and available resources. The recommended spacing varies from 7 × 7 to 12 × 12, following a square, staggered, rectangular or quincunx line.

The 60x60x60 cm hole should be done one or two months before sowing so that it is disinfected and moistened. Before sowing, a mixture (2: 1: 1) of black soil, organic matter or manure, and sand should be placed.

Sowing

At the beginning of the rain it is the ideal period to start sowing in the final field. However, in irrigated crops, sowing can be done at any time of the year.

Sowing consists of placing the pot removed from the plastic bag inside the prepared hole. The soil is heavily compacted to avoid air chambers, trying not to plant too deep.

Pruning

Avocado pruning is an agricultural practice that guarantees better yields, since it avoids the proliferation of vegetative branches. In fact, effective pruning stimulates the creation of producing branches that generate flowers and fruits.

A plant without pruning maintenance branches out disproportionately. Therefore, the loosening of the branches is facilitated by the weight of the fruits and the action of the wind.

Likewise, pruning allows better aeration and lighting of the plants, avoiding the formation of microclimates that promote the attack of pests and diseases. On the other hand, frequent pruning maintains the plant's bearing, facilitating phytosanitary practices and harvesting.

Fertilization

Avocado cultivation requires constant fertilization throughout its production process, as it is very demanding in terms of nutritional requirements. Effective fertilization influences plant vigor, leaf color, flowering, fruiting, and harvest performance.

Organic fertilizer applications such as compost or manure from poultry, cattle and horses allow maintaining the nutritional balance of the soil. Regarding chemical fertilization, one kg of fertilizer with a high content of N and K is recommended for each year of age.

Fertilization is applied in furrows parallel to the planting line or in shallow holes near the plant. The first annual fertilization is applied at the beginning of the rains, and the other two every two months.

Chemical fertilization should be subject to soil analysis, since texture, pH, and electrical conductivity determine the availability of nutritional soil particles.

From the age of 13, the maximum amount of fertilizer to apply is 12 kg per plant, provided that the production is constant, resorting to foliar micronutrient fertilizations when the plant shows signs of deficiency.

Harvest

The avocado is harvested immature generally, however, must have reached physiological maturity or harvest maturity (³ / ₄), in order to support a longer shelf where the ripening process concludes.

Avocado fruits for harvest. Source: pixabay.com

Before harvesting, it is not advisable to apply systemic pesticides to the crop. Limiting the application of contact chemicals to just one to two weeks before harvest.

Storage is carried out in places with a controlled temperature and atmosphere, in order to delay ripening. Once transferred to its destination, ethylene can be applied so that the consumer obtains it to the point of maturity.

Pests

Trips

The Heliothrips haemorrhoidalis species is one of the largest economic pests that affects avocado cultivation. Fruits affected by thrips show dents at the pericarp level that reduce commercial quality.

Severe attacks produce the defoliation of leaves, flowers and fruits, in addition they cause wounds that become a gateway for various phytopathogenic fungi.

Branch borer

The beetle Copturus aguacatae lays its eggs on young branches. When the larvae emerge they cause damage to the tender tissues. In fact, the pest forms galleries within the tissues, weakening the branches that are broken by the weight and action of the wind.

Copturus aguacatae. Source: cesvver.org.mx

Avocado Leaf Root

Nymphs of the pale yellow Psilido Trioza anceps cling to and feed on the surface of young leaves. The attack causes the formation of galls or protrusions that ends up affecting the functionality of the leaves.

Small Bone Borer

The species Conotrachelus perseae and C. avocatae cause direct damage to the crop, promoting the detachment of the fruits. The larvae of these coleopterans penetrate the fruit to the seed, where they feed until the fruit falls.

Bone Bore Moth

The Stenoma catenifer moth is a tiny yellowish lepidopteran whose larvae penetrate the fruit to the seed on which they feed. The incidence in tender shoots is manifested with the wilting of leaves and branches until the branches have completely dried.

Stenoma catenifer. Source: cesvver.org.mx

Red spider

The Oligonychus sp. It is an imperceptible reddish mite that attacks the surface of the leaves, sucking the sap. During severe attacks it discolors the leaves, affecting the underside of the shoots, leaves and flowers.

Diseases

Avocado wilting or sadness

The causal agent of this disease is Phytophthora cinnamomi, which affects the root causing general wilting of the plant. In fact, it causes foliage chlorosis on young branches, weak fruits and eventually the death of the tree.

Trunk and branch cancer

Generalized disease caused by the fungi Nectria galligena, Fusarium episohaeria and Phytophthora sp. The symptoms of cancer in the trunk are manifested as a tear of the bark, initially dark until developing a whitish powder on the surface.

At the level of the branches on the lesions, a white granular dust is observed. The affected plants present a general chlorosis, which can cause the total collapse of the tree.

Anthracnose or smallpox

The symptoms caused by Colletotrichum gloeosporioides are the presence of irregularly shaped brown spots across the leaves. The attack begins on the old leaves and then moves on to the young leaves, branches and flowers.

In the fruit, the damage appears as strong necrotic spots that stop development and affect the final quality. It is the disease that causes the greatest economic losses before, during and after harvest.

Pendulum ringing

Phytopathogenic fungi of the genera Xanthomonas and Diplodia cause a ring or incision at the level of the fruit peduncle. The berry grows round in shape, with purple bark, and tends to mummify without falling from the tree.

Wilting

Caused by the Verticillium albo-atrum fungus, the symptoms are manifested at the foliar level as a general wilting and subsequent death of the plant. Internally, necrosis of the vascular tissues occurs, affecting the effective flowering and fruiting of the plant.

Properties

The main use of avocado as a farm crop is the consumption of fresh fruit. A high percentage is consumed directly or processed as a dressing in various culinary recipes.

Avocado is used in various recipes. Source: pixabay.com

Avocado pulp is high in protein and lacks cholesterol, making it ideal for the daily diet. In addition, it has vitamin E, unsaturated fats and filosterol, which may have some effect in preventing cancer.

The leaves, bark and seeds are used in traditional medicine, either through cooking or the extraction of essential oils. Likewise, it is used in cosmetology as a raw material for the manufacture of creams, emulsions and oils for the skin.

References

1. Alligator Pear. Persea americana Mill. (2018) Encyclopedia of Life. Recovered at: eol.org
2. Cañas-Gutiérrez, Gloria Patricia, Galindo-López, Leonardo F., Arango-Isaza, Rafael, Saldamando-Benjumea, Clara I., (2015) Genetic diversity of avocado cultivars (Persea americana) in Antioquia, Colombia. Mesoamerican Agronomy 26 (1) Redalyc. ISSN 43732621013.
3. Avocado Crop (2004) National Coffee Association - Anacafé ®. Income Diversification Program in the Coffee Company. 25 pp.
4. The cultivation of avocado (Persea americana Miller.), A fruit with extraordinary nutritional, curative and industrial properties (2015) National Administrative Department of Statistics (DANE). Monthly Bulletin, Nº 40.
5. Ferrer-Pereira, H. (2012). Contributions to the taxonomic knowledge of the genus Persea (Lauraceae) in Venezuela. Hoehnea, 39, 435-478.
6. Chickpea Solís Marvin (2011) Avocado Manual. Good Cultivation Practices Variety Hass. Frailes Agricultural Services Agency. San Jose Costa Rica. 89 pp.
7. Persea americana (2018) Wikipedia, The Free Encyclopedia. Recovered at: wikipedia.org.