Persea americana Miller
Family
Lauraceae
Synonyms
Persea gratissima Gaertn.f., Persea drymifolia Schlecht. & Cham., Persea nubigena L.O.Williams.
Vernacular Names
| Malaysia | Avokado, apukado. |
| English | Avocado. |
| Indonesia | Adpukat, avokad. |
| Papua New Guinea | Bata (Pidgin). |
| Philippines | Avocado. |
| Cambodia | ‘avôkaa. |
| Thailand | Awokado. |
| Vietnam | Bo’, lê dâù. |
| French | Avocatier. |
Geographical Distributions
The probable area of origin of Persea americana is a Chiapas-Guatemala-Honduras centre. The Spanish conquest found it indigenous in Central America from Mexico to Peru and east to Venezuela. During the 17th Century, it became established on islands of the Caribbean but it was not until the 19th Century that it spread beyond Central America and reached Southeast Asia (Indonesia, the Philippines). At present, P. americana is grown in many tropical and subtropical countries.
Description
P. americana is a dome-shaped, evergreen tree, conforming to Rauh’s architectural model that can reach up to 20 m tall. The primary anchorage roots penetrate to 3-4 m deep, but the tree is largely supported by a shallow (to 0.5 m deep) unsuberized secondary root system.
The leaves are arranged spirally, simple and entire, variable in shape and size. The petioles are 1.5-5 cm long. The blade is elliptic to lance-shaped, ovate or obovate, measuring 5-40 cm x 3-15 cm, reddish when young, turns dark green, waxy above, glaucous beneath and with prominent midrib and veins.
The inflorescences are panicles of cymes, produced at the end of twigs, mostly indeterminate, end in a vegetative bud and many-flowered. The flowers are bisexual, with 3-merous, fragrant and greenish. The perianth is in 2 whorls, with 3 outer and 3 inner tepals, measures about 5 mm long and densely hairy. There are 9 stamens in 3 whorls and plus 1 whorl of 3 staminodes. The inner whorl stamens bear 2 orange nectaries at the base. The pistil is with a 1-celled ovary, slender style and simple papillate stigma.
The fruit is a large fleshy berry, single-seeded, pyriform or spherical and measures 7-20 cm long. It is yellow-green to maroon and purple and the weight ranges from 50 g to 1 kg. The exocarp is 1-3 mm thick and smooth to warty. The mesocarp is yellow-green and of butter-like consistency.
The seed is large, spherical, with 2 seed coats and 2 large fleshy cotyledons that enclose a small embryo.
Ecology / Cultivation
Evolution of P. americana has occurred in the rainforests of the humid subtropics and highland tropics of Central America, yet commercial production has extended to the lowland tropics and the cooler semi-arid regions of the world. The success in such diverse climates is undoubtedly due to the different tolerances of the three ecological races. The West Indian race is most sensitive to cold and may be damaged when temperatures fall below 1-2°C. However, the trees of this race are adapted to high temperatures (28-36°C with a 4-5°C diurnal range). Mexican and Guatemalan race trees can withstand -4°C for short periods; the optimum daytime temperatures for growth are 25-33°C with an 8-10°C diurnal range. Established trees will tolerate temperatures to 40°C, but prolonged exposure with low relative humidity results in severe stress and loss of productivity. The leaves have a high stomatal density (40 000-73 000 cm-2, only on the underside) and limited vascular network typical of rainforest species. The photosynthetic rates are low (characteristically 5-9 µmol CO2 m-2 s-1) and leaves reach light saturation at about 25% of full sunlight. Trees do not respond to variations in day length. The trees and fruit are susceptible to wind damage and in exposed sites shelter should be provided.
P. americana requires a well-drained aerated soil because the roots are intolerant of anaerobic conditions; waterlogging for more than 24 hours can kill trees. The root growth is shallow and a low frequency of root hairs limits the uptake of water and nutrients. Roots are most active at soil temperatures of 18-28°C; growth and water relations in the tree are disrupted when the soil temperature falls to 13°C. P. americana is successfully grown where annual rainfall is as low as 300 mm (supplemented with irrigation) and in excess of 2500 mm. Year-round maintenance of soil moisture is necessary for a high yield. The critical periods of water demand are during flowering and fruit set, 3 months later when early fruit drop occurs, and during the following period of fruit filling and maturation. Prolonged wet periods lead to fruit losses from anthracnose. P. americana is sensitive to salinity; electrical conductivity and chloride content of irrigation water should not exceed 550 µmhos and 80 mg/kg respectively. When roots have been damaged by root rot, chloride-based fertilisers should be avoided. A pH of 5.0-5.8 is optimum for the growth and fruit yield.
Line Drawing / Photograph
References
- Plant Resources of South-East Asia No. 2: Edible fruits and nuts.
