Everything you need to know about growing avocado! Learn about: 1. Botany of Avocado 2. Origin of Avocado 3. Climate and Soil 4. Orchard Cultural Practices 5. Propagation Techniques 6. Planting Operation 7. Flowering and Fruiting 8. Harvesting and Handling.
Botany of Avocado:
The avocado belongs to the family Lauraceae. The three ecological races have been recognised i.e. Mexican race, Guatemalan race and West Indian race. The Mexican race is included in the group Persea drymifolia and the Guatemalan and the West Indian races are included in the group of Persea americana.
i. Mexican Race:
The leaves of this race are smaller than those of Guatemalan and West Indian races and sharper at the apex. It is characterised by small fruits weighing less than 250 g. The fruit tends to ripen within six to eight months after flowering. Fruits have thin, smooth skin with a large seed fitting loosely in the central cavity. The flowers are hairy pubescent. This is a high land race. Amongst the three races, this is the most resistant to cold temperature. It does not thrive in tropical region.
ii. Guatemalan Race:
This race is native to the highlands of Central America. It tends to bear larger fruit weighing 600 g which requires a longer time to develop and ripen. The fruits ripen 9 to 12 months after flowering. The fruits have thicker, harder and rougher skin as compared to Mexican race. Its seed, held tightly in the cavity of the fruit are small. The oil content ranges between 8-15 per cent. The trees are less resistant to cold than those of the Mexican race.
iii. West Indian Race:
This group is native to the low lands of Central America. The fruits are medium sized, skin is smooth but leathery and glossy. Fruits are borne on long stalks and require upto 9 months for ripening from flowering. Seeds are large, fitting loosely in the cavity. The oil content is low i.e., 3-10 per cent. The race is the least resistant to cold. This is the race which is likely to be successful in most parts of tropical India.
Origin of Avocado:
Avocado is a fruit native to tropical America and is said to have been introduced into India in the beginning of the 9th century. Several varieties of it grow successfully in Bangalore and at Kallar and Burliar at the foot of the Nilgiri Hills. But it has not gained any popularity in this country.
It is an unusual fruit rich in fats and proteins, but has practically no taste. In tropical America, it is a staple food. It has also become very popular in the U.S.A on account of its nutritive value. The fruit has not gamed popularity in India due to lack of sweetness etc.
There are two species of this fruit belonging to the laurel family (Lauraceae). The West Indian and Guatemalan races belong to the species Persea americana and the small-fruited Mexican race to the species P. drymifolia. Avocado is tender to frost and also cannot stand the hot dry winds of North India where it makes poor growth. The West Indian race is successful in South India, especially where the rainfall ranges between 75 cm and 180 cm.
The fruit of the avocado is a somewhat pear-shaped of the size of a large pear to a small grape-fruit. It has a single large seed surrounded by buttery pulp and a hard skin. It can be propagated by layering, shield-budding, Forkert-budding, or side grafting. The layered-plants are ready in six months and make good growth when planted in the field after another six months.
The avocado tree attains a large size and should be planted 8 to 10 metres apart. Hardly any pruning is required for this evergreen tree. The trees start bearing at the age of five years and the yield in India is 100 to 200 fruits per tree. The fruits mature in May-June and August-September. The problems of avocado cultivation are frost injury, poor fruit-set, alternate bearing and foot-rot of the trees. In view of its high nutritive value, it would be worthwhile to popularize it in India.
Climate and Soil Required for Growing Avocado:
The avocado prefers mild winters of the tropics and sub-tropics. The trees are tender to frost and do not stand hot dry winds. The range of mean maximum and minimum temperatures in the Nilgiri hills in Tamil Nadu, where avocado is grown are 27.2°C to 33.9°C and 14.9°C to 22.2°C, respectively. Avocado is successful in South India especially in areas with rainfall of 75 to 190 cm. It grows fairly well on the slopes of Nilgiris between altitude of 610 and 1524 metres.
The West Indian varieties will probably grow well in the equable climate of moist regions of south, west and east India from sea-level to elevations ranging from 305 to 914 metres, but Guatemalan varieties may require much higher altitude. In region, where minimum winter temperatures of -0.5 to 3.5°C occur; only the Mexican race survives. Mexican and Guetemalan cultivars withstand low temperature of 10 – 15°C.
Avocado can be grown on a wide range of soil types. It thrives best on a loam of medium texture overlying a porous sub-soil. The plants are extremely sensitive to poor drainage and cannot stand water-logging. Heavy clay soils should be avoided as avocado succumbs quickly to wet area. Some of the loams and sandy loams of alluvial origin are excellent.
The optimum pH for, avocado is 5-7 and are intolerant to saline conditions. Shallower soils less than 60 cm in depth and with rocky or gravelly substrata close to the surface should be strictly avoided. The root system does not fully develop in such soils. The trees remain dwarf and die a premature death at a very early age and are also liable to be seriously damaged or totally uprooted in exposed windy situations.
Orchard Cultural Practices for Growing Avocado:
i. Irrigation:
The first watering should be given soon after the application of manures and the second watering on the third day, so as to ensure the wetting of the full root zone. The subsequent irrigations from February to June may be given after 6-10 days depending upon the availability of moisture in the soil and the intensity of heat in the weather.
Irrigation during the rain from July to September is not required except during prolonged dry spell. After rainy season is over, the avocado trees may again be irrigated after 15 days till the end of November. During December, water may be withheld for about a month and the orchard soil cultivated and manured prior to the flowering of trees in January.
ii. Intercropping:
Intercropping can be practiced to compensate the economic loss of initial years. Legumes or shallow-rooted crops as intercrops may be done in young orchards. The modern practice in California is to plant 400 trees per hectare (5 x 5 m) and gradually thin to a ultimate 140 trees per hectare (10 x 7 m).
iii. Manuring and Fertilization:
The avocado needs fertilization for yielding good crop over the years. Application of Nitrogen was found to be most essential for cultivation of avocado. The most productive range for yield was associated with leaf nitrogen levels between 1.6 and 2.0 per cent. Application of K had little effect on yield increment. The young avocado trees should get N, P, K in the proportion of 1: 1/2: 1 and the older trees in the proportion of 2: 1/2: 2.
To avocado plants of 1 – 3 years age, apply FYM 25 kg and NPK @ 40, 20, 35 g/plant respectively. To full grown trees of 10 years and above apply FYM 50 kg and NPK @ 200, 45, 165 g/ plant, respectively. Application of nitrogen influence fruit size and yield markedly.
At Poona, good results have been obtained by applying 45 kg of farmyard, 5 kg of castor cake and one kg of superphosphate to 7 years old trees in the month of January.
Propagation Techniques for Avocado:
The avocado is commonly propagated by seed in most of the tropical countries. Seedlings usually vary somewhat in their characteristics from their parents and do not generally breed true to type. To ensure parent quality in the progeny, it is necessary to propagate the avocado by vegetative methods such as cuttings, layering, budding or grafting.
Vegetative Propagation:
The rooting capability of avocado cuttings varies greatly depending on the races and cultivars. The Mexican race is relatively easy-to-root whereas the West Indian race is quite difficult. The Guatemalan race is intermediate in rooting ability on cuttings.
Avocado should preferably be propagated vegetatively by budding or grafting. The shield- budding, Forkert-budding or side grafting can be successfully followed. In Tamil Nadu, layering as well as approach grafting gave up to 75 per cent success. In West Bengal, chip budding was found more successful. The grafted plants become ready in six months and may be planted in the field after another six months.
Purple avocado serves as a good rootstock for avocado. The Guatemalan rootstocks are more sensitive to cold and have also proved more susceptible to high pH, chlorosis and to verticillium wilt. Mexican race rootstocks are used generally in Israel and in South Africa. West Indian rootstocks are preferred in warmer regions or where salinity is a problem.
Planting Operation for Growing Avocado:
The planting distance will have to be determined according to the vegetative vigour developed by the tree of a particular variety in a given set of environments.
The tree is planted in pits (1 x 1 x 1 m) filled with top soil mixed with well rotten farmyard manure, compost or leaf mould. The distance between plants must not be less than 10 metres. In this way 105 plants will be accommodated in one hectare. Under Poona conditions, a spacing of 8-9 metres may be adopted for both the Purple and the Green varieties. The commonly followed spacing in different areas is 7 x 7m but it may vary from 6 – 12 m in the square system.
On the sea coast and on alluvial soils where the vegetative growth of the trees would be more luxuriant, wider spacing may be necessary. The plants are planted with a ball of earth around the roots. The grafting joint should be well above the ground while planting and supported by stakes against possible damage from strong winds. If there is any danger of water-logging, they should be planted on mounds, as avocado cannot withstand waterlogged conditions.
The plants should be watered regularly during the seasons other than the monsoon and particularly during the summer, as otherwise the branches are likely to be scorched and the tree vitally damaged. The avocado tree is particularly subject to wind injury. For this reason, windy localities and sites should be strictly avoided.
Flowering and Fruiting:
Vegetatively raised plants usually bear earlier whereas seedling trees start bearing at 5- 6 years age. The plants have a marked tendency to biennial bearing and girdling increases the yield of such plants.
The inflorescence in avocado is a compound panicle of raceme with unique flower behaviour, thus, termed as protogynous, diurnally synchronous dichogamy. The female and male parts mature at different times, it synchronises in such a way that all the open flowers on a tree are female at one time and male at a different time.
The synchronisation is diurnal for each tree; flower is functionally male at one part of the day and functionally female during another part of the same day. The dichogamy is also protogynous, the pistil maturing earlier than the stamen. While the flower is structurally bisexual, it is functionally unisexual. Each flower opens twice and is closed in between, the first time it functions as a female, the second time as a male.
Based on this unique flower behaviour, avocado cultivars can be divided into two groups i.e. A and B. In group A, first opening takes place in the morning, second opening during the afternoon. In group B, the first opening is in the afternoon and the second opening in next morning. Therefore, every morning A- pistils can be fertilized by B-pollen, while during afternoon B- pistils are ready to receive A-pollen. It is reported that not all cultivars or seedling trees follow this pattern and rhythm is upset by cold or cloudy weather. The single tree is often unfruitful and mixed planting of cultivars is desirable. Pollination is done chiefly by honey-bees.
In the climate of Poona the avocado produces flowers from November to January in three main flushes. The three flushes of flower clusters do not raise from different branches but arise in succession from the extension of the same leafy shoots. The flowers produced from November to December fail to set fruit, while those produced in January set a successful crop. Similarly in the lower foot hills of Nilgiris, it has been observed that November-December flowering are occasional and not very dependable for successful setting of crop but the March and April flowering do set successful crop.
Harvesting and Handling Avocado Fruits:
Seeded avocado fruits are 8-10 times larger than seedless ones. The avocado tree starts bearing fruit after 4-5 years of planting. The fruits are harvested in August – September in South India. The fruit is clipped as soon as it changes colour from purple to deep maroon and green to greenish yellow so that it may be marketed before becoming soft with ease. The fruit (berry) is something like a pear in shape with a single large seed surrounded by buttery pulp and a hard skin.
The harvested fruit should take 4-5 days to soften after which it does not keep long. The purple avocado should be picked as soon as it shows a blush, a purple colour on its skin. In Green avocado, the brightness of the green colour of the skin usually diminishes and a slight yellowish tint develops. In storage, the purple avocado develops a deep maroon colour all over the skin within a day or two of harvesting and the Green avocado similarly becomes greenish yellow.
The purple avocado tree of 10-15 years in age may bear about 200 to 300 fruits. It has been reported that 20 – 25 years old avocado tree can yield 1000 – 1500 fruits. However, good orchards in California have been found to give a yield of 6000-12000 fruits per acre per year.
Avocado is a climacteric fruit. Mature avocado fruits ripen in 4 – 5 days after harvesting. Ripening of fruits at 15 – 21°C takes place satisfactorily.
Treatment of avocado fruits with ABA methyl ester at 220 mg/g of fresh weight immediately after picking enhanced the soluble polyphenol oxidase activity in the mesocarp, indicating an association between ABA level and fruit browning potential.
The avocado fruit is best packed in single layers in small, flat, well-ventilated wooden boxes. The fruit is padded with sufficient wood-wool to keep in position in the boxes.
The West Indian cultivars are more sensitive to low temperature than the Guatemalan and Mexican cultivars. Cold tolerant cultivars store best at 4.4°C whereas cold intolerant ones store at 10-13°C. Fruits wrapped in polythene bags and stored at gradually decreasing temperatures (2 days at 17°, 2 days at 14°, 4 days at 12° and then 8°C) do not soften for 23 days in Fuerte and 46 days in Nabal. For most varieties, the ideal storage temperature seems to be about 5.6°C to 8.9°C.