* Experimental Officer, Horticulture Research and Development Institute, Kandy, Sri Lanka.1. INTRODUCTION
Avocado is one of the popular fruit crops grown and consumed in Sri Lanka. It is also a commonly grown fruit in home gardens of the wet zone of the country. Due to its excellent adaptability to the climatic conditions of the wet zone, particularly its tolerance to rainfall during flowering, and with less demand for crop husbandry practices and few pest and disease problems, the growers select avocado as a permanent crop in their home gardens.
The first introduction of avocado into Sri Lanka is not well documented, but some evidence suggests that it could have been originally domesticated during the Dutch occupation, over 200 years ago. However, the first recorded introduction was made on 12th May 1927 during the British occupation of the island. From that time until 1940 several varieties including Datton, Puebla, Winslowson, Gottfried, St. Anne and Pollock were introduced from time to time. During the period of these introductions, the agricultural policy of the government was directed only towards promoting plantation crops such as tea, rubber and coconut and the staple rice, as a result of which the production development programmes on fruits, including avocado, received much less attention. Limited research and development, however, continued on many tropical and sub-tropical fruits and several avocado varieties and their hybrids were identified for production in the mid-country wet zone. Varieties of the West Indian and Guatemalan race were recommended for the mid-country and varieties of the Mexican race were popularized in the upper Uva region of Sri Lanka at elevations above 1,200 metres. Many natural hybrids occurred as a result of escapes from cultivation in government nurseries and today a large population of non-descript varieties thrive in village home gardens of the mid-country and up-country wet zones.
In 1986/87, another twenty varieties were introduced under the auspices of the UNDP/FAO Horticulture Project. Currently, these varieties are being tested and grown under different agro-climatic regions. At present, about 95 per cent of the trees are of seedling origin, resulting from open pollination of the previously introduced varieties. Avocados are directly consumed as fresh fruits and are also processed into fruit salad and fruit drinks. There is an ongoing research programme in processing and utilization of avocado at the Food Research Unit of the Department of Agriculture. In the 1980s, the soybean development programme of the Department of Agriculture successfully developed weaning foods (drum dried flakes) incorporating avocado, soybean and other tropical fruits.
2. PRESENT SITUATION OF AVOCADO CULTIVATION
2.1 Areas of production
Avocado is well-adapted to the wet zone of the low, mid and high country of Sri Lanka. Presently, avocado is successfully grown in the districts of Kegalle, Kandy, Matale and certain areas of Bandarawela and Nuwara Eliya. The other potential areas where avocado could be grown are Gampaha, Colombo and Kurunegala. Apart from the wet zone, avocado is becoming popular in the intermediate zone as a home garden crop. Its yield potential in the intermediate zone is equally as good as in the wet zone. At present, the total acreage under avocado is around 826 hectares. Generally 2-3 trees can be found in most home gardens. It is hard to find any large-scale plantation in Sri Lanka. Currently, an attempt is being made by the plantation sector to grow avocado on a large scale as an alternative to traditional export crops such as tea, rubber and coconut, under a new crop diversification project. The success of this attempt is still in doubt due to marketing problems in the local market as well as finding avenues to penetrate into non-traditional international markets. The Department of Agriculture is the main supplier of quality and certified planting material. Despite these interventions, productivity of the avocado remains low as modern management practices are seldom followed. There is, however, a good potential for the development of the crop as the tourist industry in Sri Lanka is likely to patronize the fruit. Apart from fresh fruit consumption, the nutritive value of the avocado has been universally recognized and several uses have been found to help promote its utilization. Present yields are low and the recorded annual production is around 11,600 tonnes.
Though several varieties were introduced from time to time in the past, due to lack of priorities for research and development programmes, these varieties were neglected and almost lost. But the expansion of this crop continued mostly through seeds, which were derived from open pollinated trees. As a result, few identified varieties were available for dissemination. The real breakthrough came with the introduction of several varieties in 1986/87 by FAO, since the establishment of a separate Division of Horticulture. As a result of long-term evaluation studies with these varieties, four varieties, namely Fuerte, Booth 7, Simmonds and Tower II were recommended and released by the Variety Release Committee of the Department of Agriculture in 1995. Prior to these introductions, West Indian varieties such as Pollock, Gottfried, St. Anne and the locally developed Purple hybrid were released from Government nurseries for production in the wet zone of the island.
Generally, locally collected seeds are used to raise seedlings as rootstocks. No specific varieties have been identified or selected as rootstocks. Fresh large seeds are preferred over small seeds to raise seedlings for grafting. One of the production constraints in the humid tropics is the severe incidence of Phytophthora root rot. Bearing trees are often found to succumb to the disease, especially if soil moisture levels exceed required limits. Selected resistant rootstocks are needed to be introduced for adaptability studies.
3. PRODUCTION OF PLANTING MATERIAL
Production of planting material is handled by the Seed and Planting Materials Division of the Department of Agriculture and registered private nurseries. These nurseries currently produce grafted plants of Pollock, Purple Hybrid and other locally selected types as well as recently recommended varieties. The major role of production of grafted plants of the new varieties is undertaken by the Horticultural Research and Development Institute. The plant nursery of this institute has so far produced and distributed nearly 8,000 grafted plants of these new varieties to the Central, Subaragamuwa and Southern provinces, both to small farmers and large-scale growers. In addition, these grafted plants were distributed to government and registered private nurseries to establish budwood gardens for future development programmes on the crop.
3.1 Methods of propagation
Wedge or cleft grafting is the most common method of propagation adapted by nurserymen, due to its high percentage of success. Stocks are wedge-grafted at the age of 4-6 weeks. Since avocados exhibit the phenomenon of polyembryony, the more vigorous nucellar seedlings are usually chosen to raise grafted plants. Rootstock seeds are either sown in seed beds or directly planted in black polythene bags of suitable size. Overgrown rootstocks can also be used for budding during the active growth period of seedlings, often indicated by a vigorous growth flush.
In addition to the production of grafted plants, a 'top-working' programme on seedling trees was successfully carried out by the Horticultural Research and Development Institute in two districts in order to popularize the new varieties. As there is some limitation in finding new lands for the expansion of avocado, this method is considered a practical way of promoting avocado cultivation. This programme is now being handled by the provincial extension services.
4. ESTABLISHMENT OF ORCHARDS
4.1 Land preparation
As a part of land preparation, growers only weed and remove other surface vegetation. As most of the land is undulating, small and large scale growers are advised to follow contour planting and to adopt soil conservation methods. Avocado plantations are seldom established on flat land as the mid-country is usually hilly and undulating. Since the crop is gradually spreading to the low-country wet zone as well, many avocado orchards are being established on somewhat level terrain. In these situations, avocado is inter-cropped with other perennial crops such as coconut, banana, jackfruit, rambutan, mangosteen, etc.
4.2 Planting season
The planting season is based on the rainfall pattern of the area. There are two planting seasons in the wet zone, namely Yala (from June to August) and Maha (from October to December). But the major planting is carried out during Yala, as it follows a short dry period with intermittent rains, rather than during the long dry period after the Maha season. Under supplementary irrigation, however, avocados can be easily established at any time of the year. Some amount of shading is necessary during the period of planting to provide the necessary growing environment to young plants.
Earlier recommended spacing of 11.5 x 11.5 metres has now been reduced to 8 x 8 metres as new grafted varieties need much less spacing. In fact, new dwarfing rootstocks have now been developed in California, Florida and Israel that require even less spacing. This gives an advantage of increasing the plant density from 100 plants/ha to 170-180 plants/ha and even more. Planting density also depends on the orchard layout. Conventional systems for avocados grown on flat land include the rectangular, square, triangular, quincunx, and the avenue planting systems. On sloping land, it is recommended that orchards be established on the contour planting system where competition between trees is minimized.
4.4 Opening of pits and planting
The size of the planting hole is generally 60 x 60 x 60 centimetres. The holes are filled with equal parts of topsoil and compost. As most of the wet zone soils are acidic, pH adjustment (to 5.5 - 6.5) is achieved by applying Kiesarite or dolomite, according to the recommendations of the Department of Agriculture. At the time of planting, or 2-3 weeks after planting, 450 grams of fertilizer mixture are applied per hole. Grafted plants are placed in planting holes with the graft union kept about 30 centimetres above ground level. Plants are staked to prevent breakage from winds and are kept tied until the tree is firmly established.
5. MANAGEMENT OF ORCHARDS
5.1 Training and pruning
Training and pruning is not an adopted practice in home gardens. In large-scale cultivations, however, training and pruning are adopted, as they give closer spacing (8 x 8 m) to allow maximum coverage of land. As a first step in pruning, the main stem is cut back at a height of 60 cm from the ground, to encourage formation of lateral branches. A maximum of 3-4 healthy lateral branches are allowed around the trunk and the rest are removed. Up to flowering (3-4 years), the basic framework is developed with a modified central leader system. After bearing commences, no pruning is effected. In case of excess vegetative growth, however, a mild pruning is carried out just after harvesting. In addition, all weak branches and diseased shoots are removed annually.
5.2 Application of manures and fertilizers
Two applications of NPK (N:P2O5:K2O - 12:14:14) is the general practice in large-scale cultivation. These are applied at the onset of the southwestern Yala and northeastern (Maha) rains. The amount increases with the age of plants, starting from 0.5 kg/year in the first year and increasing up to 3 kg/year. After bearing commences, 3 kg/year is the recommended amount per tree. Though compost is recommended in addition to NPK, large-scale growers seldom adopt this practice. In contrast to large-scale cultivation, application of compost and cattle manure is the well-adopted practice in home gardens, where application of NPK is not usually carried out.
5.3 Weeding and mulching
As the avocado is a surface feeder, clean weeding is not recommended as any damage to the root system can accelerate Phytopthora infection. Generally, farmers perform weed control by slashing and using the weeds for mulching. Chemical control is not in practice in most avocado orchards. Since weeds contribute to the spread of diseases and pests, orchards have to be kept relatively weed-free. When weeds are slashed and removed, they are used as a mulch which helps moisture retention during the dry season. In large-scale cultivation, Peuraria is grown as a green mulch to control weeds. Generally, in home gardens, mulching is not practised.
5.4 Supplementary irrigation
Like most of the other perennial fruit crops, avocado is grown as a rainfed crop. As a result of this, avocado undergoes two major water stress periods, during January to April and July to September, usually causing high flower and fruitlet drop during January to April, and heavy fruit drop during July to September. Any means of providing supplementary irrigation to the crop could easily minimize flower and fruit drop during these dry spells. Usually, in home gardens, growers resort to hand watering during these periods of stress. Most orchards minimize water loss by using live or dead mulches.
5.5 Control of pest and diseases
So far, there have been no major outbreaks of diseases recorded in Sri Lanka. Phytophthora root rot, scab and canker are the main diseases that affect avocado. As far as the post-harvest diseases are concerned, anthracnose and stem-end rot are the most common.
Fruit fly and shot hole borer are the major pests in Sri Lanka. Control of fruit fly can be achieved by use of pheromone traps immediately after fruit-set. As avocado is mainly a home-garden crop, and fetches very low prices in the local markets, chemical control measures are not adopted by the growers.
6. HARVESTING OF FRUITS AND YIELDS
Although maturity indices have been developed to detect the correct stage of maturity, traders use only the size of the fruit as an index. During the early season, fruits are often harvested premature and during the harvesting season fruits often become over-mature. Pre-mature harvesting results in poor quality fruits with very high post-harvest losses. Similarly, delayed harvesting results in very high post-harvest losses due to incidence of some diseases that attack the fruit after harvest. Fruits are harvested using a picking-pole attaching a net bag to prevent falling of fruits during harvesting. It is a common practice among traders to remove the stalk attached to the fruit before sending fruits to the market. This operation leads to mechanical damage at the stem end which predisposes the fruit to pathogenic stem-end rot development. The major cause for post-harvest losses of avocado is stem-end rot, which increases the price gap between consumer and grower.
Polysacks are used to pack and transport avocados, which causes considerable mechanical damage as these injuries serve as entry points for the microorganisms causing fruit rot. Artificial ripening is not yet practised among traders. However, keeping fruits at the collection points accelerates the ripening process due to heat buildup and ethylene liberated from other ripening fruits.
There is no form of organized marketing system available for avocado. As a general practice, fruit collectors purchase fruits from home gardens and supply produce to the wholesale dealers or to the retail dealers and outlets directly. Since the quality of marketed fruits cannot be assured, consumers are at the mercy of retailers who often sell sub-standard fruits. Under these circumstances, quality control and proper grading cannot be assured. As far as exports are concerned, quantities exported (nearly 2,400-2,600 kg in 1997) are insignificant. Rough handling and bad packaging during transport increases post-harvest losses considerably.
8. POTENTIAL FOR AVOCADO PRODUCTION DEVELOPMENT
There are two major factors that show good potential for avocado production development in Sri Lanka. It is possible to grow many of the tropical and sub-tropical types in several agro-climatic regions of the country. Moreover, in Sri Lanka, the avocado tree grows and produces crops with very little attention and management. In fact, hardly any grower uses harmful pesticides or other agro-chemicals. If at all, only large orchards would use even chemical fertilizer.
8.1 Long production seasons
As the flowering period extends from late November to June in different districts, the production seasons extend from late May to March. The peak production period falls between May and August and the low production period falls between September and March. Current studies of 'on tree storage' have shown that the off-season period of April to May could also be overcome. Therefore, year-round production will be possible in future. This gives an opportunity to improve the export potential considerably. The Mexican varieties and their hybrids perform well in the semi-dry highlands of the island, and for an export industry, this ecological niche could be exploited easily, especially if the tea-estate sector makes a move to commercial avocado production. The large fruits of the West Indian varieties are generally unsuitable for the export market but are much preferred by local consumers.
8.2 Crop diversification in the estate sector
Due to high price fluctuation of tea, rubber, coconut and spices in the international markets, the estate sector faces serious financial difficulties in managing their estates profitably. As an alternative, they are now looking for other crops for diversification. Areas where rubber, spices and tea are grown, provide suitable climatic conditions to grow avocado. As these estates manage large acreage, they can be utilized effectively to grow avocado on a commercial scale for possible export.
9. CONSTRAINTS IN AVOCADO PRODUCTION DEVELOPMENT
The major constraints to avocado development are the following:
- Poor marketing, handling, grading and packingThe Horticultural Research and Development Institute of the Department of Agriculture has developed improved production packages and introduced new technologies for avocado, but these are seldom adopted by the farmers. However, even with the current marketing system and poor prices there is a considerable number of growers earning a good income from home gardens and small avocado orchards. Though new varieties were released and recommended in 1995, due to lack of a good extension system for fruit crops, these are still not very popular among growers. Also, there is very little contribution from the Export Development Board of Sri Lanka in promoting the export of avocado.
- Low prices
- Poor quality fruit and low yield
- High harvesting losses due to premature harvesting and unsatisfactory harvesting techniques
- Poor facilities for exporters
- Lack of institutional support for pre-export quarantine
The knowledge of the average consumer with regard to the nutritional value of avocado is still very poor. Until recently, the avocado was consumed with caution as the level of fat in fruits created some kind of misconception among the people that it was unhealthy to consume. However, with the propaganda launched by the Horticulture Research and Development Institute regarding its nutritional value and its ability to control heart diseases a better awareness was created among people. But it is still a matter of conjecture whether this nutritional information on the food value of the avocado has played a role in increasing per capita consumption.
10. GOVERNMENT POLICIES AND PLANS FOR RESEARCH AND DEVELOPMENT
To overcome the major constraints and to increase productivity, several steps have been taken under the new crop productivity programme launched by the Ministry of Agriculture. Under this programme, it is envisaged to increase the present acreage of 826 hectares to 1,930 by the year 2005. Though the present yields are as low as 14 t/ha, they could be projected to increase by the application of new production technologies to 18-20 t/ha by the year 2005. Thus, the present annual production of 1,154 tonnes is estimated to increase around 33,000 tonnes. Since the average consumer is familiar with this exotic fruit, consumption among the local population is expected to increase in the future.
To achieve this target, the ongoing research programmes on performance of exotic varieties, development of phenological models for different agro-climatic regions, canopy management, improved agronomic packages, application of pest and disease control measures, development of post-harvest technology and new avenues for utilization of the fruit and its oil for the cosmetic industry, will be intensified.
Production of planting material of new varieties will be further expanded to meet the total target of 300,000 grafted plants. The ongoing 'top working' programme will be further popularized and intensified in areas where farmers currently depend on seedling trees.
With the successful implementation of the 'crop productivity enhancement programme' it should be possible to overcome the major constraints, so as to achieve year-round production of high quality fruits in the future. This will give an opportunity to meet the local as well as the export market demand, thereby increasing the avocado farmers income as well.
The consumers in Sri Lanka have become accustomed to avocado consumption over a long period of time. This positive fact is expected to underpin an increase in area and production during the next few years, using the newly recommended varieties. These varieties can be grown in upcountry Sri Lanka, where large commercial plantations are expected to be established by tea estates, in order also to promote export of fruits to the regional markets of Singapore, Hongkong and Japan.