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Avocado Tree Fantastic Variety Grafted Tree in a 3 Gallon Container. Green, paper thin skin, the most cold hardy of all the Mexican avocados. The fruit has a creamy texture with fantastic flavors. It is a vigorous growing beautiful tree. Mature tree cold hardy down to 15 degrees.

Description
Origin and Distribution
Pollination
Climate
Soil
Propagation
Spacing
Maturity and Harvesting
Yield
Marketing
Storage
Pests and Diseases
Food Uses
Avocado Oil
Food Value
Toxicity
Other Uses
Medicinal Uses

The avocado, unflatteringly known in the past as alligator pear, midshipman's butter, vegetable butter, or sometimes as butter pear, and called by Spanish-speaking people aguacate, cura, cupandra, or palta; in Portuguese, abacate; in French, avocatier; is the only important edible fruit of the laurel family, Lauraceae. It is botanically classified in three groups: A), Persea americana Mill. var. americana (P. gratissima Gaertn.), West Indian Avocado; B) P. americana Mill. var. drymifolia Blake (P. drymifolia Schlecht. & Cham.), the Mexican Avocado; C) P. nubigena var. guatemalensis L. Wms., the Guatemalan Avocado. The fruit cut open is a 'Hall'.

Description

The avocado tree may be erect, usually to 30 ft (9 m) but sometimes to 60 ft (18 m) or more, with a trunk 12 to 24 in (30-60 cm) in diameter, (greater in very old trees) or it may be short and spreading with branches beginning close to the ground. Almost evergreen, being shed briefly in dry seasons at blooming time, the leaves are alternate, dark-green and glossy on the upper surface, whitish on the underside; variable in shape (lanceolate, elliptic, oval, ovate or obovate), 3 to 16 in (7.5-40 cm) long. Those of the Mexican race are strongly anise-scented. Small, pale-green or yellow-green flowers are borne profusely in racemes near the branch tips. They lack petals but have 2 whorls of 3 perianth lobes, more or less pubescent, and 9 stamens with 2 basal orange nectar glands. The fruit, pear-shaped, often more or less necked, oval, or nearly round, may be 3 to 13 in (7.5-33 cm) long and up to 6 in (15 cm) wide. The skin may be yellow-green, deep-green or very dark-green, reddish-purple, or so dark a purple as to appear almost black, and is sometimes speckled with tiny yellow dots, it may be smooth or pebbled, glossy or dull, thin or leathery and up to 1/4 in (6 mm) thick, pliable or granular and brittle. In some fruits, immediately beneath the skin there is a thin layer of soft, bright-green flesh, but generally the flesh is entirely pale to rich-yellow, buttery and bland or nutlike in flavor. The single seed is oblate, round, conical or ovoid, 2 to 2 12 in (5-6.4 cm) long, hard and heavy, ivory in color but enclosed in two brown, thin, papery seedcoats often adhering to the flesh cavity, while the seed slips out readily. Some fruits are seedless because of lack of pollination or other factors.


Origin and Distribution

The avocado may have originated in southern Mexico but was cultivated from the Rio Grande to central Peru long before the arrival of Europeans. Thereafter, it was carried not only to the West Indies (where it was first reported in Jamaica in 1696), but to nearly all parts of the tropical and subtropical world with suitable environmental conditions. It was taken to the Philippines near the end of the 16th Century; to the Dutch East Indies by 1750 and Mauritius in 1780; was first brought to Singapore between 1830 and 1840 but has never become common in Malaya. It reached India in 1892 and is grown especially around Madras and Bangalore but has never become very popular because of the preference for sweet fruits. It was planted in Hawaii in 1825 and was common throughout the islands by 1910; it was introduced into Florida from Mexico by Dr. Henry Perrine in 1833 and into California, also from Mexico, in 1871. Vegetative propagation began in 1890 and stimulated the importation of budwood of various types, primarily to extend the season of fruiting. Some came from Hawaii in 1904 (S. P. I. Nos. 19377-19380). Now the avocado is grown commercially not only in the United States and throughout tropical America and the larger islands of the Caribbean but in Polynesia, the Philippines, Australia, New Zealand, Madagascar, Mauritius, Madeira, the Canary Islands, Algeria, tropical Africa, South Africa, southern Spain and southern France, Sicily, Crete, Israel and Egypt. Though the Spaniards took the avocado to Chile, probably early in the 17th Century and it was planted from the Peruvian border southward for over 1000 mi (1,600 km) actual commercial plantings were not established until California cultivars were introduced about 1930 into two areas within 100 mi (160 km) of Santiago where the industry is now centered. The first trees were planted in Israel in 1908, but named cultivars ('Fuerte' and 'Dickinson') were not introduced until 1924. These aroused interest in the feasibility of the crop for the southern half of the coastal plain and the interior valleys, and development of the industry has steadily gone forward, except for a period in the 1960's when much planting stock was destroyed because of marketing problems. In 1979, Israel produced 33,000 tons (30,000 MT) and exported 28,600 tons (26,000 MT). In just the last few years, New Zealand has launched a program to expand commercial production, especially in the Bay of Plenty area, with protection from wind and frost, with a view to becoming a major exporter of avocados. California produced 265 million lbs (12,045 MT) in 1976; 486 million lbs (22,090 MT) in 1981. The Florida avocado potential is estimated at 150 million lbs (6,818 MT). Both states suffer fluctuations because of the impact of periodic freezes, droughts, high winds or other seasonal factors. Presently, Mexico, with 150,000 acres (62,500 ha) is the leading producer—267,786 tons (243,000 MT); the Dominican Republic is second—144,362 tons (131,000 MT); U.S.A. (California and Florida combined) with 52,000 acres (21,666 ha), third—131,138 tons (119,000 MT); Brazil is fourth—128,934 tons (117,000 MT). Israel, with 16,000 acres (6,666 ha), is fifth; and South Africa sixth. Half of California's plantings are in San Diego County close to Mexico. As an exporter, Mexico again leads, followed by California, Israel, South Africa and Florida, in that order. Nearly all of Brazil's crop is consumed domestically..

Pollination

Many isolated avocado trees fail to fruit from lack of pollination. Commercial growers are careful to match Class A cultivars whose flowers will receive pollen in the morning with Class B cultivars that release pollen in the morning and every grower must be sure to include compatible pollinators in his grove. Bulletin 29 (1971) of the Ministry of Agriculture in Guatemala tabulates the flowering periods (varying from August to April) of 48 introduced and locally selected cultivars, and the hours of the day when each is receptive to or shedding pollen.

Climate

The West Indian race requires a tropical or near tropical (southern Florida) climate and high atmospheric humidity especially during flowering and fruitsetting. The Guatemalan race is somewhat hardier, having arisen in subtropical highlands of tropical America, and it is successful in coastal California. The Mexican race is the hardiest and the source of most of California avocados. It is not suited to southern Florida, Puerto Rico or other areas of similar climate. Temperatures as low as 25ºF (-4ºC) do it little harm. In areas of strong winds, wind-breaks are necessary. Wind reduces humidity, debydrates the flowers and interferes with pollination, and also causes many fruits to fall prematurely.

Soil

The avocado tree is remarkably versatile as to soil adaptability, doing well on such diverse types as red clay, sand, volcanic loam, lateritic soils, or limestone. In Puerto Rico, it has been found healthier on nearly neutral or slightly alkaline soils than on moderately or highly acid soils. The desirable pH level is generally considered to be between 6 and 7, but, in southern Florida, avocados are grown on limestone soils ranging from 7.2 to 8.3. Mexican and Guatemalan cultivars have shown chlorosis on calcareous soils in Israel. The tree's primary requirement is good drainage. It cannot stand excessive soil moisture or even temporary water-logging. Sites with underlying hardpan must be avoided. The water table should be at least 3 ft (.9 m) below the surface. Salinity is prejudicial but certain cultivars (see 'Fuchs-20' and 'Maoz') have shown considerable salt-tolerance in Israel. Avocados grafted onto 'Fuch-20' rootstocks and irrigated with water containing 380 to 400 ppm C1 performed well in a commercial orchard. In the Rio Grande Valley of Texas, cultivars of the Mexican race must be grafted onto salt tolerant West Indian rootstocks.

Propagation

Normally, avocado seeds lose viability within a month. 'Lula' seeds can be stored up to 5 months if placed in non-perforated polyethylene bags and kept at 40ºF (4.4ºC), thus indicating that it may be possible to successfully store seeds of other cultivars ripening at different seasons for later simultaneous planting. Fresh seeds germinate in 4 to 6 weeks, and many people in metropolitan areas grow avocado trees as novelty house plants by piercing the seed partway through with toothpicks on both sides to hold it on the top of a tumbler with water just covering 1/2 in (1.25 cm) of the base. When roots and leaves are well formed (in 2 to 6 weeks), the plant is set in potting soil. Of course, it must be given adequate light and ventilation. In nurseries, seeds that have been in contact with the soil are disinfected with hot water. Experiments with gibberellic acid and cutting of both ends of the seed with a view to achieving more uniform germination have not produced encouraging results. Seedlings will begin to bear in 4 or 5 years and the avocado tree will continue to bear for 50 years or more. Some bearing trees have been judged to be more than 100 years old. In Australia, seeds planted in early fall germinate in 4 to 6 weeks; if planted later, they may remain dormant all winter and germinate in early spring. Seedlings should be kept in partial shade and not overwatered. While many important selections have originated from seeds, vegetative propagation is essential to early fruiting and the perpetuation of desirable cultivars. However, seedlings are grown for rootstocks. For many years, shield budding was commonly practiced in Florida, but this method requires considerable skill and experience and is not successful with all cultivars. Therefore, it was largely replaced by whip, side-, or cleft-grafting, all of which make a stronger union than budding. In the past, seedlings were grafted when 18 to 36 in (45-90 cm) high. It is now considered far better to graft when 6 to 9 in (15-23 cm) high, making the graft 1 to 3 in (2.5-7.5 cm) above ground level. West Indian rootstocks are desirable for overcoming chlorosis in avocados in Israel. Avocado cuttings are generally difficult to root. Cuttings of West Indian cultivars will generally root only if they are taken from the tops or side shoots of young seed rings. But etiolated cuttings (new shoots) from gibberellin treated hardwood and semi hardwood cuttings of 'Pollock' as well as 'Lula' have been rooted with 50-60% success and, when treated with IBA, 66-83% success under mist in Trinidad. Cuttings of 'Fuchs-20' have rooted under mist with 40 to 50 or even 70% in Israel. Cuttings of 'Maoz' have rooted at the rate of 60% by a special technique developed in California. An Israeli selection, 'G.A. 13' has given 70 to 90% success in rooting cuttings under mist for the purpose of utilizing them as rootstocks in saline and high lime situations. Air-layering is sometimes done to obtain uniform material uninfluenced by rootstock, for research on specific problems. Degree of success depends on the cultivar (those of the Mexican race rooting most quickly), and air-layering is best done in spring and early summer. At times, mature avocado groves are top worked to change from an unsatisfactory cultivar, or one declining in popularity, to a more profitable one, or an assortment of cultivars for different markets. In 1957, 2,700 ";obsolete"; avocado trees in Ventura, California, were being grafted (top-worked) to mainly 'Hass', some to 'Bacon' and 'Rincon'. This procedure may involve thousands of trees in a given region. It is done in December and January in Florida. Inasmuch as avocado roots are sensitive to transplanting, it is now considered advisable to raise planting material in plastic bags which can be slit and set in the field without disturbing the root system.

Spacing

Spacing is determined by the habit of the cultivar and the character of the soil. In light soil, 25 x 25 ft (7.5x7.5 m) may be sufficient. In deep, rich soil, the tree makes its maximum growth and a spacing of 30 or 35 ft (9.1 or 10.7 m) may be necessary. If trees are planted so close that they will ultimately touch each other, the branches will die back. Some growers plant 10 to 15 ft (3-4.5 m) apart initially and remove every other tree at 7 to 8 years of age. If the surplus trees are not bulldozed but just cut down leaving a stump, application of herbicide may be needed to prevent regrowth. Ammonium sulfamate has been proven effective. In modernized plantings, space between rows is necessary for mechanical operations. Holes at least 2 ft (0. 6 m) deep and wide are prepared well in advance with enriched soil formed into a mound. After the young plant is put in place a mulch is beneficial, weeds should be controlled, and watering is necessary until the roots are well established. Generally small amounts of fertilizer are given every 2 months with the amount gradually increasing until fruiting begins. Bearing trees need, on the average, 3 to 4 lbs (1 1/2-2 kg) 3 times a year, beginning when the tree is making vegetative growth. No fertilizer should be given at blooming time; one must wait until the fruits are firmly set. Nitrogen has the greatest influence on tree growth, its resistance to cold temperatures, and on fruit size and yield. Fertilizer mixes vary greatly with the type of soil. Mineral deficiencies determined by leaf analysis, are usually remedied by foliar spraying. Magnesium deficiency was formerly a serious handicap to avocado growers in Florida and Kenya. In California, zinc deficiency has been corrected by applying zinc chelates or zinc sulfate to the soil instead of spraying the foliage. Keeping the upper soil moist has been greatly facilitated by drip irrigation, which also may carry 80% of the fertilizer requirement. Because some cultivars tend to grow too tall for practical purposes, commercial growers cut trees back to 16 or 18 ft (4.8-5.4 m), let them grow back to 30 ft (9.1 m) and top them again. But decapitation is not a perfect remedy because the tendency of the avocado tree is to grow a new top very quickly. Recently it has been found that the growth-inhibiting chemical, TIBA (triiodobenzoic acid) slows down terminal growth and encourages lateral shoots. A system of pruning to encourage lower branching is being tried on 'Lula' in Martinique. Avocado branches frequently need propping to avoid breaking with the weight of the developing fruits. Some growers find it profitable to interplant bananas until the avocado trees reach bearing age.

Maturity and Harvesting

Avocados will not ripen while they are still attached to the tree, apparently because of an inhibitor in the fruit stem. Homeowners usually consider the entire crop pickable when a few mature (full grown) fruits have fallen. This is not a dependable guide because the prolonged flowering of the avocado results in fruits in varying stages of development on the tree at the same time. The largest fruits, of course, should be picked first but the problem is to determine when the largest are full grown (perfectly mature for later perfect ripening). If picked when full grown and firm, avocados will ripen in 1 to 2 weeks at room temperature. If allowed to remain too long on the tree, the fruits may be blown down by wind and they will be bruised or broken by the fall. Florida maturity standards for marketing have been determined by weight and time of year for each commercial cultivar so that immature fruits will not reach the market. Immature fruits do not ripen but become rubbery, shriveled and discolored. Most West Indian cultivars will ripen properly if picked when the specific gravity becomes 0. 96 or lower, but 'Waldin' is fully mature when the specific gravity is still above 0.98. Guatemalan and Guatemalan X West Indian cultivars generally are harvest-mature when the specific gravity is 0.98 or lower. In California, physiological maturity of 'Bacon', 'Fuerte,' 'Hass' and 'Zutano' has been determined by measurement of length, diameter and volume, but dry weight, correlating with oil content, is considered a better maturity index. California law has, since 1925, required a minimum of 8 % oil, but oil content varies greatly among cultivars and also the climatic region where the fruit is grown. Some people complain that the 8% standard is too low for some cultivars. Maximum flavor of 'Fuerte' develops when the fruit is harvested at an oil content of 16%. Therefore, a minimum dry weight standard of 21 % has been recommended. Formerly, avocados were detached by means of a forked stick and allowed to fall, but this causes much damage and loss. Nowadays harvesters usually use clippers for lowhanging fruits and for those higher up a long handled picking pole with a sharp ";V"; on the metal rim to cut the stem and a strong cloth bag to catch the fruit. Gloves are worn to avoid fingernail scratches on the fruit. In California, studies have been made of the effects of hand clipping (leaving stem on), hand snapping (which removes the stem), tree-shaking, and limb shaking (which removes the stem from some of the fruits). All methods are acceptable if the stem scar is waxed on stemless fruits to avoid weight loss before ripening at which time the stem detaches naturally. In Australia, some growers are using hydraulic lifts to facilitate hand-picking. A tractor fitted with a triple-decked picking platform has been adopted by some large growers in Chile. Efforts to develop dwarf avocado trees by means of sandwich interstocks from low growing types have been going on in California since 1964. Avocados must be handled with care and are packed and padded in single or double-layer boxes or cartons for shipment. A special ";Bruce box";, holding 32 lbs (14.5 kg) is used for large fruit. The fruits may be held in position in molded trays.

Yield

It will be seen that the yield varies greatly with the cultivar, age of tree, the locale, weather and other conditions. The small tree, 'Ganter', has yielded 44 lbs (20 kg) annually; 'Nabal', 68 lbs (31 kg); 'Benik', 116 lbs (53 kg); 'Duke', 168 lbs (76 kg), and 'Anaheim', 220 lbs (100 kg). Close-planting in southern Florida provides yields averaging 11,000 lbs per acre (11,000 kg per ha) in young groves and nearly twice this amount is anticipated after the time has come to thin the planting by half. Girdling has been tested in Florida, Australia and Israel as a means of increasing the yield of shy bearing but popular cultivars. It must be repeated every year to be fully effective. It may decrease the yield of normally fruitful cultivars.

Marketing

Inasmuch as the avocado, outside of Latin America, has been widely regarded as a luxury fruit, large scale marketing has been dependent on consumer education and advertising. Calavo Growers of California is an enterprising association of 2,600 avocado growers. The Mayflower Fruit Association, of which Blue Anchor is a member, packs over 60% of the avocados grown in the San Joaquin Valley. The California Avocado Commission spends millions of dollars in newspaper, magazine, television, radio and other publicity financed by grower assessments. The Florida Lime and Avocado Administrative Committees, together with the Florida Division of Marketing's Bureau of Market Expansion and Promotion, spend about 1/4 million dollars annually for advertising and publicity through the Press and by means of special marketing displays and distribution of recipes. The trademarks, ";Calavo"; and ";Flavocado"; (Florida Avocado Growers Exchange), are recognized nationally and internationally. The 8% oil standard established in California kept Florida avocados out of the California market until a court decision in 1972 outlawed the discrimination against Florida fruits which average about half the oil content of California cultivars and are advocated by growers as having better flavor and fewer calories. Calavo Growers Cooperative of California now handles 57% of the local avocado crop and 33% of the Florida crop, selling directly to the retail markets. Combined Florida and California efforts have raised the rate of regular avocado consumption in the United States from 6% in the late 1960's to over 15% today. In California, the Avocado Marketing Research Information Center was created in 1983 to gather and report information on production, foreign and domestic shipments and other activities. Israel makes substantial investments in developing European markets for avocados and has attained the position of principal exporter to Europe. France and the United Kingdom are the chief consumers.

Storage

Ripening of avocados may be hastened by exposure to an atmosphere of at least 10 ppm ethylene 25 to 49 hours after harvest. The avocado does not respond to earlier treatment. Changes in pectinesterase activity and pectin content are being studied to measure ripening of avocados in storage. Dipping in latex has retarded decay in avocados stored at room temperature. Avocados ship well and are sent to overseas markets under refrigeration in surface vessels. The fruits are subject to chilling injury (dark-brown or gray discoloration of the mesocarp) in refrigerated storage and degree of susceptibility varies with the cultivar and stage at harvesting and length of time in storage. Most commercial cultivars can be held safely at temperatures between 40º and 55ºF (4.5º-12.8ºC) for at least two weeks. The best ripening temperature after removal from storage is 60ºF (15.5ºC). Removal of ethylene from controlled atmospheric storage (2% oxygen, 10% carbon dioxide) prolongs the marketable life of avocados. Reducing atmospheric pressure to subatmospheric 60 mm Hg in the refrigerated storage unit at 42.8ºF (6ºC) retards ripening of avocados by reducing respiration and ethylene production. Removed after 70 days, fruits have ripened normally at atmospheric pressure and 57.2ºF (14ºC). Experimental calcium treatments have delayed ripening and reduced internal chilling injury in storage but make the fruit externally less attractive and are, therefore, considered commercially undesirable. 'Hass' fruits dipped in fungicide 24 hours after harvest and sealed in polyethylene bags containing an ethylene absorbent (potassium permanganate on vermiculite or on aluminum silicate), have been successfully stored for 40 or 50 days at 50ºF (10ºC). Waxed 'Fuerte' avocados stored for 2 weeks at 41ºF (5ºC) and ripened at 68ºF (20ºC) ripened only 1 day later than non-waxed; however, waxing does reduce weight loss. In 1965, to overcome the problem of oversupply during the harvesting season and undersupply during the offseason, California adopted liquid-nitrogen freezing of peeled or unpeeled avocado halves, which can be thawed and served as the equivalent of fresh fruits in restaurants, on airplanes and in institutions.

Pests and Diseases

Avocados have no major insect enemies in Florida but migrating cedar waxwings feed on leaves, flowers and very young fruits and the fruits are commonly attacked by squirrels, rats and mice. The avocado red mite, Oligonychus yothersi; is the most common predator on the leaves in some groves and not in others. Red-banded thrips, Selenothrips rubrocinctus, the greenhouse thrips, Heliothrips haemorrhoidalis, and red-spider, Tetranychus mytilaspidis, may feed on avocado leaves and blemish the fruits from time to time. There are several scales also which may feed on foliage, especially the Florida wax scale, Ceroplastes floridensis, the pyriform, or soft white, scale, Protopulvinaria pyriformis, Dictyospermum scale, Chrysomphalus dictyospermi; and the black scale, Saissetia oleae. Among two dozen other minor pests in Florida are the citrus mealybug, Pseudococcus citri and avocado mealybug, P. nipae. Stinkbugs may prick the fruits leaving little dents in the skin coupled with gritty areas at the same locations inside. In California, 2 lepidopterous pests, Amorbia cuneana and the omnivorous looper, Sabulodes aegrotata, when present in large numbers, cause severe defoliation and fruit-scarring. Biological control is being achieved by release of the egg parasite, Trichogramma platneri; which is now commercially available to growers. Since 1949, the orange tortrix (a leaf roller), Argyrotaenia citrana, has been increasing as a menace to the avocado in California, the larvae feeding on twigs, terminal buds and foliage, flowers, and fruits. Since the pest requires shaded areas, it is best controlled by thinning out a close-planted grove or top-working to less susceptible cultivars. The fruit-spotting bug, Amblypelta nitida, and banana spotting bug, A. Iutescens, are important pests requiring control in Queensland. The Mediterranean fruit fly is a major hazard in Israel, but very thick-skinned fruits such as 'Anaheim' are not attacked. The Queensland fruit fly, Dacus tryoni; seriously damages only Mexican cultivars or Guatemalan X Mexican hybrids in Australia. In 1971, a nematode survey in Bahia, Brazil, revealed 9 genera of known or suspected parasitic nematodes associated with avocado tree decline. Israeli avocado growers are seeking and testing means of biological control of the more serious of the 3 dozen insects and mites preying on the crop in that country. In Mexico, the avocado weevil, Heilipus lauri; tunnels into the seeds. The major disease of avocados in South and Central America and some islands of the West Indies, in California, Hawaii, and various other areas, is root-rot caused by the fungus, Phytophthora cinnamomi, which is being combatted by the use of strict sanitary procedures and resistant rootstocks, especially 'Duke'. At the University of California, Riverside, over 750 seedlings and cuttings were being tested for root-rot resistance in 1976 and 1977 and the most promising tried out for grafting compatibility with commercial cultivars. Also, soil fumigation experiments with methyl bromide and newly developed chemicals were being carried forward. The disease has been so devastating in the high rainfall areas of New South Wales and Queensland that plantings have expanded into the semi-arid Murray Valley in the hope of avoiding it. In New Zealand, it is not a problem on deep, volcanic soils, but occurs on shallow, heavier soils. It was allegedly introduced into Chile with balled trees from California and vigorous measures are being taken to control it. Mushroom root-rot from Clitocybe tabescens may occasionally occur. Cercospora spot (brown spots on the leaves and fruits), caused by the fungus, Cercospora purpurea, may cause cracks in affected areas of the skin and thus allow entrance of the anthracnose fungus, Colletotrichum gloeosporioides, which invades and spoils the flesh. Glomerella cingulata is an important source of anthracnose in Queensland. Some cultivars are subject to scab which is readily controlled by copper sprays. More than 30 other pathogens are variously responsible for wood rot, collar rot, dieback, leafspot, stem-and rot of fruit, branch canker, and powdery mildew. Sunblotch viroid cripples young trees and damages fruits in California and Israel. So far, it is unknown in New Zealand. Stems of young trees may be affected by sunburm, and hot, dry winds cause tipburm of leaves. The avocado tree may show copper or zinc deficiency or tipburm from an excess of mineral salts.

Food Uses

Indians in tropical America break avocados in half, add salt and eat with tortillas and a cup of coffee—as a complete meal. In North America, avocados are primarily served as salad vegetables, merely halved and garnished with seasonings, lime juice, lemon juice, vinegar, mayonnaise or other dressings. Often the halves are stuffed with shrimp, crab or other seafood. Avocado flesh may be sliced or diced and combined with tomatoes, cocumbers or other vegetables and served as a salad. The seasoned flesh is sometimes used as a sandwich filling. Avocado, cream cheese and pineapple juice may be blended as a creamy dressing for fruit salads. Mexican guacamole, a blend of the pureed flesh with lemon or lime juice, onion juice or powder, minced garlic, chili powder or Tabasco sauce, and salt and pepper has become a widely popular ";dip"; for crackers, potato chips or other snacks. The ingredients of guacamole may vary and some people add mayonnaise. Because of its tannin content, the flesh becomes bitter if cooked. Diced avocado can be added to lemon-flavored gelatin after cooling and before it is set, and chunks of avocado may be added to hot foods such as soup, stew, chili or omelettes just before serving. In Guatemalan restaurants, a ripe avocado is placed on the table when a hot dish is served and the diner scoops out the flesh and adds it just before eating. For a ";gourmet"; breakfast, avocado halves are warmed in an oven at low heat, then topped with scrambled eggs and anchovies. In Brazil, the avocado is regarded more as a true fruit than as a vegetable and is used mostly mashed in sherbet, ice cream, or milk shakes. Avocado flesh is added to heated ice cream mixes (such as boiled custard) only after they have cooled. If mashed by hand, the fork must be a silver one to avoid discoloring the avocado. A New Zealand recipe for avocado ice cream is a blend of avocado, lemon juice, orange juice, grated orange rind, milk, cream, sugar and salt, frozen, beaten until creamy, and frozen again. Some Oriental people in Hawaii also prefer the avocado sweetened with sugar and they combine it with fruits such as pineapple, orange, grapefruit, dates, or banana. In Java, avocado flesh is thoroughly mixed with strong black coffee, sweetened and eaten as a dessert. Avocado slices have been pickled and marketed in glass jars. California began marketing frozen guacamole in 1951, and a frozen avocado whip, developed at the University of Miami, was launched in 1955. To help prevent enzymatic browning of these products, it is recommended that sodium bisulfite and/or ascorbic acid be mixed in before freezing.

Avocado Oil

Oil expressed from the flesh is rich in vitamins A, B, G and E. It has a digestibility coefficient of 93.8% but has remained too costly to be utilized extensively as salad oil. The amino acid content has been reported as: palmitic, 7.0; stearic, 1.0; oleic, 79.0; linoleic, 13.0. The oil has excellent keeping quality. Samples kept in a laboratory in Los Angeles at 40ºF (4.4ºC) showed only slight rancidity after 12 years. There is much interest in the oil in Italy and France. The Institut Francais de Recherches Fruitieres Outre Mer has studied the yield of oil in 25 cultivars. Joint Italian/Venezuelan studies of 5 prominent cultivars indicated that the fatty acid composition and tryglyceride structure was not influenced by variety. The oil is used as hair-dressing and is employed in making facial creams, hand lotions and fine soap. It is said to filter out the tanning rays of the sun, is non-allergenic and is similar to lanolin in its penetrating and skinsoftening action. In Brazil, 30% of the avocado crop is processed for oil, 23 of which is utilized in soap, 1/3 in cosmetics. The pulp residue after oil extraction is usable as stockfeed.

Food Value Per 100 g of Edible Portion (Flesh)*

Moisture 65.7-87.7 g
Ether Extract 5.13-19.80 g
Fiber 1.0-2.1 g
Nitrogen 0.130-.382 g
Ash 0.46-1 68 g
Calcium 3.6-20.4 mg
Phosphorus 20.7-64.1 mg
Iron 0.38-1.28 mg
Carotene 0.025-.0475 mg
Thiamine 0.033-0.117 mg
Riboflavin 0.065-0.176 mg
Niacin 0.999-2.220 mg
Ascorbic Acid 4.5-21.3 mg
*Analyses of West Indian, Guatemalen and Mexican avocados marketed in Central America.
Browning of the flesh of freshly cut avocado fruits is caused by polyphenol oxidase isoenzymes. Avocado halves average only 136 to 150 calories. The avocado has a high lipid content-from 5 to 25% depending on the cultivar. Among the saturated fatty acids, myristic level may be .1%, palmitic, 7.2, 14.1 or 22.1%; stearic, 0.2, 0.6 or 1.7%. Of the unsaturated fatty acids, palmitoleic may range from 5.5 to 11.0%; oleic may be 51.9, 70.7 or 80.97%, linoleic, 9.3, 11.2 or 14.3%. Non saponifiable represents 1.6 to 2.4%. Iodine number is 94.4. In feeding experiments which excluded animal fat, 16 patients were given 1/2 to 1 l/2 avocados per day. Total serum cholesterol and phospholipid values in the blood began to fall in one week. Body weight did not increase. Cholesterol values did not rise and 8 patients showed decreases in total serum cholesterol and phospholipids. Amino acids of the pulp (N = 16 p. 100) are recorded as: arginine, 3.4; cystine, 0: histidine, 1.8; isoleucine, 3.4; leucine, 5.5; lysine, 4.3;methionine, 2.1; phenylalanine, 3.5; threonine, 2.9; tryptophan, 0; tyrosine, 2.3; valine, 4.6; aspartic acid, 22.6; glutamic acid, 12.3; alanine, 6.0; glycine, 4.0; proline, 3.9; serine, 4.1.

Toxicity

Unripe avocados are said to be toxic. Two resins derived from the skin of the fruit are toxic to guinea pigs by subcutaneous and peritoneal injection. Dopamine has been found in the leaves. The leaf oil contains methyl chavicol. Not all varieties are equally toxic. Rabbits fed on leaves of 'Fuerte' and 'Nabal' died within 24 hours. Those fed on leaves of 'Mexicola' showed no adverse reactions. Ingestion of avocado leaves and/or bark has caused mastitis in cattle, horses, rabbits and goats. Large doses have been fatal to goats. Craigmill et al. at Davis, California, have confirmed deleterious effects on lactating goats which were allowed to graze on leaves of 'Anaheim' avocado an hour each day for 2 days. Milk was curdled and not milkable, the animals ground their teeth, necks were swollen and they coughed, but the animals would still accept the leaves on the 4th day of the experiment. By the 10th day, all but one goat were on the road to recovery. All abnormal signs had disappeared 20 days later. In another test, leaves of a Guatemalan variety were stored for 2 weeks in plastic bags and then given to 2 Nubian goats in addition to regular feed over a period of 2 days. Both suffered mastitis for 48 hours. Avocado leaves in a pool have killed the fish. Canaries have died from eating the ripe fruit. The seeds, ground and mixed with cheese or cornmeal, have been used to poison rodents. However, tests in Hawaii did not show any ill effect on a mouse even at the rate of 1/4 oz (7 g) per each 2.2 lbs (1 kg) of body weight, though the mouse refused to eat the dried, grated seed material until it was blended with cornmeal. Avocado seed extracts injected into guinea pigs have caused only a few days of hyperexcitability and anorexia. At Davis, mice given 10 to 14 g of half-and-half normal ration and either fresh or dried avocado seed died in 2 or 3 days, though one mouse given 4 times the dose of the others survived for 2 weeks. The seed contains 13.6% tannin, 13.25% starch. Amino acids in the seed oil are reported as: capric acid, 0.6; myristic, 1.7; X, 13.5; palmitic, 23.4; X, 10.4; stearic, 8.7; oleic, 15.1; linoleic, 24.1; linolenic, 2.5%. The dried seed contains 1.33% of a yellow wax containing sterol and organic acid. The seed and the roots contain an antibiotic which prevents bacterial spoilage of food. It is the subject of two United States patents. The bark contains 3.5% of an essential oil which has an anise odor and is made up largely of methyl chavicol with a little anethole.

Other Uses

The seed yields a milky fluid with the odor and taste of almond. Because of its tannin content, it turns red on exposure, providing an indelible red-brown or blackish ink which was used to write many documents in the days of the Spanish Conquest. These are now preserved in the archives of Popayan. The ink has also been used to mark cotton and linen textiles. In Guatemala, the bark is boiled with dyes to set the color. Much avocado wood is available when groves are thinned out or tall trees are topped. The sapwood is cream-colored or beige; the heartwood is pale red-brown, mottled, and dotted with small drops of gummy red sap; fine-grained; light—40 lbs per cu ft—(560-640 kg/cu m); moderately soft but brittle; not durable; susceptible to drywood termites and fungi. The wood has been utilized for construction, boards and turnery. An Australian woodworker has reported that it is suitable for carving, resembles White Beech (Eucalyptus kirtonii); is easy to work, and dresses and polishes beautifully. He has made it into fancy jewel boxes. It probably requires careful seasoning. A Florida experimenter made bowls of it but they cracked. Honeybees gather a moderate amount of pollen from avocado flowers. The nectar is abundant when the weather is favorable. When unmixed by that from other sources it produces a dark, thick honey favored by those who like buckwheat honey or sugarcane sirup.

Medicinal Uses

The fruit skin is antibiotic; is employed as a vermifuge and remedy for dysentery. The leaves are chewed as a remedy for pyorrhea. Leaf poultices are applied on wounds. Heated leaves are applied on the forehead to relieve neuralgia. The leaf juice has antibiotic activity. The aqueous extract of the leaves has a prolonged hypertensive effect. The leaf decoction is taken as a remedy for diarrhea, sore throat and hemorrhage; it allegedly stimulates and regulates menstruation. It is also drunk as a stomachic. In Cuba, a decoction of the new shoots is a cough remedy. If leaves, or shoots of the purple-skinned type, are boiled, the decoction serves as an abortifacient. Sometimes a piece of the seed is boiled with the leaves to make the decoction. The seed is cut in pieces, roasted and pulverized and given to overcome diarrhea and dysentery. The powdered seed is believed to cure dandruff. A piece of the seed, or a bit of the decoction, put into a tooth cavity may relieve toothache. An ointment made of the pulverized seed is rubbed on the face as a rubefacient—to redden the cheeks. An oil extracted from the seed has been applied on skin eruptions.