The White Sapote (Casimiroa edulis) and Wooly-Leaf White Sapote (C. tetrameria) are members of a small genus of 5 doubtfully distinct species confined to Mexico and Central America as far south as Costa Rica. The genus Casimiroa was named after a late 18th century Spanish botanist, Cardinal Casimiro Gomez de Ortego. It belongs to the Rutaceae family which includes the well known Citrus species, the Wampee (Clausena lansium), the Bael fruit (Aegle marmelos), and the Wood apple (Feronia limonia).

Other names for both fruit in Mexico and Central America are zapote blanco, Matasano, and Abache. In some other countries they are known as Casimiroa. C. tetrameria is also known as Guatemalan Sapote and as Yellow Sapote in California, in reference to the golden skin and pulp of this species.

Seedling trees of C. edulis are evergreen, rather open growing, long lived, and can attain a large size, with a height and spread of up to 18 metres. Grafted trees grow to smaller dimensions, up to 10 metres height and spread. C. tetrameria grows to slightly smaller dimensions in both seedling and grafted trees.

Leaves in both species are palmately compound, with generally 5 but varying between 3 and 7 leaflets, 5 to 14 cms. long, 2.5 to 5 cms. wide. As its common name suggests, leaves of C. tetrameria have a pubescent underside, young leaves and shoots also being slightly pubescent.

Branches are sometimes brittle when young, but become strong, wind resistant, and capable of supporting large crops. Bark colour gradually changes from bright green in young growth to an ash-grey colour on mature limbs. The root system is vigorous and extensive, and the trees are drought resistant, when established.

Flower and Fruit.
The small, pale green to cream flowers are borne mainly from late autumn to early spring. They occur in clusters or panicles, either terminally on long or short shoots, in the axils of mature leaves, or around the base of shoots a year or more old.

Fruit maturity times of C. edulis are influenced greatly by latitude. According to Popenoe, ripening season in Guatemala is April and May. In Florida the season is mainly May and June, in Mexico from May to July. Main ripening period in New Zealand is May to July. Maturity times in California are mainly from September to January, with some cultivars, Suebelle in particular, bearing some fruit all year round in coastal areas. C. tetrameria matures from July to October in California.

Fruits of C. edulis are variable in all characteristics. Size can vary from 70 to 700 grams, shape generally round or slightly oblong, sometimes slightly flattened and fruit of some trees is quite irregular in shape. Immature fruit are green in colour, in some types remaining green when ripe, some others are tinged or streaked with yellow when ripe, while others attain an even light or medium yellow colour on ripening. It is difficult to judge when varieties remaining green when ripe are ready to pick, whilst the maturity stage of 'yellow ripe' varieties is easily seen, the fruit assuming a light yellow colour when ready to pick.

The colour of the fruit pulp of this species also varies from a creamy white to yellow-orange. Fruit can be used when mature but still firm, but is generally best eaten when slightly soft, at which stage the pulp is soft, sweet, and melting. Seedling trees quite frequently bear fruit with varying degrees of bitterness in the skin and around the seeds. Named cultivars are almost all free of this bitterness. Brief descriptions of the fruit from various authors are-

Burkill - "tastes like the best pears".
Simmons - "pulp tender, with the texture of butter, sweet in taste but with a slight resinous or bitter flavour".
Popenoe - "yellowish flesh of soft melting texture and sweet or slightly bitter flavour - some trees produce small bitter fruits, others bear large ones of delicious flavour".
Thomson - (Of the better selections) ... "flesh is very sweet and juicy and just melts in your mouth. The fruit is well liked by most persons who like sweet fruits. One does not have to develop a taste for it as is the case with the avocado".

Others recognize the flavour or textures in the fruit of pears, bananas, persimmons, avocados, peaches and custard apples. The skin of the fruit is thin and ripe fruit bruise easily. Cultivars with thicker skins and firmer flesh, having better handling and keeping qualities have been selected. Mature fruit may be picked while still hard. They will ripen very well with practically no loss in quality compared with tree ripened fruits.

The relationship to citrus is readily seen in the seeds, which have the appearance of an oversize orange seed, varying between 20 and 45 mm in length. Number per fruit varies from one to five, with often one or more small abortive seeds also present.

Fruits of C. tetrameria are similar in size to fruits of C. edulis, the shape is also similar and as variable.

Fruit colour is green in immature fruits, mature fruits varying in colour from a dull to deep yellow. The pulp is of a golden yellow to orange colour. Fruit texture is slightly firmer than C. edulis. Flavour is stronger with an aromatic quality which is preferred by some people. Ramsay describes the fruit flavour as spicy and pleasant with a delicate fragrance. Others prefer C. edulis fruit, finding the flavour of C. tetrameria too strong and aromatic, at least in many seedling forms, which have a "turpentine" flavour and/or bitterness in the skin and around the seeds. The skin is thicker than that of C. edulis and the fruit have better handling and keeping qualities.

Seed is similar in appearance and size to C. edulis. However the fruit usually contains only one or sometimes 2 seeds. Trees of both species are prolific producers of fruit. They sometimes have biennial bearing habits, with a heavy crop one year alternating with a light crop the next. One seedling tree of in California of large dimensions (16.5 metres tall, 15.2 metres wide) bearing good quality fruit and with biennial heavy bearing habits, gave a recorded yield of approximately 3,000 kilograms in 1971, the "light" crop in 1972 being 200 kilograms. This tree is now propagated under the varietal name "Chestnut", after this original tree's owner.

Though this cropping is exceptional, it gives an indication of the fruit producing capabilities of the species, recognized for their heavy production. It has been claimed to be the heaviest bearing of all fruit trees, and it is certainly among the top few.

Both white sapotes are highly nutritious. Simmons states - "The fruit is rich in vitamins C and A. It is nearly as rich in carbohydrate and protein as the banana. In fact only the banana, date and fig possess more food value, pound for pound, than Casimiroa." Sugar content of the fresh fruit is up to 27%.

Sturrock gives the following analyses of each species, per 100 grams of fruit pulp.

C. edulis - water - 89.3 gms, nitrogen .025 gm, ash - 0.4 gm, calcium - 0.8 mg., phosphorous - 19 mg., iron - 0.23 mg., carotene - 0 to 103 mg., thiamine - 0. 017 to 0.03 mg., riboflavin - 0.05 to 0.06 mg., niacin - 0.57 to 1 mg., ascorbic acid - 15.7 to 56 mg.

C. tetrameria - water - 78.9 gm., nitrogen - 0.143 gm., ash - 0.48 gm., calcium - 9.9 mg., phosphorous - 20.4 mg., iron - 0.33 mg., carotene - 0.053 mg., thiamine - 0.042 mg., riboflavin - 0.043 mg., niacin - 0.473 mg., ascorbic acid - 30.3 mg., fibre - 0.9 gm.

Uses
The fruits are usually eaten fresh. They freeze very successfully, will keep indefinitely and when thawed retain their original flavour. They can be frozen whole, or the pulp can be sliced, chopped or blended before freezing, and can be used like ice cream when desired. A delicious milk shake can be made by blending fresh soft or frozen pulp with enough cold milk to give a thick milk shake. They are also eaten as a dessert with cream or with cream and sugar, with which they combine very well. They are also used in fruit salads and sherbets.

C. tetrameria is reported by Ramsay to be very good bottled in a light syrup, made into butter like apple butter, and baked in pies. Both species are dried successfully in a low oven for 12 hours or so, or sun dried in a manner similar to other fruits. Fruits for drying should be ripe and firm, not overripe or too soft. They should be peeled, seeds removed, sliced or cut into quarters or eighths before drying. The dried fruit retains its colour and flavour very well and has a nice chewy texture.

The bark, leaves and seeds contain a glucoside, casimirosine, which is used successfully to lower blood pressure and in larger amounts as a sedative, producing at the end of an hour a deep sleep which lasts four to six hours. No doubt this is the basis for the Aztec name for the fruit, cochiztzapotl, meaning "sleep-producing sapote". The fruit itself is completely innocuous, the glucoside being present only in the parts stated.

Thomson relates the case known to him of a retired U.S. Marine Corps officer, who successfully lowered his blood pressure to a satisfactory level after being advised by a doctor that his blood pressure was so high he could live only a few weeks at most. He then regularly drank a tea made by pouring boiling water over fresh or dried leaves, allowing them to steep until cool enough to drink. This apparently was entirely successful, the man living a normal life for several more years when he died a "quiet, natural death".

The seeds are reported to be roasted and eaten like nuts. Seeds should be thoroughly sun-dried and slowly roasted, when they are quite good. If roasted before they are well dried, they are sour and pungent.

The wood is moderately hard, works well, is coarse grained and takes a smooth finish. It can be used for small articles of turnery, handles, etc. It is not durable in the ground.

Climatic requirements
While indigenous to tropical latitudes, the trees are medium to high altitude species, thus the climatic requirements for best growth and fruiting are distinctly subtropical. Thomson states - "The trees do not grow in the hot lowlands but are found at altitudes of 3,000 to 9,000 feet, or occasionally to 2,000" in areas that are comparatively cool and dry. Popenoe states that it is "not altogether successful in Central America below 3,000 feet, and it thrives at elevations of 5,000 to 6,000 feet".

Areas of South and Central California, particularly along the coast, are very well suited to both species, the majority of cultivars now grown were selected there. Areas in Florida, particularly Central Florida, with a well defined cool season are also well suited and good crops are produced. Trees growing in coastal areas of the north island of New Zealand are also performing well. Burkill states "it has been brought alive into the Botanic Gardens, Singapore, but cultivated without success. Apparently the climate is too uniformly humid." Trees withstand the high temperatures experienced at times in Californian summers without ill effects.

Trees are quite cold hardy. C. edulis withstands lows of -4°C with very little damage. Its cold hardiness is, as a good guide, between that of a Fuerte avocado and that of the sweet orange. C. tetrameria is less cold hardy than C. edulis. Freezes in California in many instances which have given moderate to severe damage to this species have left nearby C. edulis with only slight damage. Cold hardiness of this species is similar to that of the Hass avocado.

The trees are drought resistant and survive in California in areas with very little rainfall, but will bear very light crops unless sufficient moisture is available during the fruit development period.

Culture
As can be seen from the above, a subtropical climate with a cool season and adequate soil moisture during the fruit development period is necessary for best growth and fruiting. If culture is attempted in tropical areas with no well defined cool season, it is necessary to induce a "dormant" state before the flowering time. This is done by withholding water, to reduce vegetative growth and encourage the development of flower buds. Thus, plants grown in this type of climate in a low, moist situation where the water supply cannot be adequately controlled, will often grow a large vigorous tree with poor fruiting habits.

Trees are not exacting in their soil requirements, growing well in sandy, sandy loam, and clay loam soils. Alkaline soils often induce nutrient deficiencies, and a slight acid (pH 5.5 to 6.5) soil generally gives best results.

Trees will not stand waterlogging and a well drained situation is necessary, though they are less sensitive than some other species such as avocados. The salt tolerance is reported to be fair. No detailed studies of nutrient requirements have been made, but as the trees do well over a wide range of conditions, nutrient levels suitable for other subtropical evergreen species should be entirely satisfactory.

Trees should be planted in full sun with spacings each way of approximately 9 metres for grafted trees. Given good conditions, young trees grow rapidly, and often, especially with seedlings, tend to grow tall and unbranched, becoming tall, ungainly, and susceptible to wind damage.

A simple and sure system of training is to top the young tree at a height of 60 to 90 cms, allowing 3 shoots to grow, then when these are 10 to 15 cms. long, wedge a spring-loaded clothes peg or similar between each young shoot and the main stem, to encourage the formation of wide-angled crotches which are structurally strong. Alternatively, the 2 lower shoots can be treated in this manner, and the top shoot allowed to grow upright, and it is then topped in a similar manner at 30 to 45 cms higher, then again after another 30 to 45 cms if desired, giving a central leader or modified central leader structure to the tree, with pairs of branches coming off at the 30 to 45 cm. intervals. Often the shoots will need cutting back again after they have grown 35 to 40 cms, to encourage further branching. Grafted trees are naturally more compact, and less training will be required, however topping long whip-like growths may be necessary with them also.

Give young trees ample moisture and nutrients to encourage growth. As with other trees, mulching is very beneficial. Although mature trees are cold hardy, young trees should be protected from frost for the first year or two, to ensure rapid unhindered development. Various frost protection methods such as wrapping the stern with insulating material, covering small trees with large plastic bags or similar, etc., are satisfactory.

Seedling trees vary in age from three to eight years from seed before bearing their first fruit. Grafted plants usually fruit within 2 to 3 years from grafting, however, under poor conditions they may take considerably longer.

Propagation
Trees can be propagated by seed, various methods of grafting or budding, air layering, or cuttings. As trees are very variable from seed, vegetative propagation of good quality cultivars is preferred. Seed should be planted in a suitable seed raising mix as soon as possible after removal from the fruit. They germinate readily and a high percentage of success with fresh seed can be expected. The seeds are not as perishable as many other tropical species, however, and cleaned and dried seed will give reasonable germination percentage up to 3 weeks after removal from the fruit. Seeds should not rattle, as this indicates over dehydration and poor germination will result.

Young trees are often shield budded or chip budded using budwood which has matured with grey bark. Tie the bud in place using regular budding tape, leaving the bud exposed. After 3 to 4 weeks, check that the bud has taken and cut the stock 1 to 3 inches above the bud. The stub left can be used to tie the new shoot to after it has grown several inches. This is very useful if the young tree is being budded in the field, as it prevents breakage of the young shoot by wind until a strong union has been formed. Whip, whip and tongue, wedge and side veneer grafts are also used, again using scionwood which has a grey colour and preferably from a shoot not in a current growth flush. Exposed portions of scions can be covered with suitable grafting mastic, or a plastic bag can be placed over the scion to prevent dehydration until a union has been formed with the stock.

Field growing trees can also be readily top worked, using bark, side or whip and tongue grafts according to the size of the stock branches or stem. Branches or trunks up to 15 cms. in diameter are successfully bark grafted.

Grafting can be done anytime of the year when stocks are growing well and suitable scionwood is available, and weather is warm enough to allow quick union and subsequent growth of the graft. Late autumn to early spring is generally unsuitable in most areas where the trees are grown.

Air layering and cuttings have both been used successfully with these species, but are not widely used due to the satisfactory and reliable methods mentioned above, which give vigorous trees with a strong root system.

Pests and diseases
Trees are generally subject to few insect pests, they are however susceptible to several insect species and the associated sooty mould. Control is by using 2 or 3 white oil sprayings in summer and early autumn on affected trees. Mites are occasionally a problem, mainly on young trees. Fruit maturing in the fruit fly season is susceptible, control measures as used with other fruit is required. Trees are not susceptible to Phytophthora cinnamomi, the root rot fungus which severely damages or kills avocados.

Prospects for home plantings and commercial development in Australia
The fruits have been an important food in the diet of the native peoples of Central America for a very long period, ranking among the principal cultivated fruits. To date they have been of minor importance in other countries, but are undergoing increasing development as home yard fruits and as a commercial crop in various other areas where they can be successfully cultivated. These include California, Florida, New Zealand and Hawaii.

For home use, one tree provides ample fruit. Cultivars with fruit maturing over an extended period are an advantage. The fruits are completely undeveloped in Australia at present, with under a dozen bearing trees growing. A large increase in the planting of these species as home yard trees throughout a wide area of Australia appears certain as the public becomes aware of their many virtues and relative ease of cultivation.

Prospects for commercial development on a small to medium scale appear good, provided fruit presented for sale are of the best quality, possible, attractively packaged. A public education approach should be adopted, e.g. by providing a leaflet with the fruit; describing the fruit, its uses and recipes, with perhaps more ambitious approaches at a later stage. As the fruits are so variable from seed, it would appear essential on a commercial basis for vegetatively propagated trees of superior cultivars to be used, in order that uniform, high quality fruit is presented for sale, thus ensuring a continuing and expanding demand for the fruit.

For commercial production, cultivars having yellow skin (more attractive to the consumer, maturity stage more easily seen by the grower) high quality flesh taste and appearance (yellow-orange colour preferred), thicker skins and firmer flesh to cause minimal possible damage and bruising during harvesting and transport, improved keeping qualities, and smaller and lesser number of seeds are preferable.

For areas where fruit mature earlier or later, varieties which will extend the season further will be an advantage.

Fruits of better cultivars are well liked by most people. As can be seen from the "Flower and Fruit" section above, it seems certain that fruit, from various latitudes of Australia, from early and late maturing cultivars, should be available for most of the year. Such a steady supply of fruit should enable a consumer awareness of the fruit to be developed - a far more difficult task when unknown fruits are available for only a small part of the year. Fruits on a given tree mature over a relatively long period, and in order to harvest fruit at the optimum stage, harvesting on about a week to 10 day cycle is necessary.

The trees are suitable for cultivation in a wide range of areas in Australia which meet the requirement outlined under 'Climate' and 'Culture' above. They are very productive and the fruit highly nutritious, important attributes for both production and marketing. The fruit produces high quality nutritious frozen and dried products and possibilities exist for the future development of this. The variability of the species gives good potential for the breeding and selection of superior types.

Whilst several cultivars suitable for commercial production are now in Australia, hopefully we will see in the future the breeding and selection and introduction of still better forms, by both private individuals and public bodies.

Cultivars
As mentioned previously, the variability in the species of White Sapote have given rise to many good quality and improving cultivars, some probably hybrids between the 2 species. One recent planting in California includes over 40 different cultivars and high quality selections. For home use, all cultivars are suitable, however 3 which are especially suited are Suebelle, which has an extended bearing season, often with some fruit year round, Luke, which is a heavy producer on a smaller size tree, up to 6 metres high in New Zealand, and McDill, for those who like large fruit, as the fruit is high quality and weighs up to 1.5 pounds. For commercial plantings, a range of cultivars should be planted to determine their performance in various areas of Australia. Quite a number are suitable for local markets, however at this stage the cultivars having qualities most suited for commercial production are Lemon Gold, Mac's Golden, and Vista.

The following cultivars, with brief descriptions where known, are present in Australia.

Casimiroa edulis

Californian origin:
Lemon Gold - nearly round or slightly flattened, weight 4 to 6 ounces, colour light yellow when mature. Excellent eating and keeping qualities, usually 4 rather small seeds. Pleasant slightly acid taste. Late maturity. Tree bears good crops every year.
Ortego - oval shape average weight 4 to 5 ounces, good eating and keeping qualities, usually only one seed. Late mid season. Tree compact, somewhat drooping habit, fairly regular cropper.
Pike - very good for home use, at present a popular commercial cultivar in California. Fruit large and symmetrical, usually 4 rather large seeds. Green skin. Average weight 9 ounces. Difficult to determine maturity stage. When picked at right stage it has excellent eating qualities and keeps fairly well. Tree alternate bearer. Early mid season.
Wilson - resembles Pike in most respects, has some bitterness in skin. Tree heavy biennial bearer.
Suebelle - Fruit shape generally smooth and round, but often irregular, turns light yellow when mature, average weight 4 to 5 ounces. Rich, soft, sweet pulp, with slight musky flavour disliked by some people. Has few and rather small seed. Fruit bruises easily and does not keep well. Long bearing season. Medium size, compact tree, bears good crops every year. Popular home use cultivar in California.
Vista - Light yellow when mature, rather firm flesh; keeps well. Somewhat half moon shape, averages about 8 ounces with 1 to 4 seeds, depending on size. Eating quality very good. Early maturity. Tree bears well with a tendency to alternate bearing.
McDill - Fruit light yellow when ripe, very large size to 1. 5 pounds, usually one to 3 large seeds. Eating quality excellent. Skin thin, does not keep well. Midseason. Tree prolific.
Chapman - Fruit large, average 10 cms. diameter, skin yellowish-green, flesh cream, 4 to 5 large seeds, flavour good. Tree prolific producer, fruit ripens September to January in California.

New Zealand origin:
Luke - uneven shape fruit, tree heavy producer, smallish size up to 6 metres high.
Henrickson - Fruit up to 10 cms. diameter, even in size, holds well on tree, transports well, has 3 to 5 large seeds.
Ferney - light yellow skin, excellent flavour, wrinkles when ripe, irregular shape, good for home and local market. Does not travel well.

Casimiroa tetrameria

Californian origin:
Mac's Golden - Fruit are 6 to 7 ounces, flesh dark yellow, few seeds. Thick skin, firm flesh, strong aromatic spicy flavour, well-liked by most people. Keeps well. Early maturity.

Florida origin:
Smathers - No details to hand.

References cited:
Burkill, I.H. - A Dictionary of the Economic Products of the Malay Peninsula.
Popenoe, W. - Manual Of Tropical And Subtropical Fruits.
Ramsay, G. W. - The Yellow Sapote - in California Rare Fruit Growers 1973 Yearbook.
Simmons, A.F. - Growing Unusual Fruit.
Sturrock, D. - Fruits for Southern Florida.
Thomson, P.H. - The White Sapote in Calif. Rare Fruit Growers 1973 Yearbook.