Yosef Mizrahi, Avinoam Nerd, Park S. Nobel
Horticultural Reviews. (1997)18: 291-320.

I. INTRODUCTION

In a stimulating article, Vietmeyer (1990) pointed out that relativelyfew plant species, most of which were domesticated thousands of years ago, serve as food for humans and animals, as medicinal plants, and as industrialcrops. Other species may be the new crops that will tolerate the changingclimatic conditions on earth-global warming and locally dryer conditionsas a result of atmospheric CO² increases-serving in marginal, infertile, dry lands where common cropsfail. Such new crops can provide diversification to enable sustainableagricultural systems and can offer commercial opportunities. Cacti mayhave the proper characteristics to fulfill such roles.

Cacti are native to North and South America and the West Indies (Gibsonand Nobel 1986). They are known around the world as unusual looking plantscoming from hot, dry, and hostile desert areas. The dicotyledonous family Cactaceae has 122 genera with approximately 1600 species, nearly all ofwhich characteristically have spines and exhibit stem succulence (Gibsonand Nobel 1986; Nobel 1988). Of the three subfamilies, the smallest (Pereskioideae) contains about 20 species, all of which have prominent leaves. About 250 species occur in the Opuntioideae, about half of which are platyopuntiaswith flattened stem segments known as pads or cladodes, including the widelycultivated Opuntia ficus-indica  (L. ) Miller. The remaining cacti, which are in the Cactoideae, are diverse in morphology and include small collectable species (e. g. , in genus Mammillaria ), barrel-shapedspecies, tall columnar species, and epiphytic vine-like species that climbon other plants (Nobel 1994). Cacti appear in various habitats, from harshhot deserts through tropical rain forests to cold areas with freezing temperatures. Most cacti grow in and arid semiarid zones with high summer temperatures; indeed, they are among the most tolerant of high temperatures of all plantspecies, tolerating 50 to 55^° C when properly acclimated. Unfortunately, many species of cacti with agriculturalpotential are damaged by freezing temperatures, such as epiphytic cactiin the genera Hylocereus  and Selenicereus  that are native to tropicalforests. Cacti shows great adaptability to various soil conditions as theycan grow in poor, infertile desert soil and have tolerance to wide rangeof soil pH (Nobel 1988). Their remarkable adaptability together with thetheir unique shapes, sizes and appearances have spread cacti around theworld.

Cacti were introduced into the Maditerranean region as early as thesixteenth century, when ships returned from the newly "discovered"America carrying cladodes of Opuntia. Today, O. ficus-indica  andother species of this genus grow so well around the Mediterranean Sea thatmany consider them to be natives. Yet special care should be taken whenintroducing plants from one area into another, especially plants as adaptiveas cacti. Introduced cacti have become dangerous weeds, as in the famouscase of Australia. In 1832 platyopuntias were used as hedges north of Sydney, and in 1839 a single specimen of Opuntia stricta  was introducedinto Sydney as an ornamental. They became naturalized and could not beremoved by plowing, since cutting the cladodes increased the number ofpropagation units and enhanced the spreading. Birds also spread the seeds. To make things worse, in 1914, Burbank's collection of various opuntiaswas introduced into Australia as forage. By 1925 prickly pear cacti suchas 0. ficus-indica, 0. stricta , and 0. vulgaris  were infestingrange lands in a rate of 100 ha/hour and 10 million hectares were infestedin Queensland (Nobel 1994). Not until the natural insect enemy of thesecacti, Cactoblastis cactorum , was introduced from Mexico were theycontrolled. Similar occurrences happened in South Africa, indicating thestrong adaptation of the Cactaceae to various conditions.

Today, cacti are grown in most countries around the world. There aremany national societies of cactus enthusiasts. Germplasm exchange is becomingincreasingly common, and journals on cacti are published in many countries. Because of the beauty of their flowers and the uniqueness of their shoots, they are important indoor and outdoor ornamentals and gardening plants, as seen in the Huntington Botanical Garden in Pasadena, California. Thereis also a whole industry of cacti as ornamentals, mainly as potted floweringplants. For example, the Christmas cactus Schlumbergera truncata  and the Easter cactus Rhipsalidopsis gaertneri  are widely enjoyed, andmanuals exist for their cultivation. Ornamental cacti deserve an entirechapter and are not be covered in this review.

Cacti increasingly serve as agricultural and industrial crops, includingas animal feed, vegetables, and fruits. Cacti are most widely used in Mexico, which has a cactus as part of its national emblem, as depicted on its flagand coins. Much research on cacti has been done in Mexico, although mostof the resulting publications are not widely disseminated or translatedinto other languages. In 1992, the Food and Agricultural Organization ofthe United Nations (FAO) established the "cactus pear network"with the aim of promoting the cactus pear as important fruit crop worldwide, and a compreshensive book on cactus pear has been published by FAO (Barberaet. al 1995). This review describes the biology of this interesting familyof plants and discusses the potential of various species of cacti thatmay serve as important crops.

II. BIOLOGICAL CHARACTERISTICS OF CACTI

A number of books on the biology of cacti are available (Gibson and Nobel 1986; Nobel 1988, 1994; Pimienta-Barrios 1990). In this review, onlycertain aspects of cactus biology relevant to horticulture are emphasized, including the special structures and physiological processes; reproductivebiology is discussed elsewhere in this volume (Nerd and Mizrahi 1996).

A. Shoots, Crassulacean Acid Metaholism

The most distinguishing vegetative feature of the Cactaceae is the areole, which occurs on a raised portion of the stem referred to as a tubercleor on a rib, which is a linear array of fused tubercles (Gibson and Nobel 1986). Areoles have meristematic activity and produce spines, includingthe nasty thin deciduous spines termed glochids that are a characteristic of opuntias (nasty because they contain barbs that cause glochids to become implanted in the skin of anyone who carelessly touches a cladode or unbrushed platyopuntia fruit). An areole can also produce another organ, such asa new cladode or a fruit (or even an entire plant). Cactus fruits alsohave areoles on their surfaces; an areole of the fruits of 0. ficus-indica  can even produce an entire new plant, underscoring the many possibilitiesfor vegetative reproduction among cacti.

The massiveness of the stems of cacti indicates that considerable amountsof water can be stored in their shoots. Indeed, such water storage cankeep certain opuntias and barrel cacti alive for up to 3 years in the absenceof water uptake from the soil (Nobel 1988). Perhaps more importantly, stomatalopening and net CO² uptake can occur for 2 to 7 weeks for suchcacti without uptake of soil water, because metabolic activity then relieson water stored in the stems. Succulence also occurs at a cellular levelfor cacti, because the cells typically contain a large, water-filled, centralvacuole that can represent 85 to 90% of the cell volume.

The large central vacuoles suggest the most unusual feature of cactiamong cultivated plants-they utilize a pathway for CO2 fixation known as Crassulacean acid metabolism (CAM). CAM was originallydiscovered in the Crassulaceae about 200 years ago based on nocturnal increasesin tissue acidity detectable by human taste buds; CAM occurs in about 7% of the approximately 300. 000 species of vascular plants (Nobel 1988, 1994). Essentially all CAM plants evolved in water-limited environments, suchas in deserts or within tree canopies without access to large soil volumes. Water loss rates for plants depend on the difference in water vapor concentration(or partial pressure) between inside the leaves or stems and the ambientair, differences that average 5- to 10-fold less at night than during thedaytime because of lower plant temperatures at night. Stomatal openingat night thus leads to less water loss by CAM plants than for stomatalopening during the daytime by C3 and 4 plants (Fig. 6. 1A).

C3 plants have the 3-carbon phosphoglycerate as their first photosynthetic product and comprise about 92% of vascular plant species, and C4 plants have a 4-carbon acid such as malate or aspartate as their first photosynthetic product and comprise about 1% of vascular plants, including many agriculturally important species (e. g., maize and sorghum).

A widely held view is that CAM species grow slowly. This is certainlytrue for various species of Mammillaria , which may be only 15 cmtall after growing for 100 years. However, the CAM pathway is only slightlymore costly in terms of utilization of light energy for net CO2 uptake than is the C4 pathway and actually is less expensive than the C3 pathway, for which 20 to 40% of the fixed CO2 is generally released by photorespiration at a high energetic cost (Nobel1991 g 1994). CAM plants therefore can take up a relatively large amountof CO2 (Fig. 6. 1B) with respect to the water lost by transpiration (Fig. 6. 1A), so their water-use efficiency (ratio of CO2 uptake to water loss) is high. Averaged over a season, the water-use efficiencyin mmol CO2 per mol H2O typically is 1. 0 to 1. 5 for C3 plants, 2 to 3 for C4 plants, and 4 to 10 for CAM plants (Nobel 1988). Moreover, certain irrigatedCAM plants can have an annual productivity that exceeds that of nearlyall cultivated C3 and C4 species. In particular, Opuntia amyclaea Tenore and 0. ficus-indica can produce an above ground dry weight of at least 45 t ha-1 yr-1 (twospecies of agave, Agave mapisaga and A. salmiana, and pineapple, Ananas comosus, are other CAM plants that are nearly as productive), whereas such high productivities have been recorded for only a few C3 and C4 species (Nobel 1991, 1994). Thus, certain CAM species are inherently extremelyproductive, which can have a major impact on future cultivation of cacti.

Fig. 6. 1. Transpiration(A) and net CO2 uptake (B) for C3/C4 (- - - - -) and CAM (-------) plants.
Data are for species exhibiting the highest ratesof net CO2 uptake and are averaged from many sources (Nobel 1991, 1994).
Stippledbars indicate nighttime.

B. Roots, Salinity Tolerance

The roots of cacti, unlike the shoots, are nonsucculent. The roots aretypically shallow (5-15 cm deep) and even for a large arborescent cactusoccur chiefly in the upper 30 cm of the soil (Gibson and Nobel 1986). Irrigationwater is generally applied only to the usual rooting depth, but excessiveirrigation can force roots to lower soil layers. As the soil dries, finelateral roots generally die, while larger roots become covered with a corkylayer (periderm). The root water conductivity decreases about 10-fold duringsoil drying, which reduces water loss from the plant tissues to the soil(North and Nobel 1992; Huang and Nobel 1994). However, water loss to adrying soil is prevented mainly by the large decreases in soil hydraulicconductivity, which can decrease 106-fold as the soil dries and water continuityamong soil particles is lost (Nobel and Cui 1992).

The many preformed root primordia (sites for new lateral roots) locatedbeneath the periderm of the main roots grow rapidly when the soil is remoistened, increasing the water and mineral absorption capacity in a matter of days. For platyopuntias, roots generate easily from areoles in contact with theground, so vegetative propagation can occur for cladodes laid on the soilsurface as well as those placed vertically in the soil. Original plantorientation should be retained for stem cuttings of columnar cacti, whoseroots develop from meristems located in the vascular cambium of the stem. For epiphytic cacti, such adventitious roots can be formed all along thestem and emerge through its epidermis (Gibson and Nobel 1986). Althoughroot generation in cacti is easy, the time varies from weeks to months, is species and temperature dependent, and can be accelerated by externallyapplied hormones.

Salinity stress has two major components: water stress and ion toxicity(Mass 1986). Cacti are relatively tolerant of water stress but are sensitiveto salinity (Nobel et al. 1984; Berry and Nobel 1985; Silverman et al. 1988; Nerd et al. 1991a, 1993b). When salinity occurs in the natural habitatsof certain species such as Cereus validus Haworth, the roots dieback and uptake of Na⁺ is avoided (Nobel et al. 1984; Nobel 1988). Ca²⁺ can often negate the toxiceffect of Na⁺ (Rengel 1992). Indeed, when cacti are irrigated with water in which theratios of Na⁺ to Ca²⁺ + Mg²⁺ and of Cl^- to (SO₄)^2- are low, they do not suffer from salinity stress (Nerd et al. 1993b). When Ca²⁺ is not abundant in the soil or the irrigation water, gypsum can be addedto reduce salinity stress. Despite their drought tolerance, most cactiare commercially unsuitable to saline areas, unless special precautionsregarding water and soil are taken, such as can be best learned from localfield trials. The few genotypes of Opuntia  that exhibit salt toleranceshould be used in breeding programs.

III. CACTI AS ANIMAL FEED

Wild and domestic animals eat cactus stems, especially species of thesubgenus Opuntia (Russell and Felker 1987a; Nobel 1994). Their high water-useefficiency makes certain opuntias ideal feed crops for semiarid regionswhere drought is common and animal food is scarce. For high-density plantings(24 plants m-1. ) and under proper management including irrigation, yieldsof 40 to 50 t aboveground dry weight ha-1, yr-1 can be obtained for platyopuntias, as already indicated (Nobel 1991, 1994).

Similar biomass yields occur onlyamong the highest producing C3 and C4 plants, which have a much lower water-use efficiency. Besides opuntiasgrown for harvesting to provide fodder for cattle and other animals, cactican be used as forage by free-ranging cattle.

In cases where animals are allowed to graze opuntias, the spines canbe burned off before the cladodes are eaten. This requires specializedburners with attendant costs of the propane fuel (Maltsberger 1991). Insouthern Texas this option is 30 to 40% cheaper than the cost of availablerelief food provided during drought (Russell and Felker 1987a). Althoughspineless genotypes are available, they are generally less resistant todrought. Indeed, the ranchers prefer the spiny types, because livestockdo not generally consume the unburned cladodes, which remain untoucheduntil needed. If range cattle had access to spineless genotypes, they wouldbe consumed in preference to the native grasses and thus eliminated. Althoughspines can also be burned off for cladodes used as fodder, mechanicallychopping the cladodes, sometimes followed by fermentation, also makes thempalatable to livestock (Fuentes-Rodriguez 1992).

Although confusion exists in the taxonomy of opuntias used as animalfeed, Opuntia ficus-indica is the most common species worldwide(Russell and Felker 1987a), 0. lindheimeri Engelm, is used in southernTexas (Maltsberger 1991; Nobel 1994), and 0. rastera We ber, 0. robusta Wendland in Pfeiff. , 0. engelmanii Salm-Dyck, 0. megacantha Salm-Dyck, and 0. phaeacantha Engelm. are used in Mexico (Fuentes-Rodriguez1991). When these plants are not cultivated, yields tend to be much lowerthan the maximal possible but are still higher than yields for C3 or C4 plants grown under drought and otherwise harsh conditions (Nobel 1994).

Growth conditions affect the quality of cladodes as an animal feed, so nutritional analysis should be made on such feed before use (Maltsberger1991). Cladodes consist mainly of water, usually about 85 to 95% by freshweight (Fuentes-Rodriguez 1991), but during water stress the water contentmay drop to 60% (Nobel 1994). In nutritional value, cladodes are similarto immature maize silage on a dry matter basis (Maltsberger 1991); theyare relatively high in fiber (average of 18%) and minerals (19%), low infats (1-4%), and medium in proteins (generally 4-8% total, with 1-2% digestible). Digestibility of cladodes is high (72%), and carbohydrates can accountfor up to 71% of their dry weight (Fuentes-Rodriguez 1991, 1992; Maltsberger1991). Like many other green plant tissues, cladodes contain carotene(a precursor to vitamin A), and vitamin C. Protein supplementation shouldalways be considered (e. g. , cotton seed, which is available in southernTexas and elsewhere, is a good source). Micro- and macronutrient supplementationshould also be considered (Maltsberger 1991). The content of nitrogen andother minerals in cladodes can be increased by fertilization (Nerd andMizrahi 1992; Nerd et al. 1993a). A clone of Opuntia stricta Haworthhas been identified with high nitrogen and phosphorus contents that satisfythe feed requirements of cattle (Nobel 1994). The laxative properties ofcladodes can be avoided by gradually increasing the cladode portion inthe feed (Maltsberger 1991). Because consumption of cladodes can improvethe flavor of milk and the color of the butter produced from it, milk fromcladode-fed cows commands higher prices in Mexican markets (Russell andFelker 1987a).

Numerous countries (Mexico, Brazil, United States [mainly Texas], Peru, Chile, South Africa, and Tunisia) are already producing significant amountsof animal feed from opuntia cladodes (Nobel 1994), reflecting their lowmaintenance cost, efficient production, and sustainability (Hamilton 1992). Selected cultivars of opuntias with high yields and high-quality cladodesshould play an increasingly important role in the livestock industry ona regular basis, not just as a drought relief source of feed. With theproper management, these cacti can be a competitive source of feed, especiallywhere water shortage is a problem. However, a major problem for the expansionof the cultivation of cacti in the United States and other countries isthe plants' sensitivity to freezing temperatures (Russell and Felker 1987b). Most members of subgenus Opuntia growing in the wild or cultivated areheavily damaged by nighttime temperatures of -10° C, although certain wild opuntia species growing in northern latitudes cantolerate temperatures below -20° C when properly acclimated, such as Opuntia fragilis (Nutt. ) Haworthand 0. humifusa (Rafinesque) Rafinesque, both of which are nativeto Canada (Nobel and Loik 1990; Loik and Nobel 1993). Indeed, breedingefforts between cold-tolerant native species and highly productive butcold sensitive commercial species should be a major objective of programsto expand the cultivation of cacti (Nobel et al. 1995; Nobel 1996).

IV. CACTI AS VEGETABLES

A traditional vegetable of Mexico is the nopalito, the name for theyoung cladodes of various species of platyopuntia, such as Opuntia -ficus-indica, 0. streptacantha Lem. , 0. amyclaea, 0. robusta, 0. inermis DeCandolle, and Nopalea cochenillifera (L. ) Salm-Dyck (Cantwell etal. 1992; Flores 1992; Pimienta-Barrios 1993). This unique vegetable, whichusually is roasted, blanched, or cooked after the spines and the youngleaves are removed, has great potential for other countries as well. Nopalitosare sold in the Mexican markets in several forms, the simplest being thefreshly harvested cladodes. Often they are sold after the spines, youngleaves, and edges are sliced off and sometimes after being cut into stripsor small cubes. This vegetable is utilized in many forms, including saladsand cooked dishes with meat. Even a delicious cactus pie can be prepared, which tastes apple-like, perhaps reflecting the high malic acid levelsin both apples and nopalitos (Master 1959).

The nutritional value of nopalitos is similar to that of many othervegetables; they contain mostly water (88-95%), some carbohydrates (3-7%), and minerals (about 1. 3%, mainly Ca2+) . Like most leafy vegetables, nopalitos are low in proteins (about 1%)and fiber (about 1%, which is still more than twice that of lettuce; Rodriguez-Felixand Cantwell 1988). They are a typical source of two important vitamins, -carotene(18-38 mg per 100 g fresh weight) and ascorbic acid as vitamin C (10-18mg per 100 g fresh weight). Nopalitos are less nutritious than spinachbut more nutritious than lettuce (Cantwell 1991). Mucilage, which is secretedfrom the cut ends of the cladodes, deters some potential consumers butcan be minimized by boiling in water for a few minutes with some sodiumbicarbonate or salt. Consumption of nopalitos can reduce the blood sugarlevels in diabetics who are not insulin dependent (Ibanez-Camacho and Roman-Ramos1979; Meckes-Lozoya and Roman-Ramos 1986; Frati et al. 1983, 1988, 1989, 1990) and also can reduce fats and cholesterol, especially the low-densitycholesterol (Frati et al. 1983; Fernandez et al. 1990, 1992), underscoringthe great potential of nopalitos as a crop.

Nopalitos come to Mexican markets from wild as well as backyard plantsof various species, from established orchards where the plants are grownas for fruits (Rodriguez-Felix and Cantwell 1988), and from special plantationswith dense plantings to maximize vegetative production. "The NopalitosCapital" is Milpa Alta, where high-quality cultivars, mainly of 0. ficus-indica, are grown. The cladodes are traditionally bailed in roundbundles (Color Plate 1) before being sent to the markets. Over 5000 haof nopalitos are cultivated in Mexico (Pimienta-Barrios 1993); the limitedplantings in the United States are mostly in southern California and Texas, where the main cultivated species is Nopalea cochenillifera. Cladodesof the specific cultivar of N. cochenillifera are spineless andless mucilaginous, greener, and more tender than those of the various Opuntiaspecies grown for nopalitos. Young cladodes of N. cochenillifera are often sold in U. S. supermarkets under a botanically incorrect term, "cactus leaves" (cladodes are stems).

Fig 1. Young cladodes (nopalitos) of Opuntia ficus-indica ina traditional round pack in Milpa Alta, ready to be shipped to a MexicoCity market.

Although more research is needed on its growth and management (Mick1991, 1992), N. cochenillifera is planted as cuttings with about20 cm between individual cladodes along rows in soil beds with 8 rows about20 cm apart. Fifty cladodes can be harvested in one year from a singlecladode planted in the spring (the first harvest is obtained in 3-4 months). High fresh weight yields of 400 to 600 t ha-1yr-1 are possible under the severe pruning that stimulates vegetative growth. Cultivar 1308 is sensitive to freezing temperatures, so it is grown underplastic tunnels filled with straw during the wintertime risk period, whenambient outside temperatures can be -10° C. These tunnels are also used to lengthen the cladode production period inthe spring and autumn, when outside temperatures are too low (Mick 1991)(Color Plate 2).

Fig 2. Oputnia ficus-indica growing in a soil bedwith tunnel for year-round production of nopalitos in Milpa Alta, Mexico.

Opuntia ficus-indica, 0. inermis, and 0. amyclaea can have youngcladodes that are low in spines. These nopalitos reach their market sizeof about 20 cm in length within 20 to 30 days, depending on the weather. The shelf life of this vegetable is usually a few weeks, provided thatproper postharvest techniques are applied (Cantwell et al. 1992). Diurnalvariation in acidity because of CAM metabolism can impose a unique postharvestproblem, because morning-harvested cladodes are very acidic, whereas afternoon-harvestedcladodes contain only 10 to 20% as much acidity (Rodriguez-Feliz and Cantwell1988). The acidity of harvested cladodes decreases with time and after1 week of storage at 20° C reaches a plateau (Cantwell et al. 1992), so packages should be markedwith the earliest day for consumption to guarantee consistent acidity levelsin the cladodes. Proper marketing and consumer information about theirquality and many uses are essential before the tremendous potential ofnopalitos will be realized worldwide (Flores 1991. 1992). Several booksand leaflets have been published describing the many dishes that can beprepared from nopalitos, such as, Cookin With Cactus (Haggerton1992).

The bases of the flower buds of N. cochenillifera (Color Plate3) can also be used as a tasty vegetable (L. Scheinvar, Autonomous Universityof Mexico, Mexico City, personal communication). The flower base containsglochids that must be removed before use, suggesting that the absence ofspines and glochids from the cladodes of N. cochenillifera is controlledby other genes.

Fig 3. Flowering plant of Nopalea cochenillifera , whose spinelesscladodes are used for nopalitos and whose glochid-containing flower bases(reseptacles) are used as a delicate low-mucilage vegetable.

When this species is grown for nopalito production withintensive cladode removal, flower buds are generally not formed, althoughmuch about N. cochenillifera remains to be determined by futureresearch. Another cactus used as a vegetable in Mexico is Acanthocereustetragonus (L. ) Humlk. (L. Scheinvar, personal communication), whichis an epiphyte that may require a trellising system and shade. This cactuslacks mucilage, which may make it more attractive to potential consumersthan nopalitos. Basic agricultural research is needed before exploitingA. tetragonus as a crop, which is also true for the leafy nonsucculentcactus Pereskia grandiflora, whose young stems are cooked as a vegetablein Vietnam (N. T. Nguyen, University of Hanoi, personal communication).

V. CACTI AS FRUIT CROPS

The greatest potential for cacti as horticultural crops, whose reproductivebiology has recently been reviewed (Nerd and Mizrahi 1996), lies in theattractive and unique fruits produced by many species in various genera. Already an established crop in some countries is the "cactus pear"(Opuntia sp), formerly known as the "prickly pear" (ColorPlate 4). The term "cactus pear, " which overcomes the negativeconnotation for the fruit of "prickly pear, " was recommendedby Frieda Caplan, a California marketer of exotic fruits and vegetables, and others and was adopted by representatives of 10 countries at the SecondInternational Conference on Tuna and Cochineal in Santiago, Chile, in 1992(Pimienta-Barrios et al. 1993).

Fig 4. Harvesting fruit known as cactus pears from Oputia ficus-indica in Sicily

In the country of origin, Mexico, 0. ficus-indica, 0. amyclaea, 0. streptacantha, 0. megacantha, and 0. inermis are cultivatedfor fruits (Pimienta-Barrios 1991, 1994), whereas in other countries themost important species is 0. ficus-indica. Cactus pear is alreadyan established commercial crop in Mexico, Italy, United States, Israel, Peru, South Africa, Chile, Argentina, Colombia, and many other Latin Americancountries. The common name of the fruit is tuna in the Latin Americancountries, ficodindia (fig of India) in Italy, tzabbar inIsrael, and sabar in Arab countries around the Mediterranean. Thefruit is spiny and has a thick peel that must be removed before reachingthe tasty flesh. Because various books on cactus pear are available (Wessels1988; Pimienta-Barrios 1990; Barbera and Inglese 1993; Barbera et al. 1995), this review focuses on some limiting factors and possible solutions toallow this fruit crop to become more widely accepted, as well as on othertypes of cacti producing edible fruits. Problems include spines, seeds, and the short period of production. Yet even with current limitations, the profitability of cactus pears in South Africa, Israel, and other countriesequals or exceeds that of common orchard crops (such as apples, peaches, and oranges), which have higher cultivation expenditures with comparablefruit prices (Brutsch and Zimmermann 1993).

A. Cactus Pears

Cactus pears have glochids (Gibson and Nobel 1986), which generallyare removed before the fruit is peeled. A simple solution would be to selectspineless cultivars, which so far do not exist-the so called "spineless"fruits are really only low in spines. Of 50 cultivars from around the worldtested under Israeli conditions, 'Direktor' from South Africa has the lowestnumber of spines but produces only a few fruits. Although a genetic approachshould not be ignored, opuntias are facultative apomictic plants, becausethey produce both sexual and asexual (nucellar) embryos in the same ovule;this leads to sexual and apomictic seeds (Perez-Reyes and Pimienta-Barrios1995), which somewhat decreases the success of hybridization experiments. Farmers wear aprons and gloves to harvest the fruits, which are mechanicallybrushed to remove the glochids and then often washed, dried, and waxed. In Israel, the cost of harvesting, brushing, waxing, sorting, and packingis about US$ 0. 30/kg, so from the marketing and consumer point of viewthe problem can be solved. Nevertheless, glochids can remain on the fruitsin some commercial shipments, which together with variations in fruit sizeare matters of quality control.

People who have consumed cactus pears from an early age are not botheredby the seeds, which readily pass through the digestive tract. In Australiawhere commercial activity with cactus pears was banned for many years dueto their devastating effect as introduced weeds (Nobel 1994), immigrantsfrom Mediterranean countries would pay high prices to obtain this fruitin spite of the seeds. Ten kilograms of fruits in unmarked wooden boxeswere sold in the late 1980s "under the table" in Sydney's wholesalemarket for Aus$ 60-80 (US$ 42-56) according to John Discusso Southern CrossProduce, Flemington Market, Sydney (personal communication). Cactus pearis presently legal in Australia and the 10-kg boxes sell for Aus$ 20-30(US$ 15-22). However, first-time tasters are often repelled by the numeroushard seeds, up to several hundred, embedded in the tasty pulp. Althoughemasculation of flowers and treatment with gibberellins can induce seedlessfruit (Gil et al. 1977; Gil and Espinosa 1980), these solutions are notreally feasible in horticultural practice. Emasculation of the flowersby hand is costly and application of gibberellins over a wide range offlower ages does not guarantee 100% seedlessness. A genotype of cactuspear exhibits vegetative parthenocarpy, so seedless cultivars may be obtainedby breeding (Weiss et al. 1993b), although other evidence indicates thatovule fertilization is necessary for the development of the funicular envelopethat makes the fruit pulp (Pimienta-Barrios and Engelman 1985; Pimienta-Barrios1991). In any case, because their seeds are a major problem in the acceptanceof cactus pears, more research should be conducted on this aspect to allowa greater adoption of this crop worldwide.

Fig 12. Cactus pear Opuntia ficus-indica ('Ofer')

Another problem of cactus pear is that the flower buds in a particularregion emerge during about 1 month in the spring. As a result, ripeningoccurs in the summer, also during about 1 month (Nerd et al. 1989, 1993a;Barbera et al. 1991; Brutsch and Zimmermann 1993). In Israel, 80% of fruitsnormally ripen during a 2-week period, which can drive prices below harvestingexpenses (the cool wet winters and hot dry summers may synchronize floweringin Israel). In Mexico with its various climates, the wide range of commercialcultivars produce fruits in June through October, but backyard plantingshave fruits from May through December (Pimienta-Barrios 1991), indicatinga genetic diversity that can be exploited in future breeding programs. Actually, in some locations, fruits of 0. ficus-indica can be producedyear-round, for example, in the Huonta Valley, Peru, and Njoro, Kenya.

A technique called scozzolatura was developed over 100 yearsago in Italy by which the first flush of flowers was removed, forcing asecond and delayed flush of flower buds, resulting in later ripening ofthe fruits (Barbera et al. 1991; Barbera and Inglese 1993). These fruitsare marketed during the autumn, avoiding competition with other summerfruits and increasing profitability, a technique also adopted in SouthAfrica (Brutsch and Scott 1991) and Israel (Nerd and Mizrahi 1993, 1994). Out-of-season fruiting can be induced in the Negev Desert by nitrogen fertilization, which causes the plants to flower after the normal period, leading to awinter crop that is more profitable than the summer crop (Nerd et al. 1991b).

In Israel, cactus pears can be harvested 10 months during the year (Fig. 6. 2). The lowest wholesale prices (equivalent to US$ 0. 80/kg) are obtainedduring the natural ripening period, which is mid-July to mid-August, andthe highest prices (US$ 3. 50/kg) are obtained from the out-of-season wintercrop. For one particular farmer, the first fruits in June obtained a 7. 3-foldhigher price than those in mid-July (Fig. 6. 2). This farm, which is locatedin the Arava valley and experiences arid desert conditions with averagemaximal daytime temperatures in July and August of 40° C (extremes 47° C), 30 mm annual rainfall, and 3500 mm annual pan evaporation, produces mangowith 2400 mm per year irrigation but cactus pear with only 400 mm, illustratingits high water-use efficiency. Thus fields in Israel can produce a wintercrop of cactus pears in addition to the normal summer crop (Nerd et al. 1991b) or a single autumn crop with higher prices (Nerd and Mizrahi 1994). Similarly, winter cactus fruits are produced in orchards that are heavilymanured (in Chile with chicken manure) or fertilized (in California). Futureyearround availability of cactus pears in international markets can alsobe enhanced by integrating northern and southern hemisphere producers.

B. Columnar Cacti

Fruits of many species of columnar cacti are consumed in Mexico as wellas other Latin American countries. These fruits are often termed pitayas or sometimes pitahayas, which can be further distinguished byadding a second name; such as pitaya dulce (the sweet pitaya), pitayaagria (sour pitaya), pitaya de Mayo (pitaya that ripens in May), or pitaya amarilla (yellow pitaya). To avoid confusion in dealingwiththe many species and genera that differ tremendously from each other, and awaiting the adoption of uniform common names worldwide, each speciesis here designated by its scientific name.

Fig. 6. 2. Pricesof cactus pears 1994 in the Israeli market. Data for solid line are averagemonthly wholesale prices for fruits of various sizes and qualities; fromlate April to late June, fruits are from storage (Nerd and Mizrahi 1993, 1994). Data for dashed line represent the farm-gate price received by onegrower for fresh fruits and were graciously provided by Yair Fine of MoshavIddan

The genus containing the most species with edible fruits is Stenocereus (Pimienta-Barrios and Nobel 1994). The three most important speciesin Mexico are Stenocereus griseus (Haworth) Buxb. , known as pitayade Mayo; S. queretaroensis (Weber) Buxb. , known as pitaya de Queretaro;and S. stellatus (Pfeiff. ) Riccob. These are cultivated in variousregions with a total area of about 2000 ha; sometimes known cultivars areintermixed with cuttings from wild plants that bear tasty and colorfulfruits. The stem cuttings are typically about 1 m in length and can producefruits in about 4 years, eventually producing about 20 t fresh weight offruits ha- yr-1. Clones differ in their pulp colors, including white, orange, pink, and various hues of red; most skins are green but may vary to red(Color Plate 5). The fruit's spines abscise upon ripening and can be removedwith bare hands. The fruit shelf life of the most commercial species, S. queretaroensis, is currently only a few days (Pimienta-Barrios andNobel 1994), but much remains to be learned about its postharvest physiology, including harvesting at various stages of fruit development and the effectsof reduced temperatures or controlled atmospheres.

Fig 5. Colored fruits of Stenocereus queretaroensis (pitayade Queretaro) in Oaxaca, Mexico.

Fruits of Stenocereus thurberi (Engelm. ) Buxb. (pitaya dulce, also known as the organ pipe cactus) are collected from the wild inArizona and northwestern Mexico. Stenocereus gummosus (Engelm. ) Gibs. & Horak (pitaya agria) grows in Sonora and Baja California, Mexico. The fruits of the famous soguaro, Carnegiea gigantea (Engelm. )Britt. & Rose, are also edible and are collected from wild plants;this species grows slowly and has little agricultural potential (Crosswhite1980). Other species that are highly appreciated in Mexico include Escontriachiotilla (Weber) Rose (jiotilla or geotilla), with small buttasty fruits. The cactus Myrtillocactus geometrizans (Martius) Cons, (garambullo) produces a berry-like, tasty, dark blue to black, small fruitof possible commercial value that can be found in local markets in thecentral part of Mexico. Two species of Pachycereus also produceedible fruits: P. pecten-aboriginum (Engelm. ) Britt. & Rose(cardon barbon) and P. pringlii (Berger) Britt. & Rose (cardonpelon; Felger and Moser 1974; 1976).

Cereus peruvianus (L. ) Miller (apple cactus) (Color plate 13) is a very promisingcolumnar cactus (Morton 1987; Nerd et al. 1993b; Weiss et al. 1993a), whichprobably originated along the subtropical southeastern coast of South America(Backeberg 1984). It has a high growth rate and produce fruit 3 to 4years after propagation from seed. The fruit is smooth and spinelessand varies from yellow to deep red (Weiss et al. 1994a).

Fig 13. Cereus peruvianus; Bar=30 mm.

Its pulp is white, juicy, and sweet and sour in taste, and contains soft, black, edible seeds. A 7-year-old plant can annually bear 60 to 80 kg of fruits, mainly in thesummer. The stems generally have spines, but spineless genotypes existand could be selected for. Attempts to domesticate various columnar cactihave recently been made in Israel with respect to fruit production (Nerdet al. 1990, 1993b). The closely related Cereus jamacaru D. C. (Scheinvar1985) has recently been planted for fruit in western Australia.

C. Climbing Cacti

An interesting group of cacti bearing edible fruit are the climbingepiphytic species that are native to the forests of northern South America, Central America, and Mexico. They grow on the shaded stems of trees andclimb within the canopy. When disconnected from the ground, these cactican take up water and minerals via their adventitious roots (Gibson andNobel 1986). Their growth can be inhibited by high radiation, such as directsunlight (Nerd et al. 1990; Raveh et al. 1993).

Although confusion has existed about their identification, climbingcacti apparently belong to two genera: Hylocereus, which has manyspecies with edible fruits, and Selenicereus, with the most importantfruit species, S. megalanthus (Schum. ) Britt. & Rose (Weisset al. 1995). Selenicereus megalanthus (pitaya amarilla) grows wildin Colombia, Ecuador, and Nicaragua at elevations between 800 and 1200m; it has been referred to as Hylocereus triangularis (L. ) Britt. & Rose (Arcadio 1986; Barbeau 1990; Morton 1987) and Hylocereus sp. Katom (Nerd et al. 1990; Raveh et al. 1993). After tasting thisyellow pitaya in Bogota in the mid 1980s, a Japanese businessman importedseveral tonnes, stimulating planting of S. megalanthus in Colombia(Cacioppo 1990). Today the fruits are gaining popularity in the Europeanmarket (Barbeau 1990; Cacioppo 1990).

Before the fruits of S. megalanthus are ripe, their areoles containseveral 1- to 2-cm-long spines that abscise upon ripening. Because thefruits are harvested before full ripening, the spines are removed witha brush (spine degradation in the soil is very slow, so spines are generallyremoved from the orchard). When ripe, the attractive fruit is yellow withraised tubercles (podaria; Color Plate 6). The flesh, which is white, juicy, sweet, with an appealing touch of acidity, is scooped from halved fruits, leaving the peel untouched. The black seeds embedded throughout the fleshare soft and edible.

Fig 6. Ripe fruits of Selenicereusmegalanthus (pitaya amarilla).

Like other climbing cacti, S. megalanthus is grown on a trellissystem. In the main country of commercial production, Colombia, many shapesand materials of trellis systems are used, including large boulders. Althoughcosts, productivities, and efficiency of labor under various trellis systemshave not been compared in detail, in Israel the trellis system is the majorexpense in establishing an orchard and has a major impact on the economicfeasibility of growing S. megalanthus. In addition, the effectsof pruning on yields and on ease of handling this crop need to be investigated. In regions where the photon flux (wavelengths of 400 to 700 nm absorbedby photosynthetic pigments such as chlorophyll) can reach 2000 to 2200mol photons m-1s--1, S. megalanthus must be grown in screened houses to prevent stem bleachingand death. The optimal shading is not yet known and its effects on vegetativegrowth as well as fruit and yield quality must be evaluated (Raveh et al. 1993). Also, protection from freezing temperatures is needed (Nerd et al. 1990). The postharvest physiology of this fruit is not well studied, suggestingthat the quality found in the international markets can be improved.

The other important climbing species is Hylocereus undatus (Haworth)Britt. & Rose (Color Plate 7), known in Mexico as pitahaya andin Central America and northern South America as pitaya roja (redpitaya). Surprisingly, this species is the most profitable crop in Vietnam, where it is known as "the dragon fruit" (thang loy inVietnamese) or "dragon pearl fruit" in Vietnam's export marketsof Hong Kong, Singapore, and Taiwan.

Fig 7. Thirteen-month-old research plantation of Hylocereus undatus at Ben Gurion University greenhouse in Beer Sheva, Israel.

In season from July through October, the fruits are offered as a special treat on Vietnam Airlines, Hylocereusundatus was apparently introduced to Vietnam by the French about 100years ago, and many Vietnamese now regard this species, which has spreadalong the eastern coast as a backyard plant, as indigenous. Commercialplantations estimated to be several thousand hectares are mainly grownamong trees that serve as inexpensive trellises; farmers prune these treesto allow more light, which they believe increases the fruit productionof H. undatus (Color Plate 8). Fruits of H. undatus are wellknown in the local markets (Color Plate 9). The main production area isalong the coast from Nha Trang in the north to Ho Chi Minh City in thesouth. The orchards, which yield 30 t fruit ha-1 yr-1, are fertilized byorganic manure and apparently contain a single self-compatible cultivar.

Fig 8. Commercial orchard of Hylocereus undatus near Nha Trang, Vietnam.

Fig 9. Fruits of Hylocereus undatus ("Dragon fruit")in Phan Rang market, Vietnam.

The fruit of H. undatus (Color plate 15), which has a red peeland large green scales, is larger, with a thicker parenchyma, than thatof S. megalanthus.

Fig 15. Hylocereus undatus; Bar=30 mm.

Upon ripening, the scales turn yellow (and other shades) and the fruitlooks like an attractive spineless ornament. Fruits of H. undatus needabout 50 days to complete development, and their pulp varies from whiteto various hues of red; fruits of S. megalanthus need 150 days tocomplete fruit development, their pulp is white with higher sugar levels, and this species is more sensitive to subfreezing temperatures. Other speciesof Hylocereus, such as H. costaricensis (We ber) Britt. &Rose (Color plate 14) and H. polyrhizus (Weber) Britt. & Rose(Color plate 16), are also candidates for domestication because they producelarge attractive fruits (Raveh et al. 1993; Weiss et al. 1994b). Crossesbetween these species occur and can result in hybrids with good horticulturalcharacteristics (Color Plate 10).

Fig 10. Ripening fruit of Hylocereus, probably a hybrid between H. undatus and H. polyrhizus.

Fig 14. Hylocereus costariscensis.

Fig 16. Hylocereus polyrhizus

VI. CACTI AS INDUSTRIAL CROPS

A. Cochineal

The most established and important industrial crop of cactus originis the red dye known as cochineal, the carminic acid used for over twocenturies as a biological stain for light microscopy as well as a dye forfabrics and foods (Nobel 1994). The dye is produced by female insects ofDactylopius coccus Costa or D. opuntiae Cockerell, whichuse Opuntia ficus-indica as their host plant (Color Plate 11). Thecladodes can be inoculated with fertile oviparous female insects in clothbags whose mesh allows the larvae to infect the cladode.

Fig 11. Infestation of cochineal insects on cladodes of Opuntia ficus indica in Los Angeles, California.

The insects, whichproliferate on healthy cladodes by extracting nutrients from the phloem(Wang and Nobel 1995), are collected when they are full of caraminic acidand have reached maximum infestation. Several hundred insects, about 2to 3 mm in diameter, can be collected by hand from a single cladode. Afterair drying, the raw material, called "grana" (meaning "seeds, "because the Spanish mistook the small insect bodies for seeds) is usedto make carmine, which in turn is used to dye various products with vividred colors of different hues as well as orange and yellow produced by varyingthe pH.

The grana quality depends on the ease of extraction of the dye (10 to26% of the insects' dry weight), which is relatively easy for the cultivatedcochineal insects, whereas noncultivated insects produce low-quality granathat obtain lower prices in the world markets (Borrego-Escalante 1992). A peak world production of dry grana of 700 t was recorded in theeighteenth century. Demand decreased in the nineteenth century, as cheaperaniline dyes were produced. However, aniline dyes are now considered unsafe(carcinogenic), so a resurgence of demand for carminic acid has occurredin the last decade, especially as dyes for the food and cosmetic industries. Current annual world production is about 300 t, with approximately 90%from Peru; the Canary Islands is the second largest producer and Mexicothe third. Conditions in the deserts of Peru are suitable for production:freezing temperatures do not occur and prevailing temperatures are 20 to 35° C; growersobtain US$ 45/kg of grana.

Because labor is the major expense for cochineal production, establishingan industry in countries where labor is expensive will be difficult. Cochinealcan be produced by growing opuntias in plantations similar to those forfruit production or by removing the cladodes to sheds in which the infestedcladodes are placed close together on hooks. The latter system was developedin South Africa where approximately 8000 ha of infested opuntias are availableto provide cladodes for cochineal inoculation; 90 mІ of sheds with cladodes from 0. 5 ha can yield 75 kg of grana per year witha value of US$ 3000 (Brutsch and Zimmermann 1993). Because good yieldsof grana in the first system means death of most of the cladodes on theplants, heavily yielding plantations generally deteriorate rapidly andmust be uprooted or pruned to the plant bases to renew vegetative growth, so use of sheds may be more efficient (Borrego-Escalante 1992).

B. Processed Foods

Nopalitos are sold not only as a fresh vegetable in Mexico but alsoas processed food, including pickled nopalitos, various salads, and cookeddishes. Fifteen firms export products, such as pickled strips or cubesof nopalitos in vinegar and a variety of prepared salads, mainly to theUnited States (Flores 1991). These processing industries absorb the seasonaloverproduction of nopalitos for local markets and also use cladodes fromwild plants, such as from 0. robusta in San Luis Potosi. Nopalitosare commercially dried only on a limited scale, probably because of thehigh amount of water in the fresh cladodes. In any case, when the foodindustries seriously consider this relatively inexpensive, high-qualityvegetable, more processed nopalito products should become available inthe future and not only in Mexico and the United States.

Because the cactus pear is the most common cactus fruit on the market, most of the processed fruit products are of cactus pear origin. Fruit juices, concentrates, jams, and jellies are common in Mexico and other Latin Americancountries. A popular product in Mexico is queso de tuna (literally, cheese of cactus pear), which is similar to cheese in consistency but issweet. Miel de tuna (honey of cactus pear) is another popular fruitproduct (Inglese et al. 1993). An alcoholic drink called colonche is producedin Mexico from cactus pears, (Flores 1991). Even in the Negev Desert ofIsrael, cactus pear ice cream is sold. Seeds of cactus pear contain 6 to20% oil, with 82 to 90% linoleic and oleic acids, 9 to 16% palmitic acid, and 1 to 2% stearic acid. Thus, cactus pear seeds left after processingthe fruit can be a source of high-quality culinary oil (Pimienta-Barrios1991;Inglese et al. 1993).

Similar products are made from fruits of other cacti, mainly in Mexico. Pitayas have been used in Mexico for many years as coloring agents andadditives to ice cream (Pimienta-Barrios and Nobel 1994). Ice cream isproduced from the variously colored fruits of Hylocereus speciesin Israel. Although fresh fruits yield the highest income to the producers, many fruits from columnar cacti tend to dehisce upon ripening and so arenot suitable for the fresh market. Overripe fruits or those with otherdefects can go to the processing industries and supplement the farmers'income (Pimienta-Barrios and Nobel 1994).

C. Mucilage and Medicinal Products

The sticky, jelly-like, water-absorbing substance found in certain plantsis known as mucilage and can occupy about 3% of the stem volume of Opuntiaficus-indica. It is produced and secreted by specific cells that canbe located at the inner side of the chlorophyll containing tissue (chlorenchyma), and large droplets are exuded when a cladode is cut (Gibson and Nobel 1986). Mucilage is considered a nuisance by many when cladodes are used as a vegetable, but as a complex polysaccharide it possesses biophysical characteristicsthat are desired by the cosmetic and food industries, which continuallylook for such chemicals from a range of plant and algal sources (Arad [Malis]and Cohen 1991). Opuntias and other cacti with large amounts of mucilagemay be a competitive source for such biochemicals, as already recognizedin Mexico (Flores 1991).

Medicinal effects and uses have been found for stems, flowers, and fruitsof cacti. As already indicated, consumption of nopalitos can improve glucosecontrol in humans with non-insulin-dependent diabetes mellitus, can reduceglucose levels and increase insulin activity under hyperglycemic conditions, and can reduce the blood levels of triglycerides, total cholesterol, andlow-density lipoprotein-cholesterol (Fernandez et al. 1990, 1992; Fratiet al. 1983. 1988a 1989, 1990; Inglese et al. 1993). Such a "healthfood" does not require any licensing, and dry nopalito capsules arealready sold in Mexico as a remedy to the above-mentioned health problems. The mode of action can be partly explained based on fiber content, butchanges in cellular sensitivity to insulin may also occur (Frati 1992). Two companies in Israel sell capsules of dried flower corollas of 0. ficus-indica to prostate sufferers for diuretic regulation (Inglese et al. 1993). Even after fruit ripening, flowers of the Israeli cultivar 'Ofer' maintaintheir dry corollas, which are easily removed and sell for US$ 13/kg (harvestingcosts half as much), providing an important additional income to cactuspear growers.

VII. FUTURE PROSPECTS

This review covers 34 species of cacti that can be crops (Table 6. 1). Great potential exists for cacti as low-input systems for developing regionsand as high-input systems for developed regions.

A. Low-Input Systems

Cacti can be grown in marginal lands of semiarid zones. In Kenya, bushclearing for conventional crops can lead to desertification, such as nearLake Baringo. Opuntia ficus-indica as well as other opuntias canserve as fruits and products therefrom, vegetables, animal feed, and asa drought-tolerant perennial for reforestation, which can provide firewood, although of low quality. In addition, the cladodes can be used for cochinealinsects for dyes and as a medicinal plant to combat diabetes mellitus, high blood pressure, and high cholesterol, and the corollas can serve asa prostate remedy. Planting of several genera and species can increasethe success of such projects and provide the diversity required for sustainability. The main input is the price of the plants.

Table 6. 1. Some cacti crops and their uses.

Botanical name	Use
Acanthocereus tetragonus  (L. ) Humlk	V
Carnegiea gigantea  (Engelm. ) Britt & Rose	F; IC
Cereus jamacaru D. C.	F; IC
Cereus peruvianus  (L. ) Miller	F; IC
Escontria chiotilla  (Weber) Rose	F; IC
Hylocereus costaricensis  (Weber) Britt. & Rose	F; IC
H. polyrhizus  (Weber) Britt. & Rose	F; IC
H. undatus  (Haworth) Britt. & Rose	F; IC
Myrtillocactus geometrizans  (Martius) Cons.	F; IC
Nopalea cochenillifera  (L. ) Salm-Dyck	AF;V
Pachycereus pecten-aboriginum  (Engelm. ) Britt. & (Engelm. ) Britt. & Rose	F; IC
P. pringlii  (Berger) Britt. & Rose	F; IC
Opuntia amyclaea  Tenore	F;MP;V
O. engelmanii  Salm-Dyck	AF
O. ficus-indica (L. )  Miller	AF;F;IC;MP;V
O. fragilis  (Nutt. ) Haworth	AF
O. humifusa  (Rafinesque) Rafinesque	AF
O. inermis  De Candolle	F;MP;V
O. lindheimeri  Engelm.	AF
O. megacantha  Salm-Dyck	AF;F
O. phaeacantha  Engelm.	AF
O. rastera  Weber	AF
O. robusta  Wendland in Pfeiff.	AF;MP;V
O. streptacantha  Lem.	F;MP;V
O.  stricta Hawort	AF
Pereskia grandiflora  Haworth	V
Selenicereus megalanthus  (Schum. ) Britt. & Rose [=Hylocereus triangularis  (L. ) Britt & Rose]	F; IC
Stenocereus griseus  (Haworth) Buxb.	F; IC
S. gummosus  (Engelm. ) Gibs. & Horak	F; IC
S. queretaroensis  (Weber) Buxb.	F; IC
S. stellatus  (Pfeiff. ) Riccob.	F; IC
S. thurberi  (Engelm. ) Buxb.	F; IC
Tricocereus pachanoi  Britt. & Rose	IC;MP

Note. AF, animal feed; F, fruit; IC, industrial crop; MP, medicinalplant; V, vegetable.

Although the productivity of some cacti is not high, the productivityof certain cacti can surpass other crops, many of which are relativelyrecently introduced, such as mango, avocado, banana, maize, potato, andtomato. These crops have been moved from continent to continent, from thetropics and temperate zones, but little movement has occurred for semiaridand arid crops such as cacti. For instance, Hylocereus undatus wasintroduced as a fruit crop to Vietnam and has become naturalized there, often climbing on backyard fences and existing trees; it is now an importantexport. Selenicereus megalanthus is exported from Colombia, initiallybased on the realization of its potential by a foreigner, which changeda backyard local fruit into a highly profitable export item.

Agroforestry, which can combat desertification and create sustainablesystems, should adopt cacti for semiarid and arid zones. Australia experiencedfive consecutive years of drought from 1989, with devastating results forits beef and sheep industries (mainly in western New South Wales and southwesternQueensland). Adopting the Texan and the Mexican approaches to the use ofvarious opuntias would have greatly improved the economic situation ofsuch Australian ranchers.

B. High-Input Systems

Can new cactus crops compete with existing successful agricultural systems?In South Africa, cactus pear competes well with established orchard crops(Brutsch and Zimermann 1993). A major problem is the introduction of newproducts into markets that are saturated with the traditional crops. Whoneeds these strange-looking cacti? However, some markets continuously seeknew products and often pay prime prices for them; adoptions in Europe ofkiwifruit from New Zealand and avocado from Israel are examples. Cactusfruits such as the fruits of Selenicereus megalanthus and Hylocereusundatus are more attractive and better tasting than avocado and kiwifruit. In western societies, health foods are in demand, a niche that can alsobe filled by cacti.

Irrigated orchards yield more than nonirrigated ones, and irrigationat the proper time can improve both fruit quantity and quality (Nerd etal. 1989), although much more research is required to optimize conditionsfor different species. As for other crops, NPK fertilization increasesthe yields as well as the number of new shoots for cacti (Nobel 1988). NPK fertilization and N alone can increase the number of floral buds for0. ficus-indica and even induce out of-season yields (Nerd et al. 1989, 1991b, 1993a). The myth that all cacti are slow growing isincorrect (Nobel 1991, 1994). Diseases and pests occur for cacti , whichhave not been researched as well as for other crops (Fucikovsky 1992, 1993). Also, like other crops, cacti need optimzation of inputs to provide maximumincome. In the case of the climbing cacti, two major expenses are expected:first, a trellis system to allow efficient management and harvesting, therebymaximizing yields and quality; and second, either nethouses and/or greenhousesto prevent damaging solar irradiation and/or temperatures.

The Cactaceae have a unique and interesting biology, yet only a fewscientists have done research to unravel their remarkable mechanisms ofgrowth and survival in harsh and stressful environments. Outside of Mexico, even fewer scientists are involved with the agricultural aspects of cacti. Most research publications are unavailable to industrial and scientificpolicy makers worldwide. Resources are generally allocated to the well-known, well-established common crop plants, while the opportunities for new cropssuch as cactus pears, Hylocereus fruits, and nopalitos remain obscure. The Cactaceae not only have a special significance to countries where wateris a major limiting factor and where desertification has taken its toll, but also offer economic opportunities to every entrepreneur willing todevelop new consumer tastes capitalizing on the increasing worldwide acceptanceof cactus products.

LITERATURE CITED

The list of Literature (88 positions) you can find here.

Подготовлен CD-диск:

Теперь Вы можете заказать CD-диск Культивар Редакция приглашает Вас заказать CD-диск с полным содержимым всех вышедших номеров нашего электронного журнала. На диске собраны все статьи и все полноразмерные фотографии к ним. Диск предназначен для автономного просмотра без подключения к интернету. Как заказать диск