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Vine Cacti Cytology

Chromosomes in the Cactaceae have a base number of n = 11 (Gibson and Nobel 1986). Cultivated Hylocereus species (H. costaricensis, H. polyrhizus, and H. undatus) and most investigated Selenicereus species are diploids (2n = 22), although the highly cultivated S. megalanthus (syn. Mediocactus megalanthus or M. coccineus; Moran 1953; Infante 1992; Weiss et al. 1995) is tetraploid (2n = 44; Beard 1937; Spencer 1955; Lichtenzveig et al. 2000). Selenicereus megalanthus has morphological features of both Hylocereus and other Selenicereus species (Britton and Rose 1963) and is cross-compatible with several Hylocereus spp., suggesting that S. megalanthus originated from an intergeneric hybridization between species of Hylocereus and Selenicereus (Lichtenzveig et al. 2000).

No major barriers seem to limit interspecific crossing among Hylocereus spp. Fruits obtained by such crossings are large, and the majority of the seeds germinate (Weiss et al. 1994b). Their hybrids show a normal meiosis, with 11 bivalents at metaphase I, and produce pollen of high viability and seeds with high germination rates (Lichtenzveig et al. 2000). Pollen viability for S. megalanthus is significantly lower than that for Hylocereus spp. and is associated with the pairing of multivalents and consequently the occurrence of univalents at metaphase I, which leads to pollen or ovules with chromosomal disorders (Lichtenzveig et al. 2000). Selenicereus megalanthus crossed with Hylocereus hybrids are triploids, aneuploids, or polyploids with different chromosome numbers (N. Tel-Zur, S. Abbo, and Y. Mizrahi, unpublished observations). The ability to produce hybrids by interspecific and intergeneric crosses is utilized in Israel for breeding cultivars with desired fruit characteristics (such as improved taste) or greater environmental flexibility. Modern molecular techniques (Chapter 15) may elucidate the genetic relationship among vine cacti underlying such features. An effective procedure has been developed for DNA extraction from Hylocereus and Selenicereus (Tel-Zur et al. 1999).

Pollination

Studies of breeding systems conducted in Israel (Weiss et al. 1994a; Nerd and Mizrahi 1997; Lichtenzveig 2000) show that Hylocereus spp. are self or partially incompatible, and foreign pollen (pollen of other Hylocereus spp.) is required for fruit set. Selenicereus megalanthus is self-compatible, as fruit can set with its own pollen. However, in certain clones larger fruit are obtained using pollen of other S. megalanthus clones, indicating partial self-incompatibility (Lichtenzveig et al. 2000). Climate conditions can also affect compatibility; at the end of the warm Israeli summer, high temperatures decrease H. undatus fruit set with self pollen. Natural pollinators of vine cacti seem to be bats and hawkmoths (Nerd and Mizrahi 1997). In orchards of vine cacti planted in the tropics, pollination is achieved without human intervention. In Israel, pollination is done by hand due to a lack of pollen vectors (Weiss et al. 1994a). Pollen preservation (Metz et al. 2000) allows for cross-pollination for times when there is no synchronization between the flowering of different Hylocereus crops.

Environmental Constraints

Vine cacti are native to tropical regions of North and South America, using their triangular slender stems, equipped with adventitious roots, to spread on trees. They are successfully cultivated outdoors in cloudy tropical regions (Central America and the Far East); e.g., H. undatus grows successfully in southern Vietnam and Taiwan without any shading (Fig. 11.1A). However, in Israel, where solar radiation is high (noon photosynthetic flux densities can reach 2,200 pmol m-2 s-1 in the summer), plants exposed to full sunlight can bleach, degenerate, and produce low quality fruit with poor color and low sugar concentrations (Raveh et al. 1997, 1998; Mizrahi et al. 1997; Mizrahi and Nerd 1999). Hence, plants are maintained under shade nets (Fig. 11.1B). Certain species, such as H. costaricensis and H. polyrhizus, have a higher light tolerance, probably due to their waxy thick skin that reduces the transmittance of light to the inner tissues of the stem. Orchards for such species in Israel are established in net houses with shading ranging from 20 to 60%—the higher shading being used in warmer regions (Mizrahi and Nerd 1999). The intensity of solar radiation changes during the daytime and depends on season, so control of light should be considered. Plants of Hylocereus spp. exposed to full sunlight in the spring have early blooming and early seasonal fruit production.

Vine cacti are sensitive to chilling temperatures and the stems bleach when night temperatures decline below about 5°C. Severe injuries appear when air temperatures approach zero; round yellow lesions develop along the stems and stem segments die. Subfreezing temperatures (-3°C) kill most of the collected germplasm in Beer-Sheva, Israel (Mizrahi and Nerd 1999). Observations in Beer-Sheva show significant differences among species in cold tolerance, as frost events totally damage Hylocereus sp. #10487 (unidentified species cultivated in Israel) and Selenicereus megalanthus, moderately damage H. undatus, and slightly damage H. costaricensis and H. polyrhizus. Plants recover easily when temperatures rise, but yields are reduced. In areas with cold temperatures, plastic coverings or glasshouses are recommended (Mizrahi and Nerd 1999).

In Israel water and fertilizer are commonly applied by drip irrigation almost year-round, except in the rainy periods (Nerd and Mizrahi 1998; Nerd et al. 1999). Vegetative growth and fruit production in the hot internal valleys (Jordan and Arava) occur later than in the more moderate coastal region. A well-developed canopy (1.8 m high in rows that are 2.5 m apart) is obtained for H. undatus at the 3rd year in the coast region, whereas 5 to 6 years is required in the valleys; annual fruit yield of the full canopy orchard is 32 to 40 tons ha-1 at the coast versus 2 to 3 tons ha-1 in the warmer and drier valleys. Because the rates of fruit-set and the average fruit weight are similar for the valleys and the coast, the small number of flowers produced in the valleys is likely the predominate factor in the low yields. The high summer temperatures (monthly maximum/minimum air temperatures are 38/25^, 7 to i0°C higher than those at the coast) or the saline irrigation water in some locations (electrical conductivity of soil water = 3-4 de-cisiemens m-1 at Arava versus i dS m-1 near the coast) probably inhibits flower induction. High summer temperatures in the valleys cause daily net CO2 uptake to be small or negative for vine cacti (Raveh et al. 1995), so deficiency of photosynthate can also explain the slow growth rate and low fruiting in the valleys.

In response to high air temperatures (43-46^) that occur during warm summers in Israel, stems can turn brown and become liquefied (Fig. 11.1B). Hylocereus undatus is the most sensitive of the cultivated vine cacti; in the summer of 1998 in the Arava Valley, about 50% of its total stem length was damaged versus less than i0% for H. costaricensis and H. polyrhizus, and none for S. megalanthus. Similar results occur for a germplasm collection that is located in a greenhouse in Beer-Sheva under unusual extreme summer temperatures (Mizrahi and Nerd 1999). Shade reduces the heat damage.

Trellis Dragon Fruit Taiwan
Figure 11.1. (A) Hylocereus undatus on single-plant trellis system in Taiwan and (B) H. undatus (on left) and Hylocereus polyrhizus (on right) on row trellis system under shade net (shade cloth) in Israel, where injury occurred on H. undatus at high summer temperatures of 45°C.

Fruit Properties

Fruits of vine cacti are medium-sized to large berries with a thin, colored peel and white or colored, juicy pulp (Table 11.1) containing numerous small, soft, digestible seeds. The peels of Hylocereus spp. have scales that contribute to the attractive appearance of the fruits, which also are used decoratively. For Selenicereus megalanthus, the peel is covered with spiny tubercules, but the spines are readily shed upon ripening. Fruits of Hylocereus crops are usually large (up to 1,000 g), two- to threefold heavier than those of S. megalanthus.

Studies in Israel (Weiss et al. 1994b; Nerd and Mizrahi 1998, 1999; Nerd et al. 1999) show that fruit growth for H. costaricensis, H. polyrhizus, H. undatus, and S. megalanthus follows a sigmoid pattern, with a low or negligible growth rate during the last phase when ripening occurs. A change in peel color (color-break) indicates the beginning of the last phase. For H. polyrhizus, which has a red-violet pulp, the accumulation of pulp pigments occurs in parallel with the development of peel color. During the last phase, pulp content (as a percentage of fruit fresh weight) increases markedly (from 20-30% at the beginning to 60-80% at the end of the phase), pulp titratable acidity declines, and pulp contents of soluble sugars and soluble solids increase (reaching maximal levels of 7-9% and 14-18%, respectively, of the fresh weight at full color). Degradation of starch, which increases in the pulp prior to ripening, accounts partially for the accumulation of soluble sugars. For H. undatus, amylase and invertase activity is correlated with the increase in pulp soluble sugars (mainly fructose and glucose), which reach their highest concentrations at the center of the pulp (Wu and Chen 1997). The fruits are classified as nonclimacteric, reflecting the low production rates of CO2 and ethylene during ripening (Nerd and Mizrahi 1998; Nerd et al. 1999).

Palatability tests on fruits picked at different ripening stages (determined according to the number of days after anthesis or the appearance of peel color) indicate that fruits are most palatable at advanced ripening stages or at full color. Similar to many other fleshy fruits, growers tend to harvest the fruits of vine cacti prior to full ripeness when the peel is still mostly green in order to prolong the marketing life of the fruit (Barbeaue 1990; Cacioppo 1990). However, ripening of such fruits is not as good compared with those left to ripen on the vine. For example, fruits of S. megalanthus picked at color-break and held at 10 to 20°C attain the physical appearance of fruits ripened on the plant and their acidity decreases, but the soluble sugars remain low and the flavor is poor (Nerd and Mizrahi

1999). Hence, the optimum stage for harvesting fruits of vine cacti for high consumption quality under usual storage conditions should be at close to full ripeness, as evidenced by almost full or full color development.

The shelf life of fruits of Hylocereus species is about 7 to 10 days at room temperature (about 20°C; Nerd et al. 1999). Shelf life is limited by senescence symptoms, such as a sharp decline in acidity and sugars, scale yellowing and shriveling, and fruit softening. Fruits can be stored for 14 days at 10 to i2°C and longer under lower temperatures (4-6°C), but upon transfer to room temperature they tend to develop chilling injury symptoms, such as peel browning and decay. Similarly, fruits of S. megalanthus are sensitive to chilling temperatures, but the storage life (at 10-i2°C) is at least twice as long as for Hylocereus fruits (Nerd and Mizrahi 1999).

Vine cacti produce several floral flushes during the flowering season, and predicting the harvest time is important for orchard management and fruit marketing (Mizrahi and Nerd 1999). Little is known about the effect of plant and environmental factors on the duration of fruit growth for vine cacti, but temperature appears to be a dominant factor. In Israel Hylocereus spp. produces three or four flushes during the warm season (June-October); 30 to 35 days elapse from anthesis to full fruit color when daily temperatures average 25°C, but 40 to 45 days are required when daily temperatures average 20°C (Nerd et al. 1999). Flowering of S. megalanthus in Israel occurs mainly in the autumn, when air temperatures decrease and the duration of fruit development is much longer than for Hylocereus spp. The increased development time is due to the lower temperatures during fruit growth and the lower inherent growth rate for the fruit of S. megalanthus (Nerd and Mizrahi 1998). The time from anthesis to full ripening for S. megalanthus varies from 120 days (average daily temperatures of 25°C) to 180 days (20°C). The positive correlation between air temperature and fruit growth enables the development of a heat-unit model to predict the period from anthesis to maturity for S. megalanthus (Nerd and Mizrahi i998).

Columnar Cacti

Columnar cacti are much less cultivated for fruit than are vine cacti, and little is known about their environmental flexibility (Mizrahi et al. 1997). Among them, Stenocereus spp. are the most cultivated. They are planted in Mexico in or near their natural habitats, which have a semitropical climate with both summer (about 65%) and winter rains for a total of 400 to 800 mm annually (Pimienta-Barrios and Nobel 1994; Pimienta-Barrios et al. 1997). Monthly av erages of daily air temperatures range from 8 to i8°C at night and from 24 to 34°C during the daytime. Temperature fluctuations from the coldest to the warmest month is only 8°C at any particular site. Each species will be considered separately.

Stenocereus queretaroensis

Stenocereus queretaroensis is probably the commercially most important species of the genus (Pimienta-Barrios and Nobel 1994). It is also the most investigated (Nobel and Pimienta-Barrios 1995; Pimienta-Barrios et al. 1997; Pimienta-Barrios 1999). Fruits reach the local markets from three sources: (1) wild stands, (2) wild stands enriched with cuttings of selected clones (managed in situ), and (3) cultivated selected clones established from cuttings in home gardens and small plantations (Fig. 11.2). Many commercially productive stands come from relict ones, namely those associated with archeological sites dating back as long as 2,300 years BP (Benz et al. 1997). Today's plants are offspring from ancestors selected in pre-Columbian times, with better horticultural features having evidently gone through selection by humans for many years (Benz et al. 1997).

Fruit weights of S. queretaroensis average 100 to 200 g. The pulp is very tasty, has different colors according to the clone (white, pink, orange, red of various hues, and purple), and contains soft edible small seeds. The spines are soft, abscise upon ripening, and can easily be removed by hand. The best clones are found in relict stands near arche-oligical sites, and fruit productivity per plant correlates with the canopy width, probably due to length of the branches on which the fruits are produced. Annual production of i00 fruits per plant yields about i7 tons fresh weight ha-1 year-1 from the best orchards (Benz et al. 1997). The best-known clone is 'Mamey,' whose fruit can reach the size of 165 g fresh weight. The peel is 18 to 24% of the fruit fresh weight under cultivation, which is better (lower) than for the much more common cactus pear, whose peel is about 45% of the fruit fresh weight (Pimienta-Barrios et al. 1997). The fruit shelf life is only a few days, partly because the fruits split (dehisce) and the pulp is exposed to contamination by bacteria and fungi. This very short shelf life, even for non-splitting fruit, is the main constraint on its commercialization (Pimienta-Barrios et al. 1997). In spite of this shortcoming, workers involved with this fruit earn the same to three times as much as other wage earners in the region (Benz et al. 1997). Another important factor that limits the domestication of S. queretaroensis is its relatively low growth rate. Ten years are required for an orchard to obtain large enough fruit production to reach

Cactusexpert
Figure 11.2. Orchard of Stenocereus queretaroensis in southwestern Jalisco, Mexico. Photograph courtesy of Park S. Nobel.

profitability. On the other hand, 100 years of production are expected from this plant, reaching its peak at 40 years of age (Pimienta-Barrios et al. 1997). This pitaya does not respond to traditional management, such as irrigation and fertilization, possibly due to symbiotic association with mycorrhizae or genetic inflexibility (Pimienta-Barrios and Nobel 1995; Pimienta-Barrios et al. 1997).

Stenocereus queretaroensis in Mexico flowers in February and March, the beginning of the dry season. Fruits ripen mainly in May and are harvested at the ripe stage. The soluble sugars comprise 10 to 11% of the fruit fresh weight for various cultivars (Pimienta-Barrios et al. 1994, 1997). The fruits are sour (pH 4.5-5.0), with the acid content ranging between 0.15 to 0.5% of the fruit fresh weight. Fruits of S. queretaroensis have to be sold immediately because of a very short storage and shelf life, as they readily split open (Pimienta-Barrios and Nobel i994; Pimienta-Barrios et al. i997); this, as already indicated, is the main restricting factor in the commercialization of this species.

Other Stenocereus Species

Stenocereus stellatus is the commercially second most important columnar cactus in Mexico. Known locally as "xoconochtli," archeological evidence shows that it was consumed by humans as long as 7,000 years BP (Chapter

9). Today S. stellatus has the same three major sources of fruits as for S. queretaroensis (Casas et al. 1997, i999a,b). It is grown in semitropical areas with average annual temperatures of 17 to 24°C and annual rainfall of 440 to 760 mm. Fruit weight is less than that of S. queretaroensis, ranging from 20 to 80 g; the number of fruits per plant varies from 12 to 187. The maximum density of plants in home gardens is 780 ha-1, and the highest yield is 3.3 tons ha-1 year-1. Fruits vary in skin color—some are green (preferred in home gardens) and most are red. Pulp color is red in wild ones, whereas under cultivation pink, purple, yellow, orange, and white pulp can also be found. In the wild the taste is usually sour, whereas cultivated fruits are sweet and sometimes insipid. Some fruits are very spiny, but others have few spines. Upon ripening, spines can be easily removed. Locals prefer the less spiny, larger sweet fruits with a green peel and white flesh (Casas et al. 1997, 1999a). Plantations established from cuttings (about i m in length) bear abundant fruits during the fourth year, although some fruits may be obtained one year after planting but are followed by no fruits in the second year (Casas et al. 1997). In the Negev Desert of Israel, even under fertigation (irrigation with water plus specific nutrients), S. stellatus produces low amounts of small fruits with no promise of being a commercial orchard crop (Nerd et al. 1993). As for many other columnar cacti, this species flowers nocturnally with self-incompatibility. Also, some genotypes cannot pollinate each other, suggesting that S genes are active (Casas et al. 1999b).

Stenocereus griseus is of a more tropical nature than the other cultivated Stenocereus species (Silvius 1995). Its common name, Pitaya de Mayo, means ripening in May (Mizrahi et al. 1997). The fruit is relatively large (100-200 g) and of good quality, similar to other Stenocereus spp. In Venezuela there are two ripening seasons, May-early June and late August-early September, corresponding to the rainy seasons (Silvius i995). In Israel when regularly ferti-gated (Nerd et al. 1993), flowers appear in late April to May and again in July and in October. Fruits occur in late May (hot valleys) and June to August, but no fruits occur from the October flowering, possibly because temperatures at this time will not support fruit growth. It is sensitive to sub-freezing temperatures and has a poor tolerance to salinity (Nerd et al. 1993). Stenocereus griseus is harvested and marketed only in Mexico (Pimienta-Barrios and Nobel 1994).

Cereus peruvianus

Cereus peruvianus has only recently been domesticated and its origin is obscure, although possibly it comes from Brazil (Mizrahi and Nerd 1999). Cereus jamacaru from north eastern Brazil and C. uruguayanus from Argentina are closely related species or even the same one (Taylor and Zappi 1992; R. Kiesling, personal communication). The species is common in gardens in tropical and subtropical countries and has been planted commercially on a small scale in Israel. In comparison to various Stenocereus spp. examined in Israel, C. peruvianus has significantly higher growth and precocious yielding (Nerd et al. 1993). The common commercial trade name given by the Israeli export company AGREXCO is 'Koubu' to distinguish between the fruit of this species and other pitayas (Mizrahi and Nerd 1999).

Growth and fruiting of C. peruvianus in Israel are significantly higher near the coast than in the internal warm valleys or the cold Negev Highlands, where frost (air temperatures decline to -7°C) damages the plants (Nerd et al. 1993). The species is sensitive to salinity (electrical conductivity of the irrigation water of 4 dS m-1), particularly when Na and Cl are the predominating ions (Nerd et al. 1993). Israel uses C. peruvianus as a fruit crop, but in South Africa it is considered a weed (Moran and Zimmerman 1991). In Brazil it is used for its valuable gum and polysaccharides (Alvarez et al. 1992, 1995), and various vegetative micropropagation techniques have been developed (Deoliveira et al. 1995; Machado and Prioli 1996). Cereus peruvianus is self-incompatible and requires cross-pollination to obtain fruits (Weiss et al. 1994a; Silva and Sazima 1995; Nerd and Mizrahi 1997). In spite of its nocturnal flower opening, daytime-active honey bees can act as pollinators using the few hours the flowers are open in the late evening or early morning (Weiss et al. 1994a; Nerd and Mizrahi 1997; Mizrahi and Nerd 1999). However, when large plants produce hundreds of flowers in a wave in Israel, honey bees fail to cross pollinate the flowers efficiently; hand pollination is then needed to obtain high fruit set and large fruits.

Cereus peruvianus during the warm season in Israel produces several flower flushes. Fruit development differs significantly from that of vine cacti, exhibiting a double sigmoid growth curve with an early and a late rapid growth phase and a slow intermediate growth phase (Weiss et al. 1994a; Wang 1997). Color-break designates the beginning of the last phase, and fruits are fully colored at the end of this phase. During the last phase, pulp fresh weight increases significantly, whereas peel fresh weight remains almost constant; for fully developed fruits, the pulp comprises 70 to 80 % of the fruit fresh weight versus 15 to 20% for young fruits. Ripening occurs during the last phase; firmness and acidity decrease and soluble sugars and total soluble solids increase (to 8-10% and 12-13% of pulp fresh

Figure 11.3. Fruits of H. undatus packed in Israel for export to Europe.

weight, respectively) at full color (Wang 1997). Similar to vine cacti, the optimum harvest stage is when the fruits are close to or at full ripeness. Fruits of C. peruvianus tend to crack during ripening and in certain genotypes black areas appear on the peel when fruits mature or are touched during harvest. The tendency for both disorders is genetically inherited and can be overcome by clonal selection. For C. peruvianus in Israel, about 40 days elapse from anthesis to full color when daily temperatures average 28°C versus 42 to 47 days when temperatures average 24°C (Wang 1997). Fruits of C. peruvianus are similar to those of S. megalanthus with regard to storage and shelf life.

Vine and Columnar Cacti as World Fruit Crops Hylocereus

The most widely cultivated vine cactus is the red pitahaya, Hylocereus undatus (red peel, white pulp; Fig. 11.3). Its utilization as a major commercial fruit crop has its origins in Vietnam (V. Van Vu, personal communication). The plant was introduced to Indochina by the French around i860, where it is now considered to be a native plant. Orchards in Vietnam are established from selected clones, and the estimated cultivated area in southern Vietnam is 6,000 ha. The fruits produced ("dragon fruit," or thang loy in Vietnamese) are common in local markets and are also exported to Asian and European countries. Hylocereus undatus is now spreading in many Asian countries, such as Thailand, Laos, Indonesia, Cambodia, Taiwan, and recently Japan (Okinawa), using clones from Vietnam. Horticultural research in Taiwan indicates a strong local interest in the fruit (Feng-Ru and Chung-Ruey i997a,b). Other vine pitahayas, such as H. costaricensis and S. mega-lanthus, were also introduced to Taiwan and are used for both cultivation and breeding. In addition to the fruit, fresh and dry flowers are also consumed in Taiwan as a vegetable. The development of the H. undatus industry is also very intensive in Mexico (Ortiz 1999; Canto 2000), and the estimated present planted area there is about 2,000 ha, half of it in the Yucatan peninsula where it can be found in the wild and has been utilized from pre-Columbian times. Most of the crop in Mexico is sold in local markets.

year

Figure 11.4. Increase in plantation area and fruit yields of vine cacti in Israel during the 1990s.

year

Figure 11.4. Increase in plantation area and fruit yields of vine cacti in Israel during the 1990s.

In Israel the cultivation of H. undatus is expanding rapidly, reaching nearly 20 ha in 2000. Export to Europe started in 1996 with 10 tons and in 1999 was about 130 tons (Fig. 11.4). Under the dry climate of Israel, fruit quality is high and most of the harvested crop is marketable. The main difficulties for export are the short storage life of the fruit and the non-stable fruit supply; flowering and harvests occur in waves (Mizrahi and Nerd 1999). Also other countries, such as Australia, New Zealand, the United States (Florida and California), Spain, and the Philippines, are developing the cultivation of H. undatus.

Hylocereus costaricensis (red peel, red pulp) is cultivated mainly in Nicaragua, established from clones selected from the wild. The fruits ripen during the rainy season and most of the yield is heavily infested with insects, bacteria, and fungi so that only a small fraction of harvested fruit can be sold as fresh fruit. Export is mainly to Europe under the brand name 'Pitanica.' Today most of the cultivated 6,000 ha are aimed at pulp production, highly demanded by the food industry in the United States and Europe as a natural food ingredient and a colorant (Ortiz 1999; Canto 2000). Guatemala is also producing significant quantities of this fruit, with several other types of red peel/red pulp vine pitahayas. Fruits of Hylocereus polyrhizus have a red peel, as for H. costaricensis, but have a red-violet pulp. The crop is planted in Israel as a pollinator for H. undatus. Usually red vine pitahaya orchards consist of 20% H. polyrhizus and 80% H. undatus. Because of the sour taste, fruit H. polyrhizus appeals to some consumers more than that of H. undatus. Selected hybrids produced by inter- or intra-specific crossings are also cultivated, usually on a local basis and on a small scale (Mizrahi and Nerd 1999; Ortiz 1999; Canto 2000).

Selenicereus megalanthus

The fruit of Selenicereus megalanthus (yellow peel, white pulp), often known as "yellow pitaya" but also as pitahaya, is the most tasty vine cactus fruit (Mizrahi et al. 1997; Mizrahi and Nerd 1999). The first country to grow this species for export was Colombia at the request of a Japanese businessman, who appreciated the fruit. Significant planting started in Colombia in 1986 and export to Japan started in 1989 but soon ceased due to pests (eggs and larvae of insects) found where the corolla connects to the fruit. Fruit was then exported to Europe, which is not as concerned with tropical pests and has become the most important export market for yellow pitaya (also now shipped from Ecuador via Colombia). Planted areas in Colombia reached 4,000 ha in 1990 but later were reduced to 250 ha as result of disease problems, such as fusarium (which attacks the plant) and especially Drechslera cactivora (which infects the base of the pre-mature fruit and induces yellowing; Valera et al. 1995; Bibliowicz and Hernandez 1998). Accessions introduced into Israel from Colombia, although similar in morphology, vary in fruit characteristics and growth behavior, indicating different genotypes (growers in Colombia do not keep track of the origin of the material used for planting). This has been confirmed by DNA finger-printing analysis developed for vine cacti (Tel-Zur et al. 1999). Fruit of S. megalanthus obtains prime prices in Europe, higher than any other cactus fruit, due to its delicious taste (Ortiz 1999; Canto 2000; J. Rosenbaum, personal communication). Other yellow-peel vine cacti are available—some clones of Hylocereus undatus from Mexico and H. costaricensis from Nicaragua—whose qualities are similar to that of the common red-peel clones of these species. The present sources of fruit of S. megalanthus shipped to Europe are Colombia, Ecuador, and Israel.

Stenocereus and Cereus

Stenocereus spp. are cultivated only in Mexico. The fruits are tasty, resembling those of figs. Usually they are collected and sold in close proximity to where they are harvested and their price is relatively low (Benz et al. 1997). When they reach Mexico City, their price can be as high as U.S. $6 per kilogram. In the 1990s, efforts were directed to converting them into sustainable fruit crops (Pimienta-Barrios and Nobel 1994; Casas et al. 1997, i999a,b; Pimienta-Barrios et al. 1997). The total cultivated area for Stenocereus spp. in Mexico exceeds 2,000 ha. The main limiting factors are the short storage and shelf life, in large measure because

Stenocereus Peruvianus

of the tendency of the fruit to split during ripening. Cereus peruvianus is under domestication in Israel (Fig. 11.5) and is sold in Europe. The fruit lacks spines, has much longer storage and shelf life than that of Stenocereus, and is similar to that of S. megalanthus. As an index of the acceptability of such new cactus fruits, C. peruvianus was marketed for the first time in 1998 and was accepted very well in both local and European markets, due to its beautiful appearance, delicate sour-sweet taste, and unique aroma. Among eight clones released for cultivation in Israel, only two have proved to be promising for further planting. Unlike the others, their fruits do not tend to split upon ripening or to develop black spots under storage; similar efforts to develop the cultivation of C. peruvianus exist in California and Texas.

Conclusions and Future Prospects

Pitahayas and pitayas, unlike many other new crops, are appealing to consumers unfamiliar with the fruit because of their delicate texture and taste and their unusual and attractive appearance. Slow growth and development of the plants, low fruit yields, and especially the very short shelf life of the fruit (about 2 days) limit wide cultivation of Stenocereus species; commercial plantings occur in their area of distribution, and fruits are mainly marketed locally by growers and by people collecting fruits from wild plants. However, pitahayas and Cereus peruvianus are promising new worldwide crops. They have precocious and high yields and a longer fruit shelf life, which enables marketing of the fruit over long distances. Indeed, their cultivation is rapidly spreading around the world, and their fruits are available in supermarkets and specialty shops.

Pitahayas and pitayas increase the diversity of cultivated fruit crops, which may be used either for sustainable agriculture systems (e.g., Stenocereus queretaroensis; Fig. 11.2) or for the intensive fruit industry (e.g., Hylocereus un-datus; Fig. 11.1). These cacti can compete successfully in profitability with common fruit crops. Because of the high water-use efficiency of Crassulacean acid metabolism (CAM) (Nobel 1994), the low water demand of pitahayas and pitayas represents a significant advantage in arid and semiarid regions not only because of the direct water savings but also because the environmental damage caused by heavily irrigated common crops is avoided. Pitahayas can also be used as sources for new products, such as colorants and polysaccharides for the food industry or their edible flowers.

The recent expansion of fruit crops from vine and columnar cacti has been based mostly on wild plants from southern North America (Mexico), central America, and northern South America (Colombia), where these fruits are traditionally used by local people. The plants are found mainly in home gardens or on marginal lands. Thus, professional breeding of improved cultivars should be an important objective, because most of the available material is a result of superficial selection based on a few visible traits.

Definition of the available plant material by taxonomic, molecular, and genetic studies is essential for these breeding efforts. Intergeneric and interspecific crosses are easily achieved among vine cacti, so growers can utilize hybrids as well as unidentified material as future cultivars. However, the appearance of diverse types of fruits in the markets can lead to confusion and marketing problems. The lack of distinct common names for existing crops (Table 11.1) already causes confusion for marketing.

Much research is required in order for pitahayas and pitayas to be established successfully as world crops. Horticultural treatments as well as orchard management practices have to be developed. Improved postharvest treatment is important. Pitahayas growing in structures are convenient candidates to be fed with CO2; stomata open for CAM plants during the night when CO2 enrichment can be done without overheating problems. The dramatic development of pitahayas and pitayas as fruit crops supports the recent trends to develop ethnic fruits as new crops and to utilize the underexploited cactus family as a source of new crops. Unlike some other new crops, a large gap exists between research and the commercialization of pitahayas and pitayas—a gap that must be filled for successful cultivation.

Literature Cited

Alvarez, M., S. C. Costa, H. Utumi, A. Huber, R. Ber, and J. D. Fontana. 1992. The anionic glycan from the cactus Cereus peruvianus—structural features and potential uses. Applied Biochemistry and Biotechnology 34: 283295.

Alvarez, M., S. C. Costa, A. Huber, M. Baron, and J. D. Fontana. 1995. The cuticle of the cactus Cereus peru-vianus as a source of a homo-alpha-D-galacturonan. Applied Biochemistry and Biotechnology 51: 367-377.

Barbeau, G. 1990. La pitahaya rouge, un nouveau fruit exotique. Fruits 45: 141-147.

Beard, C. E. 1937. Some chromosome complements on the Cactaceae and a study of meiosis in Echinocereus pa-pillosus. Botanical Gazette 99: 1—21. Benz, B. F., F. M. Santana, J. E. Cevallos, E. M. Munoz, J. A. Rosales, and M. A. Rosales. 1997. The structure and productivity of relict stands of pitaya (Stenocereus queretaroensis; Cactaceae), Jalisco, Mexico. Economic Botany 51: 134-143.

Bibliowicz, A., and S. M. Hernandez. 1998. Organismos Fungosos Presentes en las Estructuras Reproductivas de la Pitaya Amarilla. Universidad Nacional de Colombia, Santafé de Bogotá.

Britton, N. L., and J. N. Rose. 1963. The Cactaceae: Description and Illustrations of Plants of the Cactus Family. Vols. I & II. Dover Publications, New York.

Cacioppo, O. G. 1990. Pitaya: una de las mejores frutas producida por Colombia. Informative Agroeconómico, Febrero: 15-19.

Canto, A. R 2000. Pitahayas. Estado Mundial de su Cultivo y Comercialización. Fundacion Yucatan Produce, Universidad Autónoma, Chapingo, Mexico.

Casas, A., B. Pickersgill, J. Caballero, and A. Valiente-Banuet. 1997. Ethnobotany and domestication in Xoconochtli, Stenocereus stellatus (Cactaceae), in the Tehuacan Valley and La Mixteca Baja, Mexico. Economic Botany 51: 279-292.

Casas, A., J. Caballero, A. Valiente-Banuet, J. A. Soriano, and P Davila. 1999a. Morphological variation and the process of domestication of Stenocereus stellatus (Cactaceae) in central Mexico. American Journal of Botany 86: 522-533.

Casas, A., A. Valiente-Banuet, A. Rojas-Martinez, and P Davila. 1999b. Reproductive biology and the process of domestication of the columnar cactus Stenocereus stellatus in central Mexico. American Journal of Botany 86:

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