Reprinted from: Perspectives on new crops and new uses. 1999. J. Janick (ed.), ASHS Press, Alexandria, VA. Climbing and Columnar Cacti: New Arid Land Fruit Crops Yosef Mizrahi and Avinoam Nerd* In Israel, scarcity of water, high input prices, and market competition limit the number of orchard crops that can be grown profitably. Our approach to the further development of the horticultural industry in the dry regions of Israel—the Negev and Judean deserts—is thus to establish new crops that will demand high prices in the export markets (Mizrahi and Nerd 1996). To this end, about 40 species of rare or wild fruit trees were introduced by us into these dry regions in a number of locations that differed in terms of soil, water, and climate (Nerd et al. 1990; Mizrahi and Nerd 1996). Emphasis was placed on candidates of the Cactaceae because of their high water-use efficiency (5–10 times higher than that of most conventional crops), resulting in low water requirement (Nobel 1988, 1994). The high water-use efficiency of cacti is provided by their unique photosynthetic pathway—crassulacean acid metabolism (CAM). In CAM plants, the stomata open and CO2 uptake takes place during the night when evaporation is low. Among the Cactaceae, there are about 35 species that have a potential for cultivation as fruit, vegetable, or forage crop species (Nobel 1994; Mizrahi et al. 1997). Starting in 1984, we have introduced, for investigation as potential crop species, 17 members of the subfamily Cactoidae (Nerd et al. 1990; Mizrahi and Nerd 1996). Among these, four climbing (epiphytic) species and one columnar species have already been planted as commercial crops, and their fruits are being exported successfully to European markets as exotic fruits from Israel. The main reasons that these crops have made their way onto the market within so short a time after introduction are their precocious early yield- ing (three to four years after seeding or one to three years after propagation from cuttings) and their accept- ability in the markets. At present, our studies are aimed at examining the environmental adaptations of the species and their reproductive biology mode and at developing appropriate agrotechnological practices. In addition, a breeding program accompanied by cytological and molecular studies is being carried out in order to develop improved clones for cultivation. This review is divided into two parts. The first part deals with the climbing cacti of the genera Selenicereus and Hylocereus and the other with the columnar cactus Cereus peruvianus. CLIMBING (EPIPHYTIC) CACTI Taxonomy We collected wild or cultivated types of climbing cacti from a variety of sources—amateur cactus lovers, growers, botanical gardens, and backyards. We very soon realized that there is tremendous confusion about the taxonomic identity of these cacti: accessions with the same name were found to be of different species. We are currently applying cytological and molecular techniques to determine the proper taxonomic identities of the species that we have introduced (Lichtenzveig 1997). These species belong to at least to two different genera, Selenicereus and Hylocereus. From the genus Selenicereus we will elaborate here only on one species S. megalanthus, currently grown in Israel and in Colombia, where it is known as yellow pitaya (Hunt 1989; Barthlott and Hunt 1993), Acces- sions of S. megalanthus were introduced by us as H. triangularis or H. undatus and were later classified as S. megalanthus (Weiss et al. 1995; Mizrahi et al. 1997). We have 37 selected clones from this species. From the genus Hylocereus, we have introduced the following species, some with a number of clones (Table 1): H. undatus, H. polyrhizus, H. purpusii, H. ocamponis, and H. costaricensis (Britton and Rose 1963; Barthlott and Hunt 1993). In addition, we have introduced some promising unidentified clones of Hylocereus (Hylocereus sp.), the best of which was designated as 10487. Of these species, only the ones that are currently being grown in Israel for export are described in this paper, as follows: H. undatus, H. polyrhizus, and Hylocereus *The authors thank the Fleischer Foundation and Harry-Stern & Hellen-Zoref Fund for Applied Research at BGU, for supporting this program. Special thanks to Mrs. Inez Mureinik for editing the manuscript. 358 sp. The later two species are not cultivated any where else in the world to the best of our knowledge. Some of these and other species are grown elsewhere: H. costaricensis, ( several commercial clones) as grown in Nica- ragua (known as red pitaya); H. undatus, in Mexico (known as pitahaya), in other Latin American countries (known as pitaya), in Vietnam (known as dragon pearl fruit or thang loy) (Mizrahi et al. 1997), and according to colleagues there, in Guatemala. Horticulture At the beginning of our program, there was very little information available in the scientific literature on cultivation and biological background of these cacti. This information was mainly in Spanish in the form of hard-to-get dissertations and professional brochures (Mizrahi et al. 1997). We thus set out to investigate both horticultural and physiological aspects of climbing cacti and the results of our studies have been published in the professional literature, as follows: reproductive biology (Weiss et al. 1991, 1994a,b; Nerd and Mizrahi 1997), shading requirements (Raveh et al. 1993, 1996, 1998), and fruit development, ripening, and post-har- vest handling (Nerd and Mizrahi 1998, 1999). Here, we will summarize some of the results and give details of new unpublished data to provide an up-to-date picture of the state-of-the-art know-how and marketing. Light tolerance. The climbing cacti originate in shady habitats of subtropical and tropical America. In Israel, the canopy suffers from bleaching and die back when these species are grown outdoors as a result of the intensive irradiation (noon photosynthetic photon flux densities can reach as much as 2200 mmol photons m-2 s-1). Our studies showed that for optimal development they have to be planted in nethouses and the re- quired shade level (ranging between 30–60%) depends on the particular species as well as on the location (Fig. 1) (Raveh et al. 1996, 1998). H. polyrhizus and H. costaricensis are the most light tolerant, probably because of their unique skin characteristics (a wax cover and a thick skin). The radiation stress is exacerbated by high temperatures, as discussed below. Temperature tolerance. Sub-freezing temperatures damage the climbing cacti, and for most species 0°C is the minimal threshold for cultivation. Among the investigated species, Hylocereus sp. (10487) was the most sensitive to low temperatures and suffered cold injury when the temperature fell below 4°C. In the areas of the Negev with low night temperatures, the climbing cacti have to be cultivated in plastic- or glass-houses. Symptoms of cold injury are round lesions that expand along the stems. Plants recover easily when tempera- ture increases. Our long-term observations showed that in the hottest parts of the Negev (Arava and Jordan valleys), where extreme summer temperatures (Fig. 3, 4) may rise up to 45°C, (average 39°C), annual flower produc- 40 Plastic only 30 +Net 20 10 Shoot damage (m) 0 H. polyrhizus H. undatus H. sp. (10487) Species Fig. 2. Heat and radiation damage to three Hylocereus species growing in a greenhouse in Beer-Sheva in the summer of 1998. The damage was estimated as the length (m) of stem that was liquefied along the trellis system. The net pro- vided over 60% shade. Selenicereus megalanthus was not damaged by the high temperature. The Fig. 1. Cactus grown in a nethouse. numbers are averages per plant ± SE. 359 tion was very low, being about 15–20% of that obtained in areas with more moderate temperatures (where the average summer temperatures are lower by approximately 7°C). The timing of flowering was also affected by temperature. In areas with more moderate temperatures, flushes of flowers appeared in Hylocereus species from May to November and in S. megalanthus from September to December. Table 1. Species of the crawling cacti Hylocereus and In the hotter areas, flowering of both gen- Selenicereus introduced by Ben-Gurion University of the era was restricted mainly to the cool sea- Negev sons, May and Oct./Nov. for Hylocereus species and Nov./Dec. for S. megalanthus. No. of clones In physical terms, H. undatus showed the Grown greatest sensitivity to the extremely high Species Introduced commercially temperatures of the hot valleys: segments of stems at the surface of the shrubs turned H. costaricensis (Weber) 1 brown and became liquefied. The spell of Britton & Rose unusually high temperatures during the past H. ocamponis (Salm-Dyck) 1 summer in Beer-Sheva (4–5°C above the Britton & Rose multiannual average) (Fig. 3, 4) resulted in H. polyrhizus Weber 7 2 extensive damage to H. undatus, but very H. purpusii Weingart 1 small to the other species and nil to Hylocereus sp. 8 2 Selenicereus megalanthus (Fig 2). The H. undatus (Haworth) 27 3 damage becomes more intensive when Briton & Rose combined with high light radiation (Fig 2). S. megalanthus (Schum.) 37 6 Raveh et al. (1995) also reported physi- Britton & Rose ological damage to Hylocereus undatus Total 82 13 when grown under 35/45°C night/day tem- perature regime. The results of these stud- Outdoor Greenhouse-Beer Sheva ies indicate that these climbing cacti should 40 40 not be planted in extremely hot areas. H. Maximum Maximum undatus should be avoided, others may be manipulated with different shading regimes 30 30 and/or other agrotechniques, the feasibil- 20 20 ity of which should be tested. Minimum Reproductive biology. Studies on the Minimum Average temp (˚C) 10 10 reproductive biology of these cacti, includ- Qetura 1998 ing the work of Weiss et al.