• Background and Aims Hylocereus and Selenicereus are native to tropical and sub-tropical America. Based on its taxonomic status and crossability relations it was postulated that H. megalanthus (syn. S. megalanthus) is an allotetraploid (2n = 4x = 44) derived from natural hybridization between two closely related diploid taxa. The present work aimed at elucidating the genetic relationships between species of the two genera. • Methods Crosses were performed and the putative hybrids were analysed by chromosome counts and morphological traits. The ploidy level of hybrids was confirmed by fluorescent in situ hybridization (FISH) of rDNA sites. Genomic in situ hybridization (GISH) was used in an attempt to identify the putative diploid genome donors of H. megalanthus and an artificial interploid hybrid. • Key Results Reciprocal crosses among four diploid Hylocereus species (H. costaricensis, H. monacanthus (syn. H. polyrhizus), H. undatus and Hylocereus sp.) yielded viable diploid hybrids, with regular chromosome pairing. Reciprocal crosses between these Hylocereus spp. and H. megalanthus yielded viable triploid, pentaploid, hexaploid and aneuploid hybrids. Morphological and phenological traits confirm the hybrid origin. In situ detection of rDNA sites was in accord with the ploidy status of the species and hybrid studied. GISH results indicated that overall sequence composition of H. megalanthus is similar to that of H. ocamponis and S. grandiflorus. High sequence similarity was also found between the parental genomes of H. monacanthus and H. megalanthus in one triploid hybrid. • Conclusions The ease of obtaining partially fertile F₁ hybrids and the relative sequence similarity (in GISH study) suggest close genetic relationships among the taxa analysed.

Until 1994, only scarce research existed on these plants; however the worldwide interest in this novel fruit crop is evident, as numbers of pitaya-related publications have grown rapidly, especially during the past decade .There is a big confusion about both botanical and commercial names and there is a need to clear this point. Herein, we attempt to review existing knowledge on the taxonomy, breeding and other horticultural characteristics of this unique crop. This paper comments abou taxonomy,breeding,physiology and horticultura e chatera ristics,postsharvest and uses.

Crosses between the diploid Hylocereus polyrhizus, as the female parent, and the tetraploid Selenicereus megalanthus, as the male parent, yielded triploid and aneuploid hybrids. The fruits of these hybrids combined the attractive appearance of Hylocereus fruits with the delicious taste of S. megalanthus fruits. The aim of this work was to assess the fertility and breeding potential of the triploid and aneuploid hybrids with a view to developing an improved vine cactus crop. Pollen mother cells at metaphase I revealed univalents, bivalents, trivalents, and occasionally quadrivalents. Chromosome distribution at anaphase I revealed different classes of chromosome segregation as well as lagging chromosomes. At metaphase II, parallel and tripolar spindles were observed. The occurrence of triads was frequent, whereas dyads were rarely observed. Pollen stainability varied among the clones studied ranging from 9.8% to 18.6%. The diameters of the stained pollen grains varied widely, probably as a result of the number of chromosomes. Despite the allotriploid origin of our hybrids, functional female and male gametes were produced in considerable proportions, most likely as a result of balanced chromosome segregation. The triploid and aneuploid clones studied yielded viable seeds whose number per fruit was strongly dependent on the pollen donor.

Summary To obtain out-of-season cropping and flowering of the tropical vine cacti Selenicereus megalanthus and Hylocereus undatus, the following agricultural manipulations were tested: photoperiodic light applied for 3, 6 or 9 h after sunset; shading (to produce 80%, 60% or 40% of sunlight); flower thinning (when buds were 2–5 cm, 15–25 cm or at anthesis, or by not pollinating the flowers); or separate application of the following growth regulators [N-(2-chloro-4-pyridinyl)-N-phenylurea (CPPU); gibberellic acid (GA₃); a commercial mixture of gibberellins (GA₄ and GA₇) with benzyladenine (BA) known as Perlan^™; paclobutrazol (PBZ); or ethephon (Ethrel^™)]. Photoperiod and radiation did not alter the pattern of flowering. Maximum flower yields were obtained under 60% sunlight for H. undatus and under 60% or 40% sunlight for S. megalanthus. Removal of young flower buds delayed flowering and late cropping in H. undatus, but with no loss in total flower yield. In both species, CPPU promoted precocious flowering and, in H. undatus, it increased total flower yield, whereas GA₃ delayed flowering and decreased total flower yield. Hence, CPPU can be used to obtain early fruit production, and GA₃ or flower thinning (in H. undatus), to delay cropping.

Several different species of the columnar cacti of the genera Stenocereus and Pachycereus, were introduced into different semi-arid ecozones in Israel and most of these efforts were of disappointing outcomes, the only exception being the Cereus peruvianus (L.) Miller,which bore plenty of fruits, some of them of good taste. The original seeds of this plant were obtained from the late Mr. Amram (Ron) Kodish, who collected seeds from various private gardens in Southern California which bore fruits of reasonable qualities. The initial success of this species led us to initiate an intensive research study, and today it is already fruit-crop, marketed mainly in Israel under the name " Koubo" . This paper will describe our work of domestication of this new cactus fruit crop in Israel.

Climatic changes have created the imminent need for the development of new crops for arid regions. We started to domesticate and introduce wild and exotic fruit trees to our deserts in 1984. We tested different species in five eco zones in Israel, differing from each other in terms of maximum and minimum temperatures, type and degrees of salinities, water evaporation rates, rainfall, etc. We succeeded in cultivating pitaya species using hybrids from the Hylocereus and Selenicereus genera, and with a different species from the Cactaeae Cereus peruvianus, which we named Koubo. These two species are from the Cactaceae family, known for high water use efficiencies (WUE). We already have investors who started the semi-commercial production of Marula, Sclerocarya birrea sbsp. Caffra, and Argan—Argania spinosa. In spite of the fact that we developed good clones and knowledge of how to grow and ship White Sapote, Casimiroa edulis, and Indian jujube, Ziziphus mauritiana, we failed due to a lack of marketing research and development, which is essential for such a project. We have gene banks of some other new fruit crops waiting for investors to grow and bring them into the domestic and world markets.