High summer temperatures inhibit flowering in vine pitaya crops (Hylocereus spp.)

The cultivation of vine pitayas, a group of new cactus fruit crops originating in tropical America, has spread to tropical and subtropical regions throughout the world. Data are presented on the growth and fruiting of two red pitayas - Hylocereus undatus and Hylocereus polyrhizus - at four sites in Israel differing in the quality of the irrigation water and climate. The sites are Sede Nizzan and Ma'abarot, located on the coast, with recycled water (EC = 1.3-1.4 dS m^-1) and moderate summer temperatures (mean maximum at midsummer of 34 and 32°C, respectively); Qetura in the Arava Valley, with saline water (EC = 3.2-3.4 dS m^-1) and high summer temperatures (mean maximum at midsummer of 38°C); Gilgal in the Jordan Valley, with fresh water (EC = 0.8-0.9 dS m^-1) and temperatures as at Qetura. Vegetative growth at Qetura was slower than at the other sites, a result attributed to the water deficit induced by the salinity of the irrigation water there. At the coastal sites flowering occurred in both summer and autumn, with three or four flushes (prolific in the autumn), while at the valley sites it was restricted to autumn, with a single sparse flush (less than five flowers per 1 m row). Five years after planting (all the orchards had reached their full size), annual fruit yields were 34 t ha^-1 at Ma'abarot, 28 t ha^-1 at Sede Nizzan, and 5 t ha^-1 at Qetura (fruits were not harvested at Gilgal). As percent fruit-set and fruit weight were similar in all the plots examined, it follows that yields were a function of the number of flowers produced at each site. Analysis of the results indicates that the high summer temperatures prevailing in the valleys inhibited flower production in the two study species.