2019 ASHS Annual Conference

Heat stress is a major factor limiting agriculture in drylands. Thus, improving the tolerance of crops to high temperatures or/and introducing new species of high economic value that are intrinsically adapted to extreme conditions could make an important contribution to local economies in drylands. Promising minor crop candidates with high economic value are vine cacti of the genus Hylocereus (known as pitaya or dragon fruit). As members of the Cactaceae, these species can grow in poor and marginal soils, and they exhibit a range of specific adaptations to extreme drought conditions. Indeed, pitaya plants show four- to sixfold higher water use efficiencies than other fruit crops grown under similar conditions in the Negev desert of Israel. However, high temperatures damage pitaya plants and drastically reduce – and even inhibit – flowering, thus reducing yields and profitability. Nonetheless, effective breeding and selection may provide the means for expansion of this fruit crop to additional dryland areas the world over. The main objective of this research was thus to study heat tolerance in a group of Hylocereus species, including the diploids H. undatus and H. monacanthus, the tetraploid H. megalanthus, and several interspecific-interploid hybrids. Rooted cuttings growing in pots were exposed to daily heat stress (45/35ºC) in growth chambers for eight days, and their performances were compared with those of cuttings growing under control conditions (25/20°C). Cell membrane stability, chlorophyll fluorescence (F_v/F_m), chlorophyll content and acid accumulation decreased in all parental species and hybrids under heat stress, but the magnitude of the damage was lowest in the allotetraploid designated Z-10. Compatible solutes, such as total soluble sugars and proline, accumulated under heat stress in all the studied species and hybrids, with the highest accumulation being observed in the allotetraploid Z-10. Under the high temperature conditions, Z-10 exhibited increased activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) and significantly higher expression of heat shock proteins, such as HSP1 and HSP70, than the other species and hybrids. Overall, the results presented here show that high temperatures could have significant effects on the physiological status of vine cactus plants and that the allotetraploid Z-10 may be more tolerant to heat stress than its parental lines. Thus, our results suggest that following interspecific hybridization tolerance to high temperatures could be enhanced, a phenomenon that may be attributed to “hybrid vigor” or heterosis, a topic that deserves further investigation in Hylocereus.