Title : Performance Of Hylocerus (Cactaceae) Hybrids Under High Temperature Stress
Abstract:
Hybridization, an effective method to obtain genetically improved agricultural crops, can be exploited to generate novel hybrids with desired traits, such as, enhanced growth, survival rate, and heat and disease tolerances. In this research, we studied two hybrids (i.e., the allotetraploid Z-10 and the allotriploid S-75) and their parent species (i.e., the diploids Hylocerus monacanthus and H. undantus and the tetraploid H. megalanthus) under short- and long-term heat stress. Short-term heat stress was applied by collecting leaf discs from mature stems and placing them in a water bath for 30 minutes at 35, 45, 55 or 65°C. Long-term heat stress was applied by exposing rooted cuttings placed in pots to day/night temperatures 45/35°C at 90% relative humidity for 14 days. Plants subjected to short- and long-term heat stress were compared with control plants exposed to day/night temperatures of 26/20°C. Assessments of electrolyte leakage levels and of the maximum efficiency of PS II photochemistry (Fv/Fm) after plant exposure to short- and long-term heat stress showed lower electrolyte leakage and more efficient PSII photochemistry in the two allopolyploids, i.e., Z-10 and S-75, than in their parent species. Our results suggest that the enhanced availability of carbohydrates (soluble sugars in the form of glucose) observed in the two hybrids relative to the parent species contributes to membrane integrity and photosynthetic activity under high temperature stress. Nocturnal acid accumulation was significantly lower in long-term heat-stressed plants compared to control plants, and hybrids showed higher nocturnal acid levels compared to parent species. Overall, the results presented here suggest that high temperatures could have significant effects on the physiological levels of vine cacti plants, among which the allopolyploid lines may be more tolerant to heat stress than their parent lines. From the present study it is evident that the thermo-tolerance to high temperature can be efficiently altered and improved through hybridization. This study provides an insight to the researcher to be focused on new synthetic allopolyploid lines.
