Evaluation of Paclobutrazol Spraying on Salinity Hardiness of Peach- Almond Hybrid (GF677) Rootstock

Salinity is a common abiotic stress that seriously affects crop production in some parts of the world, particularly in arid and semi-arid regions. The deleterious effects of salinity on plant growth are associated with low osmotic potential of soil solution (water stress), nutritional imbalance, specific ion effect (salt stress), or a combination of these factors. Paclobutrazol (PBZ), a member of the triazole plant growth inhibitor group, is a broad-spectrum gibberellin biosynthesis inhibitor. Triazoles have both fungal toxicity and plant growth regulatory effects. They also increase tolerance of various plant species to biotic and abiotic stresses, including fungal pathogens, drought, air pollutants, and low- and high-temperature stress. According to our knowledge, there are no reports on the effects of exogenous PBZ enhancing vegetative peach- almond hybrid (GF 677) rootstock tolerance to salt stress. Therefore, the objective of this work was the possibility test of this idea that PBZ application would protect GF 677 rootstock from damaging effects of salinity.
One-year-old rooted cuttings of GF 677 were grown in in plastic pots in the research greenhouse of Agricultural College, Isfahan University of Technology of Iran. The minimum and maximum temperatures during the experiment period were 19 and 32˚C, respectively. After cutting establishment (3 months), the plants were sprayed twice (with a 7 days interval) with 0 (control), 20 and 40 mg l-1 PBZ to the point of run-off. One week after the second foliar application of PBZ, each plants was subjected to one of several salt stress treatments. The salt treatments (0, 25 and 50 mM NaCl) were applied to the pots intervals in 0.5 l of irrigation water. To avoid osmotic shock, the NaCl concentration was increased gradually. The layout was a 3×3 factorial experiment in a completely randomized design, with four replications. The experimental measurements were carried out 60 days after beginning the salt treatments.
The results showed that salt stress and application of PBZ significantly affected injury rating valve (IRV). The Injury rating value of plants was found to increase significantly as the salt concentration was raised. After exposure to salt stress those plants that did not receive PBZ exhibited higher symptoms of salt injury. There was a significant interaction between salinity and PBZ application. The lowest IRV in all NaCl concentrations observed when 20 mg l-1 PBZ was applied. Salinity caused significant decrease leaf parameters so that the lowest means of leaf number (12.5) and leaf fresh weight (6.52 g) were recorded at 50 mM NaCl treatment, showing a 55.80% and 41.78% decrease compared with the control, respectively. The application of PBZ significantly increased leaf number, with the largest increase when 40 mg l-1 PBZ was applied. The interaction between salinity and the application of PBZ showed that at 25 mM NaCl maximum valve of leaf number was observed in plants after spraying with 40 mg l-1 PBZ. Relative leaf chlorophyll (RLC) was not affected by salt stress. Application of PBZ significantly increased relative RLC value compared with the control, with the largest increase in RLC measured when 20 mg l-1 PBZ was applied. The interaction between salinity and the application of PBZ showed that at 50 mM NaCl maximum valve of RLC was observed in plants after spraying with 20 mg l-1 PBZ. The proline content of leaves was significantly influenced by the salt stress and PBZ application, but not their interaction. Salinity stress, increased proline content in the leaves of salt-treated plants. At 50 mM NaCl, proline content was maximum compared to those of the controls and other salt levels. PBZ treatment increased proline content in leaves. The highest proline content was obtained from leaves of the plants treated with 40 mg l-1 PBZ (55.62μmol g-1 FW), which was 39.18 % more than the control. Salt stress significantly reduced the relative water content (RWC) with maximum reduction observed in plants grown by 50 mM NaCl. Application of PBZ significantly increased RWC compared with the control, with the largest increasing in RWC at 20 mg l-1 PBZ application. Leaf electrolyte leakage was affected by both salt stress and PBZ application. Salt stress significantly increased leaf electrolyte leakage, with a maximum increase observed in plants grown by 50 mM NaCl. The application of PBZ significantly decreased electrolyte leakage in leaf discs, with the largest decreaseing in leaf electrolyte leakage measured at 20 mg l-1 PBZ application..There was a significant interaction between salinity × PBZ concentrations. However, the greatest decreasing in leaf electrolyte leakage occurred at 40 mg l-1 PBZ in non-saline condition. In this study, the correlation between vegetation and physiological parameters of GF677 plants subjected to salt stress was analyzed. These correlations suggested that salt injury symptoms was negatively correlated with number and fresh weight of a leaf, RWC, RLC, but positively correlated with proline content and leaf electrolyte leakage.
in overall, this investigation revealed that salt stress had an inhibitory effect on the vegetative growth of GF 677 plants. The responses of GF 677 plants to the PBZ treatments suggest that the application of PBZ could partially increase the survival capacity of GF 677 plants and protect the plants against injuries such salt stress.