Effect of rootstocks grafting and boron on the antioxidant systems and salinity tolerance of loquat plants ( Eriobotrya japonica Lindl.)

Abstract

Salinity causes serious economic losses in loquat production, emphasising the needs to explore new ways to reduce the losses. Grafting of loquat plants on anger rootstock did not affect growth of loquat plants with 20 mM (moderate concentration) and 35 mM (high concentration) NaCl in the nutritive solution. However, when grafted on loquat rootstock, 20 mM NaCl produced a 44% decrease in plant growth, whereas the higher NaCl concentration used produced a 65% of plant growth inhibition. The addition of B did not produce significant changes in plant growth in any case. Leaf Na concentration increased in salt-treated loquat plants, the rise being higher when plants were grafted on loquat rather than anger rootstocks. In contrast, leaf Cl contents did not show changes in loquat plants, independent of the rootstock used. Only in loquat plants grafted on loquat rootstocks did B additions produce an accumulation of B in leaves, in the absence and in the presence of NaCl stress. Moderate salt-treatment produced an increase in APX and a decrease in PPO in plant grafted on loquat rootstock, whereas an increase in MDHAR, PPO as well as a decrease in SOD was observed in those plants subjected to the higher salt treatment. In the presence of low salt concentration (5 mM, control plants), B additions brought about an increase in APX and MDHAR and a fall in POX and PPO in plants grafted on anger rootstocks. However, a decrease in PPO was observed in plants grafted on loquat rootstocks. In plants grafted on loquat rootstocks and treated with 20 mM NaCl, 0.2 mM B additions produced a decrease in APX and a rise in POX, whereas in the presence of the higher NaCl concentration, B produced an increase in APX and DHAR and a decrease in POX and PPO activities. In contrast, in salt-treated plants grafted on anger rootstocks, both B levels produced an increase in SOD, whereas a decrease was produced in PPO activity by effect of 0.2 mM B in plants treated with 20 mM NaCl. However, in plants treated with the higher NaCl level, 0.2 mM B produced a strong increase in DHAR. In both cases, salinity produced an oxidative stress as shown by the increase in lipid peroxidation, the values being higher in plants grafted on loquat rootstocks. The presence of B produced a decrease in the lipid peroxidation values, suggesting that B additions afforded some protection to the membranes, mainly in plants grafted on anger stocks. This response was correlated with the higher SOD, MDHAR and DHAR activity values observed under these conditions. Overall, the data suggest that anger plants seem to be a better rootstock for loquat plants than their own loquat rootstock. Also, leaves from loquat plants grafted on anger rootstocks seem to have a higher antioxidant capacity, as deduced from the data on SOD, MDHAR and DHAR activities as well as lipid peroxidation data.