Native Mediterranean Pyrus rootstock, P. amygdaliformis and P. elaeagrifolia, present higher tolerance to salinity stress compared with Asian natives

Abstract

The salt tolerance of native Asian pear species, Pyrus betulaefolia Bunge., P. pyrifolia Nakai, and P. xerophila Yu, and native Mediterranean ones, P. amygdaliformis Vill. and P. elaeagrifolia Pall., were examined by irrigating them with 75 mM and 150 mM NaCl solutions for 30 days. Native Mediterranean species did not develop leaf injury during the 30-day NaCl treatments, but native Asian species developed leaf injury. Concerning the shank, fine roots, and whole plant, bioregional differences in Na and Cl contents were small. However, the Na and Cl contents of the leaves of native Mediterranean species were markedly less than those of native Asian species in both NaCl concentrations. Therefore, the native Mediterranean P. amygdaliformis and P. elaeagrifolia may have some salt exclusion mechanisms in the shank which restrict Na and Cl transport to the leaves. The stem water potential and Ci/Ca ratios were decreased by NaCl treatments in native Mediterranean and native Asian species. Thus, the photosynthetic decline by NaCl treatment observed in these species might have been caused by stomatal closure, which is likely to be induced by decreased water potential in the plant body. However, the photosynthetic rate of native Mediterranean species under NaCl stress was higher than native Asian species. Therefore, low concentrations of Na and Cl in the leaves of native Mediterranean species might prevent crucial decreases of photosynthetic rates under NaCl stress. The present results imply that native Mediterranean P. amygdaliformis and P. elaeagrifolia have a higher salt tolerance than native Asian P. betulaefolia, P. pyrifolia and P. xerophila. These native Mediterranean species would be useful in providing genetic resources as salt-tolerant rootstock for the Japanese pear.