INFLUENCES OF NACL ON THE GROWTH, PHOTOSYNTHESIS, ION AND WATER RELATIONS IN ROOTSTOCKS OF JAPANESE PEAR

In this study, three experiments were conducted: In Exp. 1, salt tolerance was tested in five Asian Pyrus rootstock species: Pyrus betulaefolia, P. calleryana 8, P. pyrifolia, P. fauriei, and P. dimorphophylla 6. Four-month-old seedlings were subjected to NaCl solutions. P. betulaefolia showed the highest salt tolerance and P. dimorphophylla 6 also exhibited higher salt tolerance. In contrast, P. calleryana 8, P. fauriei, and P. pyrifolia exhibited lower salt tolerance with severe leaf injuries leading to defoliation and death. In Exp. 2, salt tolerance of native Asian pear species, P. betulaefolia, P. pyrifolia, and P. xerophila, and native Mediterranean ones, P. amygdaliformis and P. elaeagrifolia, were examined by irrigating NaCl solutions. Native Mediterranean species did not develop leaf injury during the 30-day NaCl treatments, but native Asian species developed leaf injury. The Na and Cl contents of the leaves of native Mediterranean species were markedly less than those of native Asian species. 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. In Exp. 3, influences of NaCl treatments on ion uptake and gas exchange of the Japanese pear ‘Akibae’ grown on the rootstocks P. betulaefolia, P. calleryana and P. pyrifolia were investigated. The leaf Na and Cl contents and the decrease in photosynthetic rate for P. betulaefolia rootstock were lower than those for the other rootstocks. ‘Akibae’ grown on P. betulaefolia exhibits a higher salt tolerance than those grown on P. pyrifolia and P. calleryana. These results suggested that P. betulaefolia may have a salt exclusion mechanism in the root, and this character is maintained even if scion cultivars were grafted. Therefore, P. betulaefolia is a useful rootstock for Japanese pear cultivation under saline conditions.