Salinity-induced callus browning and re-differentiation,root formation by plantlets and anatomical structures of plantlet leaves in two Malus species

Apple (malus domestical.) is widely grown in northern china. however,soil salinization has become one of the most severe factors limiting apple productivity in some regions including the loess plateau. in our study,the regeneration systemof both rootstock rehd (malus robusta rehd) and scion fuji (malus domestica borkh. cv. fuji) was established in vitro. the two malus species were cultured on the ms medium containing 0 or 150 mm nacl to examine salt-induced effects on callus browning and re-differentiation,root formation of plantlets and anatomical structures of plantlet leaves at 15 days old callus and plantlet stages. salt stress caused a marked increase in callus browning rate,while a decrease in re-differentiation rate,rooting rate,root number and length in both species. additionally,anatomical structures of plantlet leave showed salt-induced damage such as reduced palisade tissue and intracellular chloroplast,incomplete development of xylem and severe damage of the phloem tissue. salt stress also caused a few adaptive structural features in leaves including increased thickness of upper and lower epidermis,elevated proportion of spongy tissue and formation of lignified vessels. the responses of the two malus species did not differ significantly at the differentiation stage. however,they were more sensitive to salinity at the callus stage than those at the plantlet stage in each species. therefore,callus stage has been found to be more suitable for evaluating responses of the two apple species to salt stress. the fuji and rehd could be treated as a good scion/rootstock combination of apple to adapt to soil salinity based on their similar degree of salt stress-tolerance. © 2016,pakistan botanical society. all rights reserved.