Improved stomatal regulation and ion partitioning boosts salt tolerance in grafted melon.

Grafted plants are often more tolerant to stresses such as salinity than non-grafted controls. The wide literature available usually attributes the increased tolerance to ion exclusion or accumulation within the rootstock, impaired stress signaling, improved water relations, or increased vigor attributable to grafting perse. Besides, as far as salt tolerance goes, a rootstock, -a scion- and a rootstock x scion effect may be generally observed. In order to dissect differential response components in grafted melon, salt stress was imposed on several rootstock/scion combinations in four experiments under different environmental conditions and locations across Europe. The rootstock used was an interspecific squash (Cucurbita maxima x Cucurbita moschata) ‘RS841’, combined with two Cantaloupe (Cucumis melo var. cantalupensis) cultivars namely ‘London’ and ‘Brennus’, against both self-grafted and non-grafted controls. Physiological (leaf gas exchanges, porometry and overnight transpiration), morphological (plant biomass and stomatal features), and biochemical (main ion concentrations and partitioning) adaptations to 0, 40 and 80 mM NaCl were monitored. Salinity impaired plant size more dramatically in non-grafted plants, whereas symptoms were reduced in self-grafted or interspecific grafting. Lower stomatal conductance under salinity resulted in higher water use efficiency in grafted plants. Nevertheless, the interspecific rootstock presented reduced nutritional imbalances as compared to self- and non-grafted melons.