Grafting Tomato as a Tool to Improve Salt Tolerance

Salinity in soil or water is a serious threat to global agriculture; the expected acreage affected by salinity is about 20% of the global irrigated lands. Improving salt tolerance of plants through breeding is a complex undertaking due to the number of traits involved. Grafting, a surgical mean of joining a scion and rootstock of two different genotypes with the desired traits, offers an alternative to breeding and biotechnological approaches to salt tolerance. Grafting can also be used to circumvent other biotic and abiotic stresses. Increasing salinity tolerance in tomato (Solanum lycopresicum L.), a highly nutritious and economical vegetable, will have greater impact on the vegetable industry, especially in (semi) arid regions where salinity in soil and water are more prevalent. Besides, plants also experience salt stress when water in hydroponic system is recycled for tomato production. Grafting high yielding but salt-susceptible tomato cultivars onto salt-resistant/tolerant rootstocks is a sustainable strategy to overcome saline stress. Selection of salt-tolerant rootstocks though screening of available commercial and wild relatives of tomato under salt stress conditions is a pre-requisite for grafting. The positive response of grafting exerted by tolerant rootstocks or scion-rootstock interactions on yield and fruit characteristics of tomato under saline conditions is attributed to several physiological and biochemical changes. In this review, the importance of tomato grafting, strategies to select appropriate rootstocks, scion-rootstock interaction for growth, yield and quality characteristics, as well as the tolerance mechanisms that (grafted) plants deploy to circumvent or minimize the effects of salt stress in root zones are discussed. The future challenges of grafting tomato are also highlighted.