Solanum habrochaites introgression line grafted as rootstock in cultivated tomato maintains growth and improves yield under cold and drought stresses

Grafting tomato (Solanum lycopersicum L.) onto introgression lines (ILs) derived from S. habrochaites with introgression of a quantitative trait locus (QTL), stm9, for shoot turgor maintainer located on chromosome 9 has been suggested for improving yield under abiotic stresses. However, the physiological and agronomic responses of grafts with IL rootstocks to low root-zone temperature (RZT) and drought stresses are not yet clearly understood. Therefore, recurrent parent (RP) grafted onto IL and donor (D) rootstocks, and self-grafted IL and RP were examined at different combinations of optimal (20°–26°C RZT and well-watered) and suboptimal (10°C RZT and well-watered, and 20°–26°C RZT and cyclic drought) temperatures. Graft combinations were compared with self-grafted controls for dry weights, stomatal conductance (gs), leaf parameters, osmotic adjustment, and stress tolerance index. The RP grafted onto IL rootstocks regulated gs efficiently, retained the green trait, and produced higher biomass than the self-grafted RP. The IL rootstocks improved tolerance of the scion to drought and low RZT. Potential of IL rootstocks for improving tomato production under stressed conditions is discussed.