Double-root-grafting enhances irrigation water efficiency and reduces the adverse effects of saline water on tomato yields under alternate partial root-zone irrigation

Since most world regions face freshwater (FW) shortages, water-saving irrigation and irrigation with saline water (SW) are currently two inevitable agricultural practices for crop production. However, these two practices generally have adverse effects on crop yields. In this study, we investigated the effects of double-root-grafting (DRG) on plant growth, crop yields, tomato quality and root-zone properties under alternate partial root-zone irrigation (APRI) with FW or SW. Self-rooting (SR), DRG, conventional irrigation (CI), APRI, FW and SW were considered in the experimental design to create treatments that included (i) SR-CI-FW, (ii) SR-APRI-FW, (iii) DRG-APRI-FW, (iv) SR-APRI-SW and (v) DRG-APRI-SW. The DRG used here is a 'tongue approach grafting' method in which grafted plants retain both rootstock (eggplant) root and scion (tomato) root in order to maximize the effectiveness of grafting under abiotic stress. The tested salinity level was 3.51 mS cm(-1) which had exceeded the threshold salinity of tomato (2.50 mS cm(-1)). In general, APRI application increased water pro-ductivity by 22.2-35.6%, but decreased fruit yields by 9.1-18.8% in SR plants (SR-APRI-FW vs. SR-CI-FW). However, under APRI conditions, DRG plants showed higher rate of plant growth and less salinity damage as compared to SR plants. Application of DRG significantly (P < 0.05) increased tomato fruit yields by 7.9-17.2% under standard conditions (DRG-APRI-FW vs. SR-APRI-FW) and by 14.2-27.4% under salinity conditions (DRG-APRI-SW vs. SR-APRI-SW). Taken together, double-root-grafting enhanced irrigation water efficiency and reduced the adverse effects of saline water on tomato yields under alternate partial root-zone irrigation.