Reassessing the salinity tolerance of greenhouse roses under soilless production conditions

Abstract

The performance of modern greenhouse-grown roses under intensive nutrient and water management practices questions their traditional classification as a salt-sensitive species, and emphasizes the need to reassess their salinity tolerance. Container-grown 'Bridal Pink' roses (on R. manetti rootstock) in a peat moss-based growing medium were irrigated, using moderate leaching fractions (25% targeted, 37.5 % actual), with complete nutrient solutions supplemented with NaCl at 0, 5, and 10 mM. These salt concentrations affected the electrical conductivity (EC) and Cl concentrations measured in the leachates, but had no significant effects on flower yield and quality over four growth and flowering flushes (≈29 weeks). Cumulative yields over this period increased an average of ≈13% per leachate EC unit. Thereafter, the applied NaCl concentrations were increased 3-fold to 0, 15, and 30 mM and the plants continued to be evaluated for another four flowering flushes. No significant differences in cut-flower yield and quality were observed among salt treatments despite further increases in leachate EC and Na and Cl concentrations. Symptoms of salt injury were visually observed during the last three flowering cycles, and most heavily on the oldest foliage of plants receiving the highest salt concentration (30 mM), but not on the foliage of harvested shoots. The concentration of most nutrients in leaf tissue was not significantly affected by any of the treatments over the course of the experiment. Leaf Na concentrations were not affected by NaCl applications, averaging 42 mg·kg-1 across treatments. Conversely, leaf Cl concentrations increased significantly and cumulatively over time with salt additions, and ranged from 1.0 to 17.5 g·kg-1 (0.1 to 1.75%). Regression analyses revealed that average relative dry weight yields increased with leaf Cl concentrations up to 4.0 g·kg-1 (0.40%), but were depressed at higher concentrations.