Growth, quality and nutrient responses of azalea hybrids to salinity

Yield, quality and leaf nutrient status of the azalea (Rhododendron x spp.) hybrids 'Delaware Valley White' ('DVW'; 'Mucronatum' Hybrid) and 'Hershey's Red' ('HR'; Kurume Hybrid) was evaluated under greenhouse conditions. Plants were grown in 7-L containers filled with a sphagnum peat: pine bark: sand medium (4:2:1 v/v) and fertigated for 15 weeks with complete nutrient solutions having 0, 6 and 12 mM NaCl-CaCl2 (2:1 molar ratio). Regardless of salinity stress, 'DVW' plants had dry weights and leaf areas significantly higher than in 'HR' plants. Salinity, however, caused differential growth and quality responses between the hybrids. Growth in 'DVW' plants decreased with salinity increases, with 22.6% and 32.4% reductions in total dry weight and leaf area, respectively, observed at 12 mM salt compared to controls. Conversely, salinized 'HR' plants showed no differences in yield parameters with respect to the controls, albeit plants receiving 6 MM salt had 14.0% and 7.1% more total dry weight and leaf area, respectively, with respect to the controls. Plant quality, as assessed by visual symptoms of salt injury, was significantly reduced by salt increases in 'DVW' plants, but was not affected in 'HR' plants. While unaffected by salinity, leaf K+ status in 'HR' plants was lower than in 'DVW', which showed increases in K+ concentration with salt increases. Leaf Ca2+, Cl- and Na+ concentrations increased with added salinity in both hybrids. The 'DVW' plants, however, accumulated exceedingly higher levels of Cl- and Na+ (up to 3.33% and 5,650 ling Kg(-1), respectively) than in 'HR' plants (up to 1.31% and 463 ing Kg(-1), respectively). Yield and quality were negatively and significantly correlated to increases in leaf Cl- and Na+ concentrations only in 'DVW' plants.