Effects of Sodium Chloride On Growth and Morphology of Two Petunia Cultivars

Saline irrigation water may arise from seawater incursion of aquifers, use of reclaimed municipal water, or in greenhouse/nursery water capture and reuse systems. Many floriculture species are sensitive to salt accumulation in the root zone, showing severe symptoms when exposed to high soluble salts such as leaf marginal necrosis and ultimately reduced plant growth.  However, the quantitative effects of increasing NaCl stress on growth and morphology have not been reported for most floriculture species.

 The objective of this project was to determine the effect of NaCl salinity on growth and morphology of Petunia x hybrida [Vilm]. ‘Bravo White’ (BW) and ‘Mitchell Diploid’ (MD).  Plants were grown hydroponically, so that a stable root-zone salt treatment could be maintained through frequent replenishment of the nutrient solution. Six week old seedlings were established in 4 L hydroponic containers with a modified Hoagland’s solution for 2 weeks prior to receiving NaCl treatments.  Plants were exposed to 0, 20, 40, 60 and 80 mM NaCl amended to the nutrient solution for the 4 week treatment period resulting in average electrical conductivity of 1.64, 4.69, 6.37, 8.07, and 9.45 dS/m, respectively. Nutrient solution in each bucket was replaced weekly. 

Both cultivars responded similarly to salt treatment, as ANOVA found no cultivar by salt treatment interaction for any of the measured parameters. Leaf Chlorophyll index (SPAD units) of BW, was reduced from 33 to 26 as NaCl increased from 0 to 80 mM, whereas in MD chlorophyll index was reduced from 41 to 33 SPAD units. Leaf surface area (LSA) was reduced from 7555 to 2744 cm² in BW, and from 7385 to 1826 cm² as NaCl concentration increased. Fresh matter of both cultivars was reduced from 63-67% and dry matter was reduced by 62-65% as NaCl concentration increased from 0 to 80mM. In general, morphological parameters (height and width) were less affected by salt than growth parameters (LSA, FW/DW). For example, plant width and height of BW was reduced by 34% and 22% respectively as NaCl increased to 80 mM.  For both cultivars a significant difference in growth/morphological parameters was not observed as NaCl increased from 0 to 20 mM.  However, quantitative models suggest a moderate reduction in growth at 20 mM NaCl.   BW and MD can be grown hydroponically with slightly saline solution (20 mM NaCl) to produce visually acceptable plants.  More research is needed to determine salt effects in peat-based substrates typical of greenhouse production.