A new method to evaluate salt tolerance of ornamental plants

The traditional methods to evaluate salt tolerance of plants use mainly data of growth and crop productivity. In the case of ornamental plants it is also essential to evaluate the effects on the visual quality of the plants, since the beauty in the acquisition of an ornamental plant is not always associated with its size. So, we tested a new method to assess salt tolerance of four ornamental species, comparing with traditional ones. The experimental design was in completely randomized blocks, in a 10 x 4 factorial arrangement, with four replications, ten levels of electrical conductivity of irrigation water-ECw (0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0, 12.0 dS m(-1)) and four ornamental species (Catharanthus roseus, Allamanda cathartica, Ixora coccinea and Duranta erecta). Two salinity tolerance assessment methods, which are based only on quantitative growth data, were evaluated and compared with a new method, named ornamental index (Orn index) that considers growth data and visual analysis. Our results showed that the two traditional assessment methods converge to indicate I. coccinea and D. erecta, respectively, with higher and lower capacity to grow under salt stress. However, these methods present clear differences in the results between quantitative data (biomass production) and qualitative analyses (flower production and overall plant appearance). The new method (Orn index) adequately separated the four ornamental species according to their tolerance to salinity, as follows: I. coccinea (moderately tolerant), C. roseus and D. erecta (moderately sensitive), and A. cathartica (sensitive). Hence, the Orn index, including quantitative and qualitative aspects, should be recommended to evaluate salinity tolerance in ornamental species, especially for garden flowers of commercial interest.