Classificação da tolerância à salinidade em plantas ornamentais utilizando-se diferentes metodologias

Abstract

Plant responses to salinity are observed mainly in terms of growth, productivity and physiological variables. In the case of ornamental plants, it is also essential to evaluate the effects on the quality of the plants, since the beauty in the acquisition of an ornamental plant is not always associated with its size. Within this context, the effects of stress intensification and the salt tolerance of four ornamental species were evaluated, using growth data, physiological responses and sensorial analysis. The research was conducted in the experimental area of the Agrometeorological Station of the Federal University of Ceará-UFC, Brazil, in a greenhouse, from September to November 2016. The experimental design was in completely randomized blocks, in a 10x4 factorial arrangement, with four replications, ten levels of electrical conductivity of irrigation water (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). The work was presented in two parts: Chapter 1. Intensification of saline stress in the initial development of four ornamental plant species - In this chapter, growth and morphophysiological responses were evaluated at 30 and 60 days after the beginning of saline treatments. Chapter 2. Comparison of methodologies for evaluation of salinity tolerance in ornamental plants using growth, physiological and sensorial analyzes - Three salinity tolerance evaluation methods were compared using growth data, physiological responses and sensorial analyzes. The methodologies were as follows: 1st. Threshold salinity value (adapted from Maas and Hoffman, 1977); 2nd. Percentage of 25% reduction for pre-defined salinity ranges (adapted from Miyamoto et al., 2004); 3rd. Percentage of 20% reduction for each salinity level (adapted from Fageria, 1985). The time and increase in salt concentration intensified the effects of saline stress on plants, but the responses differed among the species studied. The higher tolerance of the I. coccinea species seems to be related to the maintenance of foliar morphophysiological characteristics. The three methodologies used converge to indicate the species I. coccinea and D. erecta, respectively, with higher and lower capacity to adjust under salinity conditions. The leaf gas exchange data were adequate for the classification of the tolerance to salinity, regardless of the methodology used. The plant height, stem diameter and relative chlorophyll index were inadequate for salinity tolerance classification, and this inadequacy was more significant when using the adapted methodology of Miyamoto et al. (2004). The qualitative evaluation of ornamental plants depends on a number of factors, but the maintenance of the green color of the leaves and, especially, the production of flowers, can eliminate negative effects caused by low and moderate levels of salinity on the plant growth. In this sense, a methodology similar to that of Miyamoto et al. (2004) for the elaboration of a global index involving quantitative and qualitative characteristics, may be promising for the evaluation of the salt tolerance of ornamental plants.