Regression equation for correlation between Spad index and photosynthetic pigments under saline stress in African mahogany culture

Abstract

The quantification of the levels of photosynthetic pigments is of paramount importance, especially in the evaluation of the photochemical capacity of plants under saline stress. However, laboratory procedures for the titration of these pigments, such as chlorophyll, have expressive laboratory apparatus and specific reagents. This study aimed to evaluate a regression equation for correlation between SPAD index and photosynthetic pigments in African mahogany plants, Khaya senegalensis, under saline stress. The plants were cultivated in vases containing washed sand, in a greenhouse. Salinity was established by adding NaCl, with levels of electrical conductivity: 1.0 • 3.38 • 15.14 • 29.90 • 42.61 • 53.60 dS m ­-1 , in a completely randomized design (DIC) . The total chlorophyll contents were determined in the laboratory using a spectrophotometer and, in the plants, the SPAD index was quantified directly under the leaves. By regression analysis, through data evaluation with the STATISTICA program, the significant correlation between the SPAD index and total chlorophyll was expressed by the equation: Total chlorophylls = -41.0166 + 1.0338 EC, allowing this result to be direct quantification of the levels of photosynthetic pigments using the SPAD index.