Correlation of the SPAD index with absolute leaf pigments in irrigated lettuce culture in the Northwest Paraná, Brazil

Abstract

Photosynthesis is the most important biochemical process that takes place in plants and chlorophyll is the main pigment involved in it. Current destructive methods for determining chlorophyll content are accurate, but time-consuming and relatively expensive. The SPAD (Soil Plant Analysis Development) is a portable chlorophyll meter that provides an instant and nondestructive reading of the green color of leaves. As an important source of vitamins and antioxidants such as vitamins C, carotenoids and fiber content, lettuce (Lactuca sativa L.) plays a crucial role in human nutrition, being one of the most popular staple plant foods among the population. Considering the possibility of management based on the characteristics of photosynthetic pigments, the study aimed to relate the SPAD index values with the content of leaf pigments in lettuce. The study was conducted in the Northwest region of Paraná, Brazil. The experiment was carried out in a completely randomized design with 48 leaf samples being determined the SPAD index and the content of leaf pigments. The determination of the SPAD index was performed with the SPAD-502 equipment (Minota®) with three readings per sample. For the extraction of leaf pigments, chlorophyll (a; b), total chlorophyll (a + b) and carotenoids, acetone was used as an extractor and the reading was performed in a spectrophotometer. The SPAD index was correlated with the levels of chlorophyll a (0.93), chlorophyll b (0.89), total chlorophyll (0.93) and carotenoids (0.95) in lettuce leaves. Through the SPAD, the chlorophyll content in lettuce leaves can be determined in a representative way.