Effect of salinity on seed germination, growth and metabolic activity of pitaya seedlings [stenocereus thurberi (Engelm.) buxb.]

Abstract

The Cactaceae is an important resource in the arid and semi-arid zones of Mexico, this family is naturally distributed in the Americas. Pitaya (Stenocereus thurberi) is an important endemic species of the Sonoran Desert that has received little attention despite its diverse uses, distribution and endemism. In the environment where pitayas thrive, salinity is a common condition, and its effects in physiological traits has been poorly recorded in the literature. In this study, NaCl effect was evaluated on germination, and seedlings growth and metabolic changes. For the latter, heat or metabolic activity (q), respiration rate (RCO2), metabolic efficiency (Rq/RCO2) and growth rate (RSGΔHB) were determined. These variables were analyzed using isothermal calorimetry at 25°C in pitaya seedlings. Final germination and plantlet survival rate were not affected by salinity; however, mean germination time, aerial biomass production, root growth and the calorimetric variables mentioned above were directly affected according to salt concentration. Although seedling size decreased, contents of chlorophylls a, b, and total chlorophyll (a+b) and total carotenoids showed an increase as a function of NaCl concentration. Variables evaluated showed different salinity tolerance, reaching maximum values between 4,000 and 6,000 ppm of NaCl. As far as pigment synthesis, salinity treatments caused increases in chlorophylls and carotenoids. This increment was more conspicuous at salinity treatments above 8,000 ppm.