Évaluation de la tolérance à la salinité du myrte (Myrtus communis) aux stades germinatif et plantule

The salinity tolerance and development of diverse myrtle ecotypes were evaluated in relation to salinity, at the germination and plantlet stages. Six myrtle ecotypes (Tébaba, Jbel Abderahmane, Diar Ferjan, Ain Bacouche, Ain Dhebla, and Ouchetata) were used to conduct germination tests, as well as cultivation to the plantlet stage. Disinfected seeds were germinated in a controlled growth chamber (RH, 80%; temperature, 25 °C) using different saline treatments (0, 2, 4, 6, 8, 10, and 12 g·L–1 NaCl. Seedlings were cultivated in a greenhouse, in boxes filled with perlite. The seedlings were given Knop’s nutrient solution, up to the four-leaf stage. Thereafter, the saline stress treatments were applied as increasing concentrations of NaCl added to the Knop solution. The effects of salinity on germination varied with ecotype and concentration of NaCl. A progressive decrease in the rate of germination for myrtle was observed with increasing concentration of NaCl. Moreover, germination was delayed by salinity, especially with susceptible ecotypes. Ecotypes from Ouchetata and Diar Ferjan germinated better in presence of salt than did the Jbel Abderahmane ecotype. The growth of myrtle plantlets cultivated under salt stress was also variable according to ecotype and salt concentrations. Growth of aerial, as well as root parts, was reduced by NaCl concentrations higher than 6 g·L–1. The number of leaves was also affected by salinity; a reduction of five leaves was observed for most ecotypes when increasing NaCl from 0 to 12 g·L–1. It is concluded that development of myrtle under saline stress differs according to the development stage (germination, plantlet), and that the ecotypes tested can germinate and grow in the presence of 12 g·L–1 NaCl. This salt tolerance, observed at early stages, remains to be confirmed for the adult plants. This work was conducted as an essential preliminary step in preparing to cultivate myrtle in saline soils or soils irrigated with salt water, for prospective commercial exploitation of the essential oils of this species.