Production des luzernes des régions pré-sahariennes du Maroc en conditions salines

Lucerne production in the pre-saharian regions of Morocco under saline conditions

The behaviour of three lucerne strains (two local populations from the pre-saharian regions of Morocco and one cultivar, Siriver, of Australian origin) was observed under conditions of variable salinity (0, 4, 8, 12 and 16 g NaCl/l in the irrigation water) ; their 'infectivity' and their nitrogen use efficiency after inoculation with two local strains of Sinorhizobium meliloti were also evaluated. There were two controls without inoculation : one with and one without nitrogen supply.
In a first trial, the contents of the main mineral elements (nitrogen, phosphorus, potassium, calcium, sodium, magnesium and chlorine) were measured in the above-ground parts and in the roots. From 4 g NaCl/l upwards, salinity caused a decrease in the dry matter production of both shoots and roots ; furthermore there was an increased uptake of Na+ and Cl- and a reduced uptake of K+, Ca++ and N. The Moroccan populations appeared to be relatively more tolerant to salt. This could be linked to a greater aptitude to use the Na+ and Cl- absorbed from the medium for osmotic regulation and to a better selectivity for potassium (high K+/Na+ ratio).
A second trial showed that nodulation occurred at a salt level as high as 16 g NaCl/l and that the supply of nitrogen, be it from fertilizer or from symbiotic fixation, did reduce the depressive effect of salt. The nitrogen fixation efficiency of the bacterial strains varied with the NaCl concentration and with the lucerne genotype. In each of the traits, it could be seen that the effect of the Sinorhizobium strains and of lucerne genotypes was not simply additive. The breeding of an adequate genetic material must be based on the selection of performing combinations of a Sinorhizobium genotype and a lucerne genotype.