MARITIME PINE DIEBACK ON THE WEST-COAST O F FRANCE - GROWTH-RESPONSE TO SODIUM-CHLORIDE OF 3 GEOGRAPHIC RACES IN VARIOUS EDAPHIC CONDITIONS

The responses of 3 geographic races of maritime pine, French (''Landai s''), Iberian (''Iberique'') and Moroccan (''Tamjoute'') to salt stres s were studied on original soils and hydroponic culture. Landais and I berique pine seeds were collected from pine trees from west France and the genetic origin was determined by terpene shoot analysis on trees. Tamjoute seeds were collected in the Tamjoute mountains (Morocco). Ho mogenous seedlings were planted in calcareous sand from forest site at the ''Pays de Monts'' and ''Oleron'' (table I) and salt stress was ap plied to the Oleron soil after 12 months of culture and maintained for 60 d (experiment 1). In the quartz (2-4 mm) culture system, plants we re supplied with fresh nutrient solution twice per h. Four stress leve ls were obtained with the addition of 0, 50, 150, 250 mM NaCl to the b asic solution. Total heights were measured nearly twice per month (fig 1). The 3 curves showed well-synchronized height growth. The winter d ormancy was clearly marked and the NaCl stress was installed at the ma ximum and linear growth stage. The final inflexion of the curve was du e to the NaCl toxicity. Growth in the Pays de Mont treatment was compl etely absent and dieback symptoms appeared at the end of the first gro wing season, showing that the Tamjoute pines were more resistant (tabl e II). Dry weights of roots, stems, and needles were evaluated after t he stress period for the Oleron soil (tables III, IV). Genotypic respo nse was not significant and the salt stress slowly reduced final bioma ss and particulary root weight. Analyses of variance showed significan t differences in final harvest weights among geographic races in the s econd experiment (table V). The most vigorous race was found to be the Landais with 22% gain compared with the Iberique, and 36% gain compar ed with the Tamjoute race. Dry matter allocation was very similar betw een Landais and Iberique, but conversely, Tamjoute showed stronger roo t allocation. Toxic symptoms of NaCl on plant organs were not detected after 60 d culture at 250 mM NaCl concentrations but the final biomas ses were reduced substantially 40% less than the control (table VI). G rowth (fig 2) was calculated by substracting the final weights from th e initial weights of the same plant and estimated by linear regression on the total height. The regressions were established from data of th e first harvest for each geographic race (table VII). Tamjout appeared to be more resistant to salt stress than Landais on Tamjoute.