Effect of salt stress in diploid and tetraploid citrus rootstocks

Lands surfaces submitted to salt stress are in large extension. This increase is due to a pull up of salts from the soil after irrigation and also to the use of water loaded in salt for watering. The selection of rootstocks that associate tolerance to salinity and other abiotic and biotic stresses such as tristeza is then a great challenge for the next decade and may allow the maintaining of the citrus industry in the Mediterranean area. Since somatic hybridization is one of the new strategies for rootstock breeding and leads to allotetraploid genotype, it was necessary to investigate if polyploidy itself could have an impact for salt tolerance. We studied several diploids and tetraploids rootstocks (Citrange Carrizo, Poncirus Pomeroy, Cleopatra Mandarin and Commune Mandarin) submitted to a two months salt stress. Tetraploid rootstocks were nucellar auto tetraploid selected by flow cytometry among progenies of diploid reference genotypes. Plants were 5 months old and the concentration of NaCl applied was 50 mM. We studied the growth of the plants (elongation of the stem and leaves fall) and the mot, shoot and leaf ion content. Our results indicate that diploids plants treated with salt grow slowly when compared to the controls even so Commune Mandarin and Cleopatra Mandarin were less sensitive (no leaf fall was observed). Tetraploids were more resistant to salt stress when compared to diploids (less leaves fall for Citrange Carrizo and Poncirus Pomeroy) and the growth rate was even higher for Cleopatra and Commune Mandarin plants when compared to the controls. Investigation of ion content shown larges differences between the different organs studied and between salt treated plants and controls. The role of root chloride exclusion and sodium accumulation in the leaves to promote salt tolerance in function of the level of ploidy is discussed. (Texte intégral)