Physiological responses of Tunisian grapevine varieties to bicarbonate-induced iron deficiency.

Plants are frequently submitted to iron deficiency when growing on calcareous soils, which contain high concentrations of bicarbonate. The purpose of this study was to investigate the variability of physiological responses of Tunisian grapevine varieties to bicarbonate-induced iron chlorosis. Vine woodcuttings of seven autochthonous Tunisian varieties (Khamri, Mahdaoui, Blan3, Saouadi, Arich Dressé, Beldi and Balta4), two rootstocks (140Ru and S.O.4), and an introduced table variety (Cardinal) were cultivated on inert sand for 2 months using a complete nutrient solution (20 microM Fe) that was either well supplied or not supplied with 10 mM HCO3-. Young leaves of plants cultivated on bicarbonate-enriched medium showed characteristic symptoms of iron chlorosis, although the intensity of the symptoms depended on the variety and the rootstock. Chlorosis score confirmed these observations since the most sensitive varieties showed the highest values. This variability in tolerance to iron deficiency was also displayed when analysing the physiological parameters (shoot length, plant dry weight, and chlorophyll concentration) and the iron contents in the 4th leaf. Analysis of morphological and physiological parameters showed three behaviour groups. The first one corresponded to tolerant varieties (Khamri, Mahdaoui, and the root-stock: 140Ru), the second included moderately tolerant vines (Saouadi, Arich Dressé, Blanc3, and the rootstock: S.O.4) and the third represented the sensitive ones (Balta4, Beldi, and Cardinal).