Physiological response and productivity of sunflower under saline conditions in Southern Italy

Physiological and morphological response, ion accumulation and seed yield of Sunflower (Helianthus annuus, L.) were studied in response to saline irrigation in southern Italy in 1996. Control plants (I0) were irrigated with plain water whereas two salt treatments (I05 and I1) were irrigated with plain water added with commercial NaCl. Electrical conductivity (ECw) of irrigation water was 0.9 for I0, 8.9 for I05 and 15.4 dS m-1 for I1. Soil salinity, ECe, at anthesis reached 3.1 in I05 and 4.6 dS m-1 in I1, with available soil-water remaining above 50% throughout the season. Such soil conditions resulted in "mild" plant water stress as shown by leaf water potential (?t) that was only -1.3 in I0 and -1.6 MPa in I1 at about the maximal development of crop and with a maximal difference between treatments throughout the season of 0.56 MPa. A moderate reduction in ?t severely affected LAI which at the end of anthesis decreased by 33% in I1 compared with the control, whereas gas-exchange was not impaired. Ion analysis showed that Na+ was accumulated in the bottom leaves. Difference in Na+ leaf content between Io and I1 was evident at end of growth showing that the osmotic effect was responsible for the reduction in LAI. The loss in seed yield which was reduced 11% in I05 and 15% in I1, compared with I0, is attributable to the leaf area index reduction. The ratio between biomass and water uptake did not differ between treatment and it was about 4.1 g m-2 mm-1 . These data indicate that in our conditions productivity of sunflower showed sensitivity to mild soil salinity.