Osmotic adjustment and yield maintenance under drought in sunflower

The value of osmotic adjustment (OA) as a trait which can contribute effectively to yield maintenance under drought, has not been established for sunflower (Helianthus annuus L.). We screened a set of 25 inbred lines reputed to differ for drought tolerance for OA expressed in the 8-leaf stage; crossed the extreme lines (high and low OA); and selected four individuals (two high OA, two low OA) from the F2 population derived from this cross. Crops of F3 families obtained by self-pollination of these individuals were grown under a rain-out shelter and subjected to a 30-day drought ending at anthesis. High OA families expressed greater OA(ft) [OA at full turgor, estimated as the difference in osmotic potential between droughted and control treatments] than low OA families at the end of the drought period (0.23 MPa vs. 0.04 MPa). Crops of high OA families extracted more water from the profile during the stress period (117 mm vs. 63 mm) had greater shoot biomass and harvest index (HI) at physiological maturity, and greater grain yield (ca. 30%). There was no effect of OA on these variables in the irrigated controls. Grain size, rather than grain number, was the yield component most affected by level of OA. Yield maintenance under drought conditions was attributable to variations in post-drought shoot biomass increase and HI increase. We conclude that OA can contribute to drought tolerance in sunflower and stress the need to develop markers for this trait. (C) 2002 Elsevier Science B.V. All rights reserved.