Effect of osmotic adjustment on root length and dry matter partitioning in sunflower (Helianthus annuus L.) under drought stress

Field experiments were conducted on sunflower (Helianthus annuus L.) with high- and low-osmotic-adjustment genotypes to ascertain the role of osmotic adjustment (OA) in sustaining achene yield (AY) and its stability under water-deficit conditions. The results indicated that high-osmotic-adjustment (HOA) genotypes were superior in terms of achene yield, root length, dry root weight, root-to-shoot ratio, harvest index (HI), and number of achenes per head under drought stress. The superiority of HOA for AY genotypes was due to efficient translocation of photosynthates to the roots, as indicated by the significant relationship of all root traits with OA and better mobilization of reserves to the developing head by the OA as suggested by a very strong relationship of OA with HI. Among different yield components, OA showed the highest relationship with the number of achenes per head, suggesting that reserves mobilized by OA were utilized to produce a large number of achenes per head. Genotype AMES-10103 belonging to the HOA group showed its superiority over other genotypes under drought stress. Among all traits, HI has shown its promise for selection of high yielding genotypes under drought stress.