Grain Yield Stabilizing Physiological Characteristics of Sunflower under Limited Irrigation Condition

Physiological response of sunflower to water withholding in flowering stage was evaluated under optimum and limited irrigation in 2 years. The highest effect of drought was imposed on leaf water potential، proline content، seed yield، leaf area and shoot dry weight. Seed yield reduced as much as 40% with limited irrigation. Seed yield was reduced 40% by drought stress. Drought had no effect on root dry weight، shoot to root ratio، harvest index، specific leaf area، chlorophyll fluorescence، SPAD value and osmotic potential. There were significant correlation of shoot and root dry weight، leaf area، SPAD value، leaf temperature، proline content، relative water content and chlorophyll fluorescence with seed yield. Among the 16 inbred lines and according to the changes in proline and relative water content، leaf area، chlorophyll fluorescence and seed yield، BGK-329 and RGK-21 were identified as more tolerant and sensitive lines، respectively. Shoot dry weight and leaf temperature had a quadratic while osmotic adjustment had a cubic relationship with seed yield. The results indicated that under limited irrigation، sunflower growth is dependent to balance between plant water statues and photosynthetic area which according to the genotype is affected by proline content، osmotic adjustment، chlorophyll fluorescence، SPAD value and leaf temperature. Contribution of these components is reflected in characteristics like that shoot and root dry weight and finally in seed yield which determines general growth، drought tolerance and stability of yield under limited water condition.