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Utilization of leaf temperature for the selection of leaf gas-exchange traits to induce heat resistance in sunflower (Helianthus annuus L.)

Kalyar, T., Rauf, S., Teixeira da Silva, J. A., Haidar, S., Iqbal, Z.
Photosynthetica 2013 v.51 no.3 pp. 419-428
Helianthus annuus, correlation, fruits, gas exchange, heat, heat stress, heat treatment, heritability, hybrids, leaves, photosynthesis, progeny, screening, seeds, selection criteria, temperature, transpiration
Heat stress is a major production constraint of sunflower worldwide. Therefore, various populations (parental, F₁, F₂, F₃, and plant progenies) of sunflower were screened for leaf gas-exchange traits with the objectives to formulate selection criteria of heat resistance and development of heat-resistant lines. Initial screening and F₂ seeds exposed to heat stress (45°C) resulted in the development of an adapted F₂ population that showed leaf gas-exchange and morphological traits better than the unadapted population. Correlation coefficients of traits were partitioned into direct and indirect effects via a path analysis technique to determine the cause of their relationship with a basic parameter such as a reproductive head mass (HM). Path analysis showed a positive direct effect of leaf temperature (Tₗₑₐf) (0.32) on HM and also an indirect effect (0.77) of the transpiration rate (E) on HM. Moreover, Tₗₑₐf showed high heritability estimates. Tₗₑₐf was used to select superior plants within the F₂ population. This selection brought about an improvement in the net photosynthetic rate (P N) and E as it was indicated from progeny performance and realized heritability. Progenies selected on the basis of Tₗₑₐf also showed an increase in achene yield and heat resistance over unselected F₃ progenies and a commercial hybrid.