Genetic Correlation, Correlated Response and Indirect Assessment of Photosynthetic and Cell-Membrane Damages by Using SPAD-Chlorophyll Content Under Post-Anthesis High-Temperature Stress in Wheat.

High temperature stress has a major impact on plants by damaging photosynthetic capacity and cell membrane integrity, resulting in partial or total dysfunction of the plants. Chlorophyll fluorescence and cell membrane stability (CMS) are reported to be associated with abiotic stress tolerance including high temperature stress in wheat. Estimation of the genetic variations and large scale breeding application of those traits under stress are difficult because of time consuming and complex method of estimation. The objectives of the study were to assess potential use of SPAD-Chlorophyll content as indirect selection parameter for chlorophyll fluorescence and CMS, and achieve genetic gain for heat tolerance in wheat. A population comprised of 103 recombinant inbred lines from a cross between Ventnor (tolerant) and Karl 92 (sensitive) was evaluated for those three traits in F₉ and F₁₀ generations under long-term post-anthesis heat stress conditions. Plants were exposed to the high temperature stress (36^o/30^oC day/night temperature; relative humidity 80%; and photoperiod 16/8 hours) after flowering. Chlorophyll fluorescence and SPAD-Chlorophyll content data were collected at 0, 4, 7 and 10 days after high temperature stress, while CMS was measured at 7 and 10 days only. Preliminary data analysis showed strong genetic variations for all three traits. High narrow-sense heritability (parent-offspring regression and realized heritability) were observed for those traits. SPAD-chlorophyll content showed higher heritability and genetic gain compared to chlorophyll fluorescence and CMS. Very strong phenotypic correlations were existed among three traits. SPAD-chlorophyll content explained 70-80% and 65-73% variability of chlorophyll fluorescence and CMS, respectively, under heat stress conditions. Results demonstrated that SPAD-chlorophyll content could be used as indirect selection parameter for chlorophyll fluorescence and CMS under high temperatures stress, and effective genetic gain could be made for heat tolerance in wheat.