Characterization of photosynthetic performance during natural leaf senescence in winter wheat: Multivariate analysis as a tool for phenotypic characterization

In the current research, we used chlorophyll fluorescence measurements and photosynthetic pigment content to evaluate onset and rate of the flag leaf senescence every 7 d beginning at the flowering stage (0 d after flowering, DAF) until late senescence stage (35 DAF) on three winter wheat field-grown varieties (Alka, Zitarka, and Olimpija) with the similar maturation time. OJIP curves implied that flag leaves of variety Alka detained the longest photosynthetic efficiency, while the earliest symptoms of senescence onset were indicated by positive L-band at 7 DAF and K-band at 14 DAF in variety Olimpija. A shift in I-P phase in the wheat flag leaves suggested the reduction of first acceptors in PSI, implying degradation of photosynthetic apparatus. Performance index (PItotal) proved to be the sensitive indicator of senescence; it decreased very early at 7 DAF in the flag leaves of variety Olimpija compared to Alka and Zitarka. Principal component analysis elucidated quantum yield of energy dissipation and dissipated energy flux per reaction centre as the earliest indicators of senescence in wheat flag leaves and thus showed that multivariate approach may be useful in detection of senescence onset. Sustainability indexes (SIs) corroborated the statistical significance results of evaluated parameters implying that SIs can be used as user friendly data analysis for screening purposes. Selection for functional stay-green trait could contribute to increasing crop yields.