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@ARTICLE{Agarwal:1041663,
      author       = {Agarwal, Avinash and Colwell, Filipe de Jesus and Correa
                      Galvis, Viviana Andrea and Hill, Tom R. and Boonham, Neil
                      and Prashar, Ankush},
      title        = {{T}wo-fold red excess ({TRE}x): a simple and novel digital
                      color index that enables non-invasive real-time monitoring
                      of green-leaved as well as anthocyanin-rich crops},
      journal      = {Plant methods},
      volume       = {21},
      issn         = {1746-4811},
      address      = {London},
      publisher    = {BioMed Central},
      reportid     = {FZJ-2025-02368},
      pages        = {24},
      year         = {2025},
      abstract     = {Background: Digital color indices provide a reliable means
                      for assessing plant status by enabling real-time estimation
                      of chlorophyll (Chl) content, and are thus adopted widely
                      for crop monitoring. However, as all prevalent leaf color
                      indices used for this purpose have been developed using
                      green-leaved plants, they do not perform reliably for
                      anthocyanin (Anth)-rich red-leaved varieties. Hence, the
                      present study investigates digital color indices for six
                      types of leafy vegetables with different levels of Anth to
                      identify congruent trends that could be implemented
                      universally for non-invasive crop monitoring irrespective of
                      species and leaf Anth content. For this, datasets from three
                      digital color spaces, viz., RGB (Red, Green, Blue), HSV
                      (Hue, Saturation, Value), and L*a*b* (Lightness,
                      Redness-greenness, Yellowness-blueness), as well as various
                      derived plant color indices were compared with Anth/Chl
                      ratio and SPAD Chl meter readings of n = 320 leaf
                      samples.Results: Logarithmic decline of G/R, G-minus-R, and
                      Augmented Green-Red Index (AGRI) with increasing Anth/Chl
                      ratio (R2 > 0.8) revealed that relative Anth content
                      affected digital color profile markedly by shifting the
                      greenness-redness balance until the Anth/Chl ratio reached a
                      certain threshold. Further, while most digital color
                      features and indices presented abrupt shifts between
                      Anth-rich and green-leaved samples, the proposed color index
                      Two-fold Red Excess (TREx) did not exhibit any deviation due
                      to leaf Anth content and showed better correlation with SPAD
                      readings (R2 = 0.855) than all other color features and
                      vegetation indices.Conclusion: The present study provides
                      the first in-depth assessment of variations in RGB-based
                      digital color indices due to high leaf Anth contents, and
                      uses the data for Anth-rich as well as green-leaved crops
                      belonging to different species to formulate a universal
                      digital color index TREx that can be used as a reliable
                      alternative to handheld Chl meters for rapid high-throughput
                      monitoring of green-leaved as well as red-leaved crops.},
      cin          = {IBG-2},
      ddc          = {570},
      cid          = {I:(DE-Juel1)IBG-2-20101118},
      pnm          = {2171 - Biological and environmental resources for
                      sustainable use (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2171},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {39979976},
      UT           = {WOS:001443166800003},
      doi          = {10.1186/s13007-025-01339-y},
      url          = {https://juser.fz-juelich.de/record/1041663},
}