Fluorescence data was collected using a MINI-PAM-II fluorometer (Walz Heinz GmbH, Effeltrich,
Germany). To conduct measurements, the leaf clip was attached to a leaf and measurements of
photosynthetically active radiation (PAR) and the photosynthetic efficiency of photosystem II (PhiPSII) were
recorded. This was repeated ~10 times per plot. Each FI plot was followed by its RI plot counterpart. Plots of
blocks 1 and 4 were measured 49 days after sowing between 14:45 and 15:45. Plots of blocks 2 and 5 were
measured 48 days after sowing between 15:00 and 17:00. All blocks were measured 50 days after sowing
between 10:24 and 12:49. The fluorescence kinetics of saturation pulse analyses for measurements wereinspected using WinControl-3 Software (version 3.29-rev.1112) (Walz Heinz GmbH, Effeltrich, Germany).
Measurements that did not pass inspection were discarded from subsequent analyses.
PhiPSII values were clustered according to genotype, treatment and PAR level using custom R scripts.
PAR was divided into four levels: low (<500 μmol photons m -2 s -1 ), mid-low (500-1000 μmol photons m -2 s -1 ),
mid-high (1000-1500 μmol photons m -2 s -1 ) and high (>1500 μmol photons m -2 s -1 ). Agglomerative hierarchical
clustering was applied on the scaled PhiPSII means for all plots using the ‘agnes’ function of the R package
