2.2. SPAD readings, chlorophyll concentrations and Fe contents
The first new leaves appeared approximately 15 days after the beginning of the experiment and from then on the degree of chlorosis was estimated non-destructively in the youngest fully expanded apical leaves from five plants of each treatment using a portable SPAD-502 meter (Minolta, Osaka, Japan). Six SPAD readings were recorded for each leaf, homogeneously distributed from the apex to the base of the leaf, to obtain a representative degree of leaf chlorosis. SPAD readings were converted to total Chl using the calibration curve:
y=0.45x2 −1.11x+32.56(R2 =0.98;n=31;P < 0.001)
where y is the Chl concentration (mol m−2) measured spectrophotometrically and x is the SPAD readings measured in strawberry leaves (Pestana et al., 2011a).