Leaf samples collected from field plots of nine lettuce varieties established in the Early (ES) and Late (LS) Summer of 2002 and 2003 in Celeryville, Ohio, were subjected to spectrophotometric measurement of anthocyanin concentrations and/or color analysis based on colorimeter and spectroradiometer readings and human panelist ratings. Interactions between year (Y), planting date (PD), and variety (V) main effects for anthocyanin concentration were significant due to shifts in response magnitude, but not direction. Anthocyanin levels were higher following LS than ES planting, regardless of Y and V, and PD effects were pronounced in 2002, when differences in average daily temperature between ES and LS plantings tended to be larger. Also, regardless of Y and PD, anthocyanin levels followed the pattern `Impuls' > `OOC 1441' > `Valeria' > `OOC1426' > `Lotto' > `SVR 9634' `OOC 1434' > `OOC 1310' > `Cireo'. Treatment-based color differences were also evident in colorimeter and spectroradiometer readings. And, panelists differentiated field-grown samples based on red color intensity. Strong correlations between analytical and instrumented and human panelist-based measures suggest that instrumented assessments of red color intensity may serve as reliable proxies for direct measures of anthocyanin levels or human panelist ratings, particularly if the aim is to establish color differences between major experimental groups and assign a quantitative, repeatable value to red color intensity.
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