Determining the storage potential of iceberg lettuce with chlorophyll fluorescence

Field stress during growth was hypothesized to negatively influence the photosynthetic apparatus and storage quality of iceberg lettuce (Lactuca sativa L.). The objectives of this study were to assess the sampling variation associated with chlorophyll fluorescence (CF) measurements of iceberg lettuce and to investigate their use as at-harvest indicators of the storage potential of 'Ithaca 989' and 'Salinas 88 Supreme' cultivars of iceberg lettuce. CF varied among heads, leaves, and locations within a single leaf. However, when measured at the same location on several heads, CF measurements had the same level of variability as other parameters used to evaluate quality. Several at-harvest CF measurements (particularly FV/FM) correlated strongly (r ∼ 0.8) with ratings describing the overall visual quality and decay of 'Ithaca 989' lettuce after 7, 14, and 21 days storage. These ratings had a narrower range of observations for the cultivar 'Salinas 88 Supreme' and were consequently poorly correlated with CF. However, both cultivars had excellent correlations between rib discoloration and day 0 or day 1 t1/2 measurements. This supports the hypothesis that the at-harvest CF of a subset of individuals, randomly sampled from within a group, can be correlated with postharvest quality of the entire group.