Evaluation of markers for the traceability of potato tubers grown in an organic versus conventional regime

Identification of parameters discriminating organic and conventional produce should help prevent misconduct and could provide a firm basis for comparative assessment of the two types of produce. In this report, we compare for selected markers organically versus conventionally grown tubers in four separate field trials. Within each field trial, organic and conventional tubers were subjected to the same pedoclimatic conditions as they were grown in adjacent plots. In all sites and in both cultivars tested, irrespective of environment, organic tubers exhibited a significant enrichment in 15N per thousand when compared to their conventional counterparts. Also, the sum of all samples from the four sites (organic versus conventional) showed higher delta 15N per thousand (7.17 ± 48% versus 3.36 ± 38%; means ± CV%; n = 39; P < 0.001); furthermore, setting as threshold value for assignment in the organic group the lowest delta 15N observed for organic samples (i.e. + 4.3), only 15% of conventional tubers were misclassified. On the other hand, further parameters selected on the basis of reports of alterations as a consequence of agricultural technique -- ascorbic acid, protein content and dry matter -- did not show consistent trends of variation throughout the four field trials. We conclude that, as opposed to other relevant parameters, 15N enrichment appears as a promising discriminative marker.