Monitoring phenolic maturation of seventy genotypes of Vitis viniferae L. using the polyphenolic meter index method

Abstract

Evolution of grape phenolic maturation (of 70 genotypes) was monitored using the Polyphenolic Meter Index (PMI) method. The experiment was carried out in 2011 in experimental vineyards in Rauscedo, Italy. Samples were collected at three ripening stages: 1) 30 days before harvest; 2) 15 days before harvest, and 3) at harvest. On average, the evolution of maturation was followed by an increase in PMI, which ranged from 197.2 at the first ripening stage to 221.6 at harvest. This change was accompanied by a reduction in the difference between the maximum and minimum PMI values (85.6 to 64.7) as well as by a reduction of the standard deviation (23.1 to 16.5). Increasing PMI values during maturation indicated higher content of phenolic compounds and better maturation uniformity among grains. When comparing varieties and clones, observed differences were in some cases more significant between clones than varieties. Among the 70 genotypes, the highest PMI was observed for Cabernet Franc VCR 402 (PMI 265) and Marzemino VCR 114 (PMI 260). In contrast, clones that showed the lowest PMI and/or lowest maturation uniformity were: Gaglioppo VCR 141 (PMI 160), Uva Rara VCR 363 (PMI 176) and Vranac VCR 128 (difference PMI max-PMI min 184). Thus, the PMI method allowed for a quick evaluation of maturation of a relatively large number of grape genotypes.