Anthocyanin Composition of Merlot is Ameliorated by Light Microclimate and Irrigation in Central California

Francés. An experiment was conducted in central California on Merlot to determine the interaction of mechanical leaf removal (control, pre-bloom, post-fruit set) and applied water amounts [sustained deficit irrigation (SDI) at (0.8) and regulated deficit irrigation (RDI) at 0.8 (bud break-fruit set) – 0.5 (fruit set-veraison) – 0.8 (veraison-leaf fall) of estimated vineyard evapotranspiration (ETc) on productivity and berry skin anthocyanin content, composition and its unit cost per hectare. The pre-bloom leaf removal (applied ~100 GDD prior to bloom) treatment consistently maintained at least 20% of photosynthetically active radiation in the fruit zone in both years of the study, while post-fruit set leaf removal was inconsistent across years. The RDI treatments reduced berry mass, while the post-fruit set leaf removal treatment reduced berry skin mass. The pre-bloom treatment did not affect yield in either year. Exposed leaf area and leaf area to fruit ratio (m2/kg) were reduced with leaf removal treatments. The RDI treatment consistently advanced Brix in juice. Anthocyanin concentration was improved with pre-bloom leaf removal in both years while irrigation treatments had no effect. Proportion of acylated and hydroxylated anthocyanins were not affected by leaf removal treatments. In both years SDI increased di-hydroxylated anthocyanins while RDI increased tri-hydroxylated anthocyanins. Pre-bloom leaf removal when combined with RDI optimized total skin anthocyanins (TSA) per hectare while no leaf removal and SDI produced the least. The cost to produce one unit of TSA was reduced 35% with the combination of pre-bloom leaf removal and RDI treatments when compared to no leaf removal and SDI. This study provides information to red wine grape growers in warm regions on how to manage fruit to enhance anthocyanin concentration and the proportion of hydroxylation while reducing input costs through mechanization and reduced irrigation.