Carbon partitioning between shoot organs following early leaf removal

¹ Department of Horticulture, Michigan State University, East Lansing, MI, USA
² Dipartimento di Scienze delle Produzioni Vegetali Sostenibili, Universitá Cattolica del Sacro Cuore, Piacenza, Italy
³ Department of Agricultural and Environmental Sciences, University of Udine, Udine, Italy
⁴ Dipartimento di Scienze Agrarie, Alimentari e Ambientali, Universitá di Perugia, Perugia, Italy

^* Corresponding author: sabbatin@msu.edu

Abstract

In grapevines, basal leaf removal at bloom often induces a reduction of fruit set. The effect is related to a reduction in carbon availability for different plant organs competing for photosynthates. To understand and quantify carbon allocation among major sink organs following the early basal leaf removal, the effect of early basal defoliation was studied in Pinot noir grapevines. The experiment was performed in Michigan, a cool climate viticultural region, and three levels of defoliation were imposed at full bloom: (1) no leaves removed (DF-0); (2) six leaves removed from six basal nodes (DF-6); and (3) ten leaves removed from ten basal nodes (DF-10). A week after the defoliation treatment, ¹³C pulsing was executed to the defoliated shoots. Photosynthesis (Pn), carbon distribution, fruit set, vine performance and basic fruit composition were measured. LR treatments induced higher P_n when compared to LR-0. The highest ¹³C allocation (%) was recorded in the shoot apex of the LR-10 treatment and LR-10 had the lowest percentage of ¹³C transported to the cluster, with a reduced fruit set of about 60% when compared to LR-0. The severity of leaf removal reduced significantly fruit set and increased shoot apex sink strength at the expense of the cluster.