Abstract
The present study was undertaken to determine variation in the accumulation pattern of sugars in leaves and berries at different developmental stages of forty-two muscadine grape genotypes. In order to compare the sugar accumulation patterns and source sink relationships between bunch and muscadine grape genotypes, twelve-bunch grape genotypes were also studied. Leaf and berry sugar concentrations among the genotypes were significantly different (P[less-than or equal to] 0.05) at different developmental stages. Sugar concentrations in the leaves of muscadine genotypes varied from 1.94% (w/v) to 8.30% at the pre-flowering stage; 0.36% to 4.52% at the flowering stage; 2.19% to 4.10% at the young fruit stage; 2.25% to 6.05% at the medium fruit stage; 2.39% to 7.79% at the mature fruit stage; and 1.67% to 7.09% at the ripe fruit stage. Accumulation of sugars in berries varied from 0.61% to 2.25% at the young fruit stage; 0.38% to 3.18% at the medium fruit stage; 1.11% to 11.37% at the mature fruit stage; and 4.46% to 16.08% at the ripe fruit stage. The mean sugar concentrations over the developmental stages of the leaf and berry were tested using the RANK procedure that helped to assign the grape genotypes into seven distinct groups. Significantly higher leaf sugar content at fully developed/mature fruit stage (stage 5) and preflowering (stage 1), suggests that there are higher leaf sugar requirements after veraison (berry ripening) and during flowering. Change of grouping study shows that 17 genotypes that were in the lower leaf sugar group were moved to the upper group in terms of berry sugar concentration, 12 genotypes maintained their rank whereas 25 genotypes showed decreases in their rank. Further studies are suggested to study the impact of leaf sugar concentration on characteristics contributing to berry sugar such as leaf biomass, number of catkins per vine, number of berry cluster per vine, number of berries per cluster berry, size and levels of key enzymes involved in sucrose synthesis.
