The Glucose-Fructose ratio of wild Tunisian grapes

Abstract

Glucose and fructose make up the bulk of sugars in grapes at all stages of development of the berry. The present study was made to determine the glucose/fructose balance of 17 wild grapes Vitis vinifera subsps. sylvestris growing under Mediterranean conditions of Tunisia for future breeding programs and selection. Cultivar “Meski Rafraf” (MKR) was used as reference for evaluation of wild ecotypes. Grape samples were collected from the North-west of Tunisia during 2014 and 2015. Glucose and fructose were the main sugars described in wild berries. Sucrose was present in little amount (<0.1 g/100 g FW). Except for ecotype 33 (EC.33), glucose was higher than fructose in all accessions. EC.46 is high-glucose ecotype (9.69 g/100 g FW) and would yield less sweet and better-balanced musts. EC.10 and EC.13 are high-fructose ecotypes (6.49 and 6.45 g/100 g FW respectively) and would result in sweeter tasting musts at lower total sugar content. The glucose/fructose ratio of wild Tunisian grapes varied over a wide range, from at least 0.26 (EC.33) to 12.38 (Cap Negro 6/2000) with differences being highly significant (p < 0.01). Grapes from cultivar “Meski Rafraf” showed an average value of 1.22. This cultivar belongs to the same homogeneous subset composed by EC.01, EC.10, EC.13, EC.15, EC.26 and EC.33. The level of reducing sugars in grape berry should represent an ideal tool for harvest date prediction and for sensory evaluation of wild grapevines. This study will help to lay out the foundation for accelerating the progress of trait improvement of quality in local grapevine resources.

Keywords

• vitis vinifera sylvestris
• genetic diversity
• reducing sugars
• glucose
• grapevine germplasm
• sustainable viticulture