Grafting: A possibility to enhance health-promoting and flavour compounds in tomato fruits of shaded plants?

The quality of tomato fruits may deteriorate under abiotic growing conditions, such as low radiation. The aim of this study was to investigate whether grafting two scions (‘Piccolino’, ‘Classy’) onto two commercial rootstocks (‘Brigeor’, ‘Maxifort’) was able to enhance carotenoids (lycopene, β-carotene) and flavour compounds (sugars, acids, aroma volatiles) in tomato fruits of shaded plants. Radiation reduced by 50% due to shading decreased the fruit's concentrations of sugars (glucose, fructose) by up to 13% and of β-carotene by up to 16% in both scions due to decreased photosynthesis, which may further account for the decreased synthesis of volatiles. Interestingly, several volatiles such as (Z)-3-hexenal, 3-methylbutanol and 6-methyl-5-hepten-2-one increased following shading. Grafting onto ‘Brigeor’ decreased yield and fruit number independent of the scion. Photosynthesis of shaded tomato leaves as well as concentrations of fruit sugars was diminished by up to 12%, latter independent of the rootstock. Furthermore, grafting ‘Classy’ onto ‘Brigeor’ decreased carotenoids by 8%, resulting in a decrease of three carotenoid-derived volatiles (geranylacetone, β-cyclocitral and β-ionone). Titratable acids were increased by both shading (by 9%) and grafting (by 6%). In addition, lignin-derived volatiles such as methyl salicylate and guaiacol were enhanced by grafting both scions. However, grafting was unable to enhance the decreased fruit concentrations of sugars, β-carotene and five volatiles of shaded grown plants. Furthermore, the results of the experiments depended on the rootstock scion combination used.

► Interaction between grafting and shading on carotenoids and flavour compounds.
► Shading decreased photosynthesis resulting in less precursors for volatiles.
► Shading and grafting increased acids and several aroma volatiles.