How grafting affects the quality of tomato fruits

Grafting is getting more and more popular in tomato production, owing to advantages, such as increased plant resistance to abiotic and biotic stress. Tomato fruits are widely eaten fresh and the quality is important for both consumer and producer. We studied how grafting affected the quality of tomato fruits. The experiments were conducted under a substrate culture system in the greenhouse. The scion tomato cultivar was 'Lucius' and the rootstock tomato was 'Guozhen No. 1'. Self-grafted 'Lucius' plants were used as the control. We analyzed the fruit quality of the first and the third clusters and found that, compared to the control, total soluble sugars and lycopene content in 'Guozhen No. 1' grafted tomato fruits were significantly increased. Total soluble sugars contents in the first and third clusters were increased by 9.0 and 10.3%, respectively. Lycopene contents in the first and third clusters were increased by 24.9 and 26.6%, respectively. The gene expression of lycopene cyclase (LCY), phytoene dehydrogenase (PDS) and phytoene synthase (PSY1 and PSY2) in fruit at different development stages (green stage, turning stage, red stage and full ripening stage) were measured by Q-PCR. The results showed that the transcription levels of two lycopene synthesis genes PDS and PSY1 were remarkably higher in 'Guozhen No.1' grafted fruits than those in the control. Net photosynthesis was also measured and no significant difference appeared. There was no significant difference in vitamin C and titratable acidity among the treatments. Besides 'Guozhen No. 1', a second tomato rootstock, 'Jingfan 302', was also used as rootstock to graft 'Lucius', but no noticeable improvement in fruit quality attributes was found.