Grafting Does Not Influence the Nutritional Content of Organic Heirloom Tomatoes

Vegetable grafting is gaining popularity in the United States as an innovative approach to overcome soilborne pests and diseases. Many recent studies have documented successful use of grafting to manage fusarium wilt, bacterial wilt, and root-knot nematodes, as well as various abiotic stresses. However, it is also important to determine if resistant rootstocks influence fruit quality attributes. The objective of this study was to examine the grafting effect on nutritional quality of organic heirloom tomato fruit. The field trial was carried out on certified organic land during the spring 2010 season. Two popular heirloom cultivars, Brandywine and Flamme, were grafted onto two rootstock cultivars, Multifort (interspecific) and Survivor (intraspecific). Non-grafted and self-grafted scions were used as controls. Treatments were arranged in a randomized complete block design with 5 replications. Soluble solids, pH, titratable acidity, vitamin C, and carotenoid content were measured. No significant differences were observed in soluble solids, pH, titratable acidity, and vitamin C content among grafted and non-grafted treatments. The two scion cultivars, Brandywine and Flamme, showed significant differences in concentrations of the carotenoids including lycopene, β-carotene, and lutein. These differences are most likely attributable to the varietal differences. ‘Brandwine’, characterized by large, red beefsteak tomato fruit, contained significantly higher concentration of lycopene than ‘Flamme’, a golf ball-sized orange tomato. However, there were no significant differences between grafted and non-grafted treatments within cultivars. The ‘Flamme’ fruit exhibited a significantly higher level of β-carotene than the ‘Brandywine’ fruit except for the comparison between self-grafted ‘Flamme’ and non-grafted ‘Brandywine’, which was not significantly different. Lutein content also varied between cultivars. Results of this study showed that the use of grafting as an effective pest and disease control practice did not result in a negative impact on nutritional quality of organic heirloom tomato fruit. Overall, the two types of rootstocks, i.e., interspecific vs. intraspecific, led to similar levels of measured attributes.