2017 ASHS Annual Conference

Despite the benefits of using grafted plants for managing soil-borne diseases and improving fruit yield in field tomato production, the high cost of grafted tomato production is still considered the main limitation to widespread adoption of tomato grafting. A two-year field study was performed at the University of Florida, Plant Science Research and Education Unit, Citra, FL in Fall 2015 and Spring 2016 to explore the potential of reducing plant population by increasing in-row plant spacing to lower total transplant cost in grafted tomato production. ‘Tribute’, a determinate tomato cultivar, was grafted onto three hybrid tomato rootstocks: ‘RST-04-106-T’, ‘Estamino’, and ‘Multifort’. Non-grafted ‘Tribute’ was used as a control. Plants were grown in fumigated raised beds with drip irrigation. Five different in-row spacings, i.e., 0.46, 0.61, 0.76, 0.91, and 1.07 m, were used with a constant between-row spacing of 1.83 m, corresponding to plant populations of 11960, 8970, 7176, 5980, and 5126 plants per hectare, respectively. A split plot design with four replications was used, with spacing as the whole plot factor and grafting the subplot factor. Total marketable fruit yield on a per plant basis was significantly higher in grafted ‘Tribute’ with ‘RST-04-106-T’ compared with the non-grafted control in Fall 2015, whereas the significant yield improvement was observed in all the grafted treatments in Spring 2016. The in-row spacings of 1.07 and 0.46 m resulted in the highest and lowest marketable yield per plant, respectively, in Fall 2015; however, an inconsistent effect of spacing was found in Spring 2016. Grafting by plant spacing interaction was not found in either season. An increase in fruit number contributed to the enhanced yield in grafted plants in both seasons. Moreover, grafting resulted in greater average fruit weight in Spring 2016. Total marketable yield per hectare was significantly affected by grafting and plant spacing in both seasons. Non-grafted ‘Tribute’ showed a significantly lower yield than grafted plants with all three rootstocks used in Spring 2016, but the yield increase as a result of grafting was not observed in plants grafted with ‘Estamino’ in Fall 2015. The in-row spacings of 0.46 and 0.61 m led to significantly higher marketable yields per hectare than that of 0.91 and 1.07 m spacings in both seasons, while the yield did not differ significantly between the plant spacings of 0.61 and 0.76 m. Results from this study suggested the possibility of increasing plant spacing in grafted tomato production.