Yield and Fruit Quality of Field-grown Grafted Tomato with Different Plant Spacings

Plant spacing is a major production factor affecting tomato growth and yield as well as economic returns. As growth promotion and yield improvement are increasingly recognized as benefits of grafting it is important to determine the performance of grafted tomato plants in response to different planting densities. In this field experiment conducted at the University of Florida, Plant Science Research and Education Unit, Citra, FL in Fall 2015, determinate tomato ‘Tribute’ was grafted onto three hybrid tomato rootstocks, including ‘Estamino’, ‘Multifort’, and ‘RST-04-106-T’, while non-grafted ‘Tribute’ was used as a control. Plants were grown in a fumigated field with five different in-row spacings (i.e., 0.46, 0.61, 0.76, 0.91 and 1.07 m). The experiment was arranged in a split plot design with four replications with spacing as the whole plot factor and grafting the subplot factor. Results showed that although the average fruit weight was not significantly affected by either grafting or spacing, marketable fruit number and weight per hectare were markedly impacted. Grafting with ‘RST-04-106-T’ and ‘Multifort’ resulted in significantly higher total marketable fruit weight as opposed to non-grafted plants, while plants grafted with ‘RST-04-106-T’ also had higher total marketable fruit number than all other treatments including the non-grafted control. Marketable fruit weight and number were significantly higher in plants grown at 0.46 and 0.61 m than that at 0.91 and 1.07 m. The regression analysis suggested that grafted plants especially those with ‘Multifort’ and ‘RST-04-106-T’ could be grown at wider spacing while maintaining/improving marketable yield in contrast to non-grafted plants. Neither grafting nor spacing showed any significant influence on tomato fruit soluble solids content, titratable acidity, and pH. Interestingly, ‘Tribute’ grafted onto ‘Estamino’ and ‘RST-04-106-T’ exhibited higher ascorbic acid concentrations as the in-row spacing increased, whereas the opposite trend was observed in tomatoes from the non-grafted plants and plants grafted with ‘Multifort’. Grafting with ‘RST-04-106-T’ significantly increased fruit dry matter content as compared with non-grafted and other grafted plants. With respect to lycopene content, grafting resulted in significantly higher levels despite the rootstock cultivar used. Lycopene content at 0.46 m spacing was significantly lower than other spacing treatments. Grafting did not affect tomato total phenolic content but the 0.61 m spacing led to a significant increase in total phenolics of tomato fruit than the 0.46 and 1.07 m spacing treatments.