Influence of Grafting and Planting Density on Fruit Yield and Root-knot Nematode Control in Tomato Production

The high cost of grafted seedlings still remains the main barrier for widespread adoption of grafting among vegetable growers in the United States. Given the improved disease resistance and enhanced growth and yield in grafted plants, it is suggested that plant population may be reduced to lower the cost associated with the use of grafted plants while maintaining desirable yields. In this study, ‘Tribute’ tomato as the scion was grafted onto two commercial tomato rootstocks with root-knot nematode resistance, ‘Multifort’ and ‘RST-04-106-T’. Non-grafted and self-grafted ‘Tribute’ were included as controls. The  study took place in a certified organic field in Citra, FL, during the Fall 2012 season. A split-plot design with three replications was used with spacing as the whole-plot factor and grafting treatments in the subplots. The four in-row spacing treatments evaluated were 0.61 (recommended spacing), 0.76, 0.91, and 1.07 m, with a constant between-row spacing of 1.83 m. In addition to fruit yield assessment, the effectiveness of resistant rootstocks for root-knot nematode control was also examined. Total marketable fruit yield was significantly affected by the spacing and grafting treatments (P < 0.01), moreover, there was a significant spacing × grafting interaction (P < 0.01). At the in-row spacings of 0.91 and 1.07 m, grafting with the two rootstocks resulted in similar marketable yields compared with non-grafted and self-grafted ‘Tribute’. In contrast, at the in-row spacings of 0.61 and 0.76 m, plants grafted with ‘Multifort’ showed significantly higher marketable yields than the ‘Tribute’ controls and plants grafted with ‘RST-04-106-T’. Grafting with ‘RST-04-106-T’ also led to a significant increase of marketable yield in comparison with non-grafted ‘Tribute’ at the 0.76-m spacing. The spacing treatments did not demonstrate significant impacts on marketable yields of non-grafted ‘Tribute’ and ‘Tribute’ grafted onto ‘RST-04-106-T’, while self-grafted ‘Tribute’ tended to have a higher yield at the 0.61-m spacing than other spacing treatments. Interestingly, the marketable yield of grafted plants with ‘Multifort’ did not differ significantly between the spacings of 0.61 and 0.76 m, whereas yields in these two lower spacing treatments were significantly higher than those at 0.91 and 1.07 m. A significant reduction (P < 0.01) in root galling was observed in plants grafted with the two rootstocks relative to non- and self-grafted ‘Tribute’. Under an intermediate level of root-knot nematode infestation, results from this study indicated the potential of decreasing planting density as a cost-saving approach in grafted tomato production.