Rootstock Effects On Nitrogen Assimilation In Tomato Plants Under Greenhouse Conditions

With regard to enhanced vigor and yield observed in grafted tomato plants, few studies have examined the underlying physiological mechanisms in addition to improved nutrient uptake. The objective of this study was to determine changes of nitrogen assimilation in leaves and roots of tomato plants as a result of grafting (Solanum lycoperscium). A popular tomato cultivar Florida-47 was used as scion and grafted onto two interspecific tomato rootstocks including ‘Beaufort’ and ‘Multifort’. Non-grafted and self-grafted ‘Florida 47’ were used as controls. The plants were grown under greenhouse conditions and provided with an optimum supply of essential nutrients and water using a controlled fertigation system. Levels of nitrate and reduced nitrogen and nitrate reductase activity in leaf and root samples were measured at three growth stages, i.e., vegetative, first harvest and final harvest. Grafting with the two vigorous rootstocks did not alter positively the activity of nitrate reductase as similar levels of enzyme activity were observed between the grafted and non-grafted plants throughout the production cycle. There was a greater activity of the nitrate reductase in the leaves than in the roots, indicating a higher level of nitrate assimilation in the leaves. Similar patterns were also observed on the nitrate concentrations in leaves and roots without significant differences between grafted combinations and controls. However, the two rootstocks significantly increased the total and marketable yields of ‘Florida 47’ as compared to non-grafted and self-grafted controls. Specifically, grafting with ‘Multifort’ resulted in an increase of 61 and 62% of the marketable yield in comparison with the non-grafted and the self-grafted ‘Florida-47’, respectively. More in-depth studies are warranted to better understand the underlying physiological mechanisms that drive the enhancement in vigor and yield of grafted tomato plants in addition to nitrogen assimilation. Analysis of the plant growth hormones including cytokinin and auxin is underway which may provide more insights into the physiological processes contributing to the enhanced productivity of grafted tomato plants.