Is the vigour of grafted tomato plants related to root characteristics?

This research was carried out to assess the effects of root characteristics on vigour of grafted tomato plants. The trial was carried out in a cold greenhouse during spring seasons. Tomato plants (cv. Durinta F1) were grafted on three rootstocks (Beaufort, Heman and itself) and grown in two different pot sizes (5 and 10 L per plant). At the full ripening stage of the 1st truss, dry matter production, leaf area, scion and rootstock diameter, transpiration and root length were measured. Root density, distribution and substrate exploitation were measured only in plants in the 5 L pot size at three depths. To evaluate hair root characteristics (root diameter, number and length of root hair), plants were transplanted and grown in water culture (15 L pots) in order to avoid any damage determined by separation of the root sample from the substrate. The plants grafted on Beaufort produced 9.8% more epigeous dry matter than those grafted on Heman and no differences were observed in both rootstocks compared to the control. The mean density of roots was higher in both grafted plants (+25.3% in the mean of rootstocks) with respect to the self-grafted one. The roots of selfgrafted plants were about 18% shorter than the other rootstocks when cultivated in 5 L pots. This difference was reduced when the plants were cultivated in the 10 L pot volume. No significant differences were found in root diameter and root hair length whereas Beaufort gave the highest number of root hairs (45% and 71% higher than Heman and Durinta, respectively). Grafted tomato grown under optimal conditions of soilless cultivation showed only slight differences due to the genotype of rootstock in spite of differences in root characteristics.