Effects of Grafting Position and Exogenous Abscisic Acid On Survival of Grafted Tomato Plants and Rootstock Sucker Incidence

Vegetable grafting is commonly practiced in Asia and many Mediterranean countries to overcome problems associated with intensive cultivation. Benefits from grafting include increased resistance to soil-borne pathogens and nematodes, improved yield and fruit quality, and enhanced tolerance to environmental stresses. The tube grafting method is widely used in North America to produce grafted tomato transplants because of its ease and speed. However, sucker production from axillary meristems of rootstock cotyledons is commonly experienced and additional labor cost is required for their removal. To avoid this problem, grafting can be performed below the rootstock cotyledons to remove the axillary meristems associated with the cotyledons. This study was conducted to determine the effects of different grafting positions on survival rate and sucker incidence in grafted tomato transplants. Abscisic acid is known to be involved in promoting stomatal closure, thereby reducing transpiration rate. In this study, we also assessed the effectiveness of exogenous abscisic acid application on increasing survival rate of grafted tomato plants. ‘Multifort’ and ‘Florida-47’ were used as the rootstock and scion, respectively. Four-week old tomato seedlings were grafted above and below the rootstock cotyledons, with and without exogenous application of abscisic acid in different treatments. Self-grafts of ‘Multifort’ and ‘Florida-47’ were used as controls. After grafting, the plants were kept in a healing chamber for 4 days, followed by gradual acclimatization to greenhouse conditions for another 4 days. Plants were then transplanted into 4-inch pots to mimic field conditions. The survival rate, number of rootstock suckers, and distance between soil surface and the graft union in each treatment were recorded. There was no difference in survival rates between plants grafted above and below the rootstock cotyledons. However, when exogenous abscisic acid was applied, survival rate of plants grafted below the rootstock cotyledons was significantly lower. Rootstock sucker incidence was higher in plants grafted above the rootstock cotyledons although suckers took a longer time to develop in ‘Florida-47’ self-grafts. Soil surface to graft union distance was also shorter for plants grafted below the rootstock cotyledons. From our study, we recommend grafting of tomatoes below the rootstock cotyledons to reduce sucker incidence. However, care must be taken during transplanting to ensure that the graft union is well above the soil surface to prevent formation of adventitious roots from the union. The influence of abscisic acid on the survival rate and growth characteristics of grafted tomato plants deserves further research.