Use of Unrooted Grafted Vegetable Cuttings: I. Effects of Healing Duration and Transportation Temperature

Grafting of vegetable seedlings is a unique horticultural technology to overcome soil-borne diseases and pests and to add extra vigor to the plants under various environmental stress conditions. In order to advance the use of grafting in U.S. vegetable production in open fields, key issues to address include 1) increasing the propagation capacity to meet the expected large number of seedlings necessary to supply the demands of typically large farms and 2) reducing production costs. Traditionally, vegetable grafting is a labor-intensive process involving much training and logistics. However, the seasonal nature of nursery operations due to the limitation of transportation of the grafted seedlings is problematic when nurseries are interested in introducing vegetable grafting to serve producers who are interested in using the technology. To address this issue, we examined factors affecting quality and growth of unrooted grafted cuttings as a means to improve the distribution of grafted materials and for nurseries to centralize the labor-intensive grafting operation to serve producers in various regions (i.e., various planting seasons).  Grafted tomato and watermelon cuttings (‘Durinta’ tomato or ‘Tri-X 313’ watermelon scion with ‘Aloha’ tomato or ‘Strong Tosa’ interspecific hybrid squash rootstock’, respectively) were harvested after 0, 1, 3, 5, or 7 days of healing after grafting and kept for 72 hours in a dark chamber maintained at 10 (tomato), 12 (watermelon) or 20 °C (both species). The results showed that it required a minimum of 3 and 5 days of post-grafting healing for tomato and watermelon, respectively, before harvest in order to maintain growth and development rates after 3-day simulated transportation, as equivalent to non-treated cuttings (control). Transportation at a lower temperature (10 °C for tomato or 12°C for watermelon) seems to contribute to maintaining better visual cutting quality than 20°C. Although more research needs to be done to establish protocols suitable for various species and scion-rootstock combinations, effective use of unrooted grafted cuttings in nurseries with and without grafting capabilities may become a breakthrough technology to advance the use of grafted plants in the United States.