Establishing Optimum Conditions for Shipping Un-Rooted Grafted Cuttings of Solanum lycopersicum

Grafted tomato seedlings have been utilized in US greenhouse vegetable production for over a decade. The limited source of grafted seedlings has forced US growers to purchase the seedlings from propagators in Canada.  Increased shipping cost are making it harder for US growers to more widely introduce grafted plants, including in open fields. To address this issue we examined the use of un-rooted grafted cuttings, a technology used in Asia, for shipping long distances. Previous research has been done on optimum environmental conditions (air-temperature, and light) for long distance transport of grafted tomato seedlings (Kubota, and Kroggel, 2006). Little data is available for the optimum environmental conditions for transporting un-rooted grafted cuttings. We also needed to determine the optimum timing for harvesting grafted cuttings. In this experiment, the grafted seedlings (‘Durinta’ scion and ‘Aloha’ rootstock) were produced using the tube grafted method, then harvested on five different days after grafting (Day 0, 1, 3, 5, and 7).These harvested grafted cuttings were placed in darkness for 72 hours at two different air temperatures to simulate travel conditions (10^oC and 20^oC). All experimental grafted cuttings except the control were wrapped in a wet paper towel, placed in an air tight bag, and hung vertically to avoid stem bending gravitropism. After 72 hours the grafted cuttings were planted in a tray with moist media that was placed under frequent misting in an overhead irrigated greenhouse. 70% shade cloth was applied to reduce the incident radiation. For the next 48 hours the plants were kept inside a plastic dome to keep the grafted cuttings in near 100% humidity. Subsequently the plants were covered only at night for the following 5 days to root before observing percent rooting and measuring fresh and dry weights, stem length, and number of leaves length > 2.5cm. Our preliminary experiment showed that grafted cuttings harvested on Days 0 and 1 exhibited a 50% mortality regardless of temperature. The grafted cuttings harvested on Days 3 and 5 showed nearly 0% mortality which was comparable to the non-treated control. In contrast, air temperature during simulated transportation did not affect the mortality, percent rooting or growth of the grafted cuttings. The overall quality, however, was better maintained at 10^oC than 20^oC. This suggests that grafted tomato seedlings need to be healed at least 3 days before harvesting and shipped at 10^oC temperature to assure highest re-rooting success.