Use of Unrooted Grafted Vegetable Cuttings: II. Shipping Trials Report

Among many challenges associated with introduction of vegetable grafting to U.S. propagation nurseries, the seasonal nature of vegetable plant propagation is crucial to address. U.S. vegetable production inherently has various cropping systems with different transplanting seasons, yet the limitations of perishable seedling transportation (refrigeration requirement, weight and volume of soil and trays) forces the propagators to only serve producers within limited distances (< ~500 miles radius). To be able to ship a grafted, healed plant, but with the roots and soil removed (unrooted grafted cuttings) would theoretically allow large numbers of plants to be packed into insulated shipping boxes. This could make feasible overnight, long distance shipping of large numbers of plants used by larger commercial growers, who would then root the cuttings and grow them on to transplant stage. Additionally, the shipping of unrooted grafted cuttings would overcome some quarantine issues and allow shipping to locations where soil importation is restricted. Together with our preceding growth-chamber based study to find the environmental factors affecting the quality and growth of unrooted grafted cuttings, we conducted shipping trials in winter season of 2012/2013. We shipped healed, unrooted watermelon (‘Tri-X-313’ scion on ‘Strongtosa’ hybrid squash rootstock) grafted cuttings from Tucson AZ to Columbus OH, and back again, using overnight air freight, resulting in approximately 48 hours in shipping conditions. Plants were packed in various orientations and the temperature inside the package was recorded using a self-logging thermometer. A small number of grafted cuttings were kept immobile in a dark chamber maintained at a constant temperature of 12°C as a control comparison.  For the trials conducted on 11/27-29 and 2/11-13, plant temperature during the shipment was in a range of 9 – 28°C and 12.5 – 23°C respectively. Upon receipt after two-day shipping, the cuttings showed minor signs of chilling injury and/or physical deformation (bending) but all cuttings were successfully rooted in greenhouse.  Compared with control cuttings stored at 12°C, all visual quality parameters were significantly reduced for the shipped plants. Differences in some, but not all visual quality parameters between control and shipped plants became insignificant after rooting and grow-out (a total of 12 days). However, control plants maintained greater fresh and dry weight even after rooting and grow-out. Further studies are needed to test shipments using various container designs (e.g. inserts to reduce the mechanical stress and insulation methods to reduce the temperature fluctuation) to minimize the impact of long-distance transportation.