The Grafted Heirloom Tomato System for Organic Production In High Tunnels: Are There Advantages In the Absence of Diseases?

Tomato grafting is widely practiced in Asia, the Mediterranean, and large hydroponic greenhouses in North America but has not been field tested in the U.S. to any great extent. It is practiced elsewhere to confer resistance to soil borne diseases and abiotic stressors. It is unclear, however, whether there is a yield advantage or penalty for the utilization of grafting in the absence of soil borne diseases or stressors such as high salinity. In a study using organic practices, conducted at the Center for Environmental Farming Systems (CEFS) in Goldsboro, NC in 2007 and 2008, we compared yields, fruit quality and time to harvest for the heirloom ‘Cherokee Purple' grafted on both ‘Maxifort' and ‘Beaufort' rootstocks with non-grafted and self-grafted (re-attached to own roots, 2008 only) plants. We also compared optimum planting dates of each system in order to maximize the spring/summer production period. In 2007, tunnel plantings were 20 March, 3 April and 19 April (date of field planting). In 2008 tunnel plantings were 4 March, 18 March and 17 April (date of field planting). For planting dates 1 month earlier in the high tunnels, peak harvests were 21 days earlier compared to the field system in both 2007 and 2008.  Overall, minimum, maximum, average, and soil temperatures were higher in the tunnels, but differences were greatest in March and April. Total yields were greater for plants grown in tunnels compared to field-grown plants in both years, with the highest yields for those planted earliest. Yields were greater for plants grafted on commercial rootstocks compared to non-grafted and self-grafted plants (2008 only) across both years. In 2008, the highest yielding treatment was high tunnel plants grafted on ‘Maxifort' rootstock. Overall insect damage was higher in the field compared to the high tunnel system while cat-facing (rough fruit) and blossom-end rot incidence were higher in tunnel crops compared to the field. The yield response to grafting was greater in the tunnel plantings than in the field in 2008. No major soil borne disease problems were present during the study period but there was foliar disease pressure, tomato spotted wilt virus and gray leaf spot (Stemphylium spp.). In 2008, both gray leaf spot incidence and tomato spotted wilt virus was greater in the field than the tunnel plantings.