2017 ASHS Annual Conference

High tunnel production is generally used for season extension through mitigation of extreme low temperature. Mild winters in the subtropics reduce the need for this type of season extension. However, high tunnels may provide season extension in other ways, such as reducing heat in summer production by application of shade cloth, and avoiding exposure to rain and prolonged dew, which are common in the humid subtropics and favor disease development. Tomato grafting has also shown potential to increase yields due to enhanced plant vigor and reduced biotic and abiotic stress. An organic tomato trial was conducted in Citra, FL during the spring 2016 season to determine the impacts of open field and high tunnel production systems and grafting on plant health and crop performance. ‘Garden Gem’ and ‘Tribute’ tomatoes were each grown grafted onto ‘Multifort’ with non-grafted tomato plants as the control. A split-split plot design with three replications was used (production system as the whole plot factor, tomato cultivar as the subplot factor, grafting as the sub-subplot factor). Significant fruit yield improvement by high tunnel production was observed in both cultivars. On average, high tunnel production increased total fruit yield by 43% over the open field system and increased the percent marketable yield from 49% to 65%. The high tunnel system thereby increased the total marketable yield by 87% over the open field system. Biometric data correlated with yield data, as plant height throughout the season and final biomass were found to be greater in the high tunnel system. Horsfall-Barratt disease ratings showed that the high tunnel had significantly less disease pressure (predominantly early blight caused by Alternaria solani) throughout the growing season. This resulted in an extended harvest period of 3 weeks in the high tunnel system, contributing considerably to the yield differences between the two production systems. Grafting increased total yield by 34% and increased marketable yield by 42%, accompanied by increased plant height and stem diameter throughout the season as well as greater final biomass in grafted tomato plants. Grafting also significantly reduced root galling and root-knot nematode (Meloidogyne spp.) population in the soil. Interestingly, a reduction in the early blight severity was also exhibited in grafted plants compared with the non-grafted plants. These results demonstrate the benefits of high tunnel systems and grafting for organic tomato production in the subtropics.