Yield and Fruit Quality of Grafted Tomato Plants in Organically Managed High Tunnels Containing Zones with Different Compost Application Histories

Documenting the performance of grafted plants under a wide range of conditions will allow many to benefit more reliably from grafting as an emerging technology in the U.S. The goal of this research was to document grafted and ungrafted plant performance in organically-managed high tunnels containing zones with different compost application histories, using fruit yield and quality as primary indicators. Studies were conducted in 2012, 2013, and 2015 using a split-plot design with compost application history as the main plot and grafting combination as the subplot. Two compost treatments were included, one with annual compost application since 2003 and the other with no soil amendment since 2002. Two commercial rootstocks (‘Maxifort’ and ‘Emperador’) and one experimental line (‘338’) grafted to the same scion (‘Moskvich’) and ungrafted ‘Moskvich’ controls were employed in 2012 and 2013; two commercial rootstocks (‘Maxifort’ and ‘Estamino’) grafted to (‘BHN589’) and ungrafted ‘BHN589’ controls were used in 2015. Ripe fruits were harvested weekly 8-9 times to measure weight and number of total fruit, marketable fruit, and fruit showing blotchy ripening, and a subset of fruits was analyzed for Brix, pH and titratable acidity (TA). Consistent yield trends were observed across the 3 years. Yield was greater in plots with a history of compost application and in plots containing grafted plants. Average marketable fruit weight was not different among grafting and compost treatments in 2012 and 2013, but it was larger for grafted versus ungrafted plants in 2015. Likewise, percent marketable yield was higher in compost-amended versus non-amended and grafted versus ungrafted plots in 2013 and 2015, perhaps because compost application and grafting were associated with declines in the percent of fruit showing blotchy ripening in both years. However, Brix tended to be lower in fruit from grafted versus ungrafted plants across all years, while pH was higher in fruit from grafted versus ungrafted plants in 2012 and 2015. TA was not affected by grafting, but it was higher with compost application in 2012. The compost-grafting interaction was not significant for most variables. We conclude that compost application and grafting can increase fruit marketable yield and alter some fruit traits, including Brix and blotchy ripening. Grafted plants have a higher yield potential than ungrafted ones regardless of whether compost was applied to soils previously or not.