Fruit Yield and Composition as Functions of Grafting and Irrigation Regimen in an Organic High Tunnel System

Grafting, rootstock (RS) and irrigation regimen effects on the yield and composition of tomato (Solanum lycopersicon L.) fruit taken from organic high tunnel plots were documented in 2009 and 2010. Four-five week old scion (S; 'Cherokee Purple') seedlings were grafted, using the cleft method, to seedlings of two experimental rootstocks (314, 338) developed at OARDC. Ungrafted S control plants were also prepared. Grafted plants produced three-four new leaves during the healing phase and were scored and sorted according to quality and vigor. Thereafter, in late April of each year, a uniform subset of high quality plants were set into single-row, raised-bed, drip-irrigated, 6.5-m² plots containing 9 plants of a single genotype. Plots were replicated four times and arranged in a randomized complete block design within a 9 m x 24 m single poly-layer high tunnel. All plots were covered at the soil line by black, semi-permeable polyvinyl fabric and supplied by a standard drip irrigation line plumbed to operate independently from others within the different irrigation regimen. After being set, plants were pruned to the third node and trellised using a Florida stake and weave system. All plots were irrigated concurrently for the first 30-40 days after establishment, followed by the onset of flowering. Thereafter, irrigation events occurred every three (‘standard’) or six (‘reduced’) days depending on regimen with approximately 6.4 mm water delivered per event regardless of regimen. Irrigation in ‘standard’ plots totaled approximately 12 cm over the final 60 d and 17 cm over the final 90 d of the study in 2009 and 2010, respectively. Total and marketable fruit yield (number, weight) were recorded at weekly-biweekly intervals nine times in 2009 and eleven times in 2010 before fruit production and ripening stalled. Total and marketable yield were greater in grafted than ungrafted ‘standard’ plots in both years and in ‘reduced’ plots in 2009. Yield in ‘reduced’ plots was unaffected by grafting in 2010, possibly due to two instances of water infiltration from rainfall-fed surface flow. Fruit Brix values were greater in grafted plants under both irrigation regimens in 2009 and in ‘standard’ plots in 2010 but were lower in ‘reduced’ plots in 2010. Brix values tended to increase through time in all treatments in both years. Fruit pH was unaffected by either grafting or irrigation regimen. Overall, the data suggest that water relations and fruiting characteristics may differ between grafted and ungrafted tomato plants.