2017 ASHS Annual Conference

We set out to determine the separate and combined effects of a microbial crop biostimulant (MCBS) and grafting on early growth of greenhouse tomato. The experiment was repeated three times (June-July 2015 and 2016, and November 2016-January 2017) at the OARDC in Wooster, Ohio. Each run lasted five weeks from transplanting to completion of data collection and employed a split plot design with four replications. A commercial MCBS (‘Environoc 401’) containing multiple species of nitrogen-fixing and phosphorous-solubilizing bacteria was applied to tomato seedlings grafted onto three different rootstocks (‘SuperNatural’, ‘Maxifort’, and ‘Estamino’) and the ungrafted scion ‘BHN 589’. Non-inoculated plants were used as a second control. Grafted plants were purchased from Plug Connection (Vista, California) in Runs 1 and 2 and prepared at OARDC in Run 3. Grafted and ungrafted plants (6-8 weeks old with 4 true leaves) were transplanted to 15-cm diameter plastic pots filled with Promix (Premier Horticulture, Québec, Canada) medium. Half of all plants were drenched with 50 ml of microbial solution around the stem and beneath the canopy at 3, 5, and 7 days after transplanting. Non-inoculated plants received only the same amount of water. Each drench contained 3.3 x 10⁶ colony forming units (CFUs), giving a total of 10⁷ CFUs per plant. Plant height, stem diameter at 5 cm above the soil, total branch length, and total number of opened flowers and fruit were measured weekly in all runs, while percent leaf coverage and root fresh and dry biomass were only measured in Runs 1 and 3, respectively. Generally, inoculated plants were statistically or numerically taller, and had greater total branch length and more opened flowers and fruit than non-inoculated plants at each weekly measurement in all runs. Stem diameter was greater in inoculated plants only in Run 2. Regarding grafting effects, ‘BHN 589’-‘SuperNatural’ and ‘BHN 589’-‘Maxifort’ plants were taller and had larger total branch length than ungrafted plants in the first two runs. ‘BHN 589’-‘Estamino’ plants were similar in all vegetative variables to ungrafted plants but had the largest number of opened flowers and fruit in all runs. Most additive effects (grafting and inoculation effects used in combination > arithmetic sum of grafting and inoculation effects) were observed starting at two weeks after transplanting. The data indicate that grafting and microbial crop biostimulants can be used alone or in combination to enhance early growth in greenhouse-grown tomato.