Bonnie H. Ownley, Roberto Pereira, Danesha Seth, Choo Hamilton, and Mary Dee

There were significant increases in growth of ‘Mountain Spring’ tomato plants seeded in potting mix amended with the 2.5% bacterial growth medium carrier control and bacterial treatments LS255, LS256, and LS257. The growth increases were pronounced in the early part of the season, which resulted in these treatments being large enough for transplant significantly earlier than other controls and treatments. These treatments also flowered earlier than other treatments. However, growth promotion and early flowering with these bacterial treatments were not greater than with the 2.5% carrier control. This suggests that the carrier control was in large part responsible for the growth promotion and subsequent early flowering observed.

Bacillus subtilis GB03 is a beneficial bacterium with activity against soilborne fungal root pathogens. Treatment of seed with GB03 has been reported to promote growth and increase yields in several crop species. The objective of this study was to determine the effect of applying GB03 in combination with other beneficial bacteria to potting mix at seeding on early growth and flowering of tomato.

Tomato seeds (Mountain Spring) were planted in Speedling potting mix amended with six bacterial treatments and three controls on March 30, 2000. Seedlings were produced in 128-cell styrofoam float trays placed on a greenhouse bench. The bacterial treatments were LS290, LS213, LS254, LS255, LS256, and LS257. Each treatment included Bacillus subtilis GB03 and one other beneficial bacterium in a growth medium carrier. The controls were untreated plants, and plants treated with 1.0 and 2.5% bacterial growth medium carrier. Treatment LS290 was mixed in 1.0% carrier while all other bacterial treatments were applied with 2.5% carrier.

Tomato seedlings were transplanted to the field when the mean shoot height of a specific treatment was approximately 20 cm (8 in). On May 8, the 2.5% carrier control, and bacterial treatments LS255, LS256, and LS257 were transplanted to the field. On May 19, the 1% carrier control, and bacterial treatments LS290 and LS213 were transplanted. On May 26, the untreated control was transplanted to the field. The seedlings were planted in five blocks (replicates) and treatments were arranged in a randomized complete block design. Each treatment plot consisted of one 17-ft mounded row with red plastic mulch and trickle irrigation. Plots were not fumigated. There were 12 plants per plot and treatment plots were spaced 6 ft apart. Fertilizer (10-10-10) was applied prior to planting at 400 lb/ acre. Fungicides and insecticides were applied as needed.

Growth measurements of tomato plants were recorded on April 25 (27 days after seeding) and June 8 (70 days after seeding). Measurements included number of leaves, shoot height, shoot fresh weight, root length, and root fresh weight. The percentage of plants in each treatment that were blooming was determined at 71, 74, 77, 81, and 83 days after seeding.

Growth measurements. At 27 days after seeding, there were significant differences between treatments for number of leaves, shoot height, fresh shoot weight, root length, and fresh root weight (Table 1). These growth variables were greatest with the 2.5% carrier control and treatment LS257. An intermediate growth response was observed with the 1% carrier control and treatments LS290, LS213, LS254, LS255, and LS256. The untreated control had significantly lower values for the measured growth variables than all other treatments.

Table 1. Effect of treatment on growth of tomato plants at 27 days after seeding.

At 70 days after seeding, there were significant differences between treatments for all of the measured growth variables (Table 2). The untreated control plants were significantly smaller than other treatments. The 2.5% carrier control and treatments LS255, LS256, and LS257 were significantly larger than other treatments. These were also the treatments that were transplanted to the field on the earliest date due to greater growth. The 1% carrier control and treatments LS290, LS213, and LS254 were intermediate in growth response at 70 days after seeding.

Table 2. Effect of treatment on growth of tomato plants at 70 days after seeding.

Flowering. There were significant differences between treatments in percentage of plants blooming at 71, 74, 77, and 81 days after seeding (Table 3). Similar to the growth response data, the 2.5% carrier control and treatments LS255, LS256, and LS257 had the highest percentages of flowering plants on the first four evaluation dates. On day 83, there were no significant differences between treatments and controls for percentage of plants blooming.

Table 3. Effect of treatment on percentage of tomato plants flowering at 71, 74, 77, 81, and 83 days after seeding.