Biorational approaches for management of bacterial wilt and bacterial spot on tomato

Biorational approaches for management of bacterial wilt and bacterial spot on tomato

Objectives/Performance Targets

1. To develop strategies in integrated management of bacterial wilt:

a. Evaluate the efficacy and application methods of new biofumigants and reduced risk compounds in control of R. solanacearum on tomato under greenhouse and field conditions.

b. Determine efficacy of the SAR inducer, Actigard, in reducing bacterial wilt on susceptible tomato cultivars under field conditions at different inoculum levels, and evaluate integrated effectiveness and economics of field application of Actigard, biofumigant (thymol), and commercial tolerant or resistant tomato genotype (FL 7514, BHN 669) in the management of bacterial wilt.

c. Using the data obtained in objectives 1a and 1b to develop and implement best management strategies for bacterial wilt on tomato in naturally infested commercial tomato fields. On-farm research and demonstrations will be conducted in collaboration with growers and extension agents in north Florida and southern Georgia.

2. To optimize integrated management of bacterial spot with the SAR inducer Actigard, PGPRs and bacteriophages.

a. Determine if lower rates of Actigard can be applied to enhance disease control without affecting tomato yield and identify resistant lines to determine if they respond to PGPRs.

b. Determine the effects of modified application strategies of the SAR inducer (Actigard) and PGPRs in combination with bacteriophages.

c. Combine the best strategies in 2a and 2b for management of bacterial spot in field experiments to achieve maximum reduction of the disease and copper bactericide application. On-farm research and demonstration will be conducted in north Florida and southern Georgia and economic benefits will be analyzed.

3. To determine, through Cost Benefit Analysis of each field trial, the management strategies yielding the greatest financial returns to the grower.

Accomplishments/Milestones

Two experiments were conducted in fall 2008. The first, designated Experiment A (Table 1), was to look at using reduced rates of Actigard with susceptible and bacterial spot-tolerant genotypes for control of bacterial spot of tomato. The second experiment, designated experiment B (Table 2), was a reduced risk experiment to look at the role of plant growth promoting rhizobacteria (PGPR) and bacteriophage (supplied by OmniLytics. Inc., Salt Lake City, UT) for control of bacterial spot of tomato. On August 12, 2008 tomato plants were planted in rows covered with white plastic mulch spaced 6 feet apart and plant within rows spaced 20 inches (50 cm) apart. The middle two of each plot plants were sprayed on August 30, 2008 with a suspension of Xanthomonas perforans strain Xp621 at 108 CFU/ml, amended with 0.025% Silwet L-77. The plants were first sprayed from August 25 through October 27, 2008. The applications were conducted using Solo backpack sprayer. The treatments applied are listed in Tables 1 and 2. The experiments were set up in a completely randomized block design with four replicates per treatment and 15 plants per replicate. The plants were evaluated for disease intensity by estimating percent of leaf area affected by bacterial spot on September 19, October 2, 16, and 27. Disease ratings were performed using the Horsfall-Barrett scale which is based on the percent of foliar area affected (1 = 0%; 2 = 0-3%; 3 = 3-6%; 4 = 6-12%; 5 = 12-25%; 6 = 25-50%; up to 12 = 100%). The data from disease assessment and harvest were analyzed using SAS PROC GLM and Waller test (Table 3 – 6).

In the reduced rate experiment 1/10 X rate of Actigard effectively controlled bacterial spot on the tolerant line (8314) compared to the standard Kocide + Mancozeb treatment early in the experiment (Table 3); however, as the experiment continued, Actigard provided no improved disease control. The tolerant genotype had significantly less disease than the susceptible genotype (Bella Rosa) at the end of the experiment. In general by the end of the experiment none of the treatments in the tolerant variety were significantly different. Yields for all treatments were not significantly different (Table 5).

In the reduced risk experiment (Table 4) twice weekly applications of bacteriophage provided significantly better disease control than the standard copper-mancozeb treatment at the end of the season. Yield differences were not observed for any of the treatments.

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