Management of tomato bacterial spot in the field by foliar applications of bacteriophages and SAR inducers

Various combinations of the harpin protein, acibenzolar-S-methyl, and bacteriophages were compared for controlling tomato bacterial spot in field experiments. Harpin protein and acibenzolar-S-methyl were applied every 14 days beginning twice before transplanting and then an additional four applications throughout the season. Formulated bacteriophages were applied prior to inoculation followed by twice a week at dusk. A standard bactericide treatment, consisting of copper hydroxide plus mancozeb, was applied once prior to inoculation and then every 7 days, while untreated plants served as an untreated control. Experiments were conducted in north and central Florida fields during fall 2001, spring 2002, and fall 2002. In three consecutive seasons, acibenzolar-S-methyl applied in combination with bacteriophage or bacteriophage and harpin significantly reduced bacterial spot compared with the other treatments. However, it did not significantly affect the total yield compared with the standard or untreated control. Application of host-specific bacteriophages was effective against the bacterial spot pathogen in all three experiments, providing better disease control than copper-mancozeb or untreated control. When results of the disease severity assessments or harvested yield from the bacteriophage-treated plots were grouped and compared with the results of the corresponding nonbacteriophage group, the former provided significantly better disease control and yield of total marketable fruit

A leaf spot and blight of greenhouse tomato seedlings incited by a Herbaspirillum sp.

A leaf spot and blighting were observed on leaves of tomato transplants from a producer in Florida in 2001 and 2002. A nonfluorescent bacterium was isolated consistently from affected tissue. The typical bacterium was a gram negative, strictly aerobic, slightly curved rod with one or two flagella. Sequence analysis of the 16S rRNA indicated that two representative strains, F1 and SE1, had greater than 99% nucleotide sequence identity with Herbaspirillum huttiense and H. rubrisubalbicans. The cellular fatty acid composition of the total of 16 tomato strains was very similar to H. huttiense and H. rubrisubalbicans. Based on carbon utilization, six of nine strains tested with the Biolog system were identified as Herbaspirillum spp. The tomato strains were oxidase positive and grew at 40 degrees C, but were negative for levan production, pectate hydrolysis, and arginine dihydrolase activity. Based upon this polyphasic analysis, we concluded that the strains were most closely related to H. huttiense, although placement in this species would require further analyses. However, the tomato strains and H. rubrisubalbicans, but not H. huttiense, caused confluent necrosis when infiltrated at high concentrations into tomato leaves and were able to produce leaf spot symptoms on inoculated tomato seedlings in the greenhouse. Using pulsed-field gel electrophoresis, we determined that there was considerable variability between the strains collected in 2001 and 2002

Improved efficacy of newly formulated bacteriophages for management of bacterial spot on tomato

Bacteriophages are currently used as an alternative method for controlling bacterial spot disease on tomato incited by Xanthomonas campestris pv. vesicatoria. However, the efficacy of phage is greatly reduced due to its short residual activity on plant foliage. Three formulations that significantly increased phage longevity on the plant surface were tested in field and greenhouse trials: (i) PCF, 0.5% pregelatinized corn flour (PCF) + 0.5% sucrose; (ii) Casecrete, 0.5% Casecrete NH-400 + 0.5% sucrose + 0.25% PCF; and (iii) skim milk, 0.75% powdered skim milk + 0.5% sucrose. In greenhouse experiments, the nonformulated, PCF-, Casecrete-, and skim milk-formulated phage mixtures reduced disease severity on plants compared with the control by 1, 30, 51, and 62%, respectively. In three consecutive field trials, nonformulated phage caused 15, 20, and 9% reduction in disease on treated plants compared with untreated control plants, whereas plants treated with PCF- and Casecrete-formulated phage had 27, 32, and 12% and 30, 43, and 24% disease reduction, respectively. Plants receiving copper-mancozeb treatments were included in two field trials and had a 20% decrease in disease in the first trial and a 13% increase in the second one. Skim milk-formulated phage was tested only once and caused an 18% disease reduction. PCF-formulated phage was more effective when applied in the evening than in the morning, reducing disease on plants by 27 and 13%, respectively. The Casecrete-formulated phage populations were over 1,000-fold higher than the nonformulated phage populations 36 h after phage application

Integration of biological control agents and systemic acquired resistance inducers against bacterial spot on tomato

Two strains of plant growth-promoting rhizobacteria, two systemic acquired resistance inducers (harpin and acibenzolar-S-methyl), host-specific unformulated bacteriophages, and two antagonistic bacteria were evaluated for control of tomato bacterial spot incited by Xanthomonas campestris pv. vesicatoria in greenhouse experiments. Untreated plants and plants treated with copper hydroxide were used as controls. The plant growth-promoting rhizobacteria or a tap water control were applied as a drench to the potting mix containing the seedlings, while the other treatments were applied to the foliage using a handheld sprayer. The plant growth-promoting rhizobacteria strains, when applied alone or in combination with other treatments, had no significant effect on bacterial spot intensity. Messenger and the antagonistic bacterial strains, when applied alone, had negligible effects on disease intensity. Unformulated phage or copper bactericide applications were inconsistent in performance under greenhouse conditions against bacterial spot. Although acibenzolar-S-methyl completely prevented occurrence of typical symptoms of the disease, necrotic spots typical of a hypersensitive reaction (HR) were observed on plants treated with acibenzolar-S-methyl alone. Electrolyte leakage and population dynamics experiments confirmed that acibenzolar-S-methyl-treated plants responded to inoculation by eliciting an HR. Application of bacteriophages in combination with acibenzolar-S-methyl suppressed a visible HR and provided excellent disease control. Although we were unable to quantify populations of the bacterium on the leaf surface, indirectly we determined that bacteriophages specific to the target bacterium reduced populations of a tomato race 3 strain of the pathogen on the leaf surface of acibenzolar-S-methyl-treated plants to levels that did not induce a visible HR. Integrated use of acibenzolar-S-m ethyl and phages may complement each other as an alternative management strategy against bacterial spot on tomato

Using Facebook Advertising to Connect with Extension Audiences

There is considerable interest in using social media to reach Extension audiences. The study\u27s main objective was to assess the effectiveness of Facebook promotion and event advertising on creating new client contacts as measured by Likes. The results show the fan base for each county increased slowly prior to and following the Facebook ad, while it increased more rapidly during the advertisement period. Thus, Facebook advertising appears to be an effective tool to increase awareness of Extension Facebook pages. Extension professionals should consider investing in Facebook advertising to expand their fan base

DDIS and Diagnostic Networks: Building Partnerships for Safer Trade

Movement of agricultural products is one of the primary means of introduction of new diseases and pests. The agricultural inspections that take place at the ports of entry target higher-risk commodities, but inspect only an estimated 1-2% of total shipments. According to the Department of Commerce (U.S. Census Bureau, Foreign Trade Statistics), U.S. agricultural exports increased 26.72% from 2006 to 2007 and imports increased 10.12% over the same period. Imports from the Caribbean alone totaled $451,098,000 in 2007. The economic impact of trade cannot be underestimated, and neither should the possibilities for newly introduced pests. Early detection and accurate diagnosis of diseases and other pests is vital to any eradication efforts. In addition, communication between countries regarding pest detections increases awareness and allows for targeted survey programs. These efforts cannot happen without robust diagnostic capability and communication systems in place. The National Plant Diagnostic Network (NPDN) was developed by the USDA-CSREES in 2002 to quickly detect and accurately diagnose plant pests and initiate communications, and has become the standard for creation of similar systems such as the International Plant Diagnostic Network (IPDN) and the Caribbean Region Diagnostic Network (CRDN). The CRDN represents this effort in the Caribbean basin, tying diagnostic laboratories and personnel together via technical training and the Digital Diagnostic and Identification System (DDIS). Participants in this network utilize a secure online system to log and share diagnostic data in a confidential environment. This coupled with technical training increases the availability of expertise in the region, and helps to establish a baseline of pest knowledge that will support phytosanitary and trade decisions

Development of an Integrated Management of Tomato Bacterial Spot - A Strategy That Lives in Practice

Tomato bacterial spot, caused by Xanthomonas spp. complex, is a constant threat to tomato (Solanum lycopersicum) commercial production, but is especially severe in Florida and the southeastern US when weather conditions become conducive for disease development. In an effort to develop more sustainable strategies for reducing severity of the disease, we investigated various combinations of PGPR strains, bacterial antagonists, bacteriophages and SAR inducers (harpin, acibenzolar-S-methyl) in greenhouse and field trials. The idea was to search for alternative treatments that could be integrated with conventional practices, in order to improve disease control and yield responses. After screening single treatments and their combinations for efficacy in a series of greenhouse experiments, acibenzolar-S-methyl (ASM) and phage treatment provided the most promising results. In field trials, carried out in three consecutive seasons, ASM significantly reduced disease severity compared to the untreated control. However, the combination of ASM and formulated host-specific phages provided an additional reduction in disease pressure and resulted in more efficient foliar disease control than ASM, phage, or copper-macozeb alone. Integrated application of phages, ASM and other practices is currently widely used in greenhouses and production fields in Florida as a part of a standard integrated management strategy for tomato bacterial spot control. http://www.actahort.org/books/808/index.ht

Bacterial spot management on tomatoes

Bacterial spot of tomato, incited by Xanthomonas campestris pv. vesicatoria, is a perennial problem in commercial fields in Florida. Various strategies have been used to control this disease including applying copper bactericides, antibiotics and various other chemicals. Although copper compounds and streptomycin were initially effective in disease control, the presence of strains resistant to these compounds has reduced the efficacy of these compounds. Systemic acquired resistance (SAR) compounds have become a popular alternative to conventional bactericides. One that has shown promise for bacterial spot control is acibenzolar-S-methyl (ASM). Other SAR compounds tested have had variable results. A second strategy which has excellent promise is the application of bacteriophages specific to the bacterial spot pathogen. Following the development of an application strategy, which included a modification in formulation and the timing of bacteriophage applications, bacteriophages were improved in efficacy. We have conducted studies using various combinations of bacteriophages and SAR compounds. In three consecutive seasons, ASM applied in combination with bacteriophage significantly reduced bacterial spot compared to the other treatments. Application of host-specific bacteriophages was effective against the bacterial spot pathogen in all experiments, providing better disease control than copper-mancozeb or untreated control. When results of the disease severity assessments or harvested yield from the bacteriophage-treated plots were grouped and compared to the results of the corresponding non-bacteriophage group, the former provided significantly better disease control and yield of total marketable fruits. Although ASM applications controlled bacterial spot,yield was not significantly improved compared to plots receiving no ASM applications. Bacteriophages offer an excellent alternative to conventional disease control strategies and combining it with ASM shows promise