Low soil phosphorus (P) availability is a notable limitation for legume nodulation, nitrogen fixation and yield, and it is therefore important to improve legume growth under P-deficient conditions. This study aimed to determine the effects of coinoculation with Rhizobium and plant growth promoting rhizobacter (PGPR) on the nitrogen fixation and nutrient uptake of white clover (Trifolium repens) in a P-deficient soil. White clover plants were inoculated with one of the two Rhizobium strains CHB1120 and CHB1121 alone or coinoculated with either of the Rhizobium strains and one of the two PGPR strains, Bacillus aryabhattai strain Sb and Azotobacter vinelandii strain G31. White clover inoculated with either CHB1120 or CHB1121 alone and coinoculated with one of the two Rhizobium strains and the PGPR significantly enhanced nodule numbers compared with the non-inoculated control. The coinoculation of either CHB1120 or CHB1121 and Sb showed a significantly greater level of nitrogenase than the single inoculation of CHB1120 or CHB1121. In addition, the single inoculation of CHB1120 or CHB1121 and their coinoculation with PGPR significantly increased nitrogen contents in both shoots and roots under P-deficient conditions. The coinoculation of CHB1121 and G31 showed the greatest N content in shoots. Moreover, the single inoculation of the two Rhizobium strains and their coinoculation with G31 and Sb significantly increased the K, Ca, and Mg contents in shoots compared with the non-inoculated control. In summary, the PGPR used in this study can enhance the symbiotic potential of rhizobia under low P conditions.

Acibenzolar-S-methyl (ASM), a plant activator known to induce systemic acquired resistance, has demonstrated an ability to manage a number of plant diseases, including bacterial spot on tomato caused by four distinct Xanthomonas spp. The aim of this study was to evaluate application rate and frequency of ASM in order to optimize field efficacy against bacterial spot in Florida, while minimizing its impact on marketable yields. ASM was applied biweekly (once every 2 weeks) as a foliar spray at a constant concentration of 12.9, 64.5, and 129 μM throughout four field experiments during 2007–08. A standard copper program and an untreated control were also included. Overall, biweekly applications of ASM did not significantly reduce disease development or the final disease severity of bacterial spot compared with the copper-mancozeb standard or the untreated control. Only one experiment showed a significant reduction in the final disease severity on plants treated with ASM at 129 μM compared with the untreated control. Three additional field trials conducted during 2009–10 to evaluate the effects of weekly and biweekly applications of ASM at concentrations of 30.3 to 200 μM found that weekly applications provided significantly better disease control than biweekly applications. The tomato yields were not statistically improved with the use of ASM relative to the untreated control and standard copper program. Weekly ASM applications at rates as low as 75 μM (equivalent to 1.58 g a.i./ha in 100 liters of water or 0.21 oz. a.i./acre in 100 gallons of water) to 200 μM (equivalent to 4.20 g a.i./ha in 100 liters of water or 0.56 oz. a.i./acre in 100 gallons of water) were statistically equivalent in managing bacterial spot of tomato without significantly reducing yield compared with the untreated control.

Sclerotium rolfsii is a soilborne fungus that causes southern blight on a wide range of plants in tropical and subtropical regions of the world. Eighty-four isolates collected from Florida, Georgia, Louisiana, South Carolina, Texas, and Virginia were paired and assigned to 23 mycelial compatibility groups (MCGs), of which 11 MCGs consisted of a single isolate. Isolates within an MCG typically originated from different hosts and different geographical areas, with the exception of MCG 11. In all, 13 of the 15 isolates in MCG 11 originated from peanut in Georgia and Florida, while the other 2 isolates originated from potato in Virginia and from the ornamental Barlaeria cristata in Florida. Significant differences in the size and number of sclerotia produced in vitro existed between isolates from peanut and other hosts. Nineteen isolates representative of the most common MCGs (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, and 18) were tested for pathogenicity on tomato, pepper, and peanut. All isolates were pathogenic on all hosts but virulence differed significantly among isolates. Isolates collected from peanut were the most virulent on all three hosts compared with isolates collected from tomato and pepper. ‘Georgia Green’ peanut was more susceptible to peanut isolates from Georgia than to the other tested isolates. Of the two tomato entries, the commercial tomato ‘Tygress’ was less susceptible than the previously reported resistant breeding line 5635M to many of the S. rolfsii isolates tested, with the exception of the peanut isolates collected from Georgia. These initial findings suggest that considerable variation exists among S. rolfsii isolates throughout the southern United States, with some indications of specialization for the isolates collected from peanut.

The overuse of chemical fertilizers deteriorates soil quality, and the application of organic amendments has been proposed as an alternative to mineral fertilizers. This study aimed to investigate the effects of organic amendment types on soil properties, the soil microbiome, and tomato growth. Tomato seedlings were grown in soils applied with ten fertilizer treatments, including a no fertilization control, a chemical fertilization control, and eight organic amendment treatments. Compared with the chemical fertilization treatment, the application of manure compost significantly increased the shoot dry weight of tomato plants. In addition, manure compost and tea seed meal remarkably increased soil organic matter (SOM) in comparison with the no fertilization and chemical fertilization treatments. Moreover, manure compost significantly increased soil-exchangeable K and Mg. The application of neem cake and manure compost significantly increased both bacterial diversity and richness. The relative abundance of Lysinibacillus was significantly positively related to the shoot and total dry weights of tomato plants, and its relative abundance was positively influenced by SOM and soil-exchangeable K. Overall, the manure compost used in this study can increase SOM, soil-exchangeable K and Mg, and the relative abundance of Lysinibacillus, consequently promoting tomato growth.