Introduction
We previously reported a new Pseudomonas species, P. capsici, that caused typical bacterial symptoms on pepper foliage (leaf spots and blights) under greenhouse conditions (Zhao et al., 2021). The pathogen was capable of causing fruit lesions that turned necrotic and eventually resulted in fruit rotting in pepper.
Pseudomonas capsici is closely related to P. cichorii, and strains from pepper could also rot potatoes (Zhao et al., 2021). In this research, we aimed to investigate whether biological and chemical antimicrobial products would reduce disease severity under field conditions.
Material and Methods
Biological and chemical antimicrobial products were evaluated in a spray program for their efficacy in managing bacterial leaf spot caused by P. capsici. Bell pepper ‘Aristotle’ was transplanted into two row-beds covered with 18-in. white plastic mulch on April 3. Beds were on 6-ft centers with 1-ft plant spacing within rows. Plots were 20 ft long with 10 ft planted borders between plots.
The trial was arranged in a randomized complete block design. Four plots with 40 plants per plot (20 plants per row) were used for each treatment. Plots were drip irrigated as necessary. Fertility and insecticide treatments were applied according to the University of Georgia Extension recommendations. Natural inoculum was relied upon for initial infection.
Treatments were applied using a backpack sprayer calibrated to deliver 36 gallons/acre at 48 psi through TX-18 hollow-cone nozzles. Treatment applications were made on Sept. 9, 17, 23, and 30, and Oct. 14 and 21. Disease severity was assessed on Oct. 13, 20, and 27 as percentage leaf area with symptoms per plot. Area under disease progress curve (AUDPC) was calculated using disease severity ratings from the four assessment periods.
Data were analyzed in the software ARM (Gylling Data Management, Brookings, SD) using Fisher’s protected LSD test at P ≤ 0.05. The mean rainfall received during September and October was 3.5 in. and 5.8 in., respectively. The average high and low temperatures for the month of September were 92 °F and 72 °F, respectively, and for the month of October were 85 °F and 68 °F, respectively.
Results and Discussion
Bacterial leaf spot symptoms were first observed on Oct. 13, with disease severity significantly higher in the nontreated control plots (68.8%) than in the biological or chemical-treated plots. However, significant differences among the treated plots were not observed. Disease progressed gradually over a period of 3 weeks, and the final severity rating was taken on Oct. 27.
Based on final disease severity and AUDPC, significant differences among the biological and chemical products were not observed except for the Kocide 3000 and Manzate Pro-Stik spray program, which had a significantly lower AUDPC value compared to other treatments. Phytotoxicity was not observed with any of the products evaluated.
| Treatment and rate of product per acre | Application no.z | Initial disease severity (%) on Oct. 13y | Final disease severity (%) on Oct. 27y | AUDPCx |
|---|---|---|---|---|
| Serenade ASO 4 qt | 1–6 | 38.5 bx | 73.8 b | 849.4 b |
| Serifel 16 fl oz | 1–6 | 26.2 b | 75.2 b | 836.8 b |
| Nordox 1 lb | 1–6 | 25.8 b | 66.3 b | 660.0 b |
| LifeGard 2 fl oz | 1–6 | 25.0 b | 63.8 b | 676.8 b |
| Double Nickel 6 qt | 1–6 | 38.2 b | 75.0 b | 763.2 b |
| Stargus 4 fl oz | 1–6 | 37.5 b | 67.5 b | 680.0 b |
| Oxidate 5.0 0.5 fl oz/gallon | 1–6 | 27.5 b | 72.5 b | 826.5 b |
| Forticept 1.28 fl oz/gallon | 1–6 | 32.8 b | 78.8 b | 722.5 b |
| Regalia 4 qt | 1–6 | 36.5 b | 78.2 b | 865.6 b |
| Vacciplant 22 fl oz | 1–6 | 36.3 b | 62.0 b | 669.4 bc |
| Howler 3.5 lb | 1–6 | 48.5 ab | 78.2 ab | 865.5 b |
| Kocide 3000 1.5 lb Manzate Pro-Stik 2 lb | 1–6 | 12.5 b | 52.5 bc | 485.5 c |
| Forticept 0.9 fl oz/gallon Oxidate 5.0 0.5 fl oz/gallon | 1–6 | 45.0 b | 78.8 b | 926.8 b |
| Nontreated check | — | 54.8 a | 100.0 a | 1438.2 a |
| P-values | 0.0002 | 0.0217 | 0.0044 | |
| Means followed by the same letter within each column are not significantly different according to Fisher’s protected LSD test at P ≤ 0.05. zApplication dates: 1 = Sept. 9, 2 = Sept. 17, 3 = Sept. 23, 4 = Sept. 30, 5 = Oct. 14, and 6 = Oct. 21. yDisease severity was rated on a 0 to 100 scale (0 = no infection and 100 = 100% of leaf area infection) on Oct. 13, 20, and 27. xAUDPC was calculated from ratings taken on Oct. 13, 20, and 27. | ||||
Reference
Zhao, M., Koirala, S., Chen, H.-C., Gitaitis, R., Kvitko, B., & Dutta, B. (2021). Pseudomonas capsici sp. nov., a plant-pathogenic bacterium isolated from pepper leaf in Georgia, USA. Inter. J. System. Evolutionary Microbio., 71(8), 004971. https://doi.org/10.1099/ijsem.0.004971
