CONICET | Buscador de Institutos y Recursos Humanos

Plants are continually exposed to external factors (both biotic and abiotic) throughout their life cycle, which can affect their development. The use of microorganisms, or their metabolites, to protect plants from potential pathogen attacks is an area of growing interest. Xanthomonas vesicatoria Xcv Bv5-4a is the causal agent of bacterial spot disease in tomatoes and peppers. The symptoms of this disease are small, irregular, dark, watery lesions on the leaves and early flower drop. Implementing good cultivation practices is essential to reduce the risk of diseases and subsequent economic losses. Therefore, having high-quality seeds is crucial for initiating successful production. Tailocins are antimicrobial agents capable of inhibiting the growth of other microorganisms as a competitive mechanism. P. fluorescens SF4c produces two types of tailocins, R1 and R2. Previously in our laboratory, we constructed mutants producing a single tailocin (R1 or R2). R2-tailocin showed antimicrobial activity against strain Xcv Bv5-4a. The aim of this study was to evaluate the effect of SF4c-tailocins on tomato seeds and their impact on strain Xcv Bv5-4a infection. First, tomato seeds were disinfected. Then, the following treatments were applied on seeds: R1/R2 tailocins, R1 tailocin, R2 tailocin and TN50 buffer (control). The seeds were allowed to dry and incubated in seedbeds until germination. At 30 days, plants with different treatments were divided into two groups, one of them was sprayed on the leaves with the pathogen XcvBv5-4a and the other group was not infected. Plants were harvested 15 days post-infection. The severity, incidence, and dry weights of all treatments were measured and statistically analyzed through analysis of variance. Results showed that infected plants and treated with SF4c-tailocins exhibited higher shoot and root dry weights compared to other treatments. There were no statistically significant differences when the infected plants were treated with a single tailocin (R1 or R2), compared to the control. Regarding disease severity, a lower infection percentage (less severity) was observed in plants whose seeds were treated with tailocins, whether R1/R2, R1, or R2. Furthermore, a considerable decrease in disease incidence was observed when tailocins were applied to seeds. Reductions exceeding 20% in disease severity were achieved in the experiments, demonstrating the promising potential of applying SF4c-tailocins for controlling bacterial spot disease in tomatoes. This finding is significant for seed treatment as it may indicate that tailocins induce a systemic plant defense response.

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