Abstract
The aim of this work was to investigate the most promising natural antimicrobials effective for the growth suppression of Xanthomonas spp. bacteria. The research objects were Xanthomonas spp. strains isolated from tubers and stem of plants growing in Lithuania: Xanthomonas translucens NRCIB X6, X. arboricola NRCIB X7, NRCIB X8, NRCIB X9, and NRCIB X10; the supernatants of lactic acid bacteria Lactococcus lactis strains 140/2, 57, and 768/5, Lactobacillus helveticus strains 14, 148/3, R, and 3, Lb. reuteri 3 and 7, Streptococcus thermophilus 43, Enterococcus faecium 59-30 and 41-2; endophytic bacterial strains Bacillus, Pseudomonas, and Paenibacillus spp.; and essential oils of lavender (Lavandula angustifolia), grapefruit (Citrus paradisi), pine (Pinus sylvestris), thyme (Thymus vulgaris), rosemary (Rosmarinus officinalis), peppermint (Mentha piperita), lemon (Citrus limetta), aqueous extracts of blueberries (Vaccinium myrtillus), and cranberries (Vaccinium vitis-idaea). The antimicrobial activity of tested substances was determined by agar diffusion method. Supernatants of Lb. reuteri strain 7 and Lb. helveticus strains 14, R, 3, and 148/3 were found to have a high antimicrobial activity against Xanthomonas spp. bacteria strains when compared to the positive control—1.0% copper sulfate (diameter of inhibition zones was 28.8 ± 0.7 mm). The diameter of inhibition zones of supernatants ranged from 23.3 ± 0.6 mm to 32.0 ± 0.1 mm. Thyme (2.0%) and lavender (2.0%) essential oils inhibited the growth of Xanthomonas spp. strains. The diameter of the inhibition zones was from 14.7 ± 0.8 mm to 22.8 ± 0.9 mm. The aqueous extracts of blueberries had a weak antimicrobial activity. The diameter of inhibition zones ranged from 11.0 ± 0.2 mm to 13.0 ± 0.2 mm.
Highlights
Published: 22 December 2021Bacterial diseases of plants cause devastating damage to crops and significant economic losses [1,2,3]
All gram-negative bacteria were tested for hypersensitive reaction (HR) on tobacco
Our studies revealed that only five isolates belong to the genus Xanthomonas: one strain was classified as X. translucens (Xt)
Summary
Bacterial diseases of plants cause devastating damage to crops and significant economic losses [1,2,3]. They cause about 12% of plant-origin food loss every year. The bacterial genus Xanthomonas, belonging to the family Xanthomonadaceae, harbour some of the most devastating plant pathogens that continually cause food safety problems. Together, all of these taxa can infect many plants found in agriculture, forest, or natural ecosystems. As many as three species of Xanthomonas are among the ten economically and scientifically significant pathogenic bacteria compiled by scientists [2]. Particular attention has been paid to these species due to the very wide range of plants and the exceptional potential pathogenicity to their plant hosts—the main pathogens of rice and cassava, X. oryzae pv. oryzae, and X. axonopodis pv. manihotis, respectively, and X. campestris pathovars, which are causal agents of many crops worldwide [2]
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