A new strain Lacticaseibacillus paracasei M₁₂ and perspectives of its use against Erwinia amylovora

The current investigation was conducted to assess the antagonistic activity of Lacticaseibacillus paracasei M₁₂, a novel strain, against the pathogenic agent Erwinia amylovora E22, which causes fire blight in fruit crops. The E. amylovora E22 strain was isolated from Golden Delicious floral colonization dynamics and specificity of Aureobasidium pullulans strains used to suppress fire blight in apple fruit. The L. paracasei M₁₂ strain was collected from the phyllosphere of the garden cenosis in the Almaty region of Kazakhstan. Identification of both isolates relied on morphological and biochemical tests as well as PCR analysis. Results indicated that the zone of pathogen growth inhibition due to the action of the L. paracasei M₁₂ strain was 41.5 ± 1.5 mm. The maximum inhibitory activity of this antagonist was observed on the 7th day of fermentation. Lactic acid constituted the largest percentage in the cultural broth component composition (43.55%) and exhibited inhibitory effects against E. amylovora E22. Evaluation of various concentrations of the broth in vitro demonstrated that the use of the original broth (100%) resulted in complete inhibition of pathogen growth. A parallel outcome was observed in tests conducted on immature pear fruits, where those treated with 100% of M₁₂ culture broth exhibited complete protection against fire blight infection, while 50% and 20% concentrations showed a slight appearance of the disease. Furthermore, the incorporation of TWEEN® 80 as an adhesive agent enhanced the antagonistic activity of the L. paracasei M₁₂ strain in vitro. Consequently, the L. paracasei strain M₁₂ emerges as a promising candidate for the development of a novel biopesticide targeting fire blight. It was shown that the biological efficacy of L. paracasei M₁₂ against fire blight during double treatment of Aport and Starkrimson fruit trees was 80.3% and 80.7%, respectively.