Biopesticides against apple disease Erwinia amylovora

This study was conducted to evaluate the antagonistic activity of two new strains Lacticaseibacillus paracasei M12 and Lactobacillus plantarum 17M against the pathogen Erwinia amylovora, which causes fire blight on apple flowers. The Lacticaseibacillus paracasei M12 strain was collected from the phyllosphere of the garden cenosis of the Almaty region of Kazakhstan, and the Lactobacillus plantarum 17M strain was collected from the collection of "Scientific Production Center of Microbiology and Virology" LLP. Erwinia amylovora was isolated based on the floral colonization dynamics of the apple cultivar Golden Delicious. Identification of strains was based on morphological and biochemical tests, as well as PCR analysis. Lacticaseibacillus paracasei M12 and Lactobacillus plantarum 17M strains were superior in limiting the growth of the pathogen Erwinia amylovora in all liquid media tested.

The maximum inhibitory activity of Lacticaseibacillus paracasei M12 was observed on the 7th day of fermentation. Lactic acid constituted the largest percentage (43.55%) in the component composition of the Lacticaseibacillus paracasei M12 culture broth and exhibited an inhibitory effect against Erwinia amylovora. The results showed that the zone of growth inhibition of the pathogen due to the action of the Lacticaseibacillus paracasei M12 strain was 41.5 ± 1.5 mm. In addition, the inclusion of TWEEN® 80 as an adhesive agent enhanced the antagonistic activity of Lacticaseibacillus paracasei M12 strain in vitro.

Analysis of secondary metabolites produced by the Lactobacillus plantarum 17M strain in a liquid medium showed that they consist predominantly of acetic acid (53.2 ± 4.3%), lactic acid (16.3 ± 2.3%) and 2,3- butanedione (14.84 ± 4.1%). A study on the effect of these compounds on the growth of Erwinia amylovora revealed that lactic acid at a concentration of 5% exhibits inhibitory activity but is not toxic to apple flowers. The efficiency of the culture liquid of the Lactobacillus plantarum 17M strain, diluted with sterile water and added to the Erwinia amylovora inoculum at a concentration of 10 and 20%, was 76.7 ± 5.8% and 88.3 ± 12.6%, respectively.

Therefore, the present study confirms the potential of using Lacticaseibacillus paracasei M12 and Lactobacillus plantarum 17M strains as active microbial agents to combat bacterial fire blight in fruit crops in Kazakhstan. This study was funded by the Ministry of Science and Higher Education of the Republic of Kazakhstan, research grants BR18574022 "Microbial preparations for bacterial fire blight control of fruit crops".