Molecular characterization of apple endophytic bacteria and biological effect on Alternaria rot on apple

Apple rot disease, caused by Alternaria alternata, is causing significant losses in apple production, especially in post-harvest periods. Alternaria alternata, was isolated from rotten apple fruit of cv Amasya. Identification of the strain isolated from rotten apple fruit was made by ITS sequence and morphological analysis. In the present study, 58 different endophytic bacteria strains were isolated from apple fruit for use in apple rot disease control. Among the isolated strains, 26 endophyte strains were determined to inhibit the radial growth of mycelia of A. alternata in binary culture in PDA media. Based on 16S rRNA sequencing analysis, these antagonistic endophytic bacteria strains were identified as Bacillus ssp. Bacillus methylotrophicus (ib17) showed the highest significant inhibitory effect on the mycelial growth of A. alternata at a rate of 79.5% in PDA medium. The results of in vivo experiments showed that Bacillus licheniformis (ib20) achieved 100% biocontrol when endophyte bacterial strains were inoculated 24 h before the inoculation of A. alternata. When the three bacteria species and A. alternata were inoculated simultaneously, Bacillus myloliquefaciens (ib1), Bacillus licheniformis (ib21) and the Endophytic bacterium (ib16) showed the highest biocontrol efficacy against A. alternata at 81.8%. Furthermore, when the bacterial strains were inoculated at 24 h after inoculation of A. alternata, B. licheniformis (ib21) showed the highest biocontrol efficacy of 83.3% against the fungal pathogen compared to the controls. The endophytic bacterial strains produced fungal cell wall hydrolysing enzymes such as chitinase, cellulase, amylase and protease. According to the results of this study, apple endophytic bacteria are potential candidates to control apple decay caused by A. alternata through cell wall hydrolysing enzymes and reduce disease severity. However, the efficacy of the biological control was dependent on the applied time of epiphytic bacterial strains. Further research is needed on the biochemical mechanisms underlying the activity of these bacteria against A. alternata.