Identification and screening apple endophytic bacteria applied at different times for biological control of Alternaria rot on apple in Turkey

Abstract

Abstract In this study, an isolate of Alternaria alternata, the causal agent of apple fruit rot, was isolated from rotten cv Amasya Apple and identified based on ITS gene analysis and morphological analyses. Out of 58 different endophytic bacteria isolated from internal tissues of apples, twenty-six isolates caused the radial growth inhibition of A. alternata in dual cultures. Based on 16S rRNA sequencing analysis, these endophytic antagonistic bacteria were identified as Bacillus ssp. Bacillus methylotrophicus(ib17) exhibited the highest significant inhibitory effect on the mycelial growth of A. alternata at a rate of 79.45% under in vitro conditions. The in vivo analysis revealed that the biocontrol efficiency of the Bacillus licheniformis(ib20) against A. alternata reached 100% with a treatment duration of 24 h before the introduction of A. alternata. When the bacteria and A. alternata were introduced simultaneously, Bacillus amyloliquefaciens(ib1), Bacillus licheniformis(ib21), and Endophytic bacterium (ib16) showed the highest biocontrol effect against A. alternata at 81.8%. Moreover, when the bacteria introduced 24 h after A. alternata, Bacillus licheniformis(ib21) showed the highest biocontrol efficacy at 83.3% against the fungus compared to the controls. The endophytic bacteria could produce fungus cell wall hydrolyzing enzymes such as chitinase, cellulase, amylase, and protease. According to the results of this study, apple endophytic bacteria are a potential candidate to control apple rot caused by A. alternata due to cell wall hydrolyzing enzymes, as well as to reduce disease severity. However, further research needs to be carried out on the biochemical basis of their activity against A. alternata.