Disease suppression, growth promotion and colonization attributes of resident endophytic bacteria against white root rot (Dematophora necatrix Hartig) of apple.

The inherent potential of apple plants was investigated to explore bacterial endophytes and their role in suppressing Dematophora necatrix, the causative pathogen of white root rot disease. Resultantly 34 endophytic bacteria isolated from healthy apple plants, and subsequently 6 most efficient isolates viz., Bacillus megaterium strain EA3, Enterobacter sp. strain EA7, Bacillus megaterium strain EK2, Stenotrophomonas maltophilia strain EK6, Acinetobacter nosocomialis strain ES2 and Pseudomonas aeruginosa strain ES8 depicting anti-pathogen interactions through preliminary screening were assessed further under in vitro, glasshouse and field conditions against white root rot pathogen/disease. Maximum mycelial growth inhibition (80.37%) was obtained with S. maltophilia strain EK6 encouraging for its seed treatment and soil application thereby providing significant effective control (87.91%) of white root rot under glasshouse conditions to other five bacterial endophytes evaluated simultaneously, followed by field efficacy of 83.70%. In addition, it has significantly enhanced the growth parameters of apple trees under both glasshouse and field conditions. The inoculated healthy plants were assessed for endophytic colonization which revealed maximum endosphere colonialism by S. maltophilia strain EK6. Additionally, confocal microscopic images of transverse sections of root cells colonized by bacterial endophytes as compared to untreated control implied their persistence and establishment in endosphere of apple seedlings. The study provides the first report on interaction between apple associated bacterial root endophytes and D. necatrix. The obtained endophytic strains could be employed as alternative for mitigating white root rot disease in future.