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

Abstract

The inherent potential of apple trees was investigated to explore bacterial endophytes and their role in suppressing Dematophora necatrix, the incitant of white root rot disease. Resultantly 34 endophytic bacteria secluded 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 further assessed under in vitro, glasshouse and field conditions against white root rot disease. Maximum mycelial growth inhibition (80.37%) was obtained in S. maltophilia strain EK6 encouraging for its seed treatment and soil application thereby providing significant effective control (87.91%) of white root rot under controlled culture situations as compared to other five bacterial endophytes evaluated simultaneously, followed by field efficacy of 83.70 per cent. In addition, it has significantly enhanced the growth parameters of apple trees under both the situations. The inoculated healthy plants were assessed for endophytic colonization which revealed maximum endosphere colonialism by S. maltophilia strain EK6. Additionally, confocal microscopic explication 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. This investigation emphasized the first evidence of interaction between apple associated bacterial endophytes and D. necatrix, therefore these endophytes could be employed as alternative for mitigating white root rot disease in future.