Interactions between plant growth promoting rhizobacteria, foliar-feeding insects and higher trophic levels

Kiran Gadhave

Research output: ThesisDoctoral Thesis

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Several rhizobacteria promote plant growth and suppress numerous plant diseases; however, the roles of these bacteria in altering plant chemical defences against foliar insects, changing plant-associated microbial community and in shaping plant-insect-natural enemy multi-trophic interactions have been sparsely explored. The aim of this project was to study the effects of different Bacillus species on calabrese (Brassica oleracea) growth parameters, biochemistry and endophytic bacterial community, the life history traits and population dynamics of different foliar-feeding insects and their common natural enemies. The magnitude of effects of Bacillus spp. on a variety of these parameters varied between and within control and treated plants. Preliminary experiments showed that a commercial Bacillus mixture was not as effective as native Bacillus species in promoting plant growth. All Bacillus treatments significantly altered the life history traits of B. brassicae in the laboratory conditions. B. subtilis, B. amyloliquefaciens and mixed treatments significantly increased the onset of reproductive maturity and plant biomass, and changed foliar indole glucosinolate levels. However, the effects of all Bacillus species on insect herbivores were contrasting; the infestation of B. brassicae was significantly reduced in a temperate climate, and that along with two aphids; Myzus persicae and Lipaphis erysimi was increased in the tropics. The natural enemy responses on all experimental plants, in both field studies, were aphid density dependent. The diversity, evenness and abundance endophytic bacteria differed across control and treated plants. It is recommended that discrepancies in the results of bacterial inoculants use in different conditions can be reduced through a careful tailoring of bacterial species in inocula with soil and crop. It is concluded that Plant Growth Promoting Bacillus accelerate calabrese maturity and increase biomass, alter endophytic bacterial diversity, evenness and abundance, and shape above ground interactions via significant changes in aphid field infestation levels, which are site-specific and which indirectly extend up to the natural enemy level.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Gange, Alan, Supervisor
Award date1 Jun 2015
Publication statusUnpublished - 2015


  • plant growth promoting rhizobacteria
  • Bacillus
  • plant-insect interactions

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