Isolates of Bl, which were initially recovered from surface-sterilised cabbage (Brassica oleracea var. capitata) seeds, were able to colonise brassica plants in the laboratory and field. The bacterium was recovered from surface-sterilised leaf, stem and root sections of seedlings after inoculation with Bl vegetative cells under laboratory conditions, and from mature cabbage plants sprayed with Bl in a field trial. The identity of the recovered bacterial isolates was confirmed by PCR through amplification of 16S rDNA and two strain-specific regions. The effect on diamondback moth (DBM) insect herbivory was tested with cabbage seedlings treated with one isolate (Bl 1951) as the strains are toxic to DBM after direct ingestion. While no effect on DBM larval herbivory was observed, there was a significant reduction of DBM pupation on the Bl 1951 colonised plants. The presence of Bl 1951 wild type cells within cabbage root tissue was confirmed by confocal microscopy, establishing the endophytic nature of the bacterium. The bacterium was also endophytic in three other brassica species tested, Chinese kale (Brassica oleracea var. alboglabra), oilseed rape (Brassica napusvar. oleifera) and radish (Raphanus sativus).
Fig 1. Phylogenetic tree of 16S rDNA sequences of the Brevibacillus laterosporus1821 and 1951 samples recovered from cabbage seedlings 23 days after incubation.
Formatted in Geneious . The scale bar represents the nucleotide substitutions per site (the number of changes per 100 nucleotide sites). The red bracket indicates the position of the Bl 1821 and 1951 potential endophyte samples and the Bl 1821 and 1951 16S rDNA derived from the stock cultures as positive controls (+). Abbreviations: B. = Bacillus; Br. = Brevibacillus.