A number of studies have demonstrated the ability of bacteria
or their byproducts to control plant diseases (Emmert and
Handelsman, 1999; Shoda, 2000). Our results indicate that P.
luminescens and X. bovienii bacteria and/or their metabolites are
suppressive to three important pathogens of peach and pecan,
and that the activity of these metabolites was observed on three
different substrates including soil (as well as disease lesions on terminals
and leaf surfaces, as shown previously). The relative toxicity
of treatments varied depending on the target fungal pathogen; X.
bovienii exhibited higher toxicity to F. effusum on pecan terminals
whereas P. luminescens was superior against the peach pathogen
A. tabescens in soil. Substrate may also be important in determining
relative toxicity, e.g., both P. luminescens and X. bovienii exhibited
an inhibitory activity to A. tabescens in the zone of inhibition tests
conducted on agar, yet only P. luminescens was active in soil.