Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2014
Publication Date: 5/2/2014
Citation: Weiland, G.E. 2014. Pythium species and isolate diversity influence inhibition by the biological control agent Streptomyces lydicus. Plant Disease. 98(5):653-659.
Interpretive Summary: Pythium is a common soilborne pathogen that kills tree seedlings. We evaluated the effect of a biocontrol agent, Streptomyces lydicus, to reduce the growth of 150 Pythium isolates representing 16 Pythium species. We found that Streptomyces lycidus reduced the growth of all 150 Pythium isolates, and that the amount of growth reduction was strongly dependent on the isolate and species tested. For example, isolates of Pythium irregulare were 72-83% smaller in the presence of the biological control agent, while isolates of Pythium torulosum were only 63-69% smaller. This indicates that the biological control agent works better at controlling the growth of some Pythium species better than other Pythium species, and may help explain why biological control sometimes does not work in the field. Knowledge of the impact of biocontrol agents on different species of pathogen is essential to improve biocontrol efficacy.
Technical Abstract: Disease control of soilborne pathogens by biological control agents has often been inconsistent under field conditions. One factor that may contribute to this inconsistency is the variability in response among pathogen populations and/or communities to the selected biological control agent. One hundred fifty Pythium isolates, originally obtained from the soil of three forest nurseries and representing 16 Pythium species, were exposed to Streptomyces lydicus in an in vitro assay. Percent inhibition (culture diameter) and isolate mortality were recorded for each isolate and the data were analyzed for effects of species, isolate, and location (nursery). Although S. lydicus inhibited the growth of all Pythium isolates, significant differences in the amount of inhibition were observed among Pythium species (P < 0.001) and between isolates of the same Pythium species (P < 0.001). No effect of location was observed. Similar to culture inhibition, isolate mortality in the presence of S. lydicus was also found to vary among species and isolates, but not by location. Results indicate the importance of isolate-to-isolate and species-to-species variability in mediating pathogen response to biological control agents. Future studies assessing the efficacy of biological control agents should be tested against multiple pathogen species and/or isolates to increase the chances for biological control success.