PythiumSpecies and Isolate Diversity Influence Inhibition by the Biological Control AgentStreptomyces lydicus

Abstract

Weiland, J. E. 2014. Pythium species and isolate diversity influence inhibition by the biological control agent Streptomyces lydicus. Plant Dis. 98:653-659.Disease control of soilborne pathogens by biological control agents (BCAs) is often inconsistent under field conditions. This inconsistency may be partly influenced by pathogen diversity if there is a differential response among pathogen species and isolates to selected BCAs. The responses of 148 Pythium isolates obtained from soil at three forest nurseries and representative of 16 Pythium spp. were evaluated in the presence of Streptomyces lydicus strain WYEC108 in an in vitro assay. Percent growth inhibition, inhibition zone distance, mortality, and growth rate were recorded for each isolate, and data were analyzed for effects of species and isolate. Responses of three Pythium spp. (Pythium irregulare, P. sylvaticum, and P. ultimum) were further analyzed for a location (nursery) effect. Although S. lydicus inhibited all Pythium isolates, differences in percent growth inhibition, inhibition zone distance, and mortality were observed among Pythium spp. and isolates. Small but significant location effects were also noted. Growth rate also varied among Pythium spp. and isolates and was found to strongly bias percent growth inhibition and, to a lesser degree, inhibition zone distance; depending on which measure was used, slowergrowing isolates appeared less sensitive (growth inhibition) or more sensitive (inhibition zone) to S. lydicus than faster-growing isolates. Results illustrate the importance of using multiple, representative pathogen isolates in preliminary BCA inhibition assays as well as accounting for the effect of pathogen growth rate on pathogen inhibition by BCAs. Future studies should take pathogen diversity into account when evaluating biological control efficacy.

Integrating Host Resistance and Plant Protectants to Manage Pythium Root Rot on Geranium and Snapdragon

“…was also determined in an in vitro assay that evaluated growth inhibition of several Pythium spp. isolates from Oregon nurseries (Weiland, 2014).…”

“…on geranium than snapdragon. It has been shown that the efficacy of biological control agents in controlling soilborne diseases can be variable (Handelsman and Stabb, 1996;Leisso et al, 2009;Linderman et al, 2008;Weiland, 2014;Whipps and McQuilken, 2009). Inconsistent results may be related to biotic and abiotic factors that affect the antagonistic properties of the biocontrol agents.…”

“…Inconsistent results may be related to biotic and abiotic factors that affect the antagonistic properties of the biocontrol agents. These factors may include the influence of the microbiome inhabiting the rhizosphere of the plants, genotypic variability of the host plant and the pathogen, and environmental conditions including temperature, relative humidity, and ultraviolet radiation (Paulitz and B elanger, 2001;Guetsky et al, 2002;Weiland, 2014). Differences in the efficacy of the biological control agents evaluated in this study may depend on the Pythium spp.…”

Efficacy of reduced rate fumigant alternatives and methyl bromide against soilborne pathogens and weeds in western forest nurseries

“…An alternative explanation for the failure of biocontrol to work in our study may be that the biocontrol agents were not equally active against all members of the soilborne pathogen community at each nursery. For example, we know that the Pythium community at each nursery is unique (Weiland, 2011) and that the biocontrol agent S. lydicus WYEC108 does not inhibit all Pythium species and isolates from forest nurseries to the same degree (Weiland, 2014). Pythium species such as P. ultimum were inhibited less by S. lydicus than other species like P. irregulare (Weiland, 2014).…”

“…For example, we know that the Pythium community at each nursery is unique (Weiland, 2011) and that the biocontrol agent S. lydicus WYEC108 does not inhibit all Pythium species and isolates from forest nurseries to the same degree (Weiland, 2014). Pythium species such as P. ultimum were inhibited less by S. lydicus than other species like P. irregulare (Weiland, 2014). Therefore, disease control may be compromised in soils where both pathogens are present.…”