J. Chen et al., COMPATIBILITY OF SYSTEMIC ACQUIRED-RESISTANCE AND MICROBIAL BIOCONTROL FOR SUPPRESSION OF PLANT-DISEASE IN A LABORATORY ASSAY, Molecular ecology, 5(1), 1996, pp. 73-80
Systemic acquired resistance (SAR) and microbial biocontrol each hold
promise as alternatives to pesticides for control of plant diseases. S
AR and Bacillus cereus UW85, a microbial biocontrol agent, separately
suppress seedling damping-off diseases caused by oomycete pathogens. T
he purposes of this study were to investigate how expression of SAR af
fected the efficacy of biocontrol by UW85 and if UW85 treatment of pla
nts induced SAR. We devised a laboratory assay in which seedling dampi
ng-off disease, induction of SAR, and growth of UW85 could be quantifi
ed. Seedlings of Nicotiana tabacum Xanthi nc were germinated on moist
filter paper and transferred after 7 days to water agar plates (40 see
dlings per plate). Zoospores of oomycete pathogens (Pythium torulosum,
Pythium aphanidermatum, or Phytophthora parasitica) were applied at c
oncentrations that caused approximate to 80% seedling mortality within
10 days. Seedling mortality was dependent on zoospore inoculum concen
tration. The level of disease suppression caused by treatment with UW8
5 depended on the UW85 dose applied. SAR was induced with 0.5-mM salic
ylic acid or 0.1-mM 2,6-dichloroisonicotinic acid. Expression of an SA
R-related gene was confirmed by northern analysis with a probe prepare
d from a tobacco PR-1a cDNA. Induction of SAR suppressed disease cause
d by each of the oomycete pathogens, but did not alter the growth of U
W85 on roots. Treatment of seedlings with UW85 did not induce the expr
ession of PR-1a. The combination of induction of SAR and treatment wit
h UW85 resulted in additive suppression of disease as measured by seed
ling survival.