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Oxidative Burst Elicited by Bacillus mycoides Isolate Bac J, a Biological Control Agent, Occurs Independently of Hypersensitive Cell Death in Sugar Beet

December 2003 , Volume 16 , Number  12
Pages  1,145 - 1,153

Rebecca L. Bargabus , Nina K. Zidack , John E. Sherwood , and Barry J. Jacobsen

Department of Plant Science and Plant Pathology, Montana State University, 119 AgBioSciences Facility, Bozeman 59717-3150, U.S.A.


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Accepted 22 August 2003.

Response of sugar beet cultivars C40 and USH11 to syringe infiltration of live and dead Bacillus mycoides isolate Bac J, a biological control agent, and virulent and avirulent isolates of Erwinia carotovora pv. betavasculorum was measured by monitoring systemic acquired resistance control of Cercospora beticola, specific activity of chitinase and β-glucanase, the oxidative burst, and hypersensitive cell death at the infiltration site. Priming sugar beet with B. mycoides Bac J (1 × 108 cells/ml) and avirulent isolates of E. carotovora pv. betavasculorum (1 × 106 cells/ml) reduced C. beticola symptoms by nearly 70% on distal, untreated leaves. Systemic resistance responses elicited by live B. mycoides Bac J and avirulent E. carotovora pv. betavasculorum isolates, measured by assays for chitinase and β-glucanase, were statistically equivalent, and biphasic hydrogen peroxide production was observed. Although similar in timing, the second hydrogen peroxide burst was twofold lower for B. mycoides Bac J than for avirulent E. carotovora pv. betavasculorum. Hypersensitive cell death was elicited by aviru-lent E. carotovora pv. betavasculorum but not B. mycoides Bac J. An oxidative burst was elicited by spray-applied B. mycoides Bac J under both light and green light conditions, indicating that the signal produced by B. mycoides Bac J was not reliant on the stomata for entry into sugar beet. A working model for signal delivery and systemic resistance induction by B. mycoides Bac J in sugar beet is proposed.



© 2003 The American Phytopathological Society