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ARS Home » Research » Publications at this Location » Publication #74342
Title: BIOLOGICAL CONTROL OF DAMPING-OFF OF CUCUMBER CAUSED BY PYTHIUM ULTIMUM WITH A ROOT-COLONIZATION-DEFICIENT STRAIN OF ENTEROBACTER CLOACAE

Author
item Roberts, Daniel
item Dery, Pierre
item HEBBAR, PRAKASH - OICD
item Mao, Weili
item Lumsden, Robert

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Research was performed to determine how long plant-beneficial bacteria must remain on seeds and plant roots to protect the plant from the pathogen Pythium ultimum. This information is required for the selection of strains that have the appropriate characteristics for controlling this plant pathogen. It was determined that a mutant of the plant-beneficial bacterium Enterobacter cloacae was unable to grow on plant roots. It was also determined that this mutant was still capable of controlling damping-off disease caused by the plant pathogen Pythium ultimum. This research demonstrates that growth on cucumber roots by the plant-beneficial bacterium Enterobacter cloacae is not required for controlling damping-off disease caused by Pythium ultimum. This information will be useful to Scientists.

Technical Abstract: Root colonization and suppression of damping-off of cucumber was compared for wild-type strain 501R3 of Enterobacter cloacae and strain A-46, a colonization-impaired, mini-Tn5 Km mutant of strain 501R3. Populations of strain A-46 increased only 65-fold over 96 h when applied at 10**4 colony-forming units per seed. In contrast, populations of strain 501R3 increased 24,000-fold over the same period when applied at 10**4 colony-forming units per seed. Populations of strain A-46 were limited to the upper centimeter of cucumber root at 7 d and decreased to approximately 10**1 colony-forming units per gram of total root system over 42 d. Strain 501R3 was capable of becoming widely distributed along cucumber roots and was detected at populations of approximately 10**8 colony-forming units per gram of total root system at 42 d. Both strains 501R3 and A-46 provided effective biocontrol of preemergence and postemergence damping-off of cucumber caused by Pythium ultimum. Plant stands from seeds treated with 501R3 and A-46 were 93% and 92%, respectively (similar at P = 0.05), when sown in soilless mix infested with P. ultimum. The plant stand with the pathogen control was only 30%, significantly less (P = 0.05) than stands from the 501R3 and A-46 treatments. Cucumber was only briefly susceptible to damping-off caused by P. ultimum. Results from this study indicate that root colonization by E.cloacae is not required for suppression of damping-off of cucumber caused by P. ultimum due to the brief period of susceptibility of cucumber to this disease.