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Title: USE OF COLONIZATION-IMPAIRED STRAIN OF ENTEROBACTER CLOACAE IN BIOCONTROL OF PYTHIUM ULTIMUM DAMPING-OFF OF CUCUMBER AND IN SEED TREATMENTS CONTAINING COMBINATIONS OF BIOCONTROL AGENTS.

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

Submitted to: Entomophaga
Publication Type: Abstract Only
Publication Acceptance Date: 9/7/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: N/A.

Technical Abstract: The importance of root colonization for suppressing damping-off by Pythium ultimum was studied using Enterobacter cloacae strain A-46, a colonization-impaired mini-Tn5 Km mutant of E. cloacae strain 501R3 (Roberts et al. 1996. Can. J. Microbiol. 42:196-201). Strain A-46 was incapable of increasing in population in cucumber spermosphere in the absence of seed amendments while populations of strain 501R3 increased substantially. Strain A-46 was detected at populations of approximately 10**1 cfu per gram of root tissue 42 days after planting whereas strain 501R3 was detected at populations of approximately 10**8 cfu per gram. Despite being colonization-impaired, strain A-46 provided effective biocontrol of P. ultimum damping off of cucumber grown in potting mix at 24 deg C. Plant stands from seeds treated with 501R3 or A-46 were similar and stands from both treatments were greater (P < 0.05) than with the pathogen alone. Biocontrol of P. ultimum on cucumber in the absence of effective root colonization may be due to the limited time that cucumber is highly susceptible to damping-off by this pathogen. Cucumber seeds pregerminated for 29 hours or longer before sowing in pathogen-infested potting mix yielded plant stands similar to the healthy control treatment, while plant stands from non-pregerminated seeds were significantly less (P < 0.05) than these treatments. In a natural field soil containing several Pythium spp. and Fusarium spp. seed treatments that combined applications of E. cloacae A-46 and Burkholderia cepacia strains provided superior biocontrol (P < 0.05) over treatments containing either E. cloacae or B. cepacia alone.