SUPPRESSION OF FUSARIUM-MONILIFORME BY MAIZE ROOT-ASSOCIATED PSEUDOMONAS-CEPACIA

Maize seeds coated with strains of Pseudomonas cepacia antagonistic to the growth of Fusarium moniliforme in vitro were tested for their ability to suppress seedling infection by this fungal pathogen of maize. When the seeds were coated with maize root-associated P. cepacia strains, seedling infection in soils artificially infested with 10(4) cfu g-1 of the fungus was reduced by 23-80%. In contrast antagonistic P. fluorescens and Bacillus strains isolated from maize roots were less effective than P. cepacia strains. Reference P. cepacia strains tested, with the exception of strain ATCC 17616, were also unable to suppress the seedling infection. P. cepacia strains inhibited in vitro a range soil-borne fungal pathogens of maize such as Fusarium graminearum, Macrophomina phaseolina, Rhizoctonia solani, Colletotrichum lindemuthianum, and also other soil fungi such as Fusarium oxysporum and Sclerotinia sclerotiorum. P. cepacia strain 526-7, a Tn5 mutant of the wild type maize strain 526 (ATCC 53267), was less inhibitory to the growth of fungal pathogens in vitro, losing 50-100% of activity, and failed to reduce seedling infection by F. moniliforme. Based on characteristics such as biochemical reactions, disease suppression, maize root colonization and onion pathogenicity, P. cepacia strains isolated from maize roots could be differentiated from the reference strains of plant and soil origin.