SUPPRESSION OF PRE-EMERGENCE AND POSTEMERGENCE DAMPING-OFF IN CORN BYBURKHOLDERIA-CEPACIA

Burkholderia cepacia (syn. Pseudomonas cepacia) strain PHQM100 applied as a seed coating was tested in growth chamber experiments for its ab ility to suppress preemergence damping-off, and postemergence damping- off in corn induced by Pythium and Fusarium spp. The symptoms observed in bioassays with soils naturally infested with the fungal pathogens were seed rot with Pythium spp. and mesocotyl and root tissue necrosis in the presence of Fusarium spp. Three corn cultivars that differed i n their susceptibility to damping-off pathogens were used. Cultivar L was susceptible to pre- and postemergence damping-off, whereas cv. LPD P and cv. LG11 were moderately resistant and resistant to the damping- off diseases respectively. In the presence of Pythium spp., seed treat ment with B. cepacia reduced seed rot, as compared to the untreated se eds, and this reduction was more consistent in the cv. LPDP than in th e resistant cv. LG11 or the susceptible cv. L. In soils infested with Fusarium spp., seed treatment significantly reduced root and mesocotyl necrosis as compared to the untreated seeds, and this reduction was m ore consistent in the resistant cultivars LG11 and LPDP than in the su sceptible cv. L. Root colonization levels by B. cepacia were similar i n the three corn cultivars tested. Biocontrol efficiency of B. cepacia varied among cultivars mainly due to the differences in their suscept ibility to the fungal pathogens. In spite of variability and also irre spective of the soil characteristics, B. cepacia increased seedling em ergence and decreased mesocotyl and root necrosis when used as a seed coating.