The ability of Pseudomonas chlororaphis 63-28 to suppress Pythium root rot (Pythium aphanidermatum) and promote plant growth was investigated in hydroponic peppers that were predisposed or not predisposed to the disease. The biocontrol agent was introduced into the nutrient solution 10 days before the roots were inoculated with the pathogen. The root zone was maintained at 23ºC except when roots were exposed to 33ºC for three days before inoculation to induce predisposition to root rot. At constant 23ºC (no predisposition) application of P. chlororaphis at 10(7) CFU mL-1 nutrient solution delayed root browning more effectively than did higher or lower densities. In predisposed plants, densities of 10(6), 10(7) and 10(8) CFU mL-1 were equally superior. When applied at 10(7) CFU mL-1, the density of P. chlororaphis on roots of the two temperature regimes ranged from log10 5.88 to 6.45 CFU g-1 fresh roots at seven to 19 days after application. The agent delayed root browning, re-mediated predisposition to root rot, and increased growth of inoculated and non-inoculated plants. Leaf expansion was a sensitive marker of root rot and remediation by P. chlororaphis. We conclude that P. chlororaphis 63-28 has substantial potential for managing the disease regardless of predisposition.
Capsicum annuum; Pythium aphanidermatum; disease predisposition; biological control; leaf expansion
