EVALUATION OF PLANT GROWTH-PROMOTING RHIZOBACTERIA FOR BIOLOGICAL-CONTROL OF PYTHIUM ROOT-ROT OF CUCUMBERS GROWN IN ROCKWOOL AND EFFECTS ONYIELD

Three strains of Pseudomonas fluorescens (63-49, 63-28, and 15), one s train of Pseudomonas corrugata (13) and one strain of Serratia plymuth ica (R1GC4) were tested on rockwool-grown cucumbers for their ability to reduce Pythium root-rot caused by Pythium aphanidermatum. These str ains were previously selected for biocontrol ability from collections of >4000 bacteria. Strains 63-49 and 63-28 were tested on cucumber pla nts grown in rockwool in two replicated Pythium-inoculated trials cond ucted in British Columbia (B.C). Another inoculated, replicated trial was conducted in Quebec with all five strains. Cucumber yields (fruit number and weight) were measured over a ten-week harvest period. Strai n 63-49 caused an early promotion of plant growth and increased cucumb er yields at early harvests. No measurable effect of Pythium inoculati on on disease development was observed in the Quebec trial, due to unf avourable cool weather. However, 63-49 significantly increased the tot al number of cucumbers (12%) and cucumber weight (18%), compared to th e non-treated control. Strains 13, 15 and R1GC4 slightly increased the cumulative cucumber yields, but strain 63-28 had no effect. In the B. C. trial, inoculation with P. aphanidermatum reduced the number and we ight of cucumbers by 27%. Treatments of Pythium-inoculated cucumbers w ith 63-49 significantly increased fruit number and weight by 18%, comp ared to the Pythium-inoculated control. Strain 63-28 increased the cum ulative number of cucumbers over time, compared to the Pythium-inocula ted control, but the increase was less than with 63-49. The use of Pse udomonas spp. in rockwool-grown cucumbers can increase yields, both in the presence and absence of Pythium root rot, and with variable seaso nal conditions and disease pressures.