Wood chip-polyacrylamide medium for biocontrol bacteria decreases Verticillium dahliae infection on potato

The lack of consistent success of biological control of soilborne plant pat hogens may be due to the introduction of the organism into a foreign enviro nment. The hypothesized that wood chip-polyacrylamide (PAM) cores surroundi ng host plant roots could alter the soil environment to favour growth of in troduced biocontrol microorganisms, thereby reducing Verticillium dahliae i nfection of potato (Solanum tuberosum L.) in a greenhouse. A 7 cm diameter x 15 cm deep hole (core) was drilled in the center of a 20 x 30 cm deep pot (1.9 kg) containing soil infested with V. dahliae inoculum. Cores were the n filled with wood chip-PAM-biocontrol organism mixtures. Soils that had St reptomyces lydicus inoculated into wood chip-PAM cores had lower levels of V. dahliae symptoms (V-vis) and V. dahliae isolations (V-iso) than all othe r treatments in three soils. V-vis and V-iso on plants growing in soils ame nded with S. lydicus or Pseudomona corrugata inoculated into the soil itsel f (without wood chip-PAM cores) did not differ from soils that were unamend ed with these biocontrol organisms. V. dahliae biomass was lower in wood ch ip-PAM col es inoculated with S. lydicus than control or wood chip-PAM core s without biocontrol bacteria. Soils with wood chip-PAM cores inoculated wi th S. lydicus or P. corrugata generally had higher microbial biomass/V. dah liae biomass (MB/VB) ratios than control soils, ol soils with S. lydicus or P. corrugata inoculated into the soil. Wood chip-PAM cores alone and wood chip-PAM cotes inoculated with S. lydicus had higher MB/VB ratios than wood chip-PAM cores inoculated with P. corrugata. V-vis and V-iso were curvilin early correlated with the MB/VB ratios in negative relationships, respectiv ely (r(2) = 0.58, r(2) = 0.68). As the MB/VB ratio increased V-vis and V-is o decreased. Although field studies and economic evaluations are necessary, amending soil with wood chips-PAM and a biocontrol bacterium may be a valu able method to increase the effectiveness of biocontrol organisms.