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

The lack of consistent success of biological control of soilborne plant pathogens may be due to the introduction of the organism into a foreign environment. The hypothesized that wood chip-polyacrylamide (PAM) cores surrounding host plant roots could alter the soil environment to favour growth of introduced biocontrol microorganisms, thereby reducing Verticillium dahliae infection 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 then filled with wood chip-PAM-biocontrol organism mixtures. Soils that had Streptomyces lydicus inoculated into wood chip-PAM cores had lower levels of V. dahliae symptoms (V-vis) and V. dahliae isolations (V-iso) than all other treatments in three soils. V-vis and V-iso on plants growing in soils amended with S. lydicus or Pseudomona corrugata inoculated into the soil itself (without wood chip-PAM cores) did not differ from soils that were unamended with these biocontrol organisms. V. dahliae biomass was lower in wood chip-PAM col es inoculated with S. lydicus than control or wood chip-PAM cores without biocontrol bacteria. Soils with wood chip-PAM cores inoculated with S. lydicus or P. corrugata generally had higher microbial biomass/V. dahliae 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 curvilinearly correlated with the MB/VB ratios in negative relationships, respectively (r(2) = 0.58, r(2) = 0.68). As the MB/VB ratio increased V-vis and V-iso decreased. Although field studies and economic evaluations are necessary, amending soil with wood chips-PAM and a biocontrol bacterium may be a valuable method to increase the effectiveness of biocontrol organisms.