Pseudomonads contribute to regulation of Pratylenchus penetrans (Nematoda) populations on apple
Watson, T.T., Forge, T.A., Nelson, L.M. (2018). Pseudomonads contribute to regulation of Pratylenchus penetrans (Nematoda) populations on apple. Canadian Journal of Microbiology, [online] 64(11), 775-785. http://dx.doi.org/10.1139/cjm-2018-0040
Plain language summary
Many strains of bacteria in the genus Pseudomonas are adapted to colonize surfaces of roots, and some of these strains are known to deter infection of crop roots by parasites and pathogens. In this research 100 distinct colonies of Pseudomonas were isolated from the roots of cherry trees. These isolates were then screened in Petri dishes for their potential to (1) inhibit the growth of common fungal pathogens of fruit trees, (2) produce antibiotics known to be associated with the ability to inhibit such fungi, and (3) suppress infection of apple seedling roots by the plant parasitic nematode, Pratylenchus penetrans. Based on the screening, two isolates, P. fluorescens P10-32 and P. fluorescens P10-42, were selected for further study of their ability to suppress infection of roots by P. penetrans and improve seedling growth in each of three different orchard soils. The orchard soil experiment involved dipping the roots of seedlings into suspensions of the bacterial strains immediately before transplanting into each of the soils. Both strains suppressed infection of roots by P. penetrans in one of the three soils and strain P10-42 improved early seedling growth in two of the three soils. We conclude that these bacteria, which are natural inhabitants of root surfaces of fruit trees and can inhibit growth of fungal pathogens, also have the ability to deter the parasitic nematode P. penetrans, but the effect is not consistent among orchard soils.
Inoculation with antagonistic soil microorganisms has shown potential to suppress replant disease of apple in orchard soils. Pseudomonas spp. may have the potential to reduce Pratylenchus penetrans populations on apple. Pseudomonas spp. were isolated from the rhizosphere of sweet cherry and screened for antagonistic characteristics. Two highly antagonistic Pseudomonas isolates, P10-32 and P10-42, were evaluated for growth promotion of apple seedlings, suppression of P. penetrans populations, and root colonization in soil from three orchards. During the isolate screening, Pseudomonas fluorescens P10-32 reduced in vitro growth of fungal pathogens, had protease activity, had capacity to produce pyrrolnitrin, suppressed P. penetrans populations, and increased plant biomass. Pseudomonas fluorescens P10-42 reduced in vitro growth of fungal pathogens, had protease activity, suppressed P. penetrans populations, and increased plant biomass. In potted orchard soil, inoculating apple with P. fluorescens P10-32 suppressed P. penetrans populations in one of the three soils examined. Inoculation with P. fluorescens P10-42 improved plant growth in two of the soils and suppressed P. penetrans abundance in one soil. In one of the soils, P. fluorescens P10-42 was detected on the roots 56 days postinoculation. Overall, we conclude that Pseudomonas spp. play a role in suppressing P. penetrans on apple in orchard soil.