| Root-lesion nematodes, Pratylenchus spp., are serious pathogens of potato plants in temperate, tropical and subtropical regions of the world. Several management practices can control Pratylenchus spp. in soil; however, they all exhibit some limitations. Therefore, environmentally-safe, low-cost, and effective control strategies are needed as possible alternative to current strategies. This thesis was designed to assess if liquid hog manure (LHM) holds such potential. The objectives of this thesis were to determine: (i) the prevalence and identity of species of Pratylenchus spp. in Manitoba potato fields, (ii) if short-chain volatile fatty acids (VFA) in LHM are the constituents responsible for the manure's toxicity to Pratylenchus spp. using laboratory-based solution exposure experiments (iii) the effectiveness of LHM in killing Pratylenchus spp. in soil, and (iv) the impact of LHM on non-target nematode communities. Pratylenchus spp. were detected in 39% of 31 potato fields surveyed in Manitoba with population densities ranging, for positive fields, from 45 to 631 nematodes kg-1 fresh soil. Morphometrics of female nematodes and molecular diagnosis (using species-specific PCR primers and species identification confirmation by molecular sequencing of PCR products and their comparison to the GenBank database) confirmed the species of Pratylenchus present in the potato fields to be P. neglectus. Potato, cv. Russet Burbank, was found to be a poor host to two populations of Pratylenchus spp. from Manitoba potato fields. From this, we conclude that P. neglectus does not seem to be a limitation to potato production in Manitoba; thus, P. penetrans, the most wide spread and damaging species to potato, was used in successive studies to assess the use of LHM to control Pratylenchus spp. in potato fields. Under laboratory conditions, VFA (acetic, propionic, n-butyric, isobutyric, n -valerie, isovaleric, and n-caproic acids) accounted for the majority of the lethal effect of LHM exposure to P. penetrans under acidic conditions. The VFA in LHM killed Pratylenchus spp. in soil and acidification seemed to enhance this response when VFA concentration in the manure is low. LHM did not act as a soil fumigant eliminating soil trophic interactions, but increased bottom-up food web interactions. The VFA in LHM persisted in the soil for only four days with biological degradation being their mode of loss. In conclusion, LHM is potentially an effective and low-cost strategy to control Pratylenchus spp. and its efficacy improved by acidification when VFA concentration is low. |
