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on their nematicidal effect on P. penetrans, (3) Determine whether individual VFAs in the
LHM interact with each other in their toxicity to P. penetrans. In the bioassay, 300
nematodes were exposed to increasing concentrations of the VFAs in a buffered solution of
citric acid-NaOH at pH 4.5. The concentration of interest is LC 95 (the concentration that kills
95% of the nematodes in 24 hr). P. penetrans was more sensitive to acetic acid than C.
elegans whereas to the larger chain VFA, caproic acid, sensitivity was similar. Individual
VFAs vary in their lethality to P. penetrans. Valeric acid was the most lethal (LC 95 = 6.8 mM)
while Isobutyric acid was least lethal (LC 95 = 45.7 mM). Individual VFAs didn’t interact in
their toxicity to P. penetrans and their effect was additive. Our results indicate C. elegans
cannot be used as a surrogate to P. penetrans in toxicity studies using VFAs. The efficacy of
LHM to control lesion nematodes can be evaluated by assessing the VFA content in the
manure prior to application. This evaluation is facilitated by the fact that the interaction of
individual VFAs is additive.
Acidified Liquid Hog Manure Kills Plant Parasitic Nematodes but Alters
Nematode Communities and the Soil Food Web
Mahran, A. (1,2), M. Tenuta(1) & F. Daayf (2)
(1) Department of Soil Science, (2) Department of Plant Science, University of Manitoba, Winnipeg MB
Canada R3T 2N2
Volatile fatty acids (VFAs) in liquid hog manure (LHM) suppressed plant parasitic and lesion
nematodes in field, microplots and laboratory experiments. However, their effects on
nematode communities are unknown though informative in indicating if VFAs kill free-living
nematodes and if soil food webs are disturbed. Nematodes have proved to be a good tool for
determining the condition of the soil food web and thus examined in this study. A microcosm
experiment was conducted using nematodes faunal analysis as a tool to determine: (i)
whether the VFAs in the LHM have specific or general toxicity to various groups of
nematodes, (ii) if they could cause ‘biological vacuum’ in the soil where soil organisms are
killed allowing colonization by opportunistic organisms, and (iii) the degree of disturbance
they could cause to the soil food web. Acidified LHM (pH= 5.5) was added to pasture soil
harboring a wide range of nematodes, representing different trophic levels and to which
Pratylenchus penetrans was added. Nematodes analysis was conducted at intervals over a
period of 28 days to examine the changes in the nematodes community. Nematodes were
identified to the genus level. Within days of application of LHM, total numbers of nematodes
in soil were reduced with all nematode taxa being affected including P. penetrans. Fungal
and bacterial feeders’ nematodes re-colonized the soil 7 days after LHM application
indicating the presence of a ‘biological vacuum’ caused by application. After 4 weeks, the
structure index in the manure treatments had decreased while the enrichment index increased
compared to the control and acid-only treatments. LHM application caused moderate
disturbance to the soil food web with the creation of ‘biological vacuum’ and subsequent
colonization by opportunistic organisms. LHM can be used as an effective method to control
plant parasitic nematodes including P. penetrans. However, it should be used in situations to
mediate intense disease pressure and to not replace cultural methods and promotion of soil
health in controlling plant diseases and pests.
5 th International Congress of Nematology, 2008 281