Induction of short-term tolerance to nonfurnigant nematicides in stressed and unstressed populations of Xiphinema 1 index

SUMMARY Populations of Xiphinema index were stressed with monthly subnematicidal doses of either carbofuran, oxamyl or phenamiphos for five years (stressed populations). At the end of the third year, one half of these cultures were released from nematicide stress (unstressed populations). These were cultured in the absence of monthly stressing for two years. Then, both stressed and unstressed populations were treated with a subnematicidal level of nonfumigant nematicide (NFN). At various days following this treatment, nematodes were assessed for their tolerance to high concentrations of NFN. Results from this and a previous test with a wild population suggested that the demonstrated increase in tolerance to NFN may be operating by two separate mechanisms. One system is induced by the subnematicidal treatment. It is transitory and seems to operate in al1 populations. The other mechanism appears to be permanent and does not require induction. This latter system parallels resistance and operates in only certain stressed and unstressed populations of X. index.