We investigated if rates of propagation and migration were related with the level of virulence in the pinewood nematode Bursaphelenchus xylophilus using 17 offspring lines from the F-2 crosses between virulent and avirulent isolates. Virulence was tested by inoculating seedlings of Pinus thunbergii with the nematodes. The proportion of dead seedlings ranged from 13.3% to 77.8%, 20 weeks after inoculation. Migration rate of the nematodes was estimated by measuring their migration distance per unit time in an artificial substrate that imitated pathways in pine trees. Migration rate varied from 0.85 to 3.53 mm min(-1). Propagation rate was determined based on population growth on the fungus Botrytis cinerea, and it ranged between 10(3.88) and 10(4.99) per 12 days. Statistical analyses revealed that virulence was not correlated with migration rate, but was negatively correlated with propagation rate on Botrytis cinerea, suggesting that the nematodes paid some cost for virulence. Also, there was no relationship between rates of migration and propagation. Cluster analysis showed that the biological parameters varied between crossbred lines, with no kinship bias, suggesting the absence of sex-linked inheritance in virulence and rates of propagation and migration.
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