Plant-parasitic nematodes associated with forest trees in California

As a first step in assessing the importance of plant-parasitic nematodes to California forestry, soil and root samples were taken from 32 kinds of trees in the major forested areas of California. Ninety-seven percent of the 228 samples were from conifers, and 82 percent were from trees important in the lumber industry, mainly ponderosa and Jeffrey pines, coast redwood, Douglas fir, and red fir. In the rhizosphere of these trees, 97 described and 54 undescribed, species of plant-parasitic nematodes in 46 genera were found. Species varied with climate and kind of tree. Most common overall were Criconemella annulata, Xiphinema californicum, Gracilacus epacris, Pratylenchus macrostylus, Rhizonema sequoiae, Sphaeronema californicum, Trichodorus californicus, Tylenchorbyncbus cylindricus, Filenchus vulgaris, Meloidogyne sp., and Ditylenchus anchilisposomus. These nematodes were often present in large numbers and it is likely that parasitism by some species constitutes one of the stresses to California forest trees.