- The root-lesion nematode, Pratylenchus penetrans (Cobb 1917).
Filipjev and Shuurmans Stekhoven, 1941, is widely distributed throughout
Oregon and other temperate zones of the world. Economically
it is probably the most important plant parasitic nematode in Oregon
because of its abundance, wide host range of economic plants and
interactions with other plant pathogens in disease complexes.
A host range study of this nematode included many hosts which
fall into one of the four categories: vegetables, field crops, ornamentals
and weeds. Most of the plants included are commercially
grown in Oregon or are troublesome weeds. The hosts were given a
susceptibility rating. Most plants were found to be susceptible.
Some of the more susceptible hosts included the clovers, pea, radish,
sunflower and the weeds lambsquarter, pigweed and wild carrot.
Some plants found to be only slightly susceptible were bean, pepper, sugar beet, many grasses and wild oats. The African marigold was
found to be not susceptible.
New types of pear rootstocks are being actively sought to provide
dwarfness and disease resistance. A test of the susceptibility
to P. penetrans of several Pyrus spp. was conducted for additional
information. Pyrus ussuriensis Maxim. was found to be very susceptible
and P. Calleryana Dcn., a pear decline resistant rootstock,
and P. syriaca Boiss., a dwarf rootstock, to be slightly susceptible.
Other species were intermediate.
An interaction between two plant nematodes, P. penetrans, an
endoparasite, and Longidorus elongatus (de Mann, 1876) Thorne and
Swanger, 1936, an ectoparasite, was investigated using peppermint as
the common host. Results indicated that when the population of either
one of the nematodes was high the level of the other was significantly
lower. This is probably due to competition between the two nematodes
for food and space.
The association between P. penetrans and the fungus Verticillium dahliae Kleb. was studied. The two pathogens were grown in combination
and separately on peppermint in pots in the greenhouse.
Upon harvest the rhizosphere of the peppermint roots was assayed for
propagules of V. dahliae. Results indicated that when the nematode
was present there was a significant increase in the number of fungal
propagules in the rhizosphere. This increase may constitute the
necessary increase in inoculum potential of the fungus to cause the increased incidence of wilt which has been observed by several authors
when the fungus and nematode are found together.
There are many facets to the pathogenicity of P. penetrans.
Direct damage to the host as a result of feeding on host tissues is
but one facet. Control of this type of injury may be achieved by
utilizing host range knowledge in selection of cover and rotation crops
and in weed control. Interaction of this nematode with other plant
pathogens greatly increases its importance as a pathogen. Adequate
control of soil fungal diseases may be realized when the influence of
soil nematodes on such diseases is better understood.