- A study, using greenhouse and laboratory experiments, was
made of Hemicycliophora similis from Bandon, Oregon to determine:
identity and morphometrics, time and development of a life cycle,
host plant preferences and optimum environmental conditions for
reproduction and pathogenicity.
Morphometric investigations revealed discrepancies between
the measurements of this nematode species and those recorded in
nematological literature for H. similis. Personal communications
with R. P. Esser, H. J. Jensen and B. M. Zuckerman suggested the
variations noted do not necessitate describing a new species. For
purposes of this research the nematode is named Hemicycliophora
Life history investigations were conducted to determine the
number of days required to complete a life cycle and the various
stages as the nematode developed from egg to egg. Eggs mature to first-stage larvae, without sheath or spear, in 3-5 days and hatch
as second-stage larvae in 8-10 days. Second-stage larvae inoculated
onto carrot seedlings matured into third-stage larvae in 12-15 days.
Fourth-stage larvae appeared in 25-28 days, and adults were present
in 35-38 days. Embryonating eggs were observed lodged within an
incompletely shed fourth-stage cuticle attached to adult females and
within the normal sheath surrounding the adult. One molting specimen
was found with two eggs lodged within the fourth-stage cuticle. Such
eggs were seen to develop to second-stage larvae; however, none were
observed over a long enough time period to determine if larvae hatched
and emerged free of the cuticular confinement.
Evaluated as hosts were beet, broccoli, carrot, corn, dill, pea,
radish, rutabaga, tomato and turnip. Carrot, tomato and turnip supported
the highest increase in population; no substantial increase was
observed on beet, broccoli, corn and dill. The nematode formed galls
consisting of large multibranched growths and reproduced on many of
the plant species tested. Galling of seedling roots was most severe
on carrot, but slight galling was observed on beet, rutabaga and turnip.
Multibranching was observed with varying severity in all hosts.
Germination of carrot seeds was reduced substantially when grown in
sandy soil infested with H. similis. Slight germination reductions
occurred with all hosts tested except corn and pea. Adults and larvae
were observed feeding behind root tips and on nematode induced galls. Root discoloration was noted on several plants.
To evaluate temperature and soil optima, rooted cranberry
cuttings, germinated cranberry seedlings and carrot seedlings were
utilized. Carrot seeds were planted in sandy soils of two different
textures and pH, infested with H. similis and grown in three temperature
regimes: 30°C and 24°C night, 22°C day and 14°C night and
30°C day 6 °C night. The optimum temperature for reproduction on
carrot was 22°C day 14°C night in both soil types. A pH gradient
developed in cups with the least acidic pH occurring at the base corresponding
to maximum nutrient uptake by plant roots. The soil mix
in which bog sand from Bandon was incorporated developed a more
acidic condition presumably due to the additional organic N content
which supplied ammonical nitrogen. The soil mix with Newport sand
had no additional organic N and a less acidic condition developed.
Maximum nematode population and root density also occurred at the
base of the cup. Plants grown in infested soil had sparse multibranched
roots; no galls were observed in this experiment.
Cranberry cuttings were grown in sterile bog soil from Bandon,
Oregon and inoculated with 225 nematodes/450 cc soil. The optimum
temperature for nematode reproduction and plant growth was 30°C
and 24°C night. Runner growth and root dry weights were not significantly
effected by nematode feeding. Germinated cranberry seedlings were subjected to similar conditions; temperature response was similar
to that of cuttings. Root dry weights and runner growth of cranberry
seedlings was greater in nematode inoculated treatments than
non-inoculated controls: nematode feeding on cranberry roots resulted
in an increase of multibranching.
This research indicated nematode feeding was detrimental to
growth of a variety of plant species. High soil populations of
H. similis caused severe reductions to root growth and seed germination.
However, since this study was conducted in controlled conditions,
it was not substantiated that this nematode caused a reduction
of growth to field-grown cranberry plants. Further investigations are
needed to correlate these findings with field data to determine pathogenicity