|Abstract or Summary
- Self-interactions (effects of reinoculation with the same nematode)
in Meloidogyne hapla and Heterodera schachtii on Beta vulpris at
different levels of inocula with various population combinations were
studied. In M. hapla, the only significant increase of galls was
noted in treatments when 250+250 larvae were inoculated at 10-day
intervals. Longevity of plants in double inoculated treatments was
lower than single inoculated series. Similarly, lower ratios of
total soluble/reducing carbohydrates were obtained in double
inoculated series as compared to other treatments. Total quantities
of B, K, and P were lower in all inoculated plants as compared
to non-inoculated series. In H. schachtii, cyst formation was
increased from three to five fold in all double inoculation treatments as compared with single inoculated series. Longevity of plants in
double inoculated series was lower than single inoculation treatments.
Total quantities of B, K, and Mg were lower in all inoculated plants
as compared to non-inoculated control series. Lower quantities of
Mn, Cu and Zn were observed in most of the double inoculated treatments
as compared to single inoculated series.
Interactions of M. hapla with H. schachtii at different levels of inocula with all population combinations and different inoculation
periods were studied. Results indicated significant reductions of M.
hapla galls in all treatments when H. schachtii preceded the latter by
ten days in inoculation. This interaction was termed as amensalism
with M. hapla serving as an amensal and H. schachtii serving as an
inhibitor. Conversely, when M. hapla preceded H. schachtii by ten
days in inoculation, there were significant increases in cyst formation
by the latter. This relationship was termed as commensalism with
H. schachtii serving as a commensal. In both of these interactions,
however, the pre-invading parasites acted independently and had a
population growth and establishment equal to treatments receiving
either of the parasites alone. In treatments when both nematodes were
inoculated simultaneously, there were no significant changes in population
of either parasite. Relationships of this nature were termed as
neutralism. Ratios of total soluble/reducing carbohydrates were
lower in treatments when M. hapla preceded H. schachtii. These results also were reflected on plant longevity rate. Although there
were variations in longevity of plants in all treatments, the plants
inoculated with both nematodes had less longevity than those inoculated
With either parasite alone.
Further studies with longer periods between inoculations indicated
that if the majority of pre-invading parasites (M. hapla) were
in the second to fourth stages of development within plants prior to
inoculation by H. schachtii, the growth and development of the latter
was retarded. Conversely, when majority of pre-invading parasites
(M. ahap.la) were at stages of young females prior to H. schachtii
inoculation, the growth and survival of the latter was greatly increased.
As the pre-invading parasites (M. hapla,) reached stages of
fully grown (eggs were not observed) and egg - laying females in plants
prior to inoculation by H. schachtii, the growth and development of
the latter progressively decreased.
Histopathological interrelationships of M. hapla with H.
schachtii were studied. Anatomical changes due to M. hapla infection
were characterized by regions of hypertrophy and hyperplasia.
Hypertrophied cells formed giant cells within stele and their number
varied from 4-7 per nematode feeding site. Hyperplastic regions
composed of large number of relatively small compacted cells surrounded
the giant cells. Syncytia caused by feeding of H. schachtii
became dense and multinucleate. They were typically formed within stele and were limited on the side toward the nematode by endodermis
or in part by cortical cells. Histological changes in samples exhibiting
both nematodes at one feeding site were characterized by presence
of the pathological tissues induced by both nematodes. In most
cases xylem elements separated the two pathological tissues. In some
sections a single wall separated these two pathological tissues and no
dissolution of the separating walls was observed in any section.
Apparently each nematode developed normally and produced its own
characteristic pathological changes of tissue independently from the
The role of M. hapla as breaker of resistance to H. schachtii
in B. patellaris was investigated. A few poorly developed H. schachtii
cysts lacking eggs were observed in some treatments when M. hapla
preceded H, schachtii by ten days in inoculation, Results indicated
that M. hapla may play a role as a predisposing factor to infection
by H. schachtii.