Attached
The factors responsible for disease resistance of
Hevea clones to ~. gloeosporioides were st~died. First, field
observations showed that the s~sceptibility of Hevea to the
disease varied in different clones and an interaction was
seen between clones and locations. When the infection was low
incidence and severity of the disease were linearly related;
a c~rvilinear relationship was evident when the level of infection
was high.
Isolates of £. gloeosporioides varied in their growth
characteristics, morphology and spore prod~ction. They showed
differential s~sceptibility to vario~s clones.
Leachate of resistant clones suppressed the growth
of the pathogen and favo~ed appressorium formation. 1£ vitro
st~dies indicated that growth promoting s~bstances were not
cond~cive for formation of appressoria. There was no difference
either q~antitatively or q~alitatively in s~gars and amino acids
in the leachate of different clones.
Waxes and s~bstances associated with it are inhibitory
on the pathogen at high concentrations. These substances separated
by TLC showed two inhibitory zones. Phenolic and acidic s~bstances
are associated with the cr~de wax extract.
Leaves of resistant clones s~pported less germt~be
growth than s~sceptible leaves, b~t favoured appressori~m formation.
On penetration of resistant tiss~es a rapid disorganization of
the cell content was observed, arresting hyphal growth. In
s~sceptible clones hyphae invaded deeper in to the tissues and
colonized the mesophyll cells both inter and intracell~lerly;
VIII aoervuli were formed 12 h after inoculation. The migration of
nuolei towards the site of penetration was observed in resistant
olones.
There was no relationship between either total or
orthodihydroxy phenol level and field resistance of Hevea olones.
But the infection was accompanied by a change in the orthodihydroxy
phenol level, particularly in resistant clones.
In Hevea,peroxidase activity was higher than
polyphenoloxidase and inorease in peroxidase level with the
infection was more pronounced in resistant clones. Infection
also resulted in the increase of soluble protein content.
