| dc.description.abstract | The fungus Ganoderma lucidum is one of the common pathogens
of a number of tropical palms such as coconut, arecanut etc.
Although the pathogenicity of the fungus on a wide range of hosts
has been recorded, there are very few reports on the control of
this disease and little is known about the biochemical aspect of
the host plant as well as the pathogen; practically nothing is known
regarding the role played by the extracellular enzymes such as
pectolytic and cellulolytic enzymes, and phenol oxidases, which
are known to play an important role in pathogenesis.
Two enzymes namely endopolygalacturonase and laccase which
are suspected to play a major role in pathogenesis were chosen
for studies. The first part (Chapters II and III) deals with
the studies on the (a) effect of fungicides on the in vitro growth
of G. lucidum and (b) the two enzymes, endopolygalacturonase and
laccase, which are elaborated by the fungus into the culture
fluid. Studies on the effect of various fungicides, antibiotics
and phenolic compounds showed that the antibiotic cycloheximide
and the fungicides Maneb and K.C. 1584 were potent inhibitors of
the fungus growth. The arecanut tannin inhibited the growth only
at 1.0% level.
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The optimum conditions such as time, pH, effect of different
concentrations of carbon and nitrogen sources, vitamins,
casein hydrolysate and yeast extract, necessary for the growth
as well as for the elaboration of the enzyme endopolygalacturonase
showed that maximum growth was obtained by 16th day at pH 4.5
but enzyme production was maximum on 20th day at pH 5.0–5.5.
Although addition of vitamins and yeast extract enhanced the
growth they had decreased the enzyme production.
The enzyme endopolygalacturonase has been purified 65 fold
and its properties such as substrate specificity, time course of
enzyme activity, optimum pH, temperature, and the effect of enzyme
and substrate concentrations on enzyme activity have been studied.
In addition, the effect of metal ions, inhibitors, fungicides
have been carried out.
The enzyme had two temperature optima (50°C and 70°C).
Attempts to separate them were not successful. Among the fungicides,
inhibition by Blitox 50 was more significant than other inhibitors
tested. The metal ions copper, cobalt and mercury and calcium
inhibited the enzyme activity.
Based on the results obtained it is concluded (a) this high
concentration of tannin required to inhibit the growth and (b) the
high concentration of iron content and low calcium content in the
soil, may be partly responsible for the susceptibility of arecanut
palm to this fungal infection | |
