Studies on Effect of Decomposing Products of Leaf Of Cocoyam (Xanthosoma Mafaffa Schott.) On Phytophthora Palmlvora (Butl.) Butl.
Date
1978-04
Authors
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Journal ISSN
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Publisher
University of Ghana.
Abstract
Germination of P.palmivora sporangia and zoospores, growth
of the hypha and formation of the sporangia in the presence of
decomposing leaves of cocoyam were investigated.
Cocoyam leaves buried in soil, from an experimental cocoa
plot at the Cocoa Research Institute at Tafo, were rapidly decomposed and they completely rotted in 12 days. Fungal species
belonging to the genera Alternaria, Aspergillus, Cladosporium,
Curvularia, Fusarium, Penicillium, Rhizopus and Trichoderma were isolated from the decomposing cocoyam leaves. Two of the fast
growing species, Rhizopua oryzae and Rhizopus stolonifer, were
selected and used as agents for decomposition of the cocoyam leaves
under sterile conditions.
Decomposition of the cocoyam leaves in the laboratory was
carried out at 25°C and 30°C, the respective optimum temperatures
for growth of R.oryzae and R.stolonifer. Growth by both species
in Cassava-dextrose broth at the optimum temperature caused a shift
in the pH of the medium from pH 5.30 to around pH 2.30. Culture
filtrates of these fungi were therefore adjusted to neutral pH in
experiments in which they were used.
Direct germination of P.palmivora sporangia was greatly
stimulated, by about 400 per cent, by both Rhizopus culture
filtrates. Large number of germ tubes emerged from sporangia
growing in the culture filtrates of the Rhizopus species. Zoospore
germination was also improved by at least 30 per cent by culture
filtrates of both R.oryzae and R.stolonifer. R.stolonifer greatly
stimulated vegetative growth of P.palmivora, whilst R.oryzae slightly suppressed it.
Direct germination of P.palmivora sporangia was stimulated
by exudate of undecomposed dry cocoyam leaves; germination in the
exudate and in distilled water was 54.9 and 15.3 per cent,
respectively. Indirect germination and zoospore germination were,
however, inhibited by about 80 and 50 per cent, respectively, by
the leaf exudate. Vegetative growth on Cassava-dextrose agar
containing different concentrations was slightly improved whilst
sporangial formation was depressed.
. Direct germination of P.palmivora sporangia at 30°C Was inhibited by extracts of Rhizopus-decomposed cocoyam leaves.
Amendment of the R.oryzae-decomposed leaf extract with Fructose
Glucose, Maltoso or Sucrose negated the inhibitive influence. '
sodium nitrite, Asparag1ne and Ammonium tartrate also improved
direct germination in the R.oryzae-decomposed leaf extract, but addition of asparagine caused further inhibition.
The Rhizopus-decomposed cocoyam leaf extract slightly
inhibited indirect germination of P.palmivora sporangia at 20°C.
With the exception of Fructose at 1.0 percent with improved
germination there was greater depression of germination in
R.oryzae-decomposed cocoyam leaf extracts amended with Glucose,
Maltose and Sucrose of concentrations of 1.0, 2.0, 3.0 and 4.0
per cent w/v or with Ammonium nitrate, Peptone and Sodium nitrate
at 0.5, 1.0 and 1.5 per cent. Asparagine improved indirect
germination only at 0.5 per cent concentration, but slightly
suppressed it at higher concentrations of 1.0 and 1.5 per cent.
Zoospore germination was slightly inhibited by Rhizopus - decomposed cocoyam leaf extract. The inhibition was annulled by
Fructose, Glucose, Maltose and Sucrose. Higher concentrations
of Peptone and Sodium nitrate, at 1.5 per cent, supported even
poorer germination than the unamended extract, but germination
at the lower concentrations of 0.5 and 1.0 per cent in Ammonium
tartrate and Peptone-amended extract was superior.
The zoospores of P.palmivora diSintegrated in extract of
R.oryzae-decomposed cocoyam leaf extract of pH 4.0. Germination
improved gradually from 40.9 to 79.3 per cent on raising the pH
of the extract from pH 5.0 through 9.0. Optimum sporangial
germination occurred at pH 7.0 and gradually decreased as the
pH moved away from the optimum to both the alkaline and acid ends
of the pH range. There was germination at the extremes, pH 4 and
pH 9, used.
Extracts of leaves decomposed by either Rhizopus species
slightly improved vegetative growth of P.paluivora on Cassava dextrose agar but depressed sporulation with increase in concentration, from 5.0 to 20.0 per cent.
An aqueous extract of soil from the same plot at the Cocoa
Research,Institute Tafo only slightly reduced direct sporangial
germination at 30 C and zoospore germination but did not affect
indirect germination at 20˚C nor vegetative growth and sporangial
formation in P.palmivora. However, extract of the soil containing
decomposed cocoyam leaves substantially decreased zoospore germination from 14.6 per cent in the control of distilled water to 2.9
per cent., Direct sporangial gemination was similarly reduced from
40.2 in distilled water to 7.7 per cent in the extract. Vegetative growth remained unaffected but sporulation was reduced slightly
at higher concentrations (15.0 and 20.0 per cent v/v) of the extract.
The decomposition products of cocoyam leaves contained very
little nutrients. Although Glucose, Fructose, Mannitol and
Sorbitol were identified, by paper chromatography, in the exudate
of dry cocoyam leaves, at concentrations of 5.0 - 7.0, 6.0 - 7.0,
2.0 - 3.0 and less than 1.0 microgram per gram of dry leaf,
respectively, only Trehaloso,at 18.0 - 20.0 microgram per gram,
was identified in the Rhizopus-decomposed leaf extract.
The amino acids, Alanine, Amino-butyric acid and Asparagine
were also identified, by paper chromatography, at concentrations
of 1.0 - 2.0, less than 1.0 and 2.0 - 3.0 microgram per gram,
respectively, in the exudate of dry cocoyam leaves but none was
detected in the Rhizopua-decomposed leaf extract.
Description
M.Sc. Degree
Keywords
Xanthosoma Mafaffa Schott, Phytophthora Palmlvora (Butl.) Butl, Decomposing Products of Leaf Of Cocoyam, Effect, Leaf Of Cocoyam