Friesia X, 4-5

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the plant pathogens grow best on media with an initial pH of 5.0 to
6.5. It was noticed that the pH of the culture filtrates drif'ted towards
neutral point. According to LILLY & BARNETT (1951), these changes
in pH were due to changes in the relative amount of acids and bases
formed or withdrawn and to the ionization constants of these compounds.
.
The pathogen utilized all the carbon sources except organic acids
(malie and tartaric). COCHRANE (1958) has assigned three factors
which interfere with the utilization of organic acids. Firstly, the
cells are often impermeable to organic acids at physiological pH levels,
secondly, the utilization of neutralized organic acids eauses a rise of
the culture pH which may interfere with growth and thirdly, the
chelation of inorganic ions by certain organic acids; which of the
above factors may be responsible for failure of the present organism
to develop mycelial growth on the organic aeids included in the present
investigation could not be established. Present results are, however,
also not in agreement with those of AGNIHOTRI (1968) who
observed growth of Colletotrichum capsici on these organic acids.
Glucose, mannose and galaetose were found to be good sources of
carbon. Similar results have also been reported by numerous investigators
(TANDON & BHARGAVA 1964; RAINA et al. 1970; BONN &
CAPPELLINI 1970). Polysaccharides except inulin supported good
growth of the present organism. The utilization of these substanees
by fungi depends upon secretion of the necessary hydrolytic enzymes.
The poor growth on inulin may be due to the limited synthesis of
enzyme inulase. In the current study sugar alcohols (dulcitol and mannitol)
supported poor growth. Present results are in agreement with
those of CHATURVEDI (1964) and TABER et al. (1968) who reported
poor growth of Colletotrichum capsici and Alternaria raphani on
dulcitol and mannitol respectively. The faet that the present organism
grew poorly on mannitol suggests that the eulture may laek polyol
dehydrogenases and, therefore, could neither use nor synthesize mannitol.
Nitrates were found to be satisfactory sources of nitrogen. Similar
results have been obtained by THIND & MADAN (1970) and BAlS et al.
(1970). Moderate growth on calcium nitrate as compared to the good
growth on rest of nitrates may be attributed to the differences in
their metallic ions. It is apparent from Table III that the fungus was
incapable of growing in a nitrogen free medium and on sodium nitrite.
Nitrites are eonsidered to be toxie to fungi at acidic pH values. The