Environmental Engineering Reference
In-Depth Information
eccentric and centric/sub-centric forms of
Saprolegniaceae, reveals a very interesting and
characteristic pattern of global distribution of
Saprolegniaceae. For example, studies made in
the Indian subcontinent (Prabhuji
1984a
;
Srivastava
1967a
,
b
) and Brazil (Milanez
1967
,
1968
,
1970
; Milanez and Beneke
1968
), both
within tropical regions of the globe, have shown
a distinct dominance of eccentric forms over
centric and sub-centric forms. By contrast,
investigations conducted in United Kingdom
(Dick and Newby
1961
; Dick
1966
), Canada
(Dick
1971
), Iceland (Howard et al.
1970
),
United States of America (Miller and Ristanovic
1969
) and Denmark (Lund
1934
,
1978
), which
represent temperate regions of the world, indi-
cate dominance of centric and sub-centric forms
over the eccentric forms of Saprolegniaceae.
Based on such studies, a distinct eccentric
and centric (including sub-centric forms)
'Occurrence Zones' of the world may be identi-
fi ed for the members of Saprolegniaceae
(Prabhuji
2011
). Further studies in other tropi-
cal and temperate regions may yield data that
further confi rm this hypothesis.
Many of the traditional water and soil
sampling methods have been found to yield
ecologically viable results, although some are
either unfeasible or fail to provide statistically
signifi cant data. The methods adopted by
various aquatic mycologists for quantitative
assessment of water mould propagules in water
samples have not been found to provide reliable
data. By contrast, quantitative methods applied
to soil samples appear to yield reliable data.
The occurrence, distribution and periodicity
of water moulds in water bodies and soil have
also been reviewed, along with altitudinal
and global distribution patterns in relation to
oöspore type (Prabhuji
2010
,
2011
). These
fi ndings point to the need for further work to
develop new methods that yield reliable quan-
titative data from water as well as soil samples.
Further studies made in different geographical
regions of the globe would defi nitely strengthen
or modify these observations.
Physiological and Biochemical
Studies
The saprolegniaceae, in common with many
other fungi, are rather effi cient machines for the
conversion of substrate to substance given the
proper conditions. Ample evidence is to be
found in the overfl ow from their metabolism -
the accumulation of such compounds as fats,
carbohydrates and the organic acids and the
increases in dry weight and colony size
(Johnson et al.
2002
).
Actively growing cultures of water moulds
reach their maximum growth yield rather quickly
under favourable conditions and then decline
due to loss in mycelial dry weight. Darnaud
(
1972
) visualized that this pattern of colonial
development took place in three phases, namely,
active growth, stationary phase and autolysis,
which is usually represented by 2-8, 8-30 and
3-90 days period, respectively. Jain and Prabhuji
(
1985
) have given, for the fi rst time, a growth
equation for
Saprolegnia luxurians
(Bhargava &
Srivastava) Seymour and derived the value of a
constant. They divided the sigmoid curve of
growth in two parts - the exponential and straight
line part and decline and stationary part - and
indicated that the period for these parts varies in
different members due to which the value of con-
stant varies.
Miller and Ristanovi
(
1975
) studied the
nutritional variability in
Saprolegnia
. Nutritional
requirements affecting the metabolism have also
been studied by Obel (
1910
), Moreau and
Moreau (
1936a
,
b
,
1938
) and Harrison and
Jones (
1975
). Basically, the physiological and
biochemical studies on the members of oömyce-
tes have been done on the following four funda-
mental lines:
(a) Nutritional requirements during growth and
development
(b) Asexual reproductive physiology
(c) Sexual reproductive physiology
(d) Effects of various physico-chemical factors
on the life cycle
ć
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