Physiological responses of chandrashura (lepidium sativum L.) to salt stress
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Date
2004
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CCSHAU
Abstract
Chandrashura (Lepidium sativum L.) is a crop of medicinal
importance which is being cultivated in the arid and semi-arid regions of
different states like Gujrat, M.P., Rajasthan, U.P., Maharastra and to some
extent in Haryana also as a rabi crop where it is influenced by salt/water
stress. The present research deals with the physiological responses of
Chandrashura to salt stress. The effects of salts that chiefly contribute to soil
salinity viz. NaCl and Na2SO4, singly as well as in combination were studied
on seed germination, seedling growth, plant water relations, growth and
development; biochemical as well as minerals constituents and yield
attributes. To achieve the objectives of the research problem two experiments
were planned.First experiment was conducted in the controlled conditions of a
culture room with 25±1ºC temperature and 16h light, 8h dark period. The
experiment was performed in petri dishes using three salt treatments viz.
NaCl, Na2SO4 and NaCl + Na2SO4 (1:1 meq/l basis) with varying EC levels
viz. O (control), 4,8,12,14,16, 18, 20, 22, 24 and 26 dSm-1. Results revealed
that the progressive increase of EC levels not only inhibited the seed
germination but also declined the speed of germination (maguire index).
Effective delay in germination was more pronounced under Na2SO4 among
all the salt treatments at higher EC levels. All the three salt treatments were
proved deleterious to Chandrashura seedlings as they decreased the seedling
length, vigour index, fresh and dry weights of root and shoot. Na2SO4
treatment in this regard was found most detrimental to seedlings followed by
combined salt treatment and then NaCl treatment.
The above salt treatments also reduced the relative water
content in shoot of seedlings with increase of EC levels. Na2SO4 treatment
was found more effective in reducing RWC at low EC levels than NaCl
treatment. Maximum increase of membrane permeability index under
Na2SO4 treatment while minimum under NaCl treatment indicated more
toxicity of the former on plasma membrane.
In the second experiment, plants were raised in polythene bags
with sieved dune sand in screen house at varying EC levels viz. 0 (Control), 4,
6, 8, 10, 12, 14 dSm-1 of NaCl, Na2SO4 and NaCl+Na2SO4 (1:1 meq/l basis)
along with nutrients. Salt stress in general adversely affected the various
growth and developmental parameters viz. plant height, number of leaves per
plant, number of branches per plant, root volume, root and shoot dry weight,
total plant dry weight, root and shoot ratio. Among the three salt treatments,
NaCl proved most deleterious while Na2SO4 least deleterious to
Chandrashura with regard to above parameters. Significant changes in
various biochemicals were also recorded. Total soluble carbohydrates as well
as proline accumulated under increasing stress conditions created by the
salts. The accumulation of these organic solutes in different plant organs
helped plants in osmotic adjustment under salt stress. Ascorbic acid, chl ‘a’,
chl ‘b’, total chlorophyll contents undergone more reduction under NaCl
treatment than under Na2SO4 treatment. Ascorbic acid content was in
general higher in top leaves of plants. Na+, Cl- and SO42- contents of shoot
increased while K+ content decreased with increasing EC levels.
Accumulation of Na+ and Cl- was more under NaCl treatment while that of
SO42- was higher under Na2SO4 treatment.
Slight postponement in number of days to flower initiation and
preponement in crop maturity was found with increasing EC levels. All the
three salt treatments caused significant reduction in the number of fruits per
plant, 100 seed weight and the seed yield per plant with the increase of EC
levels. The NaCl treatment in this regard was more reducing then Na2SO4
treatment and caused more than 50% reduction in seed yield beyond 12
dSm-1 EC level.
The response of NaCl and Na2SO4 salt treatments was contrary
at germination-early seedling growth and later plant growth stages. NaCl was
relatively less deleterious at germination and early seedling growth stages but
found more toxic at the later plant growth stages than Na2SO4.