BSc-MSc

The study entitled "Physiological and Molecular Mechanisms of Water Stress
Tolerance in Cardamom (Elettaria cardamomum L. Maton)" was carried out in the
Department of Plant Physiology, College of Agriculture, Vellayani, Thiruvananthapuram,
and Cardamom Research Station, Pampadumpara, Idukki during 2021-2022. The
objective of the study was to analyze the physiological and molecular mechanisms of
water stress tolerance and the genetic variability for water stress tolerance in cardamom
(Elettaria cardamomum L. Maton) varieties.
The study was carried out in a completely randomized design with two
conditions: stress and irrigated condition (control) imposed on four varieties of
cardamom, namely Green gold, PV-1, PV-2, PV-3, with four replications. Cardamom
plants were planted in grow bags with a grown-up tiller and a young shoot and
maintained at the Cardamom Research Station, Pampadumpara, Idukki. After six months,
stress was created by withdrawing irrigation for 30 days during the summer season. Four
replications of cardamom plants per treatment maintained as controls were grown in grow
bags at field capacity. The observations on physiological, biochemical, and molecular
characteristics were taken from stress-induced plants and controls.
The physiological parameters of the four varieties of cardamom under stress were
compared with the control. The four varieties of cardamom showed a significant
difference in relative water content, photosynthetic rate, and stomatal conductance. The
least percentage reduction in relative water content, photosynthetic rate, stomatal
conductance, and instantaneous water use efficiency was noticed in PV-2. Under
conditions of stress, the relative water content, photosynthetic rate, stomatal conductance,
and instantaneous water use efficiency varied significantly compared to the control.
There was a significant positive interaction between varieties and conditions (stress and
irrigation) in relation to photosynthetic rate and stomatal conductance. However, no
significant interaction was observed between varieties and conditions of stress and
irrigation (control) on relative water content and instantaneous water use efficiency.
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The main effect of small cardamom varieties, such as Green gold, PV-1, PV-2,
and PV-3, on biochemical parameters like total soluble protein, MDA content, and
proline content, showed significant variation. Similarly, total soluble protein, MDA
content, and proline content differed significantly under conditions of stress and
irrigation. However, no significance was noticed in the interaction between varieties and
conditions with respect to total soluble protein. The total soluble protein of PV-2 showed
a 37.1% reduction under stress compared to the control maintained under irrigated
conditions. The maximum mean total soluble protein was recorded in Green gold under
stress (35.033). The maximum percentage increase in MDA content was analyzed in PV
3 (117.9%), and the minimum was recorded in Green gold (4.2%). The minimum
percentage increase in proline content was reported from PV-2 (85.7%), and the
maximum percentage increase was recorded in Green gold (97%).
The molecular analysis of cardamom was done using the leaf samples collected
from the plants. RNA was isolated from the samples, which were used for cDNA
synthesis for RT-qPCR. The relative fold change was analyzed using Ct values, which
showed upregulation of the dhn-1 gene under stress for PV-2 (1.151 fold) followed by
PV-1 (1.099 fold) with respect to the control.
The study confirmed that 30 days of stress as treatment was shown to be affecting
the physiological, biochemical, and molecular parameters of all the varieties (Green gold,
PV-1, PV-2, PV-3). The treatment caused significant variation in all analyzed variables.
The treatment showed a reduction in the values of relative water content, photosynthetic
rate, stomatal conductance, and total soluble protein while an increase in the values of
water use efficiency, MDA content, and proline content in all varieties. The molecular
basis of water stress tolerance studied by RT-qPCR using the dhn-1 gene primer showed
upregulation of the dhn-1 gene under stress conditions.
The results of the study indicated that all varieties (Green gold, PV-1, PV-2, PV
3) are affected by stress and all of them showed resistance to the stress. Among the
varieties, PV-2 showed the most resistance.