BSc - MSc (Int.)

The study entitled “Physiological and molecular studies in mitigating drought stress
of tomato (Solanum lycopersicum) by biochar with organic amendments” was conducted
at College of Agriculture, Vellayani, Thiruvananthapuram, during 2021-2022. The primary
objective of this study was to determine the physiological and molecular attributes of
tomato grown under water stress as influenced by biochar with organic amendments.
The experiment on tomato variety ‘Vellayani Vijay’ was conducted in a completely
randomized design in pot culture with five replications. In order to assess the effect of
biochar (BC) (0.5% w/w) and organic amendments such as vermicompost (VC) and farm
yard manure (FYM) in mitigating the consequences of water stress, individual treatments
viz. (Biochar (0.5% w/w), VC (50g/10kgsoil) and FYM (50g/10kg soil)) as well as
combined treatments viz. ((Biochar+VC) and (Biochar+FYM)) were carried out along with
T1 control (normal irrigated condition) and T7 control (water stress). The study consisted
of 12 treatments, in which T1 to T6 were irrigated normally whereas treatments designated
as T7 to T12 were subjected to 25% water stress. The present study was carried out using
biochar derived from rice husk that was subjected to maximum pyrolysis temperature of
550°C in a cylindrical iron tank. Water stress of 25% was imposed by gravimetric method
for a period of 80 days (after three weeks of sowing). The seedlings were maintained in
protected condition for the first three weeks.
Various morpho-physiological and yield parameters were evaluated at different
critical stages of the crop, such as seedling stage, vegetative stage, flowering stage, fruiting
stage and harvesting stage. Molecular studies were carried out at 50% flowering stage.
Water stress had a negative impact on morphological, physiological and yield attributes of
S. lycopersicum except total soluble solids, when compared to plants under normal irrigated
condition. Biochar treatment was found to effectively mitigate the deleterious impacts of
water stress. Plants treated with biochar outperformed the plants grown in both VC and
FYM with regard to all the physiological and morphological parameters studied. However
the best yield performance (yield and yield parameters) was obtained in the treatment with
124
biochar in combination with vermicompost. According to the results obtained it was clear
that the combined application of biochar and vermicompost increased the relative water
content, membrane stability index, chlorophyll stability index, photosynthetic rate, total
protein content, stomatal conductance, transpiration rate, plant height and primary branches
per plant under both water stress and normally irrigated conditions when compared to the
non-treated controls. This indicates the ability of biochar to retain water and thereby
increasing soil moisture content. Furthermore, under water stress, there was a significant
improvement in the morphological traits such as, root weight (57.07%), shoot weight
(33.33%), root: shoot ratio (17.91%), fruit number (43.54%), fruit size (69.93%), fruit
weight (13.10%), total soluble solids (10.32%) and yield (62.42%).
SlWRKY8 gene has an important role under drought stress conditions and is reported
to have role in the regulation of ROS pathways and mitigating the detrimental effects in
plants grown under water stress condition. In the present study, quantitative real time PCR
amplification of SlWRKY8 gene in tomato leaves (taken at 50% flowering stage) showed
an increase in the expression level of this gene in the treatments with combined application
of biochar and vermicompost, both under water stress condition (T11) (3.24 fold) and
normal irrigated condition (T5) (1.51 fold) compared to their respective controls (T7 and
T1). This indicates that BC and VC combinations can be applied to tomato plants grown
under water stress for the upregulation of SlWRKY8 genes which regulate the ABA
signaling and helps in ABA-mediated stomatal closure in water stress condition.
Taken together, the study demonstrate that, the combined application of
vermicompost and biochar not only boost crop production, but also mitigate the destructive
impacts of water stress by influencing physiological, morphological and molecular
parameters of tomato.