MSc

Stevia (Stevia rebaudiana Bertoni) is natural sweetener of the
Asteraceae family, commonly known as candy leaf, honey leaf, sweet leaf,
or sugar leaf. The plant contains steviol glycosides (SVglys), which are of
high interest in the human diet as a low calorie and high potency sweetener.
As the leaf is the main economic part of stevia, production of more leaf
biomass with higher steviol glycosides is the main criteria for crop
performance. Since both biomass production and quality are equally
important in medicinal plant cultivation, it is necessary to determine optimal
growth factors that can ensure high yield and quality.
The present study entitled “Environmental influence on yield and
quality of stevia (Stevia rebaudiana Bertoni)” was conducted at the
Department of Agronomy, College of Agriculture, Vellanikkara during the
year 2020. The objective of the study was to determine the influence of
growing conditions and planting dates on the biomass production and quality
of stevia. The study consisted of a field experiment designed in split plot
design with three replications and a pot culture. The aim of field experiment
was to find out the effect of growing condition and planting dates on yield
and quality of stevia. The main plot treatments consisted of two growing
conditions viz., open and 50 per cent shade and the sub plot treatments
consisted of four dates of planting viz., May 15th, June 15th, July 15th and
August 15th. The pot culture study was designed in completely randomized
design (CRD) to evaluate the phytochemical constituents of stevia leaves at
different growth stages.
Growth parameters such as plant height, number of branches, fresh
leaf weight, dry leaf weight, herbage yield, and total biomass yield were
significantly influenced by growing conditions and planting dates. Open
condition (8406 kg/ha) and May planting (10162 kg/ha) resulted in the
highest leaf yields of stevia. The interaction between growing condition and
planting dates was also significant. May planting under open condition
proved to be the best treatment with respect to leaf yield.
Growing conditions and planting dates had a profound influence on
physiological and biochemical parameters. May planting under open
conditions resulted in higher CGR and RGR values. Planting in May under
open condition resulted in the highest steviol glycoside content of 9.05 per
cent.
A positive correlation was observed between maximum temperature
and plant height, number of leaves, fresh leaf weight, total biomass yield and
total glycoside content. Whereas, negative correlation was found with respect
to afternoon R.H and rainfall
Pot culture study conducted to assess the variations in phytochemical
constituents of stevia leaves at different growth stages and growing
conditions revealed variations in parameters such as total carbohydrates, fat,
protein, soluble sugars, reducing sugars, non reducing sugars and steviol
glycoside contents. Total carbohydrates and moisture content was observed
to be higher under shaded growing condition, whereas open condition
resulted in higher contents of total fat, crude fibre, protein, total minerals,
total soluble sugars, reducing and non reducing sugars, total energy and total
steviol glycosides.
Total carbohydrates, total fat, moisture, total soluble sugars, reducing
and non reducing sugars and total steviol glycoside contents were higher at
flower bud initiation stage. A slight reduction in carbohydrate content was
observed towards maturity. The highest content of total protein was observed
at full bloom stage. Total energy value increased from 45 DAP, reached a
peak at flower bud initiation stage and decreased thereafter.
It can be concluded that open growing condition, planting in the
month of May and harvesting at flower bud initiation stage can be suggested
for better leaf yield and quality of stevia under Kerala conditions.