PhD

The present study “Diversity analysis and reproductive biology of milk
yam (Ipomoea digitata L.)” was carried out in the Department of Plantation
Crops and Spices, College of Agriculture, Vellayani, during 2013-16, with the
objectives of estimating the magnitude of genetic variation in morphological and
biochemical traits in milk yam accessions and identifying superior accessions
with high tuber yield and active ingredient content. A detailed study of
reproductive biology and investigations on regional variation, influence of
climatic and soil factors on phytochemical content in milk yam were also
envisaged in the study.
A survey was conducted in natural growing tracts of Kerala and twenty
accessions of milk yam (both tubers and vines) were collected. Tubers of each
accession were subjected to preliminary phytochemical screening. The
accessions were raised in the field during 2015-16 for analyzing phenotypic
diversity and were evaluated for yield and active ingredient content in
randomized block design with three replications. Ethnobotanical information
collected in the study showed that in Thiruvananthapuram District, the tuber
powder along with cow milk was mainly used as galactagogue and with honey
as a tonic whereas, in Kollam and other District the root powder was mainly
used as galactagogue and tonic for children. Traditional medical practitioners
use tubers of I. digitata for preparing galactagogues and immuno modulatory
herbal medicines. Data collected on climatic soil characters of natural growing
tracts of milk yam revealed that it has wide adaptability to varying climatic and
soil conditions.
In the initial phytochemical screening significant regional variation in
phytoconstituents were noticed and accessions T20 (Udumbanchola, Idukki)
along with T1 (Meppadi, Wayanad), T7, T16 and T9 (Kalliyoor, Pallichal and
Punnamoodu, Thiruvananthapuram) recorded superior values for phytochemical
content. High performance liquid chromatography analysis of tuber powder (T3
and T11) detected the presence of two compounds viz., Rutin and Nicotinic acid
in the tuber which has not been reported so far.
In the field experiment analysis of variance revealed significant variation
in vine, leaf (except petiole length) and yield characters. The accessions which
produced highest fresh tuber yield were T15 (870.47g), T17 (821.93g), T11
(752.3g), T12 (744.13g), T6 (698.53g) and T3 (620.27g). Among these
accessions, T11 (Kumbalangy, Ernakulam District) and T3 (Panamaram,
Wyanadu District) recorded superior values for phytoconstituents in both first
and second year analysis. Accessions T13 and T9 (Neyyattinkara and
Punnamoodu) recorded the highest values for all phytoconstituents during the
second year analysis; however their tuber yield was comparatively lesser.
Detailed investigations on reproductive biology of milk yam revealed
that the plants exhibit moderate flowering habit and produced cymose
inflorescence with bright pinkish showy flowers (5.9 x 4.2 cm) with longevity of
8-10 hrs. Pollen grains of milk yam were identified to be of monard type with
pantoporate aperture morphology and spinose exine ornamentation. Shape of
pollen was spherioidal with pointed spines. Diameter of pollen ranged from
63.6-102μm, spine length (8.28-11.5μm), inter spinal distance (5-6.7μm),
aperture diameter (2.8-4.6μm), style length (23.5-25.8mm) and length of
filament ranged from 21.2-25mm. Stigma remained receptive for eight hours
from the time of anthesis. 97.81 per cent of pollens were fertile and 94.96 per
cent pollens were found to be viable. 80 per cent fruit set was observed in open
pollination. Five different pollinators were identified visiting the flowers for
both nectar and pollens. Fruit is a capsule containing four seeds with average
size of 0.7 cm x 0.8 cm.
The characters, fresh and dry tuber yield per plant, number as well as
girth of tubers, and protein content in the tuber showed the highest difference
between PCV and GCV which indicates that the influence of environment on
these characters is considerable. But lower difference between GCV and PCV
for the biochemical characters viz., glycoside, alkaloids, carbohydrates, and
flavonoid content in tubers and morphological characters viz., mature leaf length
and breadth pointed out that the variation observed in these characters are
mainly due to genetic reasons.
High heritability coupled with high genetic advance was observed for
morphological characters viz., plant height, internode diameter and biochemical
parameters viz., carbohydrates, flavonoids and oils. This indicates additive gene
action for these characters and genetic improvement can be done by selection
based on phenotypic performance.
Significant regional variations in phytoconstituents exist in milk yam
accessions and accessions from Wyanad, Idukki and Thiruvananthapuram are
rich in phytoconstituents. The phytochemical content in milk yam tubers
increases with maturity and accessions with higher tuber yields need not be rich
in phytoconstituents and vice versa. Two promising accession with high tuber
yield and significant phytochemical content identified in the study are T3
(Panamaram) and T11 (Kumbalangy). Apart from collecting, detailed information
of reproductive biology of milk yam, the study also revealed the influence of
environment in yield and protein content of milk yam tubers. Glycoside, alkaloid,
carbohydrates, and flavonoid content in tubers were found to be genetically
controlled.
An immense scope for research in I. digitata L. exists since its
therapeutic and functional potential is not exploited deeply. Phytochemical
profiling of the tubers is necessary to get a gross idea of the contents present in
the drug which will not only help to have a chemical mapping of the drug but
also will be helpful in assessing the probable mode of action of the drug. Its
tuberisation morphology as well as anatomy, phytochemical characterization
using sophisticated and accurate analytical tools like chromatography,
spectroscopy etc. can be beneficial for authenticating the crude drug to prevent
its adulteration with Vidari (Peuraria tuberosa).