PhD

The present investigations on "Pre-zygotic incompatibility and
evaluation of open pollinated and hybrid progenies of Holostemma adakodien
Schult." was carried out at Department of Plantation Crops and Spices, College of
Horticulture, Vellanikkara during the period from 1997-200 l. The study was
aimed at understanding the incompatibility reaction in adapathiyan accessions,
studying the pollen pistil interaction and to find out effect of different methods to
break the incomaptibility barrier. It also envisages to evaluate the germplasm
accessions and hybrid progenies to exploit the variability, to select ideal types, and
to find out correlation between seedling characters and yield for screening superior
types in the seedling stage.
Adapathiyan is a profuse flowering plant bearing cymose inflorescence
in the leafaxils. Flowers are bisexual, regular, complete and actinomorphic, typical
of asclepiadaceae, the milk weed family. The peak anthesis time was between 9.00
and 10.00 am. Anther dehiscence was observed in flowers on fourth day of
opening with maximum between 11.00 and 13.00 am. Stigma remained receptive
at the anthesis time on the first day of flower opening. The receptive surface of the
stigma was found to be the five lateral sides. The different accessions showed no
variation in these basic reproductive biology.
Naturally, adapathiyan is cross pollinated by insects but fruit set is very
rare. Even with assisted pollination, the fruit set could not be increased.

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Protogynous nature of the flower, position of pollinia enclosed within
gynostegium, downward position of the flower and tight membrane covering the
lateral receptive side of the stigma block other modes of pollination and favour
insect pollination.
Study of incompatibility reaction in fifteen accessions showed that all
the accessions are self incompatible. Ten different methods were tried to break the
self incompatibility reaction and end of season (October) selfing alone was
successful in two accessions out of fifteen evaluated.
The study of pollen pistil interaction by fluorescence technique revealed
that pollen germinate profusely on the stigma, grows through the style and reaches
the ovary in self as well as cross pollinations. This shows that late acting
gametophytic self incompatibility occurs in adapathiyan and ovary is the site of
incompatibility. The study conducted in fifteen accessions. has proved the
involvement of complete self incompatibility and evidence for the occurrence of
cross incompatibility in adapathiyan. This cross incompatibility may be the
primary reason for low fruit set in adapathiyan which is naturally designed for
cross pollination.
The incompatibility reaction may be due to some inhibitory substances
Il1 the ovary. The fruit set observed for the end of season self pollination in
accession HA. 7 (6.66%) and in accession HA. 13 (3.33%) indicated that the

incompatibility reaction might be reduced at the end of growth season due to
inadequate quantity of inhibitory substance in the ovary at that time.
Characterisation of fifteen accessions of adapathiyan revealed wide
range of variability in vegetative and economic characters, indicating great scope
for selection. Eight hybrid combinations along with four parents evaluated as pure
crop and inter crop in coconut plantation revealed superior performance of
adapathiyan as pure crop in terms of yield characters. Among the eight hybrid
combinations, H3 (Purple Cordate x Green Elongate) and H4 (Purple Cordate x
Green Cordate) were found to be more heterotic for yield characters. The superior
performance of H3 and H4 may be due to the involvement of Purple Cordate (PC)
as one of the parent. Among the different bi~chemical constituents studied, soluble
sugar recorded highest content of 8.13 per cent in H2 (Purple Elongate x Green
Cordate) as inter crop and HI (Purple Elongate x Green Elongate), H2 (Purple
Elongate x Green Cordate) and PI (Purple Elongate) were on par in soluble sugar
content as pure crop. Since soluble sugar present in roots contribute to the
medicinal properties of adapathiyan, selection of hybrids with Purple Elongate
(PE) as one of the parent is desirable.
The above observations suggest the utility of Purple Cordate (PC) and
Purple Elongate (PE) types as seed parent in hybridisation programme of
adapathiyan or collection of seeds from Purple Cordate (PC) and Purple Elongate
(PE) types under open pollination.

Correlation of seedling characters with dry root yield revealed that leaf
area and inter nodal length showed significant positive correlation with yield
emphasising its use as selection indices in the seedling stage.