Floral and reproductive biology
of Sarpagandha Rauvolfia serpentina (Gentianales: Apocynaceae) in semi-arid environment
of India
R.C. Sihag 1 & Nidhi Wadhwa 2
1,2Laboratory of Bee
Behaviour & Pollination Ecology, Department of Zoology & Aquaculture,
CCS Haryana Agricultural University, Hisar, Haryana 125004, India
Email: 1 sihagrc@rediffmail.com, 2 nidhiw2009@rediffmail.com (corresponding
author)
Date
of publication (online): 26 January 2011
Date
of publication (print): 26 January 2011
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: K.R. Sasidharan
Manuscript
details:
Ms # o2337
Received 30
October 2009
Final received
29 November 2010
Finally
accepted 21 December 2010
Citation: Sihag, R.C. & N. Wadhwa (2011). Floral and reproductive biology of Sarpagandha Rauvolfia serpentina(Gentianales: Apocynaceae) in semi-arid environment of India. Journal of Threatened Taxa 3(1): 1432-1436.
Copyright: © R.C. Sihag & Nidhi Wadhwa 2011. Creative Commons Attribution 3.0 Unported License. JoTT
allows unrestricted use of this article in any medium for non-profit purposes,
reproduction and distribution by providing adequate credit to the authors and
the source of publication.
Acknowledgements: We are thankful to Dr.
C.S.Tyagi, Sectional Head, Medicinal Plants, for raising the sarpagandha plants
and providing the field facilities. The financial assistance received by NW as merit stipend from CCS HAU is
gratefully acknowledged.
Abstract: Sarpagandha plant Rauvolfia serpentina (Linn.) Benth., ex
Kurz bears small, tubular white to pinkish flowers with gamopetalous corolla,
containing nectar deep at the base of the corolla tube. Psychophilous mode of pollination
appears to be prevalent. Flowering
occurs during two summer months. Anthesis takes place in the morning when atmospheric temperature ranges
from 25-29 0C, and anther dehiscence from 28-31 0C.
Flower longevity is for a little more than two days. Nectar is produced on both the days of flower opening, and
over a wide range of ambient temperature (29-44 0C). Flowers are protogynous preventing
selfing. Pollen viability and
stigmatic receptivity are for a short duration. When compared with the ‘absolute
reproductive potential’, the ‘realized reproductive potential’ is very low.
Keywords: Fertility status, floral biology, pollination, psychophily,
reproductive potential, Rauvolfia, sarpagandha.
For figures, images, tables -- click here
Sarpagandha (Rauvolfia serpentina (Linn.) Benth., ex
Kurz.) is a medicinal plant par excellence (Blackwell
1990), producing useful alkaloids like reserpine (Sahu 1983). Various parts of this plant are used to
treat human ailments (Dutta & Virmani 1964; Farooq 2005; Ebadi 2007), in
alternative systems of medicine. Sarpagandha is a threatened species found in the sub-tropical
regions. Seed propagation is
considered to be the best method for raising commercial crop, though seed
production is highly variable and low (Bhadwar et al. 1956). To understand the
probable reasons for low seed yield and threatened status of
this plant, the present study was undertaken.
Materials and methods
Sarpagandha
seeds were sown in the field in mid November 2005 and a nursery was raised at
the Research Farm of CCS Haryana Agricultural University, Hisar (India). Ten-week old plants from the nursery
were transplanted in small plots in the last week of January (on 24 January,
2006) and the plants were raised according to the prevailing agronomic
practices (Image 1).
(i)
Floral morphology and pollination mechanism: The functional relationship between floral morphology and
probable pollinators was studied by recording floral attributes like number and
placement of floral parts; and structure and position of the ovary. Corolla length and breadth/diameter
were also measured (n = 50 in each case).
(ii)
Floral phenology: Dates
when the first flowering appeared marked commencement whereas complete absence
of flowers on the plants marked cessation of flowering. Based on this, the flowering period was
determined (n = 100 plants). Dates
of mediocre and peak flowering (number of flowers per m2) were recorded by visual observations. Temperature maxima and minima during
these periods were also recorded.
The time
of anthesis, anther dehiscence and nectar production were recorded by
confirming the opening of flower, presence of pollen and nectar in the newly
opened flowers till their shedding (n = 100
respectively). Observations were
repeated at weekly intervals till cessation of flowering. Longevity of the
flower was determined by recording the time of opening and shedding (n = 900;
flowers taken at each weekly interval = 100, total weekly observations during
flowering period = 9).
(iii)
Fertility status: Pollen
was applied by hand on the stigma in the morning after anther dehiscence with
the help of a fine brush. The lay
out plan for hand pollination experiments was as under:
(a) Self-pollination experiments (Pollination within the same flower)
- Pollen
(Day 1 flower) x Stigma (Day 1 flower)
- Pollen
(Day 2 flower) x Stigma (Day 2 flower)
(b) Cross-pollination experiments (Pollination between flowers of same
plant)
- Pollen
(Day 1 flower) x Stigma (Day 1 flower)
- Pollen
(Day 1 flower) x Stigma (Day 2 flower)
- Pollen
(Day 2 flower) x Stigma (Day 1 flower)
-Pollen (Day 2 flower)
x Stigma (Day 2 flower
Each
experiment was repeated on 50 sets of flowers and observations were recorded on
seed sets in the flowers receiving pollen.
(iv)
Duration of pollen viability and stigmatic receptivity: Pollen from the controlled/guarded
flowers was applied on the stigmas of first day and second day at an interval
of 0, 2, 4, 6, 8, 10 hours after liberation (i.e. at 0600, 0800, 1000, 1200,
1400, 1600 hr on the first day and at 0600, 0800, 1000 and 1200 hr on the
second day). Seed set was recorded
in 30 sets of flowers in each case. Recipient flowers exhibiting seed set confirmed viability of
pollen/receptivity of stigma.
(v)
Absolute and ecological reproductive potential: Number of inflorescences per plant,
flowers per inflorescence (n = 50 in each case), ovaries per flower, locules
per ovary, and ovules per locule (n = 100 in each case) were recorded. The absolute/maximum
reproductive potential of the plant (its inherent capability to produce seeds)
was derived by multiplying the average values of these attributes.
To determine
the ecological/realized reproductive potential of Sarpagandha, 50 plants were
selected randomly in the field and marked. On maturity, plants were harvested individually,seeds were taken out and counted in a seed counter. The ecological/ realized reproductive potential (number of
seeds produced per plant) of this plant was determined accordingly.
Results
and Discussion
(i)
Floral morphology and pollination mechanism: Inflorescence of Sarpagandha is terminal and consists of
small flowers in compact cymes forming a hemispherical head at the end of a
long peduncle (Image 2). Flowers
are small, pedicillate, complete and hermaphroditic with five deep red and
glabrous sepals. Five petals in
gamopetalous condition form a tubular corolla which is
swollen in the middle and white to pink in colour. Corolla tube measure 17.7 ± 0.22 mm (mean ± SD, n = 50) in
length and 2.52 ± 0.79 (mean ± SD, n = 50) mm in breadth / diameter (Figs. 1
& 2). Five stamens in
epipetalous condition are enclosed within the dilated portion of the corolla
tube. Two connate carpels have a
filiform style and large bifid stigma; a bilocular ovary has two ovules in each
locule. The flowers of Sarpagandha
have highly narrow and long tubular corolla. Such flowers make them a perfect representative of
psychophilous pollination syndrome negating all other syndromes (Barrows 1976;
Schemske 1976; Faegri & van der Pijl 1979; Suzuki et al. 1987; Sihag
& Kaur 1997).
(ii)
Floral phenology:Flowering occurred during peak summer, last week of May, when maximum &
minimum temperatures ranged between 35.2-43 0C and 20-29 0C,
and within eight days on all the Sarpagandha plants (Table 1). Flowering remained mediocre (quantified
in terms of numbers / m2) for about two weeks from early June to mid
June when maximum and minimum temperatures ranged between 33.4-42.7 0C
and 20.5-28.5 0C, respectively. The peak flowering, continued for 43 days, when ambient
temperature fluctuated between 31-40.9 0Cmaximum and 20.9-30.7 0C minimum. Thereafter, decline started till cessation in the first week
of August when maximum and minimum temperatures fluctuated between 32.6-36.3 0C
and 25.0-26.5 0C. Thus,
the plant remained in blooming stage from last week of May to first week of
August over wide range of temperature (Table 1). Temperature dependent floral phenology has been reported
earlier also (Ramani 1995; Sihag & Kaur 1995; Sihag & Priti 1997).
Flowers
started opening in the early morning between 0500-0530 hr when ambient
temperature fluctuated between 24-29 0C (Table 2). However, anthers did not dehisce on the
first day of flowering; it took place on the second day of flower opening
between 0700-0730 hr at relatively higher temperature range of 28-31 0C. Under the semi-arid sub-tropical
conditions of Hisar, flower longevity was a little more than two days - ranged
between 54-58 hr (mean ± SD = 56.53 ± 2.20, n = 900). Nectar secretion started on the first day of flower opening
between 0800 to 0830 hr in the morning and continued up to 1300 to 1330 hr in
the evening; it again started between 1500 to 1530 hr to continue till dusk at
1730hr on both the days. Nectar
production was for a longer time and at wider range of temperature, 27 to 44 0C
(Table 2). The diurnally opening
tubular flower with liberation of floral reward during day
time further makes it an example of psychophilous pollination syndrome
(Faegri & van der Pijl 1979; Sihag & Kaur 1997). The flower longevity
was very short (56.5h, n = 900, Table 2, Fig. 3), most probably due to the very
high ambient temperature regime.
(iii)
Fertility status: As
pollen was not available on the first day of flower opening, self-pollination
was not possible on day one. Whether stigma was receptive or not on the day of flower anthesis, could
not be ascertained. On the second
day, after anthesis self-pollen was available, but self-pollination resulted in
no seed set. Either stigma was not
receptive in second day flowers or due to
self-incompatibility in the flowers. These possibilities were tested through cross-pollination
experiments. Crossing also was not
possible between any two first day flowers as well as
between a first day flower as pollen donor and a second day flower as recipient
due to non-availability of pollen in the donor flower. Cross-pollination between second day flower as pollen donor and second day flower as pollen
recipient also resulted in no seed set. This again indicates self-incompatibility or non-receptivity of stigma
on the second day. However,
cross-pollination between first day flower as pollen
recipient (stigma) and second day flower as pollen donor (pollen available)
produced seeds in 100% recipient flowers, indicating protogyny in
Sarpagandha. However, fresh
self-pollen (from second day flower) could not fertilize the ovary of second day flower confirming that stigma was not receptive on the
second day after anthesis. These
experiments revealed that in the two days’ age of flower, its stigma was
receptive only on the first day as anthers dehisced on the second day when
stigma had become non-receptive. Therefore, flowers of Sarpagandha need to be cross-pollinated as in
umbelliferous plants (Sihag 1985a), onion (Sihag 1985b) and all cultivars of
litchi (Litchi
chinensis Sonn.) (Ray & Sharma 1995).
(iv) Duration of pollen viability and stigmatic
receptivity: The
pollen of Sarpagandha remained almost fully viable and stigma fully receptive
only for four hours (Fig. 4). Thereafter, viability of pollen and/or receptivity of stigma declined. These were low after eight hours and
very low after 10 hours. On the
next day, flower completely lost stigmatic receptivity,even fresh pollen did not produce seeds in the pollen-recipient flowers. Therefore, pollination has to be
completed on the first day itself, that too within a short period (< 6hr).
(v)
Absolute and ecological reproductive potential: The number of inflorescences per plant
ranged from 17 to 63 (mean ± SD = 40.5 ± 22.8, n = 50) and flowers in the
inflorescences ranged from 36 to 54 (mean ± SD = 45.4 ± 9.07, n = 50). Each
flower produced four seeds (n = 100) on an average, and the normal Sarpagandha
plant indicates a potential to produce 7355 seeds which is the absolute /
maximum reproductive potential (Rm) (Table 3). The ecological/realized reproductive potential (Re) under
Hisar conditions was, only 43.2% (3178 ± 356 seeds per plant) of its
absolute/maximum reproductive potential (Table 3). This may be due to the presence of some strong ecological
constraint(s). Factors responsible
for low ecological reproductive potential remain to be investigated.
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