Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 April 2022 | 14(4): 20859–20865
ISSN 0974-7907
(Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.6381.14.4.20859-20865
#6381 | Received 23
July 2020 | Final received 02 February 2022 | Finally accepted 04 April 2022
Reproductive biology of two
threatened and highly traded medicinal plants, Salacia gambleana
and Salacia oblonga, from the Western
Ghats of India
P.S. Krishnasree
1, P.A. Jose 2 , K. Subin 3 & T.V. Sarath
4
1 The Zamorin’s Guruvayurappan
College, Guruvayurappan College (PO), Kozhikode, Kerala 673014, India.
2,3,4 Sustainable Forest Management
Division, Kerala Forest Research Institute, Peechi,
Kerala 680653, India.
1 krishnasreeps96@gmail.com, 2
pajosekfri@gmail.com (corresponding author), 3 subink1993@gmail.com,
4 sarathtv35@gmail.com
Editor: Vijayasankar Raman, The University of
Mississippi, USA. Date of publication: 26 April 2022
(online & print)
Citation: Krishnasree,
P.S., P.A. Jose, K. Subin & T.V. Sarath (2022). Reproductive
biology of two threatened and highly traded medicinal plants, Salacia gambleana and Salacia oblonga,
from the Western Ghats of India. Journal of Threatened Taxa 14(4): 20859–20865. https://doi.org/10.11609/jott.6381.14.4.20859-20865
Copyright: © Krishnasree
et al. 2022. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: Study implemented
by the KFRI Plan Project
No. KFRI-ESTM - 07 / 2018-19 titled ‘Enrichment and maintenance of medicinal garden’ funded through Kerala State Council for Science, Technology and Environment, Thiruvananthapuram.
Competing interests: The authors
declare no competing interests.
Author details: P.S. Krishnasree—awarded MSc Degree in Botany from the Zamorin’s Guruvayurappan College,
Kozhikode, Kerala, India, affiliated to the University of Calicut, Kerala.
The publication is a part of the M.Sc.
Dissertation programme, carried out at KFRI, Peechi. P.A. Jose—Principal
Scientist and Programme Coordinator, Sustainable
Forest Management Division, KFRI, Peechi. Principal
Investigator of the Project and served Research supervisor for M.Sc. Dissertation
of Ms. P.S. Krishnasree.
K. Subin—PhD scholar at KFRI, Peechi. T.V. Sarath—Project Assistant working in the project.
Author contributions: PSK—carried out the study by her
as a part of MSc Dissertation programme. PAJ—Served
research supervisor for M.Sc. Dissertation of
PSK and manuscript correction and editing. KS—helped in reproductive biological studies in the
laboratory and preparation of map, figures and Plate for the article. TVS—helped in field data collection in the
medicinal garden.
Acknowledgements: The authors thank Dr. Syam Viswanath, Director, KSCSTE–Kerala Forest Research
Institute, Peechi, for providing facilities for the
study. Dr. P.P. Rajan, Head
of PG & Research Department of Botany, The Zamorin’s Guruvayurappan
College, Kozhikode for encouragement and support given during PG Dissertation
programme.
Abstract: Salacia is a genus of flowering
plants in the family Celastraceae, consisting of
woody climbers distributed in tropical America, Africa, and Asia. In India it
is represented by 21 species, of which 15 occur in peninsular India. Most
species of the genus have been used in traditional medicine, mainly the Ayurvedic system.
Apart from overexploitation for medicinal purposes, the low fruit set and
infestation of seeds have affected natural regeneration, and led to the rarity
of Salacia species in their natural habitats. The reproductive biology
of Salacia oblonga and S. gambleana was studied for the first time to understand
the reproductive constraints of these threatened and medicinally important
species. The flowering phenology, pollen viability, germination, stigma
receptivity, and insect-pest interaction were analyzed.
The obligatory entomophily coupled with insufficient pollinators and seed pest
infestation were found to be the main reproductive constraints responsible for
the low fruit set and poor natural regeneration of these species.
Keywords: Conservation, health care, management, medicinal
genetic resource, reproductive constraints, rarity.
INTRODUCTION
The genus Salacia contains
important medicinal plants with a wide range of therapeutic properties. In
India 21 species are reported; 15 occur in peninsular India including the
Western Ghats. The majority of Salacia species are over-harvested for
their roots, which are used in the Ayurveda and Unani systems of medicine for
treating diabetes, asthma, leukemia and ear
infections. Salacia species mainly contain salacinol, kotalanol, neosalacinol, several phenolic compounds, sesquiterpenes,
and triterpenes (Kirtikar & Basu
1975; Prakash et al. 2008; Wang et al. 2012). These components have medicinal
properties and significant applications in modern medicine. Besides their
overexploitation, these species show a low fruit set and poor natural
regeneration leading to low population size and rarity. Therefore, the existing
populations of Salacia species and their natural habitats warrant urgent
conservation and management measures.
The rarity of a plant often stems
from its biological functions, particularly its reproductive biology, which has
a significant contribution to the sexual reproduction of flowering plants.
Reproductive biology studies help in the conservation of genetic resources. The
reproductive patterns are some of the key factors leading to the abundance,
distribution and genetic diversity of the species. There is a widespread
consensus that reproductive biology studies of threatened species can help
determine strategies for in situ and ex situ conservation. Several
levels of problems can be seen in the reproduction of threatened plants, such
as infrequent flowering, flower bud fall, flower infestations, lack of
pollinators and low fruit set. Knowledge on anthesis, pollen viability and
germination, stigma receptivity, pollen-ovule ratio, breeding behavior, and pollinators are prerequisites to unravel the
biological constraints leading to endangerment of the species.
MATERIALS
AND METHODS
Study area
The study was conducted at the
herbal garden of Kerala Forest Research Institute (KFRI) Peechi,
Kerala, South India. KFRI is situated about 20 km east of Thrissur district,
spread over a 28 ha reserve forest area adjacent to Peechi-Vazhani
Wildlife Sanctuary at 10.530 N latitude and 76.347 E longitude with an altitude
of 186 m (Figure 1). The study was carried out from January to June 2019.
Salacia gambleana Whiting & Kaul (Syn. Salacia
talbotii Gamble)
Scandent shrubs, endemic to the
southern Western Ghats, occur in evergreen and semi-evergreen forests. This
species has been assessed as threatened by Sasidharan
(2017). Flowering and fruiting were recorded from January to July.
Salacia oblonga Wall. ex Wight & Arn. (Syn. Comocladia serrata Blanco)
Stout climbers, found in the
evergreen and semi-evergreen forests up to an altitude of 1,500 m. The species
has a global distribution in the Western Ghats and Sri Lanka. It has been
assessed as Vulnerable based on the IUCN Criteria A2cd (Ved
et al. 2015). Flowering and fruiting were recorded from March–May. The
root-bark is used to treat rheumatism, gonorrhea, and
skin diseases (Kirtikar & Basu
1975). This species has shown antiperoxidative properties, and is also used to
treat renal complications (Krishnakumar et al. 2000).
Methods
The study covered day-to-day
monitoring and recording of flowering phenology, such as bud initiation,
development, anthesis, stigma receptivity, pollen viability, pollen-ovule
ratio, pollination, pollinators, blooming period, pest incidence, and fruit
set. The data presented as the average values of each trial (Sreekala et al. 2008; Jose & Pandurangan
2012, 2013; Swarupanandan et al. 2013; Gopalakrishnan
& Thomas 2014).
Reproductive phenology
Data on reproductive phenology,
including the number of inflorescence per branch, number of flowers per
inflorescence, flower/ inflorescence development, blooming period, fruit
initiation and development,were recorded daily. Five
inflorescences per plant for both species were subjected for data collection.
Each inflorescence was tagged and monitored for the flower development from bud
to full bloom. The average days taken for each bud to bloom were calculated and
recorded. The number of flower buds with pest incidence was also recorded. Each
flower was tagged to observe fruit formation.
Pollen viability
Pollen grains from fully matured
flower buds were dusted into a cavity slide containing a solution of
acetocarmine, kept for one hour and then observed under a compound microscope.
The pollen grains stained red were treated as viable and others as non-viable.
A viability test was carried out in two-hour intervals.
Pollen germination
Pollen grains from fully matured
flower buds were transferred to a cavity slide containing germination medium
(Sucrose 10%). Pollen germination was counted after one hour using a compound
microscope. The pollen tubes with a longer length than pollen diameter were
treated as germinated. The experiment was repeated in two-hour intervals from
the anthesis.
Stigma receptivity
Visual observations using a hand
lens and chemical methods using hydrogen peroxide (H2O2)
were conducted. In the visual method, the stigma with wetness, turgidity and
oily nature was considered receptive and the rest as non-receptive. In the
chemical test, a drop of hydrogen peroxide was added to the stigma of a freshly
opened flower. The effervescence resulting from the peroxidase enzyme activity
was observed in the receptive stigma, and the duration of stigma receptivity
was calculated (Dafni et al. 2005).
Pollen-Ovule ratio
The number of pollen grains in
anthers per flower was counted using a haemocytometer (Shivanna
& Rangaswamy 1992). The number of ovules per
ovary was counted by the cross-section of the ovary (Cruden
1977). The pollen-ovule ratio was calculated using the following formula:
Pollen count per anther x No. of
anthers per flower
Pollen-ovule ratio = ––––––––––––––––––––––––––––––––––––––––––––––
No. of ovules per
flower
Pollination and insect
interaction
Bagging experiments were carried
out to understand the mode of pollination. The physical observation was made
throughout the flowering period, and the insect interactions were recorded day
and night. Adhesive tapes were kept on flowering branches to collect insects
for identification. The taxonomic identification of insects was made with the
relevant literature.
Fruit phenology
Fruit phenology such as fruiting
primordia, period of development including premature abscission and pest
incidence was monitored and recorded.
RESULTS
Salacia gambleana
Reproductive phenology
Bulbous and light green flower
buds were observed during the second week of January. It took about 25 days for
the bud to develop into full bloom (Figure 2). The flower started opening from
0430 h to 0500 h and was fully opened by 0930 h. Anther dehisced through the
horizontal slit from 0500 h and 0530 h. Stigma found receptive prior to the
anther dehiscence (protogynous condition).
Pollen viability and stigma
receptivity
Fresh pollen grains (on anthesis)
showed 100% viability, and gradual reduction was noticed to 98, 86, 80% after
6, 10, and 12 hours, respectively. A drastic decline to 52% was noted after 28
hours (Table 1). The hydrogen peroxide application followed by effervescence
formation confirmed the stigma receptivity up to 58 hours. The stigma then
turned brown, lost turgidity, and became non-receptive.
Pollen germination
At the time of anthesis, 96% of
pollen grains were germinated. A gradual decrease in pollen germination was
observed in succeeding hours, and 24% pollen germination was recorded at 11
hours after anthesis.
Pollen-Ovule ratio
A flower contains three to four
anthers, and approximately 277.1±165.7 pollen grains are present per anther.
Hence, the pollen count per flower was calculated as 834.56±510.5. A flower has
4.45±1.5 ovules, and pollen-ovule ratio thus estimated to 187.54:1.
Mode of pollination and insect
interaction
Flowers are not fragrant. Ants
such as Tetraponera sp., Ocecophylla
smaragdina, and Anoploilepis
gracilipes were usually found foraging during the
flowering period. O. smaragdina is an arboreal
ant that forms colonies on the host plant using leaves stitched together. The
maximum incidence of ants was observed in the peak of anthesis hours 0830–0930
h. Bagging experiments resulted in no fruit set; however, floral arrangements
per se facilitated self-pollination (Anthers placed over stigma). Further, the
incidence of ants during flowering was also found promoting cross-pollination.
A larval infestation was found in developing fruits, which later caused the
abscission of young fruits. The adult ants were collected for identification.
Salacia oblonga
Reproductive phenology
Flower bud initiation was noted
from the first week of January. The development of bud to bloom was observed
for 30 days (Figure 2). Flower opening initiated from 0130 h to 0330 h and
fully opened by 0830 h. Anthers dehisced through the longitudinal slit from
0430 h and 0530 h. The stigma was receptive prior to anther maturity (protogynous
condition).
Pollen viability and stigma
receptivity
Fresh pollen grains showed 100%
viability for up to six hours from anthesis. A gradual reduction in pollen
viability was recorded, viz., 97, 85, 64% after 8, 12, 37 hours, respectively
(Table 1). Stigma was found receptive up to 39 hours and later turned brown,
lost turgidity, and became non-receptive.
Pollen germination
At the time of anthesis, 90% of the tested pollen grains were
germinated. A sudden decline in germination percentage was noted after 6
and 12 hours with 58 and 38% germination, respectively (Image 1).
Pollen-Ovule ratio
A flower contains three to four
anthers, and approximately 4,929.05 ±1829.18 pollen grains are present per
anther. Hence, the pollen count per flower was calculated as 14,757.27
±5487.38. Each flower has 9.4±2.95 ovules and an estimated pollen-ovule ratio
of 1,573:1.
Mode of pollination and insect
interaction
Flowers are dull in appearance
and are not fragrant; however, the floral nectars attract the ants such as Tetraponera sp., O. smaragdina,
and Anoploilepis gracilipes
during flowering. Ants forage 18±6 minutes during a visit. Maximum foraging was
observed at 1030–1230 h. Ant movement caused pollen deposition on to own
stigma, facilitating self-pollination (Image 1). The developing fruits were
often damaged, and the seeds were foraged by caterpillars. The adult could not
be collected for identification.
DISCUSSION
AND CONCLUSION
As plant rarity is often directly
related to the ecology and biology of the species, knowledge on reproductive
phenological and biological functions is a prerequisite to unravel the
complexities of rarity and for effective conservation and management of the
species (Reveal 1981; Rathcke & Lacey 1985; Kempel et al. 2020). The absence of an efficient
pollination mechanism has been determined as the main disadvantage in both the
species studied. The low pollen-ovule ratio promoted cross-pollination through
insects; however, insect visits during flowering were extremely low. Floral
characteristics such as petal size, colour and nectar production have a
significant role in the reproductive success of plants (Kudon
& Whiegham 1998). Salacia species
generally have small and dull flowers (S. oblonga 0.36±0.05
cm; S. gambleana 0.55±0.09 cm) and
comparatively less nectar production.
The role of ants as pollinators
was assumed by their relative abundance compared to other insects (Gómez et al.
1996). Various floral signals, especially nectar characteristics and floral
scent, play a crucial role in attracting ants. Ants were the common
pollinators, facilitating facultative autogamy in the species. The ants
foraging in different flowers of the same plant enabled geitonogamy (Rostás & Tautz 2010). Among
the ant species, the weaver ant (O. smaragdina) was
found to be a pollination limiting factor as it acts as a key predator of some
pollinators. It affects the behavior of other flower
visitors and thus the plant’s reproductive success. Observations of Tsuji et
al. (2004) on the fruit orchard of Nephelium
lappaceum suggested that the presence of O. smaragdina nest on the plant lowered flower-visiting
rates of flying insects involved in pollination. The presence of weaver ants
might be one of the reasons for the absence of other pollinators. In this
study, an abundance of O. smaragdina ants and
the absence of other floral visitors were also observed. Subin
et al. (2018) reported that in Salacia fruticosa,
70–80% of mature fruits were found infested, and the seeds were consumed by the
caterpillars of the butterfly Bindahara moorei. A similar infestation was also recorded in Salacia
gambleana and S. oblonga
where 40–50% of immature fruits were damaged by caterpillars of B. moorei. Insect infestation of fruits and seeds and its
impact on seedling bank and subsequent rarity have been reported in many
threatened plants in the Western Ghats (Jose et al. 2004, 2016). The
observations and results of the present study are expected to aid future
studies involving the populations of the Salacia species and develop
suitable measures for their in situ and ex situ conservation.
Table 1. Reproductive biology of Salacia
gambleana and Salacia oblonga.
|
Floral characters |
Salacia gambleana |
Salacia oblonga |
|
Flowering period |
February–March |
Throughout |
|
Inflorescence type |
Axillary
umbel |
Axillary
umbel |
|
No. of inflorescence per branch
(n=26) |
42.69±25.68 |
15.34±8.69 |
|
No. of flowers per
inflorescence (n=26) |
11.5±5.33 |
5.5±1.87 |
|
Flower type |
Actinomorphic,
Hermaphrodite |
Actinomorphic,
Hermaphrodite |
|
Flower nature |
Protogynous |
Protogynous |
|
Flower colour |
Green |
Greenish-yellow |
|
Flower opening time |
0430–0530 h |
0130–03.30
h |
|
Anther dehiscence time |
0500–0515 h |
0430–0530 h |
|
Anther dehiscence mode |
Horizontal
slit |
Longitudinal
slit |
|
Odour |
Present |
Absent |
|
Nectar |
Present |
Present |
|
Number of anther per flower (n=
18) |
3 or 4 |
3 or 4 |
|
Pollen per anther (n= 18) |
277.10±165.70 |
4929.05±1829.18 |
|
Mean number of pollen grain per
flower (n= 18) |
834.56±510.50 |
14787.27±5487.38 |
|
Mean number of ovule per flower
(n= 30) |
4.45±1.36 |
9.4±2.95 |
|
Pollen:Ovule ratio |
187.54:1 |
1573.11:1 |
|
Pollen shape |
Triangular |
Triangular |
|
Pollen diameter (n= 15) |
21.264µm±2.27µm |
20.41µm±4.92µm |
|
Pollen tube length (after 2
hours) |
83.77±38.68µm |
103.37±62.11µm |
For figures &
image - - click here
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Appendix 1. Floral part
measurements.
|
Floral parts |
Salacia gambleana |
Salacia oblonga |
|
Bud |
0.55±0.09 mm |
0.36±0.05 mm |
|
Pedicel |
0.40±0.07 mm |
0.05±0.008 mm |
|
Petal |
0.19±0.002 mm |
0.26±0.04 mm |
|
Sepal |
0.09±0.005 mm |
0.17±0.025 mm |
|
Pistil |
0.14±0.05 mm |
0.19±0.006 mm |
|
Stamen |
0.28±0.07 mm |
0.20±0.01 mm |
|
Anther |
0.08±0.02 mm |
0.06±0.025 mm |
|
Filament |
0.24±0.07 mm |
0.14±0.029 mm |