Seed viability and seedling survival of Melodinus monogynus Roxb., a wild edible fruit of Meghalaya

· Articles
Authors

S. Nongbri*1, E. Nongbri2, K.H.M. Pala1, P. Law1, S. Dohling & K. Makdoh1
1Department of Botany, Lady Keane College, Shillong, Meghalaya, India
2Department of Botany, St. Anthony’s College, Shillong Meghalaya, India
*Corresponding author: Shairi Nongbri; email – slnongbri@yahoo.co.uk

Abstract

The members of the genus Melodinus (Apocynaceae) have long been used in folk medicine for the treatment of various ailments. It has been reported that Medigenin, Medinin, medigenin acetate were extracted from Melodinus monogynus for medicinal purposes (Yao et al., 2014). Unfortunately, deforestation and destruction of habitat in Meghalaya has led to decrease in population of Melodinus monogynus, a wild edible fruit with medicinal importance. Hence, in view of the present status of the population of this species, it is felt that there is requirement for the knowledge of its propagation. Thus, the present study deals with seed viability and seedling survival, the two critical phases for plant regeneration by means of seeds. Fruits of Melodinus monogynus were collected during the month of December after which experiments were carried out under laboratory as well field conditions. The result of the study indicates that the species is shade-intolerant and produces orthodox seeds.

Keywords Melodinus monogynus, orthodox seeds, shade-intolerant species.

Introduction
In dry tropical forest, majority of species possesses orthodox seeds with various dormancy periods, while a few have recalcitrant seeds which possess little or no dormancy. Orthodox seeds can be stored at low temperature for a longer duration without loss of viability Khurana and Singh (2001). Under natural conditions, after successful germination, seedling, faces many constrains for its growth and survival. The establishment of seedlings is controlled by many factors such as light, soil moisture, nutrients availability in soil and competition with other plant species. Water is the most limiting resource in terrestrial ecosystems that significantly influences seedling emergence and distribution of a species. Understanding of seed viability, germination and seedling establishment is useful for the process of conservation and propagation of a species. It was reported that tropical forest species produce both orthodox and recalcitrant seeds. Many forest tree seeds, however, lose viability quickly under ordinary condition and sometimes even in cool dry storage condition (Ray and Brown 1995). This is due to high rate of moisture loss from the seed coat. Thapliyal and Connor (1997), have attributed the condition to increased leachate conductivity and decreased fatty acid content due to ageing in certain seeds, for example in Dalbergia sissoo.

After germination, competition and seasonal drought limit the growth and survival of established seedlings (Nepstad et al., 1990, 1996; Holl et al., 2000). Hau and Corlett (2003), however, added that their relative importance differs from species to species. Water is the most limiting resource in terrestrial ecosystems that significantly influences seedling emergence, survival and distribution of species (Dunne and Parker 1999; Escudero et al., 1999). Physical features such as topographical features, amount of litter, presence of rocks or woody debris, and soil texture are important characteristics of microsites that affect seedling establishment (Santos and Valio 2002; Dovciak et al., 2003; Vieira and Scariot 2006). Although, survival, growth and establishment of seedlings under different conditions are determined by the availability of light, water and nutrient resources, the competitive ability of the species and light seemed to be the major factor limiting growth and survival of many forest tree seedlings (Law 2002; Ben´?tez-Malvido et al., 2005). Apart from the mentioned factors, seedling size also seems to play an important role in seedling survival. Larger seedlings may have greater vigour and tolerance for physical and biotic mortality risks (Gross 1984). They are also able to tolerate extreme conditions for longer periods than small seedlings (Gray and Spies 1997). Kennedy et al., (2004) reported that an increase in seed reserves had a positive effect on the early growth of Lithocarpus densiflora. The objective of the present study is to understand the seed viability and seedling behaviour of Melodinus monogynus and thus propagation of the species by means of seeds.

Materials and Methods

Melodinus monogynus is a large climber with milky juice, found in sub-tropical semi-evergreen forests of Meghalaya. Fruit is a berry, globose, smooth, orange in colour and about 3 to 4 inches across. Ripe fruits are edible and often sold in the market. Ripe fruits were collected during the month of December from different community forests in and around Sohra. Germination of freshly collected seeds was studied under laboratory condition. One thousand (1000) seeds were kept for germination immediately after collection, while the remaining seeds were air dried and stored for seed viability test at an interval of three months. Another 60 fruits were preserved without drying to test seed viability difference between
seeds which have been separated from the fruit (air dried) and those which are not dried (left inside the fruit).The number of germinants was recorded daily. The newly germinated seeds were transferred to polythene bags. After three months, two hundred (200) seedlings were kept under laboratory and another two hundred (200) under net house condition (Figure 1 & 2).

     

Results

Seeds were brown in colour with more or less oval to elliptical in shape (Table 1). Under laboratory condition, germination started during spring season in the month of March and April. The species showed a progressive reduction in viability during storage at room temperature. Viability of seeds decreases on drying. Result also shows that seeds can remain viable up to fifteen months, if not separated from the fruits. Air dried seeds became nonviable after nine months of storage (Table 2). Juvenile seedling survival was high under nethouse where light availability is more compared to laboratory condition (Table 3). It was observed that mortality of seedlings under laboratory conditions was due to fungal infection.

Table 1. Seed Characteristics of Melodinus monogynus.

Parameter

Characteristic

Month of collection December
Month of germination March
Germination type Epigeal
Colour Brown
Shape Oval-Elliptical
Weight (g) 0.55 ± 0.010
Length (cm) 0.7 ± 0.010
Diameter (cm) 0.45 ± 0.020
Germination (%) 78 ± 0.300

Table 2. Seed viability (%) during storage at room temperature (± SEM, n=200)

Time interval (months)

Seeds (not dried)

Seeds (air dried)

0

90 ± 1.00

90 ± 2.00

3

71 ± 1.10

30 ± 1.60

6

38 ± 0.80

2 ± 0.60

9

15 ± 0.50

0.00

12

7 ± 0.40

0.00

15

5 ± 0.50

0.00

18

0.00

0.00

Table 3. Seedling survival (%) under laboratory and net-house condition (± SEM, n=200)

Time interval (months)

Laboratory

Net-house

0

100

100

3

71 ± 1.10

80 ± 1.00

6

18 ± 0.80

65 ± 0.30

9

15 ± 0.50

60 ± 0.35

12

7 ± 0.40

50 ± 0.40

15

6 ± 0.20

49 ± 0.30

18

5 ± 0.20

49 ± 0.30

Discussion

The decrease in seed viability after air drying could be due to loss of moisture content from the seeds. Similar seed behavior was observed by Odyuo (2004) in Syzygium tetragonum, and Nongbri (2007) in Castanopsis purpurella, both are evergreen tree species in sub-tropical semi-evergreen forests of Meghalaya. The persistence of viability for a longer duration when preserved without air drying suggests that the seeds could be of orthodox type (Ray and Brown 1995; Khurana and Singh 2001). This could be due to hard seed coat which prevents the loss of moisture from the seed.

Better survival of juvenile seedlings under nethouse condition can be attributed to better availability of light, as compared to laboratory condition. Low light availability coupled with high soil moisture content favoured growth of pathogenic fungi, which was the main cause of seedling mortality under laboratory condition. Similar observation has been made by Gómez et al., (2001) in Mediterranean woody species, and Nongbri et al., (2014) in Rhododendron arboreum, a subtropical tree species restricted to high altitudes of Meghalaya. Priliminary observation suggests that the species is light demanding and therefore can be regenerated even in community forests. The result also suggests that this plant being of high medicinal value, and exposed to severe human disturbances (deforestation, habitat loss, overexploitation etc) can be propagated and conserved through seeds.

Acknowledgement

Authors are thankful to the University Grants Commission for the financial assistance of a Minor Research Project- “Ecology of Melodinus monogynus Roxb.– an indigenous wild fruit of Meghalaya” and Principal of Lady Keane College, Shillong, for her kind support.

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