Viability and vigor of jamun (Syzygium cumini) seeds

SHORT COMMUNICATION

Viability and vigor of jamun (Syzygium cumini) seeds

K. Sivasubramaniam^*; K. Selvarani

Agricultural College and Research Institute, Department of Seed Science and Technology, Madurai, 625 104 Tamil Nadu, India

ABSTRACT

Jamun (Syzygium cumini L. Skeels) (Black plum, Damson plum) fruits weigh between 2-5 g at maturity. Fresh seeds represented 20-80% of the total fruit weight; the seed coat and cotyledons contributed 6% and 94% to the total seed weight respectively, while the weight of the embryonic axis was insignificant. Only the embryonic axis stained with Tetrazolium, not the cotyledons. The seeds are polyembryonic with up to four embryos, of which at most three germinate. Decoated seeds germinated faster than coated seeds under nursery conditions, with high significant germination percentages, dry matter production rates and vigor indices. The lack of staining of the cotyledon by tetrazolium was probably due to the presence of an impermeable layer. Decoating seeds for faster germination is recommended.

Key words: decoated seeds, embryo, Myrtaceae, polyembryony, tetrazolium

INTRODUCTION

Jamun (Syzygium cumini (L.) Skeels, Myrtaceae) (also known as Jambul, black plum, Damson plum, Duhat plum, Jambolan plum, Portuguese plum, and Malabar plum) is an evergreen tropical tree native to Bangladesh, India, Nepal, Pakistan, Sri Lanka, the Philippines, and Indonesia. Sweet-bitter jamun fruits are excellent sources of iron, calcium, phosphorus, sodium, potassium, vitamin-C and carotene, and have been reported to alleviate heart and liver ailments. Jamun seeds are known to be recalcitrant, chlorotic, multicotyledonous, and have multiple embryos, although there have been very few studies examining their seed anatomy or directed towards improving seed germination and vigor (Swamy et al. 1999, Thoke et al. 2009). The tetrazolium (TZ) test is one of the most reliable techniques used to estimate seed viability and vigor (Hosomi et al. 2011), although every species has its own specific dissection, staining, and TZ evaluation requirements (Enescu 1991). The present investigation was conducted to: 1. assess the fruit:seed and seed: seed coat, cotyledon and embryo ratios; 2. examine the polyembryonic nature of the seeds; 3. elucidate the influence of the seed coat on seed germination and; 4. determine the topographical staining patterns of jamun seeds.

MATERIAL AND METHODS

The following experiments were undertaken in the Department of Seed Science and Technology at the Agricultural College and Research Institute, Madurai, India, using fresh fruits (n = 120) collected during their period of natural dispersal (August-September/2012). The collected fruits were divided into three lots for experimental purposes: one lot (n = 25 fruits) was weighed and the seeds separated after manual maceration (to remove the fruit pulp) to determine the fruit:seed ratio, after which the seeds were dissected into their various components (seed coats, embryonic axes, and cotyledons) that were subsequently weighed to determine their seed:embryo ratio; the seeds in the second lot (n = 25) were cut in half to expose the embryonic axis and cotyledonary furrow and then placed in a 1% TZ solution for 4 hours at 40 ºC; the final lot (n = 70 seeds) was further divided into two sub-lots (35 seeds each) with and without their seed coats and were surface sterilized with 0.01% mercuric chloride at room temperature and subsequently sown into germination trays (20 × 20 × 4 cm) containing sand to assess their germination percentages and observe their polyembryonic behavior. All experiments were repeated twice to confirm their reproducibility. Germination speed was assessed after 26 days (Maguire 1962) and seedling length and their vigor indices (Abdul-Baki & Anderson 1973) were calculated. The data was statistically analyzed using SAS software and correlation analyses were performed using Microsoft EXCEL^®.

RESULTS AND DISCUSSION

The mean values of the 25 fruits of lot 1 showed that the contribution of fresh seed weight to total fruit weight ranged from 20%-80%. Seed coats and cotyledons contributed approximately 6% and 94% to the total seed weight respectively (data not shown); the contribution of the embryos to seed weight was negligible. The jamun seeds (figures 2-3) incubated in a 1% TZ solution for 4 hours at 40 ºC showed pink staining only along the embryonic axis; the chlorotic cotyledons remained unstained even though they were viable (figures 2). Similar results were reported in curry leaf seeds (Sivasubramaniam & Selvarani 2012) and may be due to a physical barrier on the cotyledon surface that prevents penetration of the TZ solution.

The maximum number of embryos observed in a jamun seed was four (figure 1), but only three seedlings emerged (figure 6). Polyembryony is a condition in which multiple embryos arise within the embryo sac by budding or by cleavage of the zygotic proembryo or from the synergids and antipodal cells (Maheswari & Sacher 1963). Discrepancies in embryo counts and emerging seedlings due to polyembryony have been reported in Calophyllum inophyllum L. (Kumaran et al. 1999, Rajesh et al. 2012), Syzygium cumini (Abdul Kadar et al. 2000), Syzygium mundagom (Bourd.) Chithra (Jose et al. 2009), and Murraya koenigii (L.) Spreng. (Sivasubramaniam & Selvarani 2012) and may be due to the existence of dormant or under-developed embryonic axes. Seeds sown without their seed coats germinated significantly faster (figure 5) than seeds with intact seed coats, but the final germination counts (taken after one month) revealed no significant difference between them, with both conditions showing 100% germination. Highly significant differences were observed, however, in terms of vigor attributes, with seeds without seed coats generating seedling with greater lengths (23.09 cm), dry matter production (0.16 g), and vigor index (16) values – while seeds with intact seed coats had lower seedling length (14.59 cm), dry matter production (0.13 g), and vigor index (13) values. Germination speed, seedling length, dry matter production, and vigor indices among seeds sown without their seed coats increased by 41.79%, 36.81%, 18.75% and 18.75%, respectively, over seeds that retained their seed coats (figure 4). Similar results were reported by Shukla et al. (2008) for decoated Terminalia arjuna (Roxb. ex DC.) Wight & Arn. seeds. Correlation studies also revealed that germination speed was significantly correlated with root length (0.993), shoot length (0.977), seedling length (0.977), dry matter production (0.984), vigor index 1 (0.976), and the vigor index 2 (0.981) (table 1) of decoated seeds. Swamy et al. (1999) and Thoke et al. (2009) suggested several treatments (including hot water, gibberellic acid, and the use of bacterial consortia) to improve seed vigor in jamun, and the present study describes a simple technique for decoating jamun seeds prior to sowing to improve early seed emergence that was more effective than the method of Swamy et al. (1999). Our study also demonstrated that jamun seeds have multiple embryos, leading to emergence of up to three seedlings per seed, and that TZ staining was confined to the embryonic axis, with other embryo parts (such as the cotyledons) remaining unstained. Further studies will be necessary to elucidate the observed differences in vigor among polyembryonic seedlings (single, double and triple seedlings) and to compare laboratory Tetrazolium test results with field performances. The simple technique of sowing freshly decoated seeds can be used for raising jamun seedling root stocks for early nursery grafting.

(received: October 30, 2012; accepted: November 07, 2012)

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Publication Dates

• Publication in this collection
  04 Jan 2013
• Date of issue
  2012

History

• Received
  30 Oct 2012
• Accepted
  07 Nov 2012