Influence of Some Pregerminaton Treatments on Seed Germination and Seedling Quality of Two Ornamental Palm Species Common in Egypt I- Golden Cane Palm (Chrysalidocarpus lutescens H. Wendl)

INTRODUCTION

Golden cane palm (Chrysalidocarpus lutescens H. Wendl., syn. Dypsis lutescens (H. Wendl) Beentje and J. Dransf.), known also as bamboo palm, yellow palm, Areca palm or butterfly palm (Fam. Palmaceae). It is a beautiful palm tree that can grow up to 6-9 m tall with a golden ringed stem (like bamboo  stem ). Its leaves are light green with long petioles arise from the main trunk and gracefully arch outward and downward distributing in all directions. It can be used in gardens as sole specimen, in front of buildings, on sides of enterances and in borders. Also used for indoor landscaping in places with enough light to add a tropical touch. It is considered a good tolerant for drought (Huxley, 1992).  

Golden cane palm is propagated mainly by seeds, which need to 2-6 months to germinate due to their hard, horny endsperm. So, such seeds must be soaked in lukewarm water for two days to enhance germination (Meerow, 1991). On other palms, Al-Fredan and Ali (2008) found that the highest germination % in doum seeds was recorded by mechanically scarified seeds for 30 min and then soaked in water for 24 h. Zarchini et al. (2011) mentioned that seeds of Cycas revoluta pretreated with hot water (70-80 °C) for 12h. germinated faster than untreated ones, while the most germination rate (GR) and value (G.V.) were obtained from seeds pretreated with hot water (100 °C) for 1 h along with 25 % H₂SO₄ for 2 h. Viana et al. (2013) reported that the highest germination rate was found when green fruits of Livistona rotundifolia had their pulp removed and soaked in tap water. On triangle palm, Shahin et al. (2014) observed that soaking the depulped seeds in concentrated H₂SO₄ for 3 h gave the best germination percentage and velocity, higher means of vigour index, seed viability and plumule length, best growth of the resulted seedlings, as well as higher content of pigments, soluble sugars and indoles in the seedling leaves.

Several reports were also obtained for ornamental trees. In this concern, Alamgir and Hossain (2005) noticed that immersing seeds of Albizia saman in tap water for 24 h may be recommended for maximal germination and initial vigorous seedlings growth in the nursery. On Acacia mangium, Bahar (2011) stated that hot water soaking for 24 h or H₂SO₄ for 15 min. soaking enhanced germination of seeds to more than 92 %. Likewise, were those results elicited by Azad et al. (2010) on albizia richardiana, Azad et al. (2012) on Albizia procera, Khan (2013) on Cassia auriculata and C. tora and Shahin et al. (2015) whom claimed that soaking seeds of Elephant apple (Dillenia indica) either in concentrated H₂SO₄ for 3 min or in tap water for 72 h gave the highest germination % and best quality of the seedlings.

 The purpose of this study, however is determining the response of Golden cane palm seeds to some pre-sowing treatments for higher germination percentage and velocity along with better seedling quality.

MATERIALS AND METHODS

The current work was performed under shade at the nursery of Antoniades Botanical Garden, Hort. Res. Inst., Alexandria, Egypt throughout the two consecutive seasons of 2014 and 2015 to overcome the hardseededness of yellow areca palm by some pre-sowing treatments, and to explore the effect of these treatments on growth and quality of the produced seedlings.

Thus, the yellow-ripened fruits of Golden cane palm (Chrysalidocarpus lutescens H. Wendl.) were collected at maturity stage (on mid September) for each season and the fleshy exocarp was removed, then were stored at room temperature inside paper bag. The mean weight of 10 seeds after exocarp removal ranged between 3.80-4.27 g. On March, 15^th, the depulped seeds were surface sterilized with 10 % solution of sodium hydrochloride for 10 minutes, then rinsed several times in a sterile distilled water and directly undergone to the following treatments:

1. Untreated depulped seeds, referred to as control.

2. Soaking in tap water for 48 hours under ambient conditions.

3. Soaking in hot water (60-70 °C) for 48 hours as thermal scarification treatment.

4. Mechanical scarification by either clefting one side of the mesocarp with a hacksaw or rasping the distal rounded end that facing the placental pointed-end with a file.

5. Soaking in concentrated sulphuric acid (98.5 %) for either 1 or 2 h. as chemical scarification treatments.

The treated and control seeds were then directly sown in 16-cm-diameter plastic pots (10 seeds/pot) filled with about 1.5 kg of sand and clay mixture (1 : 1, by volume) and kept under shade till the end of the experiment. The physical and chemical analyses of the sand and clay used in the two seasons were determined and listed in Table (1).

Table (1). The physical and chemical analyses of the used sand and clay in both seasons.

The layout of the experiments in the two seasons was a completely randomized design (Silva and Azevedo, 2009) with 3 replicates, as each pot contained 10 seeds represents one replicate. Irrigation and the other agricultural practices were done whenever needed as usually farmer did. The data were recorded as follows:

A. Germination characteristics:-

1- Germination percentage (G %) from the following equation:

     G. % = (No. germinated seeds/ Total No. sown seeds) x 100

2- Germination velocity (G.V.) in days, which equal average number of days from sowing till emergence of the final plumule.

3- Mean germination rate (MGR) in days = mean number of days till 50 % germination (Odetola, 1987).

4- Germination rate index (GRI), which calculated from Bartled equation indicated by Hartmann and Kester (1983). GRI = A + (A + B) + (A + B + C) + … /N (A + B + C ….).

- Where: A, B, C, …. etc. are number of germinated seeds counted at different times, and N is number of times at which the germinated seeds were counted.

5- Vigour index (VI) = G % x mean length of plumule (Selvaraju and Selvaraj, 1994)

6- Seed viability (SV) = number of survived seedlings in each treatment after excluding the deteriorated and dead ones (Odetola, 1987).

7- Plumule length of the germinated seeds (cm).

B. Seedling growth characters:-

At the end of each season (on July, 15^th), seedlings from the different treatments were gently lifted to measure the following parameters: seedling, sheath, leaf and petiole lengths (cm), number of leaves/seedling, number of leaflets/leaf, root length (cm) and leaves and roots fresh and dry weights (g).

C. Chemical determinations:-

In fresh leaf samples taken only from the seedlings produced in the second season, photosynthetic pigments (chlorophyll a, b and carotenoids, mg/g. f.w.) and total soluble sugars (mg/100 g f.w.) were measured according to the methods described by Yadava (1986) and Dubois et al. (1966), respectively.

Data were then tabulated and subjected to analysis of variance according to SAS Institute (2009) program and the means of various treatments were differentiated using Duncan's New Multiple Range Test at 5 % level (Steel and Torrie, 1980).

RESULTS AND DISCUSSION

Effect of pre-germination treatments on:

1- Germination characteristics:

Data in Table (2) show that soaking treatments in either tap or hot water for 48 h gave the highest germination percentage compared to control in the two seasons. However, the superiority in both seasons was for soaking in tap water treatment which slightly improved this trait over soaking treatment in hot water with non-significant differences among them. This may be attributed to that hot water may injure embryos of some seed species. In this connection, Souza et al. (2012) stated that after treating the seeds of Schizolobium parahyba with hot water, the lens detached from the coat. Blocking water from contacting the lens inhibited water absorption in hot-water-treated seeds. Moreover, Kavita and Kumar (2014) reported that seeds of Stylosanthes guianensis cv. Cook which were treated with hot water showed maximum death compared to other treatments. On the other hand, the least percent of germination was recorded by soaking in concentrated H₂SO₄ for either 1 or 2 h, whereas the seeds either clefted with a hacksaw or rasped with a file failed to germinate giving 0.0 % germination in the two seasons. This may indicate the negative effect of H₂SO₄ on seed germination of this palm due to prolonging time exposure. In this regard, Chikumba et al. (2006) found that exposing seeds of Macrotyloma daltonii to concentrated H₂SO₄ for 10 min increased germination % from 21 to 80 %, but 20-min. exposure reduced germination and increased the number of dead seeds. Combining pre-chilling with 10-min of acid treatment damaged seeds and impaired germination.

Furthermore, the least number of days to the highest germination percent (G.V.) or 50 % germination (MGR) was also achieved by soaking either in tap or in hot water for 48 h. treatments which recorded means closely near together with non significant differences in between in both seasons. However, soaking in hot water treatment shortened G.V. means to less number of days than soaking in tap water one, while prolonged MGR means to more number of days than tap water soaking treatment in the two seasons, like result was also obtained by Shahin et al. (2014) who noted that seeds of triangle palm soaked in previously boiling water failed to germinate because of rotting their pith.

Data also indicated that means of G.R.I., V.I. and plumule length (cm), as real indicators for germination vigour were greatly increased in response to the most used treatments, but the prevalence was also for soaking in tap water treatment for 48 h., which scored the highest values in the two seasons and directly followed by hot water treatment that occupied the second rank. This may indicate the hyper-ability of tap or hot water in softening the hard, horny endosperm of such seeds, which consequently permits the ease permeable of water across this soften endosperm which finally leads to activating enzymatic systems that decay the complex nutritional substances of this endosperm to produce energy required for activating the embryo.

 The previous results are in accordance with those revealed by Meerow (1991) on golden cane palm, Zarchini et al. (2011) on Cycas revoluta, Alamgir and Hossain (2005) on Albizia saman, Khan (2013) on Cassia auriculata and C. tora and Shahin et al. (2015) on Dillenia indica.

Table (2). Effect of pre-germination treatments on germination traits of Chrysalidocarpus lutescens H. Wendl palm seeds during 2014 and 2015 seasons.

- Means within a column  having the same letters are not significantly different according to Duncan's New Multiple Range Test at 5 % level.

2- Seedling growth parameters:

It is obvious from data averaged in Tables (3 and 4) that all pre-sowing treatments employed in such work improved the means of the various seedling growth traits, with significant differences relative to control means in most cases of both seasons.

Number of leaflets/leaf is the only trait which was not affected by the applied treatments. So, the differences among them were non-significant in the two seasons. In general, the mastery in all parameters of seedling growth was for soaking in tap water treatment (48 h.) that registered the tallest lengths of seedling, sheath, leaf, petiole and root, the highest No. of leaves and the heaviest fresh and dry weights of leaves and roots with few exceptions in the two seasons. Also, soaking in hot water for 48 h. treatment came to the second position giving records near, to some extent to those of the dominant treatment in most instances of the 1^st and 2^nd seasons (Photo,1).

Photo (1). A comparison between control seedling and the best treatment one (Tap water, 48 h.).

Improving growth of the resulted seedlings by tap and hot water treatments may be attributed to that these two treatments accelerate seed germination before the other treatments and consequently saving enough time for the new formed seedlings to grown better than those formed lately. Besides, soaking in water for proper time helps the water to penetrate the hard endosperm and hence increases ability of the seeds to absorb more water necessary for hydrolysis of the complex food reserves to absorbable forms. Analogous observations were also obtained by Meerow (1991) on golden cane palm, Al-Fredan and Ali (2008) on doum palm and Viana et al. (2013) on Livistona rotundifolia. In this connection, Azad et al. (2010) mentioned that hot water treatment (80 °C for 10 min) was the best for higher germination percentage of Albizia richardiana seeds and better growth of the seedlings. Likewise, Khan (2013) noted that hot water treatment (80 °C for 10 minutes) was very effective to enhance germination of Cassia uriculata and C. tora seeds and improving growth of the resulted seedlings.

Table (3). Effect of pre-germination treatments on growth traits of Chrysalidocarpus lutescens H. Wendl palm seedlings during 2014 and 2015 seasons.

- Means within a column  having the same letters are not significantly different according to Duncan's New Multiple Range Test at 5 % level.

Table (4). Effect of pre-germination treatments on leaves and roots fresh and dry weights of Chrysalidocarpus lutescens H. Wendl seedlings during 2014 and 2015 seasons.

- Means within a column  having the same letters are not significantly different according to Duncan's New Multiple Range Test at 5 % level.

3- Leaf content of pigments and sugars:

A similar trend to that obtained in case of germination and seedling growth traits, was also attained regarding pigments and sugars content in the leaves of seedlings originated from the treated seeds (Table, 5), where a marked increment was noticed in the leaf content of chlorophyll a, b and carotenoids (mg/g f.w.), as well as  total soluble sugars (mg/100 g f.w.) relative to control content in the two seasons, except of the soaking in concentrated H₂SO₄ for 1 h treatment which slightly reduced total soluble sugars content in the first season only to 1.543 against 1.557 (mg/100 g f.w.) for control. The highest content in all previous constituents, however, was also found due to soaking the depulped seeds in tap water treatment for 48 h. that gave contents surpassed those recorded by all other treatments. The second rank was also taken up by soaking in hot water treatment for 48 h.

These findings could be discussed and interpretted as indicated before in case of germination and seedling growth characters. On the same line, were those results observed by Meerow (1991) on golden cane palm, Shahin et al. (2014) on triangle palm and Azad et al. (2012) who postulated that immersion the seeds of Albizia procera in hot water (100 °C for 1 min) greatly improved germination % and leaf content of pigments, sugars, N, P and K of the seedlings originated from treated seeds. In this concern, Shahin et al. (2015) established that soakingDillenia indicaseedseither in concentrated sulphuric acid for 3 min. or in tap water for 72 h. pronouncedly improved the leaf content of chlorophyll a, b, carotenoids, total soluble sugars and indoles, but decreased total phenols content. 

Table(5). Effect of pre-germination treatments on some active constituents in the leaves of Chrysalidocarpus lutescens H. Wendl seedlings during 2014 and 2015 seasons.

Accordingly, it is advised to soak the dopulped seeds of yellow areca palm (Chrysalidocarpus lutescens H. Wendl.) in either tap or hot water for 48 h. to improve germination characteristics and quality of the resulted seedlings.