0522-B4

Effect of salinity on seed germination, early seedling growth and biochemical contents of different seed sources (provenances) of Acacia nilotica (L.) Willd.

Bimlendra K, Toky O.P And Babber.S. ¹

ABSTRACT

Ten provenances (seed sources) of Acacia nilotica were screened for seed germination and seedling growth in media having salinity (chloride or sulphate) from 4 to 16 dSm ^-1 in laboratory conditions, with a view to find out the tolerant provenances, which could be used in afforestation programs of saline soils . Banaskantha, Chandigarh, Patna, and Bhopal provenances tolerated saliniy up to 8 dSm ^-1 at seed germination and seedling growth stage., while that of Coimbatore, Baharampur and Dharwad were sensitive even at low 4 dSm ^-1 level of salinity. Chloride dominated salinity was more injurious to A.nilotica than SO₄ dominated salinity particularly at lower concentrations, however at higher levels both sulphate dominated salinity (16 dSm ^-1 ) as well as chloride dominated salinity were equally injurious. Protein and total carbohydrate contents were maximum in Banaskantha, Chandigarh provenances, however protein content declined significantly as the level of salinity increased and sugar content showed a reverse trend i.e. it increased with increasing salinity. The study is useful in screening the seed sources at an early stage, suitable to grow on saline soils.

INTRODUCTION

Twenty three percent of the total cultivable area of the world is saline (Tanji, 1990). In India alone, about 12 million ha of land is affected with salinity or alkalinity (Datta et.al., 1990) The situation is aggravating with the passing time, particularly in the region, where it is necessary to use low quality water for irrigation.

Acacia nilotica (L.) Willd (black kikkar) forms integral tree component of agroforestry systems in India.The potential of Acacia nilotica as a multipurpose tree has been recognized worldwide.It is widely used in semi-arid regions for production of fuelwood, timber and forage in energy plantations or agroforestry systems (National Academy of Sciences, 1983; Toky and Singh, 1993).

We studied genetic variation in N₂ fixing abilities of 18 provenances of this species collected from the entire range of its distribution in India (9 ⁰ N to 34 ⁰ N latitude; 72 ⁰ E to 92 ⁰ E). There were significant differences in growth and amount of N₂ fixed and stored in plants between provenances (Beniwal, et.al. 1995), also wide variation in foliar biochemical and nutrient contents (Krishan and Toky, 1995). We also reported variation in seed characteristics (Krishan and Toky , 1996). The studies are however, lacking on ecophysiological variations among seed sources of Acacia nilotica, such as salt tolerance . The density of this multipurpose tree species is particularly high in semi -arid areas of north- western, middle parts and Deccan regions of India, where salinity is a dominant factor. This is precisely the reason for the selection of this tree species for tolerance to salinity.

The present work is, therefore, an attempt to study the effect of salinity (4 to 16 dSm ^-1 ) on seed germination and early seedling growth of 10 provenances of Acacia nilotica.

MATERIALS AND METHODS

Seeds for the present study were collected from germplasm bank located on the campus of CCS HAU Hisar. These seed sources of Acacia nilotica represent different provenances collected from all over India.In the present study, 10 seed sources were taken.

The salinity levels (4 to 16 dSm ^-1 ) were prepared by using mixtures of salts; NaCl, MgCl₂, MgSo₄ and CaCl₂ for chloride dominated salinity and Na₂So₄, MgCl₂, Ca Cl₂, and Mg So₄ for sulphate dominated salinity. The salinity levels were prepared by using mixture of salts, NaCl, MgCl₂, MgSo₄, CaCl₂ for chloride dominated salinity and Na₂So₄, MgCl₂, CaCl₂ and MgSo₄ for sulphate dominated salinity. Taking into account cation, the ratio between Na : Ca + Mg was 1:1 whereas between Ca : Mg if was 1:3. The anion ratio for chloride dominated salinity was 7:3 for Cl : So₄. For sulphate dominated salinity, the cation ratio remained the same but anion ratio became So₄ : Cl = 7:3 on meq. basis (Datta and Sharma, 1990).

For this study dry pretreated (dormancy free) seeds in each case were surface sterilized with 0.1% HgCl₂ solution for 10 seconds, and then rinsed thoroghly with distilled water. Twenty five seeds were sown in each petri plate (10 cm dia.), lined with filter paper moistened with 20 ml of saline solution (in each) and with water serving as control, in B.O.D. incubator, running at constant temperature of 25 ⁰ C . Twelve hour period of light was given for day and seeds were watered, when necessary. Observations were recorded after 28 days of sowing.

The dried plant material was stored for biochemical analysis. The proteins were estimated by using Folin-Cio-Calteau reagent method (Lowry et. al. 1951) . Total soluble carbohydrates were estimated colorimetrically according to the phenol sulphuric acid method (Dubois et al., 1956).

The experiment was randomized block design. The mean value of five replications was calculated and data subjected to analysis of variance (ANOVA). Significant differences between treatments and control were compared (P >0. 05).

RESULTS AND DISCUSSION

Among 10 provenances of Acacia nilotica, seed germination was maximum in Patna provenance (71%) followed by Roorki (45%), Bhopal (41%), and Banaskantha (40%) while minimum was observed in Bahrampur provenance (21%). (Table 1) The different behavior shown by the provenances at the germination stage might be because of internal osmotic ion toxicity effect rather than for restriction of imbibitions as reported earlier (Rehman et. al. 1997).

Seedling growth in terms of dry weight, length of plumule and radicle also varied significantly (P<0.05) among provenances in response to salinity. Weight of plumule and redicle was maximum in Chandigarh provenance, followed by Banaskantha, Bhopal, Gurgaon and Patna provenances. Similarly, length of the plumule was the highest in Bhopal provenance, and length of radicle in Patna provenance. Coimbatore and Roorkee provenances showed poor growth of radicle indicating wide variations in response to salinities by different seed sources. (Table 1)

Protein and sugar contents of plumule and radicle also showed significant differences among provenances. The provenances such as Chandigarh, Banaskantha, Baharampur, Patna and Jalandhar had lesser decrease in protein content under saline conditions and more decrease was observed in case of chloride dominated salinity. Protein content of radicle also followed more or less the same trend, suggesting thereby that the adaptive nature of the provenances such as Chandigarh, Banaskantha Patna and Jalandhar. Sugar contents of plumule and redicle was maximum (63 mg/g, 49 mg/g, respectively) in Banaskantha provenance and minimum (41mg/g, 39 mg/g), respectively in Jalandhar provenance. (Table 1)

Seed germination decreased significantly (P>0.05) with increase in levels of salinity. At 12dSm ^- , the decrease in germination percent was more than 65 % and at 16 dSm ^-1 , it further decreased to 80%. (Table 2).

Similarly, the growth parameters such as plumule and radicle lengths and dry weights, decreased significantly at 8dSm ^-1 ; at 12 dSm ^-1 and 16dSm ^-1 , the decrease was more than 60% and 75%, respectively. These results were similar to other workers, who showed that in general, increased salinity results in decreased germinability and delayed rate of germination (Catalan et al, 1994). Many halophytes also exhibit such sensitivity at seedling emergence (Ayers, 1952; Kuddah and Chowail, 1964). This indicates that while the seeds are capable of using their reserves and germinate, salt concentration becomes limiting to the further seedling development. The variations observed on ecophysiological tolerance among provenances may be genetical, since we have already reported wide variations in seed germination and seedling growth (Krishan and Toky 1996), nitrogen fixing abilites (Beniwal, et.al. 1995 Toky et. al. 1995;) and biochemical contents (Krishan and Toky 1995), among the same provenances of Acacia nilotica .

Protein contents of plumule started declining significantly even at 4dSm ^-1 . However, radicle showed an increase in protein content (30%) at 4dSm ^-1 , then it showed decline, but it was lesser than that of plumule protein contents even at 16dSm ^-1 levels of salinity (75% and 25%, respectively). Similar, results were found in crops plants (Reddy and Dass, 1978; Garg and Garg, 1982; Sharma et. al . 1996). This reduction in protein contents may be explained because of enhanced degradation of protein under saline conditions (Reddy and Vora, 1985) due to increased protease activity .

The total carbohydrates contents of plumule and radical increased significantly with the increasing salinity levels. This increase in sugar contents was more in plumule as compared with that of radicle; at 16dSm ^-1 , it was 20%, 14% respectively. (Table 2) . This increase in sugar content may be because of the tendency of the embryo to adapt to the salinity. These results are in compliance with the findings of Sharma et. al. (1993) and Hans (1997). Weimberg and Shannon (1988) formulated that in wheat, increased carbohydrate levels may lead to adaptive mechanism for overcoming the adverse effects of salts. Sheoran (1980) also suggested that salinity caused a decreased _-amylase activity, thus enhancing carbohydrate contents in embryo parts. The provenances selected in the present study, showed significant variation in biochemical and nutrient contents . These differences may be attributed to genetic variations among seed sources and can be utilized in afforestation programmes .

The effect of types of salinities is exhibited in Table 3. Chloride and sulphate dominated salinities in general, have a reducing effect on growth and the reduction increased significantly as the levels of salinity increased. Germination percent was adversely affected in chloride dominated salinity as compared to sulphate dominated at all the levels. The decrease in germination percent was 20% at 4dSm ^-1 , while it was 5% at 16dSm ^-1 indicating thereby the deleterious effect of sulphate dominated salinity, was more at higher salinity levels.

Same is true with the growth parameters like seedling dry weights and protein contents. Carbohydrate however, showed a reverse effect in case of both the types of salinities i.e. an increase in carbohydrate content, was observed with the increase in salinity. However, the increase was more in chloride dominated salinity which is attributed to the reduced <-amylase activity in saline conditions and more effect in Chloride dominated salinity (Sharma et. al . 1993 and Hans 1997).

CONCLUSION

The results have clearly indicated that Banaskantha, Chandigarh, Patna and Bhopal provenances tolerated salinity up to 8dSm ^-1 at germination stage, while Baharampur and Coimbatore provenances appeared to be sensitive even at 4dSm ^-1. level of salinity.

On the basis of dry weight of plumule and radicle, and then protein and sugar contents, it has been concluded that Banaskantha appears to be most tolerant provenance. Chandigarh, Patna, Bhopal provenances can grow in highly saline conditions (8 dSm ^-1 ) with less than 50 % reduction in growth, dry weight of seedlings while Baharampur, Dharwad provenances appeared salt sensitive and can withstand salt only up to 4dSm ^-1 . Overall effect of types of salinity on Acacia nilotica provenances was more of chloride dominated than that of sulphate dominated salinity

ACKNOWLEDGEMENTS

We are grateful to the Deptt. of Non - Conventional Energy Sources (Govt. of India) for providing grants to develop germplasm of Acacia nilotica at the campus of CCS Haryana Agricultural University, Hisar.

REFERENCES

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Table-1. Response of seed sources (provenances) of A.nilotica to salinity. (The values of all the salinities pooled)

Table-2. Effect of salinity on seed germination and early seedling growth of A. nilotica (The values of all the provenances pooled).

Table-3. Effect of type of salinity (chloride or sulphate) on germination percentage and seedling growth of A.nilotica (The values are pooled data of 10 numbers of the provenances of A.nilotica.)

¹ Forestry Department
Botany Department
C C S Haryana Agricultural University, Hisar- 125004 (India)