Ibrahim M. Aref, L. I. El-Juhany and K. F. Elkhalifa. Plant Production Department, College of Agriculture,. P. O. Box 2460 Riyadh 11451, Saudi Arabia.
Effects of sodium chloride concentrations on seed germination of Acacia nilotica ssp. tomentosa and Acacia gerrardii var. najdensis
Ibrahim M. Aref, L. I. El-Juhany and K. F. Elkhalifa Plant Production Department, College of Agriculture, P. O. Box 2460 Riyadh 11451, Saudi Arabia ABSTRACT The present study was conducted to evaluate the seed germination of Acacia nilotica ssp. tomentosa (L.) Willd. Ex. Del and Acacia gerrardii (Benth.) var. najdensis Chaudhary. under salinity conditions. The experiment was carried out in Forestry Laboratory at College of Agriculture, King Saud University, Riyadh, Saudi Arabia. The collected seeds of both species were treated with boiling water then left to germinate in Petri dishes in an environmentally controlled growth chamber. Five concentrations of sodium chloride had EC of 0 (only distilled water), 2, 4, 6 and 10 dS m-1 were applied to seeds as irrigation water. Number of germinated seeds was recorded daily up to 14 days since treatments began. Results showed significant decreases in germination percentage of both acacia species due to increasing salinity. Acacia nilotica ssp. tomentosa was more tolerant than Acacia gerrardii var. najdensis. The decreases in germination percentages of both acacia species were concomitant with the increase in the concentrations of sodium chloride. Significant differences in seed germination were also detected among sodium chloride concentrations used. The recovery of the seeds that did not germinate under salinity conditions may indicate that the saline conditions were not toxic and thus the adverse effects of sodium chloride concentrations may explained as a result of lowering osmotic potential of the external solution. Key words: Acacia nilotica ssp. tomentosa, Acacia gerrardii var. najdensis, seed germination, sodium chloride INTRODUCTION Studies of environmental stresses for trees at different stages of development are very important for regeneration and consequently for successful establishment of plantations. Seed germination, as a critical stage in plant life is the most vulnerable to such stresses (Freeman, 1973; Catalan et al., 1994). Salinity is one of the most important factors affecting seed germination in the arid regions. Studies showed that sodium chloride is the most important salt affecting seed germination. Its high levels of concentration inside the soil have an adverse effect on seed germination (Mayer and Mayber, 1982). The adverse effect is attributed to ionic toxicity and the decline in osmotic pressure which do interact under saline conditions (Greenway and Munns, 1980; Levitt, 1980). The principal effects of salinity on seed germination could be summarized in the delay of seed germination, and the decline in its rate and percentage (Villagra, 1997). In Saudi
Arabia, saline water is one of the most frequent environmental stresses that face growing plants. This because groundwater represents more than 90% of water used in agricultural irrigation and it classified as very saline water (Falatah et al., 1999). They found that the salinity (EC) of groundwater from 400 samples represent eight agricultural regions of Saudi Arabia ranged between 0.2 and 29.3 dS m-1. Recently, Al-Matroud (2003) reported that salinity of groundwater from Riyadh Region (Central part of Saudi Arabia) has electrical conductivities (EC) ranged between 1.34 and 7.84 dS m-1 and dominated by sodium chloride cations. Acacias are among the most important trees in the arid regions due to their wide distribution, tolerating the harshest environmental conditions and multiple uses by the locals. Increasing the area of tree plantation is an essential issue in such conditions. In the In vitro seed germination of Acacia nilotica and Acacia raddiana, Aziz et al. (2001) reported that the germination was decreased by salinity induced by sodium chloride. They classified the two acacia species as salt tolerant. Similarly, Ndour and Danthu (1999) reported adverse effect of NaCl on the seed germination of some African acacias, and that Acacia seyal and Acacia raddiana being the most tolerant species among the group of acacia species studied. In Saudi Arabia, the performance of acacia species under saline irrigation is not clear, at least in establishment stage. The objective of the present research, therefore, is to investigate the effects of five levels of saline irrigation water representing by sodium chloride solutions graduated in concentration on seed germination of Acacia nilotica ssp. tomentosa and Acacia .gerrardii var. najdensis. MATERIALS AND METHODS Plant materials Seeds of Acacia nilotica ssp. tomentosa (L.) Willd. Ex. Del. were collected from a location about 70 km south Riyadh. While those of Acacia gerrardii (Benth.) var. najdensis Chaudhary. were collected from Hissyia valley about 50 km north Riyadh. The collected seeds were cleaned then placed in boiling water for three minutes, as a well known pre-germination treatment for most of acacia seeds. Germination condithions and treatments The experiment was conducted in a growth chamber at the college of Agriculture, King Saud university, Riyadh, Saudi Arabia. The chamber was set at 20°C day and night, and 12 hours of artificial illumination. Five solutions of electrical conductivity (EC) accounted for 0 (only distilled water: control), 2, 4, 6 and 10 dS m-1 (deciSiemens per meter) were prepared by dissolving zero, 1.28, 2.56, 3.84 and 6.40 gm L-1 of sodium chloride, repectively, in distilled water. Seeds of A. nilotica ssp. tomentosa and A. gerrardii var. najdensis were placed in Petri dishes using a completely randomized design with four replicates (Steel and Torrie 1982). Twenty five seeds were placed in each dish, resulting in 500 seeds for each species distributed into 20 dishes. The seeds were irrigated with the appropriate solutions of NaCl as set in the randomized layout and kept wet throughout the course of the experiment. Number of the germinated seed of both
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acacia species were daily counted and removed up to 14 days. The percentage of accumulated germination was calculated. The seeds that failed to germinate under the experiment conditions were washed and sown in sand soil and irrigated with distilled water for a week in order to evaluated their recovery from the impact of salinity.
Statistical analysis Data were angular transformed then analyzed statistically through analysis of variance procedure using SAS computer programme (SAS 1987). Means of both treatments and species were distinguished by Duncan's Multiple Range Test at P
