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EFFECTS OF SALINITY ON THE GROWTH AND DEVELOPMENT OF GROUNDNUT PLANT (Arachis hypogaea L.) SHAILA ISLAM SATU*, MANSORA AND SHAHREAR AHMAD

The present study investigated the effects of salinity on the growth of groundnut (Arachis hypogaea L.), variety BARI Badam-8. The plants were grown in a series of plastic pots under controlled light and temperature conditions in the growth room. Salt (NaCl) solutions of different concentrations (0 mM, 50 mM, 100 mM, 150 mM, 200 mM, and 250 mM) were added to the pots, with three replicates. Results showed that shoot height, number of plants, main root length and lateral root length significantly decreased with the increase of salt concentrations. Fresh weight as well as dry weight of shoots and roots also decreased with the increase of salt concentrations while leaf proline and protein concentrations increased. Overall results indicate that high salinity condition is not suitable for growing groundnut.


INTRODUCTION
Salinity can limit the growth and development of plants (Shanon, 1986). It is reported that 20% of the agricultural land and 50% of the world's crop land are salt affected and the area under salinity is increasing throughout the world (Yokoi et al., 2002;Ponnamperuma, 1984).
Groundnut is a tropical legume which can feed human and poultry. Lipid content of groundnut is 42-52 percent, and protein is 25-32 percent. There are many vitamin and minerals in groundnut including vitamin A, vitamin B, Riboflavin, Folate, Mg, P, Mn, and some of the antioxidant compounds such as vitamin E and vitamin D (Sharif, 1997 andKarra et al., 2013).
The climatic and edaphic conditions of coastal areas of Bangladesh are suitable for growing groundnut, but this is limited by high soil salinity and high pH (Reddy and Kaul, 1996). A groundnut cultivar needs to tolerate up to 8 dS/m salinity. Salinity decreases the growth indices of the seedlings as well as the seed size (Smart, 1994). However, cultivation of groundnut has been challenged in Bangladesh due to increased salinity over the years (Sikder and Elias, 1985).
The main objective of the present study was to identify whether the variety, BARI Badam 8, is salt tolerant by examining the effects of salinity on seed germination rate and growth parameters (shoot height, root length, fresh and dry biomass of shoot and root) under different known concentrations of salt (NaCl) solution.

MATERIALS AND METHODS
Seeds of groundnut (A. hypogaea L.), BARI Badam-8, was collected from Bangladesh Agricultural Research Institute (BARI), Joydevpur, Gazipur. Germination rate and weight of 100 seeds were recorded. Before germination, seeds were surface-sterilized with 5% sodium hypochlorite. Then, the seeds were left for three days for germination in a Petri-dish with autoclaved distilled water.
Three-day old seedlings were transferred to plastic pots previously filled with soil collected from the Botanical Garden of Jagannath University, Dhaka. Plants were supplied with salt solutions (NaCl) of six concentrations (0 mM, 50 mM, 100 mM, 150 mM, 200 mM, and 250 mM). Salt solution was applied to the pots once a week and water was applied once in every two days. Each treatment had three replicates. Thus, a total of 18 pots were used to grow plants in the growth room at the Department of Botany, Jagannath University. Ten plants were grown in each pot and the plants were allowed to grow for 6 weeks in the growth room.
Soil pH was determined from suspension of soil: water (2:1, v:w) using pH meter (Hanna pH meter, pHeP). Soil conductivity was determined in suspension with distilled water (5:1, v:w) using conductivity meter (Hanna conductivity meter). Soil moisture content (%) was determined from 10 g fresh soil after ovendrying at 80 o C for 24 h. Organic Carbon content was analyzed by Walkley and Black method (Black, 1965). Total N content was determined by Kjeldahl method (Black, 1965). Soil P content was determined by Vanadomolybdophosphoric yellow color method (Jackson, 1958).
Shoots and roots were separated from the plants. Shoot height, number of live plants, fresh weight, dry weight and main root length, lateral root length, fresh weight and dry weight were noted. Dry weight was measured after drying in oven at 60 o C for 24 h. The 1g fresh leaf was used for the extraction of proline; optical density was recorded at 520nm wavelength by spectrophotometer. Proline content being expressed per gram leaf. Fresh leaf 1 g was used for the extraction of protein.
Mean values were compared for statistical significance by Analysis of Variance (ANOVA). For data analysis, JMP 4.0 software (SAS Institute, Carry, NC, USA) and for LSD test, STAR software (Statistical Tool for Agricultural Research) was used.

RESULTS
Soil pH was 6.95, conductivity 44.67 µS, moisture content 8.25%. Organic carbon, N and P values were 0.41, 0.076 and 0.063%, respectively. Germination rate of groundnut (BARI Badam-8) seeds is presented in Table1. Germination rate and seedling length decreased with the increase of salt concentration. The highest germination rate and seedling length (100% and 1.5 cm, respectively) were obtained from control (0mM), and was followed by 50mM, 100 mM, 150 mM, 200 mM and 250 mM. The ability of a seed to germinate and emerge under salt stress indicates that it has genetic potential for salt tolerance (Tejovathi et al., 1988). Increases in NaCl concentration progressively inhibited seed germination and seedling growth.

Main root length and lateral root length
The effect of different salinity levels on main root length and lateral root length of groundnut are presented in Table 3. It showed significant difference (P<0.001 and P=0.004, respectively). Root length decreased with increasing salinity levels and ranged between (1.16 ± 0.60) cm in 250 mM and (5.70±0.10) cm in control treatment. In case of lateral root length, it also decreased with the increase of salinity and ranged between (1.33±0.66) cm in 250 mM and (4.63±0.63) cm in control treatment. Root length decreased with increasing salinity levels, as reported by Aydinsakir et al. (2015). Plant height and root length are the most important parameters for salinity because roots are in direct contact with soil and absorb water from soil and the shoots supply it to the aerial parts of the plant (Jamil and Rha, 2004). Means followed by the same letter does not differ significantly.

Shoot fresh and dry weight
The effects of different salinity levels on plant fresh and dry weight are displayed in Table 4. It showed significant difference (P = 0.004 and P = 0.001, respectively). The highest plant fresh weight was found in control (1.36 ± 0.15 g) and the lowest fresh weight was in 250 mM (0.33 ± 0.16g). The highest plant dry weight was noted in control (0.15±0.01g), and the lowest plant fresh weight in 250 mM (0.04 ± 0.02 g). It was observed that fresh and dry weights decreased gradually from control to 250 mM salt treatment.

Root fresh and dry weight
The effects of different salinity levels on root fresh and dry weight are presented in Table 4.
Root fresh and dry weight showed significant difference (P = 0.003 and <.001). Root fresh weight ranged from 0.019±0.009 g to 0.060±0.006g and dry weight from 0.002 ± 0.001g to 0.015 ± 0.001 g. The highest root fresh weight was obtained in control (0.060 ±0.006g) and the lowest root fresh weight in 250 mM (0.019±0.009g). Similar trend was found in case of root fresh and dry weights. High salinity may inhibit root and plant elongation due to slowing down the water uptake by the plant which might be another reason for this decrease (Werner and Finkelstein, 1995). Salinity can rapidly inhibit root growth and hence capacity of water uptake and essential mineral nutrition from soil (Neumann, 1995). Means followed by the same letter does not differ significantly.

Proline and Protein content
Effects of salinity on the proline and protein contents of groundnut plants are shown in The lowest protein content (0.210±0.008 mg/g) was found in control and the highest protein content (0.475±0.024 mg/g) in 250 mM salt concentrations.
Overall, results indicate that the growth parameters of groundnut (BARI Badam-8) plants were markedly affected by 250 mM salt treatments indicating that high salinity is not suitable for cultivation of groundnut. Means followed by the same letter does not differ significantly.