Effect of Nacl on Germination and Seedling Growth of Some Cotton Genotypes

Salinity is an emerging problem among the abiotic stresses of plants in Bangladesh. One easy way to cope with the problem of salinity is to exploit the genetic potential of plants for their adaptability to adverse soil conditions. Salt tolerance improvement might be achieved through selection from already existing germplasm which can be done by quick method particularly in early growth stages of crops. A laboratory experiment was conducted to determine the effect of salinity on germination and the seedling growth of five cotton genotypes. Two factors include genotypes (CB-9, CB-10, CB-12, CB-14 and CB-15) and salt solution of different concentrations (control -0 dS m-1, 4 dS m-1, 8 dS m-1, 12 dS m-1 and 16 dS m-1) were used. Relative to control treatment, germination energy and germination capacity at 16 dS m-1 was maximum in CB-12 (0.72 and 0.77 respectively) whereas germination percentage (0.99) was maximum in CB-9 and the relative value of all the above parameters was minimum in CB-15 (0.02, 0.13, 0.41 and 0.09, respectively). In case of seedling growth parameters, shoot length, seedling vigor index and dry weight at 16 dS m-1 were maximum in CB-9 (0.67, 0.64 and 0.77 respectively) relative to control whereas the relative value of all those parameters was minimum in CB-15 (0.5, 0.17, 0.31 and 0.59 respectively). Considering all germination and seedling growth parameters, CB-9 was supposed to be superior genotype followed by CB-12, CB-10 and CB-14 whereas genotype CB-15 was more susceptible than other genotypes against salinity stress. 
Res. Agric., Livest. Fish.7(2): 199-207,  August 2020


INTRODUCTION
Cotton is an important industrial crop grown under diverse soil and climatic conditions. It belongs to the genus Gossypium with four domesticated species including allopolyploids (2n = 52) Gossypium hirsutum and Gossypium barbadense, and diploids Gossypium herbaceum and Gossypium arboretum (2n = 26). Cotton is a perennial plant of tropical and subtropical origin, but is mostly grown as annual crop to get primarily lint, seed oil, and animal meal (Rehman and Farooq, 2019). In Bangladesh the area under cotton cultivation (2017-2018) is 31870 acres with a total production of 30790 MT. Chittagong, Dhaka, Khulna, Mymensing, Rajsahi and Rangpur are the cotton cultivated division in our country (BBS, 2018).
Salinity in topsoil and subsoil is one of the major abiotic environmental stresses to crop production. Worldwide, soil salinity is becoming a serious threat to agricultural productivity. Salinity affects 7% of the world's land area, which amounts to 930 million ha. The area is increasing; a global study of land use over the last 45 years found that 6% had become saline in that period (Chachar et al., 2008). Salinity has been increasing over period of time of southwest coastal region of Bangladesh and 0.223 million ha (26.7%) of total cultivated land is affected by various degree of salinity and badly hampered in the crop ecology (Iqbal, 2013). Although cotton is classified as salt tolerant crop yet it is sensitive to salinity during the emergence and early growth stages than the later developmental stages. Soil salinity is a dominated factor affecting cotton's aboveground dry mass and root development (Chen et al., 2010). Generally, the salinity reduces vegetative growth of cotton but increase in growth with low concentration of salts has also been observed (Pessarakli, 1995). Salinity decreases shoot/root ratio because shoots are sensitive than roots to salt stress (Ahmad et al., 2002). For extending cotton production in Bangladesh, it is necessary to start cultivation of cotton to all possible location. Cotton is considered as a moderately salt tolerant crop, but its yield is markedly affected due to poor germination and subsequent abnormal plant development under severe saline conditions .The success of cotton production lies partly in cultivation of salt-tolerant cotton cultivars on salt affected soils (Chachar et al., 2008). In Bangladesh, a little number of works has been carried out about salinity effect on cotton. Considering this task, this work was undertaken to examine the effect of salinity (NaCl) on germination and seedling growth of some cotton genotypes.

MATERIALS AND METHODS
The experiment was conducted in Agronomy Laboratory of Agrotechnology Discipline, Khulna University, Khulna, Bangladesh from 24 July to 12 August, 2019 to determine the effect of salinity on germination and the seedling growth of five cotton genotypes. The experiment was conducted by using two factorial completely randomized designs (CRD) with four replications. The treatments were genotypes (CB-9, CB-10, CB-12, CB-14 and CB-15) and salinity levels (T1= Control (0 dS m -1 ), T2= 4 dS m -1 , T3= 8 dS m -1 , T4= 12 dS m -1 and T5= 16 dS m -1 ). Seeds of all the genotypes were collected from Cotton Research, Training and Seed Multiplication Firm, Sreepur, Gazipur.
Glass petridishes with a tight fitting lid were used in conducting this experiment. Filter papers were used as a matrix for seed germination. Three filter papers were soaked with respective salt solutions (Control, 4, 8, 12 and 16 dS m -1 respectively). For preparing different salt solution, 1000 ml distilled water was kept in a beaker and then respective amount of salt (NaCl) was gradually added to this water. To assure the concentrations of solution, an electrical conductivity meter was used to measure the salinity levels. Before placing the seeds to petridishes, seeds were treated with Vitavex 200 @ 3 gm/ kg seed and kept them in a air tight packet for 24 hours. The number of petridishes that used in laboratory were = {5 (variety) × 5 (treatments) × 4 (replication)} = 100 A seed has considered germinated at the emergence of the radical (2 mm) (Chartzoulakis and Klapaki, 2000). After germination, seedlings were watered as and when necessary. The data were taken on following parameters- length) × germination percentage] (Podder et al., 2020) and (viii) dry weight of seedling (mg) [after 10 days of setting the seed for germination, seedlings of each petridish were dried in oven at 60 0 C until a fixed weight which was measured by an electrical balance]. Relative performance was measured by using the following formula-Relative performance = Variable measured under stress condition/ Variable measured under normal condition Then the recorded data were analyzed with the help of statistical package program MSTAT-C, Microsoft Excel and the mean differences were adjusted with Duncan's New Multiple Ranges Test at 5% level of significance (Gomez and Gomez, 1984).

Root length (cm)
The interaction between salinity levels and genotypes in relation to root length was significant at 5% level and varied from 1.46 cm to 4.42 cm. The highest root length was found in CB-10 (4.42 cm) at 8 dS m -1 which was statistically similar with 4 dS m -1 (4.28 cm) of same genotype. CB-9 also produced better results at control (3.88 cm) which was similar to CB-10 at control (3.96 cm). The lowest root length was noticed in CB-15 (1.46 cm) at 16 dS m -1 EC which was statistically similar at 12 dS m -1 (1.59 cm) of same genotype ( Table 2). Root length was reduced with increasing salinity level though their reduction varied genotypically. Relative to control (0 dS m -1 ) treatment root length at 16 dS m -1 was maximum (0.69) in CB-10 followed by CB-9 (0.63), CB-14 (0.63) and CB-12 (0.53) and minimum in CB-15 (0.5) ( Figure 5).

Shoot length (cm)
The interaction between salinity levels and genotypes in relation to shoot length was significant at 5% level. The highest shoot length was found in CB-10 (2.80 cm) at control which was statistically similar with CB-9 (2.70 cm) and same genotype (2.6 cm) at 4 dS m -1 . The lowest shoot length was noticed in CB-15 (0.74 cm) at 16 dS m -1 ( Table 2). Relative to control treatment shoot length at 16 dS m -1 was maximum in CB-9 (0.67) followed by CB-12 (0.64), CB-10 (0.64), CB-14 (0.49) and the minimum was in CB-15 (0.31) ( Figure 6).

Seedling vigor index
Due to the interaction between genotypes and different level of salinity, seedling vigor index of cotton genotypes were greatly varied. The highest seedling vigor index was found in CB-10 (645.0) at 4 dS m -1 which is statistically similar at control (642.2) of same genotype and CB-9 (641.6) at control. The lowest seedling vigor index was noticed in CB-15 (82.5) at 16 dS m -1 ( Table 2). Relative to control treatment seedling vigor index at 16 dS m -1 was maximum in CB-9 (0.64) followed by CB-10 (0.63), CB-12 (0.59), CB-14 (0.44) and minimum in CB-15 (0.17) (Figure 7).

Seedling dry weight
The interaction between salinity levels and genotypes in relation to seedling dry weight was significant at 5% level. The highest seedling dry weight was found in CB-9 (60.40 mg) at control which was statistically similar at 4dS m -1 (59.80 mg) of same genotype and CB-10 at control (58.80 mg). The lowest seedling dry weight was noticed in CB-15 (24.40 mg) at 16 dS m -1 ( Table 2). Seedling dry weight was reduced with increasing salinity level though their reduction varied genotypically. Relative to control (0 dS m -1 ) seedling dry weight at 16 dS m -1 was maximum in CB-9 (0.77) followed by CB-12 (0.77), CB-14 (0.72), CB-10 (0.71), and CB-15 (0.59) (Figure 8).

DISCUSSION
Increased salinity caused a significant reduction in germination percentage, germination rate, root and shoots length and fresh root and shoots weights of plants (Jamil et al., 2006). Ahmad et al., (2002) reported that the germination of cotton seed and emergence of seedling is generally delayed and reduced by salinity. However, varietal differences in response to salinity have also been observed. Muhammad and Hussain, (2012) reported that soil salinity can significantly inhibit seed germination and seedling growth, due to the combined effects of high osmotic potential and specific ion toxicity. Salinity decreases germination and vegetative growth with significant difference among the cultivars. Seed germinations were 47-84 % and 17-54 % at 10 and 20 dSm -1 respectively (Qadir and Shams, 1997). In present study, germination percentage was decreased with increasing salinity levels and varied from 37.50% to 100%. Relative to control, CB-15 suffered more (0.41) than CB-9 (0.99) followed by CB-10 (0.95) and CB-12 (0.84).
In root growth, no such significant genotypic difference was observed up to 8 dSm -1 rather it was increased in some cases in present study. But it was reduced with increasing salinity levels. Similar observation was found by Zhong and Lauchli, 1993. Although salinity generally causes reduced development of root but there are some findings which show increase in root growth in mild salinity. Similarly Leidi (1994) reported longer primary roots in cotton when treated with 100 mol m-3 NaCl but not in control. An inhibition, both in length and number of secondary roots was also observed at that salt concentration. Khan et al, 1995 found that reduction in shoot fresh weight and dry weight of 15 cotton cultivars with an increase salt concentration (0, 150 and 250 mol NaCl m -3 ). At 10-20 dSm -1 , decrease in leaf area, stem thickness, shoot and root weight of four cotton cultivars have been reported by Qadir and Shams, 1997. Similar pattern of result was recorded in present study root length, shoot length and dry weight of biomass was reduced with increasing levels of salinity. Sattar (2010) suggested that soil salinity affects plant growth and development by way of injurious effects of toxic ions, osmotic stress, reduced water use efficiency and the resulting nutrient imbalance. Podder et al., (2020) examined that all the parameters regarding germination and seedling growth of mungbean were affected by the increase of salinity levels though their reduction varied from genotype to genotype. Sardoei et al., (2013) recommended that salt stress affects many physiological aspects of plant growth. Shoot growth was reduced by salinity due to inhibitory effect of salt on cell division and enlargement in growing point. Saleh (2012) found that salt treatment exhibited deleterious effect on vegetative growth with genotypic variation among the four tested cotton genotypes. Salt stress impaired both seedling height and root length of all tested genotypes. Rauf et al., (2014) also found that treatments and genotypes showed significant effect on reduction of shoot length, root length and root, shoot fresh weight. He also suggested that phenolic content was found to increase significantly in all genotypes at increased salinity. Data also showed that variation in increase of phenol content was the function of salinity and not due to genotypes specificity.

CONCLUSION
Considering germination and seedling growth parameters, CB-9 was supposed to be superior genotype followed by CB-12, CB-10 and CB-14 whereas genotype CB-15 was more susceptible than other genotypes against salinity stress. Similar study should be conducted in the field to better understand the effects of salinity stress on growth and yield performance of cotton.