Influence of salinity on germination and early seedling of five wheat (Triticum aestivum L) genotypes

Salinity is one of the most significant ecological stresses that deteriorate soil health, plant growth and development. It reduces germination and delays emergence of wheat. Under saline condition wheat stands irregular and depressed crop yield. In order to enhance wheat crop production under saline stress, it is essential to better understand genotypic variance and screening of high yielding and salt tolerant wheat genotypes. The main aim of this research work was to determine the influence of three salinity treatments viz. Control, 5-dSm ̄1 and 10-dSm ̄1on available five commercial wheat cultivars such as Sindh-81, Jauhar-78, Sarsabz, T.J-83 and Z.A. 77 under invitro condition. Seeds of five commercial wheat cultivars were then incubated in dark for 24hr, 48hr, 72hr and 96 hr at 22°C. The studied parameters including germination%, root and shoot length, root and shoot dry weight were also investigated. Germination was scored after ten days of seed placement. Completely randomized design with four replications was used. The obtained result showed that the germination, length of shoot and root were increased with an increase of incubation period, while decreased in response to increasing salinity level. Overall, the variety Sarsabz showed better adaptation, followed by T.J-83, Sindh-81, Jauhar-78 and Z.A. 77 for incubation period and salinity level. Therefore, it is suggested that the Sarsabz wheat cultivar can be successfully grown under ex-situ saline condition.


Introduction
Increasing population and changing environmental conditions are of significant concerns of world food security globally. Wheat is principal source of food and major cereal crop of Pakistan [1]. Thewheat grain is esteemed as an excellent food and high quality protein. Furthermore, its kernel contains approximately 60-68% starch, 8-15% protein, 2-2.5% cellulose, 1.5-2% fat, 2-3% sugar and 1.5-2% mineral matter. Current improvement rate of important crops is inadequate to meet future requirement. Wheat production widely fluctuated due to interaction with environmental conditions. Furthermore, it is well known as moderately tolerant to saline condition. Grain yield in bread wheat is polygenic hereditary character, affected by several factors directly or indirectly [2]. Soil salinity, alkalinity and water logging damage to germinating seed and to established crop plant [3, 4]. The main root cause of the high salinity problem in the soil are the widespread application of chemical fertilizers, untreated waste water irrigation and the high amount of evapotranspiration in summer [5, 6]. Shrivastava et al.
[7]revealed that nearly 20% of all farm lands around the globe comprising augmented levels of soluble and insoluble salts. Since that the germination process is not likely without water, the foremost adverse impact of salt in soils is reflected in producing osmotic possibilities that will avoid the seeds and seedling from absorbing an adequate quantity of water. Likewise, in salty situations, seeds and seedlings absorb the high quantities of Na + and Cl − molecules, which exert their poisonous influences in plant cells [8]. In such soil condition seed and seedling tolerance to salinity becomes critical factor to success establishment of crop. Soil salinity may affect germination of seed in two ways, by decrease of water and entry of toxic ions. Soil salinity is directly proportional to NaCl concentration [9]. Therefore, evaluation of seed and seedling in-vitro is necessary, prior to sowing in the field. In the former study, Izadi et al. [10] investigated the impact of salinity stress on physiological parameters of different wheat and barley genotypes. Also, Iqbal et al. [11] examined the impact of salinity on wheat characteristics. Recently, Ibarra-Villarreal et al. [12] revealed that the potential of salttolerant Bacillus species as a promising approach to alleviate the negative impacts of saline soils on wheat. Also, Ding et al. [13] found that the vermin-compost as amendment and deep tillage system significantly increase saline-sodic soil quality and wheat yield. However, limited information is available with spiked different levels of salinity on the physiological parameters of five commercial cultivars such as Sindh-81, Jauhar-78, Sarsabz, T.J-83 and Z.A. 77 under in-vitro condition. Hence, the main aim of this work was to investigate the influence of two salinity levels on the germination and early seedling growth of five wheat cultivars under in-vitro condition.

Materials and Methods
This experiment was conducted at laboratory of Shaheed Z. A. Bhutto Agricultural College Dokri. Varieties selected for this experiment were Sindh-81, Jauhar-78, Sarsabz, T.J-83 and Z.A. 77. Three treatments viz. Control, 5-dSm¯¹ and 10-dSm¯¹. In order to inhibit microbial contamination during germination, dry grains were sterilized in dilute sodium hypochlorite solution (15%). Dry grains were put into flasks containing 50ml of 15 % Sodium hypochlorite for sterilization, a period of about 15 minute. Seeds washed with several time by distilled water. Grains were placed as crease down on a double layer of Whatman-540 paper moistened with 7ml of sterilized distilled water in petridishes. Seeds were then incubated in dark for 24hr, 48hr, 72hr and 96 hr at 22°C. Following observations were recorded: 1) Germination (%); 2) Length of shoot (cm), and 3) Length of root (cm).

Results and Discussion
Germination: Data regarded germination of seeds under optimal condition (Control) and under stress of salinity presented in (Table 1). In control, germination % of seeds of all the cultivar increased with increase of incubation period. Sarsabz and T.J-83 exhibited more germination value as compare to other cultivar at 72 hours of incubation and germination of seeds of all cultivar noted between 98-100 %, suggested that seeds were almost hundred % viable. Clear effect of salinity on germination of seed was observed in all cultivars at various salinitydoses. At EC 5d Sm¯¹ (T1), reduction of 3-5.5, 4.2-6.2, 5.2-15.8 and 7.1-12.1% over the control was observed at incubation periods of 24, 48,72 and 96 hours respectively. Germination of seed was further reduced in response to increased level of salinity. All cultivar decreased of 11.2-15.1, 15-20, 18.5-26.5 and 9 -25% over control when salinity was raised to EC 10dSm¯¹ (T₃) and Sarsabz and TJ-83 gave better performance under this salinity stress. The difference between cultivars was highly significant. Interaction between 3 factor viz; variety, salinity level and incubation period were highly significant. Results were close agreement with Mehta and Desai [9], they reported significant decreased germination with an increased level of salinity, and furthermore the suppressive action of salts on germination was due to their metabolite effect and not on the osmotic action. respectively. Difference between cultivar was highly significant at all incubation period. Interaction between various factor i.e. cultivar; incubation period and salinity level were also highly significant. Decreased shoot length observed in present study could be due to lethal effect of chloride on plumole at time of emergence of seedling. These result confirm finding of Hanna et al. [14]; Singh et al. [15], they reported that increased level of salinity potentially decreased coleoptile length and seedling growth and reduction in coleoptile growth was due to inhibition of cell elongation rather than cell multiplication.

Root length
Data regarding effect of salinity on root length presented in (